2006

Hallmann A
Morphogenesis in the family Volvocaceae: Different tactics for turning an embryo right-side out
PROTIST 157 (4): 445-461 OCT 2006

Abstract: Green algae of the family Volvocaceae provide an unrivalled opportunity to analyze an evolutionary pathway leading from unicellularity to multicellularity with division of labor. One key step required for achieving multicellularity in this group was the development of a process for turning an embryo inside out: a morphogenetic process that is now known as "inversion," and that is a diagnostic feature of the group. Inversion is essential because at the end of its embryonic cleavage divisions, each volvocacean embryo contains all of the cells that will be present in an adult, but the flagellar ends of all cells are pointed toward the interior, rather than toward the exterior where they will need to be to function in locomotion. Inversion has been studied in greatest detail in Volvox carteri, but although all other volvocacean species have to struggle with the same awkward situation of being wrong-side out at the end of cleavage, they do it in rather different ways. Here, the inversion processes of six different volvocacean species (Gonium pectorale, Pandorina morum, Eudorina unicocca, Volvox carteri, Volvox tertius, and Volvox globator) are compared, in order to illustrate the variation in inversion patterns that exists within this family. The simplest inversion process occurs in the plate-shaped alga Gonium pectorale, and the most complicated in the spherical alga Volvox globator Gonium pectorale goes only from a concave-bowl shape to a slightly convex plate. In Volvox globator, the posterior hemisphere inverts completely before the anterior pole opens and the anterior hemisphere slides over the already-inverted posterior hemisphere; during both halves of this inversion process, the regions of maximum cell-sheet curvature move progressively, as radially symmetrical waves, along the posterior-anterior axis.

Fukada K, Inoue T, Shiraishi H
A posttranslationally regulated protease, VheA, is involved in the liberation of juveniles from parental spheroids in Volvox carteri
PLANT CELL 18 (10): 2554-2566 OCT 2006

Abstract: The lineage of volvocine algae includes unicellular Chlamydomonas and multicellular Volvox in addition to their colonial relatives intermediate in size and cell number. In an asexual life cycle, daughter cells of Chlamydomonas hatch from parental cell walls soon after cell division, while Volvox juveniles are released from parental spheroids after the completion of various developmental events required for the survival of multicellular juveniles. Thus, heterochronic change in the timing of hatching is considered to have played an important role in the evolution of multicellularity in volvocine algae. To study the hatching process in Volvox carteri, we purified a 125- kD Volvox hatching enzyme ( VheA) from a culture medium with enzymatic activity to degrade the parental spheroids. The coding region of vheA contains a prodomain with a transmembrane segment, a subtilisin- like Ser protease domain, and a functionally unknown domain, although purified 125- kD VheA does not contain a prodomain. While 143- kD VheA with a prodomain is synthesized long before the hatching stage, 125- kD VheA is released into the culture medium during hatching due to cleavage processing at the site between the prodomain and the subtilisin- like Ser protease domain, indicating that posttranslational regulation is involved in the determination of the timing of hatching.

Babinger K, Hallmann A, Schmitt R
Translational control of regA, a key gene controlling cell differentiation in Volvox carteri
DEVELOPMENT 133 (20): 4045-4051 OCT 15 2006

Abstract: The complete division of labour between the reproductive and somatic cells of the green alga Volvox carteri is controlled by three types of genes. One of these is the regA gene, which controls terminal differentiation of the somatic cells. Here, we examined translational control elements located in the 5' UTR of regA, particularly the eight upstream start codons (AUGs) that have to be bypassed by the translation machinery before regA can be translated. The results of our systematic mutational, structural and functional analysis of the 5' UTR led us to conclude that a ribosome-shunting mechanism-rather than leaky scanning, ribosomal reinitiation, or internal ribosome entry site (IRES)-mediated initiation-controls the translation of regA mRNA. This mechanism, which involves dissociation of the 40S initiation complex from the message, followed by reattachment downstream, in order to bypass a secondary structure block in the mRNA, was validated by deleting the predicted 'landing site' (which prevented regA expression) and inserting a stable 64 nucleotide hairpin just upstream of this site (which did not prevent regA expression). We believe that this is the first report suggesting that translation of an mRNA in a green eukaryote is controlled by ribosome shunting.

Nozaki H, Ott FD, Coleman AW
Morphology, molecular phylogeny and taxonomy of two new species of Pleodorina (Volvoceae, Chlorophyceae)
JOURNAL OF PHYCOLOGY 42 (5): 1072-1080 OCT 2006

Abstract: The volvocacean genus Pleodorina has been morphologically characterized as having small somatic cells in spheroidal colonies and anisogamous sexual reproduction with sperm packets. In this study we examined two new species that can be assigned to the genus Pleodorina based on morphology: P. starrii H. Nozaki et al. sp. nov. and P. thompsonii F. D. Ott et al. sp. nov. P. starrii was collected from Japan and had 32- or 64-celled colonies with anterior somatic cells and spheroidal individual cellular sheaths that were weakly attached to each other within the colonial envelope. P. thompsonii from Texas (USA) exhibited four or 12 somatic cells in the anterior pole of 16- or 32-celled colonies, respectively, and had a single large pyrenoid in the chloroplast of mature reproductive cells. The chloroplast multigene phylogeny placed P. starrii and P. indica (Iyenger) H. Nozaki in a clade that was robustly separated from the type species P. californica Shaw and P. japonica H. Nozaki. Pleodorina thompsonii was resolved as a basal branch within a large monophyletic group (Eudorina group) composed of Eudorina, Pleodorina and Volvox (excluding section Volvox). Thus, Pleodorina was found among three separate lineages within the Eudorina group in which Eudorina and Volvox were also resolved as nonmonophyletic. The DNA sequences from additional species/strains as well as recognition of morphological attributes that characterize the monophyletic groups within the Eudorina group are needed to construct a natural generic classification within these members of the Volvocaceae.

Nedelcu AM, Michod RE
The evolutionary origin of an altruistic gene
MOLECULAR BIOLOGY AND EVOLUTION 23 (8): 1460-1464 AUG 2006

Abstract: Although the conditions favoring altruism are being increasingly understood, the evolutionary origins of the genetic basis for this behavior remain elusive. Here, we show that reproductive altruism (i.e., a sterile soma) in the multicellular green alga, Volvox carteri, evolved via the co-option of a life-history gene whose expression in the unicellular ancestor was conditioned on an environmental cue (as an adaptive strategy to enhance survival at an immediate cost to reproduction) through shifting its expression from a temporal (environmentally induced) into a spatial (developmental) context. The gene belongs to a diverged and structurally heterogeneous multigene family sharing a SAND-like domain (a DNA-binding module involved in gene transcription regulation). To our knowledge, this is the first example of a social gene specifically associated with reproductive altruism, whose origin can be traced back to a solitary ancestor. These findings complement recent proposals that the differentiation of sterile castes in social insects involved the co-option of regulatory networks that control sequential shifts between phases in the life cycle of solitary insects.

Duncan L, Nishii I, Howard A, et al.
Orthologs and paralogs of regA, a master cell-type regulatory gene in Volvox carteri
CURRENT GENETICS 50 (1): 61-72 JUL 2006

Abstract: The multicellular green alga Volvox carteri forma nagariensis has only two cell types: terminally differentiated somatic cells and reproductive cells. The regA gene maintains the terminally differentiated state of the somatic cells, apparently by repressing transcription of genes required for chloroplast biogenesis and thereby preventing cell growth. Because the RegA protein sequence bore no obvious motifs, we are attempting to identify regions of functional importance by searching for strongly conserved domains in RegA orthologs. Here we report the cloning and characterization of regA from the most closely related known taxon, V. carteri f. kawasakiensis. Given the closeness of the relationship between these two formas, their regA genes are surprisingly different: they differ in the number of introns and by several lengthy indels, and they encode proteins that are only 80% identical. We also serendipitously discovered a paralogous gene immediately upstream of each regA locus. The two regA genes, both upstream paralogs and several genes in Chlamydomonas (the closest unicellular relative of Volvox) encode a conserved region (the VARL domain) that contains what appears to be a DNA-binding SAND domain. This discovery has opened up a new avenue for exploring how regA and the terminally differentiated state that it controls evolved.

Short MB, Solari CA, Ganguly S, et al.
Flows driven by flagella of multicellular organisms enhance long-range molecular transport
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA 103 (22): 8315-8319 MAY 30 2006

Abstract: Evolution from unicellular organisms to larger multicellular ones requires matching their needs to the rate of exchange of molecular nutrients with the environment. This logistic problem poses a severe constraint on development. For organisms whose body plan is a spherical shell, such as the volvocine green algae, the current (molecules per second) of needed nutrients grows quadratically with radius, whereas the rate at which diffusion alone exchanges molecules grows linearly, leading to a bottleneck radius beyond which the diffusive current cannot meet metabolic demands. By using Volvox carteri, we examine the role that advection of fluid by the coordinated beating of surface-mounted flagella plays in enhancing nutrient uptake and show that it generates a boundary layer of concentration of the diffusing solute. That concentration gradient produces an exchange rate that is quadratic in the radius, as required, thus circumventing the bottleneck and facilitating evolutionary transitions to multicellularity and germ-soma differentiation in the volvocalean green algae.

Nedelcu AM
Evidence for p53-like-mediated stress responses in green algae
FEBS LETTERS 580 (13): 3013-3017 MAY 29 2006

Abstract: The tumor suppressor protein, p53, plays a major role in cellular responses to stress and DNA damage in animals; despite its critical function, p53 homologs have not been identified in any algal or plant lineage. This study employs a functional and evolutionary approach to test for a p53 functional equivalent in green algae. Specifically, the study: (i) investigated the effect of two synthetic compounds known to interfere with p53 activity; (ii) searched for sequences with similarity to known p53-induced genes; and (iii) analyzed the expression pattern of one such sequence. The findings reported here suggest that a p53 functional equivalent is present and mediates cellular responses to stress in green algae.

Hallmann A, Wodniok S
Swapped green algal promoters: aphVIII-based gene constructs with Chlamydomonas flanking sequences work as dominant selectable markers in Volvox and vice versa
PLANT CELL REPORTS 25 (6): 582-591 JUN 2006

Abstract: Production of transgenic organisms is a well-established, versatile course of action in molecular biology. Genetic engineering often requires heterologous, dominant antibiotic resistance genes that have been used as selectable markers in many species. However, as heterologous 5' and 3' flanking sequences often result in very low expression rates, endogenous flanking sequences, especially promoters, are mostly required and are easily obtained in model organisms, but it is much more complicated and time-consuming to get appropriate sequences from less common organisms. In this paper, we show that aminoglycoside 3'-phosphotransferase gene (aphVIII) based constructs with 3' and 5' untranslated flanking sequences (including promoters) from the multicellular green alga Volvox work in the unicellular green alga Chlamydomonas and flanking sequences from Chlamydomonas work in Volvox, at least if a low expression rate is compensated by an enforced high gene dosage. This strategy might be useful for all investigators that intend to transform species in which genomic sequences are not available, but sequences from related organisms exist.

Cheng Q, Hallmann A, Edwards L, et al.
Characterization of a heat-shock-inducible hsp70 gene of the green alga Volvox carteri
GENE 371 (1): 112-120 APR 12 2006

Abstract: The green alga Volvox carteri possesses several thousand cells, but just two cell types: large reproductive cells called gonidia, and small, biflagellate somatic cells. Gortidia are derived from large precursor cells that are created during embryogenesis by asymmetric cell divisions. The J domain protein GlsA (Gonidia/ess A) is required for these asymmetric divisions and is believed to function with an Hsp70 partner. As a first step toward identifying this partner, we cloned and characterized V carleri hsp70A, which is orthologous to HSP70A of the related alga Chlamydomonas reinhardtii. Like HSP70A, V carleri hsp70A contains multiple heat shock elements (HSEs) and is highly inducible by heat shock. Consistent with these properties, Volvox transformants that harbor a glsA antisense transgene that is driven by an hsp70A promoter fragment express Gls phenotypes that are temperature-dependent. hsp70A appears to be the only gene in the genome that encodes a cytoplasmic Hsp70, so we conclude that Hsp70A is clearly the best candidate to be the chaperone that participates with GlsA in asymmetric cell division.

Cheng Q, Balzer E, Miller SM, et al.
Effect of histone deacetylase inhibitors on tubulin acetylation and development in Volvox carteri (Volvocales)
JOURNAL OF PHYCOLOGY 42 (2): 417-422 APR 2006

Abstract: Volvox carteri f. nagariensis (Iyengar) possesses several thousand cells of just two types, gonida and somatic cells, that are set apart by asymmetric cell division. Because the division apparatus contains microtubules enriched in acetylated alpha-tubulin, we wished to know whether acetylated tubulin plays any role in regulating division symmetry. Two different human histone deacetylases (HDACs) have been shown to deacetylate tubulin in vivo, thereby regulating cell motility. Here we set out to determine: (1) whether HDAC inhibitors that increase tubulin acetylation in animal cells have the same effect in V. carteri, (2) whether increasing acetylated tubulin affects microtubule stability, and (3) whether increasing acetylated tubulin affects division symmetry. Embryos exposed to two HDAC inhibitors, trichostatin A (TSA) and tubacin, accrued dramatically higher levels of acetylated tubulin (and more acetylated microtubules) and were significantly more sensitive to colchicine than controls. However, while TSA-treated embryos cleaved aberrantly to produce adults with abnormal morphology, tubacin-treated embryos developed normally. We conclude that increasing tubulin acetylation subtly alters microtubule stability, but does not appear to affect cell division in V. carteri.

Michod RE, Viossat Y, Solari CA, et al.
Life-history evolution and the origin of multicellularity
JOURNAL OF THEORETICAL BIOLOGY 239 (2): 257-272 MAR 21 2006

Abstract: The fitness of an evolutionary individual can be understood in terms of its two basic components: survival and reproduction. As embodied in current theory, trade-offs between these fitness components drive the evolution of life-history traits in extant multicellular organisms. Here, we argue that the evolution of germ-soma specialization and the emergence of individuality at a new higher level during the transition from unicellular to multicellular organisms are also consequences of trade-offs between the two components of fitness-survival and reproduction. The models presented here explore fitness trade-offs at both the cell and group levels during the unicellular-multicellular transition. When the two components of fitness negatively covary at the lower level there is an enhanced fitness at the group level equal to the covariance of components at the lower level. We show that the group fitness trade-offs are initially determined by the cell level trade-offs. However, as the transition proceeds to multicellularity, the group level trade-offs depart from the cell level ones, because certain fitness advantages of cell specialization may be realized only by the group. The curvature of the trade-off between fitness components is a basic issue in life-history theory and we predict that this Curvature is concave in single-celled organisms but becomes increasingly convex as group size increases in multicellular organisms. We argue that the increasingly convex curvature of the trade-off function is driven by the initial cost of reproduction to Survival which increases as group size increases. To illustrate the principles and conclusions of the model, we consider aspects of the biology of the volvocine green algae, which contain both unicellular and multicellular members.

Solari CA, Kessler JO, Michod RE
A hydrodynamics approach to the evolution of multicellularity: Flagellar motility and germ-soma differentiation in volvocalean green algae

AMERICAN NATURALIST 167 (4): 537-554 APR 2006

Abstract: During the unicellular-multicellular transition, there are opportunities and costs associated with larger size. We argue that germ-soma separation evolved to counteract the increasing costs and requirements of larger multicellular colonies. Volvocalean green algae are uniquely suited for studying this transition because they range from unicells to multicellular individuals with germ-soma separation. Because Volvocales need flagellar beating for movement and to avoid sinking, their motility is modeled and analyzed experimentally using standard hydrodynamics. We provide comparative hydrodynamic data of an algal lineage composed of organisms of different sizes and degrees of complexity. In agreement with and extending the insights of Koufopanou, we show that the increase in cell specialization as colony size increases can be explained in terms of increased motility requirements. First, as colony size increases, soma must evolve, the somatic-to-reproductive cell ratio increasing to keep colonies buoyant and motile. Second, increased germ-soma specialization in larger colonies increases motility capabilities because internalization of non-flagellated germ cells decreases colony drag. Third, our analysis yields a limiting maximum size of the volvocalean spheroid that agrees with the sizes of the largest species known. Finally, the different colony designs in Volvocales reflect the trade-offs between reproduction, colony size, and motility.

Solari CA, Ganguly S, Kessler JO, et al.
Multicellularity and the functional interdependence of motility and molecular transport
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA 103 (5): 1353-1358 JAN 31 2006

Abstract: Benefits, costs, and requirements accompany the transition from motile totipotent unicellular organisms to multicellular organisms having cells specialized into reproductive (germ) and vegetative (sterile soma) functions such as motility. In flagellated colonial organisms such as the volvocalean green algae, organized beating by the somatic cells' flagella yields propulsion important in phototaxis and chemotaxis. It has not been generally appreciated that for the larger colonies flagellar stirring of boundary layers and remote transport are fundamental for maintaining a sufficient rate of metabolite turnover, one not attainable by diffusive transport alone. Here, we describe experiments that quantify the role of advective dynamics in enhancing productivity in germ soma-differentiated colonies. First, experiments with suspended deflagellated colonies of Volvox carteri show that forced advection improves productivity. Second, particle imaging velocimetry of fluid motion around colonies immobilized by micropipette aspiration reveals flow fields with very large characteristic velocities U extending to length scales exceeding the colony radius R. For a typical metabolite diffusion constant D, the associated Peclet number Pe = 2UR/D >> 1, indicative of the dominance of advection over diffusion, with striking augmentation at the cell division stage. Near the colony surface, flows generated by flagella can be chaotic, exhibiting mixing due to stretching and folding. These results imply that hydrodynamic transport external to colonies provides a crucial boundary condition, a source for supplying internal diffusional dynamics.

Hallmann A
The pherophorins: common, versatile building blocks in the evolution of extracellular matrix architecture in Volvocales
PLANT JOURNAL 45 (2): 292-307 JAN 2006

Abstract: Green algae of the order Volvocales provide an unrivalled opportunity for exploring the transition from unicellularity to multicellularity. They range from unicells, like Chlamydomonas, through homocytic colonial forms with increasing cooperation of individual cells, like Gonium or Pandorina, to heterocytic multicellular forms with different cell types and a complete division of labour, like Volvox. A fundamental requirement for the evolution of multicellularity is the development of a complex, multifunctional extracellular matrix (ECM). The ECM has many functions, which can change under developmental control or as a result of environmental factors. Here molecular data from 15 novel proteins are presented. These proteins have been identified in Chlamydomonas reinhardtii, Gonium pectorale, Pandorina morum and Volvox carteri, and all belong to a single protein family, the pherophorins. Pherophorin-V1 is shown to be a glycoprotein localized to the 'cellular zone' of the V. carteri ECM. Pherophorin-V1 and -V2 mRNAs are strongly induced not only by the sex inducer, which triggers sexual development at extremely low concentrations, but also by mechanical wounding. Like the extensins of higher plants, which are also developmentally controlled or sometimes inducible by wounding, the pherophorins contain a (hydroxy-) proline-rich (HR) rod-like domain and are abundant within the extracellular compartment. In contrast to most extensins, pherophorins have additional globular A and B domains on both ends of the HR domains. Therefore pherophorins most closely resemble a particular class of higher plant extensin, the solanaceous lectins (e. g. potato lectin), suggesting multivalent carbohydrate-binding functions are present within the A and B domains and are responsible for cross-linking. Our results suggest that pherophorins are used as the building blocks for the extracellular scaffold throughout the Volvocales, with the characteristic mesh sizes in different ECM structures being a result of the highly diverse extensions of the HR domains. Pherophorins have therefore been a versatile element during the evolution of ECM architecture in these green algae.

2005

Yoshida H, Yokomori T, Suyama A. A simple classification of the volvocine algae by formal languages.

BULLETIN OF MATHEMATICAL BIOLOGY 67 (6): 1339-1354 NOV 2005

Abstract: There are several explanations of why certain primitive multicellular organisms aggregate in particular forms and why their constituent cells cooperate with one another to a particular degree. Utilizing the framework of formal language theory, we have derived one possible simple classification of the volvocine algae-one of the primitive multicells-for some forms of aggregation and some degrees of cooperation among cells. The volvocine algae range from the unicellular Chlamydonionas to the multicellular Volvox globator, which has thousands of cells. The classification we use in this paper is based on the complexity of Parikh sets of families on Chomsky hierarchy in formal language theory. We show that an alga with almost no space closed to the environment, e.g., Gonium pectorale, can be characterized by PsFIN, one with a closed space and no cooperation, e.g., Eudorina elegans, by PsCF, and one with a closed space and cooperation, e.g., Volvox globator, by Ps lambda SC. This classification should provide new insights into the necessity for specific forms and degrees of cooperation in the volvocine algae. (c) 2005 Society for Mathematical Biology.

Cheng Q, Pappas V, Hallmann A, et al. Hsp70A and GlsA interact as partner chaperones to regulate asymmetric division in Volvox. DEVELOPMENTAL BIOLOGY 286 (2): 537-548 OCT 15 2005

Abstract: GlsA, a J-protein chaperone, is required for the asymmetric divisions that set aside germ and somatic cell precursors during embryogenesis in Volox carteri, and previous evidence indicated that this function requires an intact Hsp70-binding site. To determine if Hsp70A, the only known cytoplasmic Hsp70 in V. carteri, is the chaperone partner of GlsA, we investigated the localization of the two proteins during critical stages of embryogenesis and tested their capacity to interact. We found that a substantial fraction of Hsp70A co-localizes with GlsA, both in interphase and mitotic blastomeres. In addition, Hsp70A coimmunoprecipitated with GlsA, and co-expression of GlsA and Hsp70A variants partially rescued the Gls phenotype of a glsA mutant, whereas neither variant by itself rescued the mutant phenotype. Immunofluorescence analysis demonstrated that GlsA is about equally abundant in all blastomeres at all cleavage stages examined but that Hsp70A is more abundant in anterior (asymmetrically dividing) blastomeres than in posterior (symmetrically dividing) blastomeres during the period of asymmetric division. We conclude that Hsp70A and GlsA function as chaperone partners that regulate asymmetric division and that the relative abundance of Hsp70A in asymmetrically dividing embryos may determine which blastomeres divide asymmetrically and which do not.

Aono N, Inoue T, Shiraishi H. Genes specifically expressed in sexually differentiated female spheroids of Volvox carteri.

JOURNAL OF BIOCHEMISTRY 138 (4): 375-382 OCT 2005

Abstract: Volvox carteri is a multicellular green alga with only two cell types, somatic cells and reproductive cells. Phylogenetic analysis suggests that this organism has evolved from a Chlamydomonas-like unicellular ancestor along with multicellularity, cellular differentiation, and a change in the mode of sexual reproduction from isogamy to oogamy. To examine the mechanism of sexual differentiation and the evolution of oogamy, we isolated 6 different cDNA sequences specifically expressed in sexually differentiated female spheroids. The genes for the cDNAs were designated SEF1 to SEF6. The time course of accumulation of each mRNA was shown to be distinct. The expression of some of these genes was not significantly affected when the sexual inducer was removed after the induction of sexual development. Sequence analysis indicates that SEF5 and SEF6 encode pherophorin-related proteins. Of these, SEF5 has the unique structural feature of a polyproline stretch in the C-terminal domain in addition to the one found in the central region.

 Wadhwa V, Kumar S, Rai S, et al. A 'pseudo outbreak' of the contamination of blood cultures with Volvox globator.

ANNALS OF TROPICAL MEDICINE AND PARASITOLOGY 99 (7): 719-720 OCT 2005

2004

Kirk MM, Kirk DL
Exploring germ-soma differentiation in Volvox 
JOURNAL OF BIOSCIENCES 29 (2): 143-152 JUN 2004

Just A, Gruber I, Wober M, et al.
Novel method for the cryopreservation of testicular sperm and ejaculated spermatozoa from patients with severe oligospermia: a pilot study 
FERTILITY AND STERILITY 82 (2): 445-447 AUG 2004

Abstract: 

Objective: To investigate Volvox globator as an easy-to-handle vehicle and as a safe alternative for cryopreservation of functional motile sperm cells.

Design: Prospective, controlled, clinical pilot study.

Setting: Two in vitro fertilization (IVF) outpatient clinics for reproductive medicine.

Patient(s): Fifteen patients with severe male infertility (density <100 motile sperm per milliliter) who were recruited from two IVF programs. The sperm cells were not intended for clinical use after thawing.

Intervention(s): In each case, a predetermined number (n = 8) of motile and morphologically intact sperm cells were injected into each Volvox sphere and then cryopreserved. The quality of the sperm cells and the handling of the Volvox spheres were verified.

Main Outcome Measure(s): Postthaw recovery rate in cases of severe male infertility and the amount of motile sperm after thawing.

Result(s): The postthaw recovery rate was 100%. At least 60% of the sperm cells were motile after thawing.

Conclusion(s): The use of the spherical algae Volvox globator offers a promising, inexpensive, and easy approach to the cryopreservation of functional motile sperm cells. Volvox globator is an alternative in countries that prohibit the destructive use of oocytes, even after fertilization has failed.

Jakobiak T, Mages W, Scharf B, et al.
The bacterial paromomycin resistance gene, aphH, as a dominant selectable marker in Volvox carteri 
PROTIST 155 (4): 381-393 DEC 2004

Abstract: 

The aminoglycoside antibiotic paromomycin that is highly toxic to the green alga Volvox carteri is efficiently inactivated by aminoglycoside 3'-phosphotransferase from Streptomyces rimosus. Therefore, we made constructs in which the bacterial aphH gene encoding this enzyme was combined with Volvox cis-regulatory elements in an attempt to develop a new dominant selectable marker - paromomycin resistance (Pm-R) - for use in Volvox nuclear transformation. The construct that provided the most efficient transformation was one in which aphH was placed between a chimeric promoter that was generated by fusing the Volvox hsp70 and rbcS3 promoters and the 3' UTR of the Volvox rbcS3 gene. When this plasmid was used in combination with a high-impact biolistic device, the frequency of stable Pm-R transformants ranged about 15 per 106 target cells. Due to rapid and sharp selection, Pm-R transformants were readily isolated after six days, which is half the time required for previously used markers. Co-transformation of an unselected marker ranged about 30%. The chimeric aphH gene was stably integrated into the Volvox genome, frequently as tandem multiple copies, and was expressed at a level that made selection of Pm-R transformants simple and unambiguous. This makes the engineered bacterial aphH gene an efficient dominant selection marker for the transformation and co-transformation of a broad range of V carteri strains without the recurring need for using auxotrophic recipient strains.

Pappas V, Blakely S, Wetzel M, et al.
Functional analysis of the Volvox asymmetric division protein GlsA 
MOLECULAR BIOLOGY OF THE CELL 15: 218A-218A 1207 Suppl. S NOV 2004

Cheng Q, Miller SM
Cytoplasmic Hsp70 distribution correlates with asymmetric division in the green alga Volvox carteri 
MOLECULAR BIOLOGY OF THE CELL 15: 218A-218A 1206 Suppl. S NOV 2004

Kirk DL

Volvox

CURRENT BIOLOGY, 14, R599-R600; for pdf click here

Nedelcu AM, Marcu O, and Michod RE.

Sex as a response to oxidative stress: A two-fold increase in cellular reactive oxygen species activates sex genes.

P ROY SOC LOND B BIO, 271, 1591-1596; for pdf click here

Abstract:

Organisms are constantly subjected to factors that can alter the cellular redox balance and result in the formation of a series of highly reactive molecules known as reactive oxygen species (ROS). As ROS can be damaging to biological structures, cells evolved a series of mechanisms (e.g., cell-cycle arrest, programmed cell death) to respond to high levels of ROS (i.e., oxidative stress). Recently, we presented evidence that in a facultatively sexual lineage – the multicellular green alga Volvox carteri – sex is an additional response to increased levels of stress, and likely ROS and DNA damage. Here, we show that in V. carteri (i) sex is triggered by a ca. two-fold increase in the level of cellular ROS (induced either by the natural sex-inducing stress, namely heat, or by blocking the mitochondrial electron transport chain with antimycin A), and (ii) ROS are responsible for the activation of sex genes. As most types of stress result in the overproduction of ROS, we believe that our findings will prove to extend to other facultatively sexual lineages, which could be indicative of the ancestral role of sex as an adaptive response to stress and ROS-induced DNA damage.

Nedelcu AM and Michod RE. 

Evolvability, modularity, and individuality during the  transition to multicellularity in volvocalean green algae.

In Schlosser G and Wagner G (eds) “Modularity in development and evolution”. Pp. 466-489. University of Chicago Press. (for pdf click here)

2003

Desnitskiy AG.

Peculiarities of the geographical distribution of coenobial volvocine algae (Volvocaceae, Chlorophyta).

Botanical Journal (St Petersburg). 2003. Vol. 88. N 11. pp. 52-61.(in Russian, with English Summary)

Abstract:

Data on the geographical distribution of 36 species from 7 genera of the family Volvocaceae sensu Nozaki (Pandorina, Volvulina, Yamagishiella, Eudorina, Platydorina, Pleodorina and Volvox) have been summarized. Both cosmopolitan species and species with local distribution have been detected. An attempt was made to trace a correlation of latitudinal distribution of the coenobial volvocine algae with obligatory differentiated somatic cells (22 species of the genera Volvox and Pleodorina) with peculiarities of proceeding of the cell divisions during asexual developmental cycle. In high latitudes of the Northern Hemisphere (northward of 50-57° north) only 3 species of Volvox occur, in which the formation of new coenobia (a series of consecutive gonidial divisions) starts with the light period (in the morning), the rate of division is slow and the gonidial divisions are temporarily blocked in darkness.

Schmitt R

Differention of germinal and somatic cells in Volvox carteri
CURRENT OPINION IN MICROBIOLOGY 6 (6): 608-613 DEC 2003

Abstract:
Volvox carteri is a spherical alga with a complete division of labor between around 2000 biflagellate somatic cells and 16 asexual reproductive cells (gonidia). It provides an attractive system for studying how a molecular genetic program for cell-autonomous differentiation is encoded within the genome. Three types of genes have been identified as key players in germ-soma differentiation: a set of gls genes that act in the embryo to shift cell-division planes, resulting in asymmetric divisions that set apart the large-small sister-cell pairs; a set of lag genes that act in the large gonidial initials to prevent somatic differentiation; and the regA gene, which acts in the small somatic initials to prevent reproductive development. Somatic-cell-specific expression of regA is controlled by intronic enhancer and silencer elements.

Nozaki H

Origin and evolution of the genera Pleodorina and Volvox (Volvocales)
BIOLOGIA 58 (4): 425-431 JUL 2003

Abstract:
The previous molecular phylogenetic study using 6021 base pairs from five chloroplast genes suggested that two species of Pleodorina (P. californica, P. japonica) might have evolved from a Volvox-like alga by the decrease in colony cell number and size. However, number of species of the genus Volvox was very limited especially in the section Merrillosphaera. In the present study, 6021 base pairs of the concatenated five chloroplast genes from 10 strains representing seven taxa of the genus Volvox were added to the previous data matrix. The sequence data resolved two anisogamous/oogamous clades within a large monophyletic group comprising five advanced genera of the Volvocaceae (Yamagishiella, Platydorina, Eudorina, Pleodorina and Volvox), one containing Volvox sect. Volvox and the anisogamous genus Platydorina (32-celled flattened colony), and the other (Eudorina group) composed of three other sections of Volvox, Pleodorina and Eudorina. The isogamous genus Yamagishiella (32-celled colony) was positioned basally to the Eudorina group. Therefore, evolution of anisogamy with sperm packets from isogamy might have occurred twice within the Volvocaceae. Based on the present molecular phylogenetic analysis, species of Volvox and Pleodorina within the Eudorina group represented three and two, respectively, separate lineages. One the three Volvox lineages [composed of V (sect. Merrillosphaera) carteri, V (sect. Merrillosphaera) obversus, V. (sect. Merrillosphaera) tertius, V. (sect. Merrillosphaera) africanus and V (sect. Copelandosphaera) dissipatrix] was sister to the monophyletic group consisting of one of the two Pleodorina lineages (P. californica and P. japonica) and V (sect. Janetosphaera) aureus. In addition, species of Eudorina were basal to the two lineages of Pleodorina and three Volvox lineages within the Eudorina group, representing the ancestral situation of Pleodorina/Volvox (excluding sect. Volvox). Thus, reverse evolution from a Volvox-like alga to Pleodorina suggested previously appears unlikely.

Cheng Q, Fowler R, Tam LW, et al.

The role of GlsA in the evolution of asymmetric cell division in the green alga Volvox caiteri
DEV GENES EVOL 213 (7): 328-335 JUL 2003

Abstract:
Volvox carteri, a green alga in the order Volvocales, contains two completely differentiated cell types, small motile somatic cells and large reproductive cells called gonidia, that are set apart from each other during embryogenesis by a series of visibly asymmetric cell divisions. Mutational analysis has revealed a class of genes (gonidialess, gls) that are required specifically for asymmetric divisions in V. carteri, but that are dispensable for symmetric divisions. Previously we cloned one of these genes, glsA, and showed that it encodes a chaperone-like protein (G1sA) that has close orthologs in a diverse set of eukaryotes, ranging from fungi to vertebrates and higher plants. In the present study we set out to explore the role of glsA in the evolution of asymmetric division in the volvocine algae by cloning and characterizing a glsA ortholog from one of the simplest members of the group, Chlamydomonas reinhardtii, which does not undergo asymmetric divisions. This ortholog (which we have named gar1, for glsA related) is predicted to encode a protein that is 70% identical to G1sA overall, and that is most closely related to G1sA in the same domains that are most highly conserved between G1sA and its other known orthologs. We report that a gar1 transgene fully complements the glsA mutation in V. carteri, a result that suggests that asymmetric division probably arose through the modification of a gene whose product interacts with G1sA, but not through a modification of glsA itself.

Grewing A, Krings M, Galtier J, et al.

The oldest fossil endophytic alga and its unusual habitat
SYMBIOSIS 34 (3): 215-230 2003

Abstract:
Lycophyte megaspores from the Lower Carboniferous of France sometimes contain a colonial (volvocacean) alga as an endophyte. This peculiar plant-plant association was briefly described more than 100 years ago and the name Lageniastrum macrosporae introduced for the alga, but the biological significance of the discovery was never fully appreciated. Here we present a reappraisal of the original material, which to date provides the oldest unequivocal fossil evidence for endophytic algae and the only example of an alga residing in the interior of spores of vascular cryptogams.

Nedelcu AM, Michod RE

Sex as a response to oxidative stress: the effect of antioxidants on sexual induction in a facultatively sexual lineage
P ROY SOC LOND B BIO 270: S136-S139 Suppl. 2 NOV 7 2003 (for pdf click here)

Abstract:
The evolution of sex is one of the long-standing unsolved problems in biology. Although in many lineages sex is an obligatory part of the life cycle and is associated with reproduction, in prokaryotes and many lower eukaryotes, sex is facultative, occurs in response to stress and often involves the formation of a stress-resistant dormant form. The proximate and ultimate causes of the connection between stress and sex in facultatively sexual lineages are unclear. Because most forms of stress result in the overproduction of cellular reactive oxygen species (ROS), we address the hypothesis that this connection involves ROS and possibly reflects the ancestral role of sex as an adaptive response to the damaging effects of stress-induced ROS (i.e. oxidative stress) . Here, we report that two antioxidants inhibit sexual induction in a facultatively sexual species-the multicellular green alga, Volvox carteri. Furthermore, the nature of the sex response and the effect of an iron chelator on sexual induction are consistent with sex being a response to the DNA-damaging effects of ROS. In addition, we present preliminary data to suggest that sex, cell-cycle arrest and apoptosis are alternative responses to increased levels of oxidative stress.

Rudel D, Sommer RJ

The evolution of developmental mechanisms
DEV BIOL 264 (1): 15-37 DEC 1 2003

Abstract:
Over the past two to three decades, developmental biology has demonstrated that all multicellular organisms in the animal kingdom share many of the same molecular building blocks and many of the same regulatory genetic pathways. Yet we still do not understand how the various organisms use these molecules and pathways to assume all the forms we know today. Evolutionary developmental biology tackles this problem by comparing the development of one organism to another and comparing the genes involved and gene functions to understand what makes one organism different from another. In this review, we revisit a set of seven concepts defined by Lewis Wolpert (fate maps, asymmetric division. induction, competence, positional information, determination, and lateral inhibition) that describe the characters of many developmental systems and supplement them with three additional concepts (developmental genomics, genetic redundancy, and genetic networks). We will discuss examples of comparative developmental studies where these concepts have guided observations on the advent of a developmental novelty. Finally, we identify a set of evolutionary frameworks, such as developmental constraints, cooption, duplication, parallel and convergent evolution, and homoplasy, to adequately describe the evolutionary properties of developmental systems. (C) 2003 Elsevier Inc. All rights reserved.

Kato-Minoura T, Okumura M, Hirono M, et al.

A novel family of unconventional actins in volvocalean algae
J MOL EVOL 57 (5): 555-561 NOV 2003

Abstract:
The unicellular green alga Chlamydomonas reinhardtii has two actin genes, one encoding a conventional actin (90% amino acid identity with mammalian actin), the other a highly divergent actin (64% identity) named novel actin-like protein (NAP). To see whether the presence of conventional and unconventional actins in a single organism is unique to C. reinhardtii, we searched for genomic sequences related to the NAP sequence in several other species of volvocalean algae. Here we show that Chlamydomonas moewusii and Volvox carteri also have, in addition to a conventional actin, an unconventional actin similar to the C. reinhardtii NAP. Analyses of the deduced protein sequences indicated that the NAP homologues form a distinct group derived from conventional actin.

Golstein P, Aubry L, Levraud JP

Cell-death alternative model organisms: Why and which?
NAT REV MOL CELL BIO 4 (10): 798-807 OCT 2003

Abstract:
Classical model organisms have helped greatly in our understanding of cell death but, at the same time, night have constrained it. The use of other, nor-classical model organisms from all biological kingdoms could reveal undetected molecular pathways and better-defined morphological types of cell death. Here we discuss what is known and what might be learned from these alternative model systems.

Ohta H, Suzuki T, Ueno M, et al.

Extrinsic proteins of photosystem II - An intermediate member of the PsbQ protein family in red algal PSII
EUR J BIOCHEM 270 (20): 4156-4163 OCT 2003

Abstract:
The oxygen-evolving photosystem II (PS II) complex of red algae contains four extrinsic proteins of 12 kDa, 20 kDa, 33 kDa and cyt c-550, among which the 20 kDa protein is unique in that it is not found in other organisms. We cloned the gene for the 20-kDa protein from a red alga Cyanidium caldarium. The gene consists of a leader sequence which can be divided into two parts: one for transfer across the plastid envelope and the other for transfer into thylakoid lumen, indicating that the gene is encoded by the nuclear genome. The sequence of the mature 20-kDa protein has low but significant homology with the extrinsic 17-kDa (PsbQ) protein of PS II from green algae Volvox Carteri and Chlamydomonas reinhardtii, as well as the PsbQ protein of higher plants and PsbQ-like protein from cyanobacteria. Cross-reconstitution experiments with combinations of the extrinsic proteins and PS Its from the red alga Cy. caldarium and green alga Ch. reinhardtii showed that the extrinsic 20-kDa protein was functional in place of the green algal 17-kDa protein on binding to the green algal PS II and restoration of oxygen evolution. From these results, we conclude that the 20-kDa protein is the ancestral form of the extrinsic 17-kDa protein in green algal and higher plant PS IIs. This provides an important clue to the evolution of the oxygen-evolving complex from prokaryotic cyanobacteria to eukaryotic higher plants. The gene coding for the extrinsic 20-kDa protein was named psbQ' (prime).

Cole DG, Reedy MV

Algal morphogenesis: How Volvox turns itself inside-out
CURR BIOL 13 (19): R770-R772 SEP 30 2003

Abstract:
During its development, the multicellular green alga Volvox undergoes inversion, in which spherical embryos turn their multicellular sheet completely inside out. A mutant analysis has revealed that a novel kinesin motor protein is essential for completing this process.

Voigt J, Frank R

14-3-3 proteins are constituents of the insoluble glycoprotein framework of the Chlamydomonas cell wall
PLANT CELL 15 (6): 1399-1413 JUN 2003

Abstract:
The cell wall of the unicellular green alga Chlamydomonas reinhardtii consists predominantly of Hyp-rich glycoproteins, which also occur in the extracellular matrix of multicellular green algae and higher plants. In addition to the Hyp-rich polypeptides, the insoluble glycoprotein framework of the Chlamydomonas cell wall contains minor amounts of 14-3-3 proteins, as revealed by immunochemical studies and mass spectroscopic analysis of tryptic peptides. Polypeptides immunologically related to the 14-3-3 proteins also were found in the culture medium of Chlamydomonas. The levels of two of these 14-3-3-related polypeptides were decreased in the culture medium of the wall-deficient mutant cw-15. These findings indicate that 14-3-3 proteins are involved in the cross-linking of Hyp-rich glycoproteins in the Chlamydomonas cell wall.

Michod RE, Nedelcu AM

On the reorganization of fitness during evolutionary transitions in individuality
INTEGR COMP BIOL 43 (1): 64-73 FEB 2003 (for pdf click here)

Abstract:
The basic problem in an evolutionary transition is to understand how a group of individuals becomes a new kind of individual, possessing the property of heritable variation in fitness at the new level of organization. During an evolutionary transition, for example, from single cells to multicellular organisms, the new higher-level evolutionary unit (multicellular organism) gains its emergent properties by virtue of the interactions among lower-level units (cells). We see the formation of cooperative interactions among lower-level units as a necessary step in evolutionary transitions; only cooperation transfers fitness from lower levels (costs to group members) to higher levels (benefits to the group). As cooperation creates new levels of fitness, it creates the opportunity for conflict between levels as deleterious mutants arise and spread within the group. Fundamental to the emergence of a new higher-level unit is the mediation of conflict among lower-level units in favor of the higher-level unit. The acquisition of heritable variation in fitness at the new level, via conflict mediation, requires the reorganization of the basic components of fitness (survival and reproduction) and life-properties (such as immortality and totipotency) as well as the co-option of lower-level processes for new functions at the higher level. The way in which the conflicts associated with the transition in individuality have been mediated, and fitness and general life-traits have been re-organized, can influence the potential for further evolution (i.e., evolvability) of the newly emerged evolutionary individual. We use the volvocalean green algal group as a model-system to understand evolutionary transitions in individuality and to apply and test the theoretical principles presented above. Lastly, we discuss how the different notions of individuality stem from the basic properties of fitness in a multilevel selection context.

Kirk DL

Seeking the ultimate and proximate causes of Volvox multicellularity and cellular differentiation
INTEGR COMP BIOL 43 (2): 247-253 APR 2003

Abstract:
Volvox and its relatives provide an exceptional model for integrative studies of the evolution of multicellularity and cellular differentiation. The volvocine algae range in complexity from unicellular Chlamydomonas through several colonial genera with a single cell type, to multicellular Volvox with its germsoma division of labor. Within the monophyletic family Volvocaceae, several species of Volvox have evolved independently in different lineages, the ultimate cause presumably being the advantage that large size and cellular differentiation provide in competing for limiting resources such as phosphorous. The proximate causes of this type of evolutionary transition are being studied in V carteri. All volvocine algae except Volvox exhibit biphasic development: cells grow during a motile, biflagellate phase, then they lose motility and divide repeatedly during the reproductive phase. In V carteri three kinds of genes transform this ancestral biphasic program into a dichotomous one that generates non-motile reproductive cells and biflagellate somatic cells with no reproductive potential: first the gls genes act in early embryos to cause asymmetric division and production of large-small sister-cell pairs; then lag genes act in the large cells to repress the biflagellate half of the ancestral program, while regA acts in the small cells to repress the reproductive half of the program. Molecular-genetic analysis of these genes is progressing, as will be illustrated with regA, which encodes a transcription factor that acts in somatic cells to repress nuclear genes encoding chloroplast proteins. Repression of chloroplast biogenesis prevents these obligately photoautotrophic cells from growing, and since they cannot grow, they cannot reproduce.

Mori T, Kuroiwa H, Higashiyama T, et al.

Identification of higher plant GlsA, a putative morphogenesis factor of gametic cells
BIOCHEM BIOPH RES CO 306 (2): 564-569 JUN 27 2003

Abstract:
GlsA has been identified in an asexual-reproductive-cell (gonidia)-deficient mutant of Volvox as a chaperone-like protein essential for gonidia production. In this study, we isolated an angiosperm glsA (LlglsA) gene expressed during Lilium longiflorum pollen development. Immunoblot analyses showed that the strong LlGlsA expression occurred in the generative cell and its pattern during pollen development corresponded to that of alpha-tubulin. Morphological analyses succeeded in visualizing the dispersion of the strong LlGlsA signal in developing generative cells. In addition, multiple-immunofluorescence staining of LIGNA and alpha-tubulin revealed that some of the dot-like LlGlsA signals were co-localized with microtubule filaments. From those results, we suggest that angiosperm GlsA functions as a chaperone modifying various structures during male gametic cell formation. (C) 2003 Elsevier Science (USA). All rights reserved.

Nishii I, Ogihara S, Kirk DL

A kinesin, InvA, plays an essential role in Volvox morphogenesis
CELL 113 (6): 743-753 JUN 13 2003

Abstract:
In Volvox carted adults, reproductive cells called gonidia are enclosed within a spherical monolayer of biflagellate somatic cells. Embryos must "invert" (turn inside out) to achieve this configuration, however, because at the end of cleavage the gonidia are on the outside and the flagellar ends of all somatic cells point inward. Generation of a bend region adequate to turn the embryo inside out involves a dramatic change in cell shape, plus cell movements. Here, we cloned a gene called invA that is essential for inversion and found that it codes for a kinesin localized in the cytoplasmic bridges that link all cells to their neighbors. In invA null mutants, cells change shape normally, but are unable to move relative to the cytoplasmic bridges. A normal bend region cannot be formed and inversion stops. We conclude that the InvA kinesin provides the motile force that normally drives inversion to completion.

Bonner JT

On the origin of differentiation
J BIOSCIENCES 28 (4): 523-528 JUN 2003

Abstract:
Following the origin of multicellularity in many groups of primitive organisms there evolved more than one cell type. It has been assumed that this early differentiation is related to size - the larger the organism the more cell types. Here two very different kinds of organisms are considered: the volvocine algae that become multicellular by growth, and the cellular slime moulds that become multicellular by aggregation. In both cases there are species that have only one cell type and others that have two. It has been possible to show that there is a perfect correlation with size: the forms with two cell types are significantly larger-than those with one. Also in both groups there are forms of intermediate size that will vary from one to two cell types depending on the size of the individuals, suggesting a form of quorum sensing. These observations reinforce the view that size plays a critical role in influencing the degree of differentiation.

Michod RE, Nedelcu AM, Roze D

Cooperation and conflict in the evolution of individuality IV. Conflict mediation and evolvability in Volvox carteri
BIOSYSTEMS 69 (2-3): 95-114 MAY 2003 (for pdf click here)

Abstract:
The continued well being of evolutionary individuals (units of selection and evolution) depends upon their evolvability, that is their capacity to generate and evolve adaptations at their level of organization, as well as their longer term capacity for diversifying into more complex evolutionary forms. During a transition from a lower- to higher-level individual, such as the transition between unicellular and multicellular organisms, the evolvability of the lower-level (cells) must be restricted, while the evolvability of the new higher-level unit (multicellular organism) must be enhanced. For these reasons, understanding the factors leading to an evolutionary transition should help us to understand the factors underlying the emergence of evolvability of a new evolutionary unit. Cooperation among lower-level units is fundamental to the origin of new functions in the higher-level unit. Cooperation can produce a new more complex evolutionary unit, with the requisite properties of heritable fitness variations, because cooperation trades fitness from a lower-level (the costs of cooperation) to the higher-level (the benefits for the group). For this reason, the evolution of cooperative interactions helps us to understand the origin of new and higher-levels of fitness and organization. As cooperation creates a new level of fitness, it also creates the opportunity for conflict between levels of selection, as deleterious mutants with differing effects at the two levels arise and spread. This conflict can interfere with the evolvability of the higher-level unit, since the lower and higher-levels of selection will often "disagree" on what adaptations are most beneficial to their respective interests. Mediation of this conflict is essential to the emergence of the new evolutionary unit and to its continued evolvability. As an example, we consider the transition from unicellular to multicellular organisms and study the evolution of an early-sequestered germ-line in terms of its role in mediating conflict between the two levels of selection, the cell and the cell group. We apply our theoretical framework to the evolution of germ/soma differentiation in the green algal group Volvocales. In the most complex member of the group, Volvox carteri, the potential conflicts among lower-level cells as to the "right" to reproduce the higher-level individual (i.e. the colony) have been mediated by restricting immortality and totipotency to the germ-line. However, this mediation, and the evolution of an early segregated germ-line, was achieved by suppressing mitotic and differentiation capabilities in all post-embryonic cells. By handicapping the soma in this way, individuality is ensured, but the solution has affected the long-term evolvability of this lineage. We think that although conflict mediation is pivotal to the emergence of individuality at the higher-level, the way in which the mediation is achieved can greatly affect the longer-term evolvability of the lineage. (C) 2002 Elsevier Science Ireland Ltd. All rights reserved.

Laflamme M, Lee RW

Mitochondrial genome conformation among CW-group chlorophycean algae
J PHYCOL 39 (1): 213-220 FEB 2003

Abstract:
Most green algal taxa have circular-mapping mitochondrial genomes, whereas some have linear genome- or subgenomic-sized mitochondrial DNAs (mtDNA). It is not clear, however, if the circular-mapping genomes represent genome-sized circular molecules, if such circular molecules and the linear forms are the predominant in vivo mtDNA structures, or if the linear forms arose only once or multiple times among extant green algal lineages. We therefore examined the DNA components detected with homologous mtDNA probes after pulsed-field gel electrophoresis of total cellular DNA from the chlorophycean basal bodies displaced clockwise(CW)-group taxa Chlamydomonas reinhardtii and Chlamydomonas moewusii. For C. reinhardtii , the 15.8-kb linear mtDNA was the only DNA component detected, and there was no evidence of circular or large linear precursors of this DNA. In the case of C. moewusii , which is known to have a circular-mapping 22.9-kb mitochondrial genome, three DNA components were detected; these appeared to be circular (relaxed and supercoiled) and genome-sized linear DNA molecules, the latter of which likely resulted from random double-strand breaks in the circular forms during DNA isolation. In further studies, DNA from additional CW-group taxa was examined using conventional gel electrophoresis and DNA-filter blot analysis with C. reinhardtii and C. moewusii mtDNA probes. We conclude that all taxa from the "Volvox clade" (sensu Nakayama et al. 1996) of the CW-group have genome- or subgenomic-sized linear mtDNAs as their predominant mtDNA form and that these arose from a genome-sized circular form in an ancestor that existed near the base of this clade.

Hallmann A

Extracellular matrix and sex-inducing pheromone in Volvox
INT REV CYTOL 227: 131-+ 2003

Schmitt R, Sumper M

Developmental biology - How to turn inside out
NATURE 424 (6948): 499-500 JUL 31 2003

2002

Desnitski AG

Dormant stages of the green flagellate in Volvox in a natural habitat

RUSSIAN JURNAL OF DEVELOPMENTAL BIOLOGY 33(2): 107-109; 2002 (for pdf click here)

Coleman AW

Comparison of Eudorina/Pleodorina ITS sequences of isolates from nature with those from experimental hybrids
AM J BOT 89 (9): 1523-1530 SEP 2002

Abstract:
Internal transcribed spacer (ITS) regions of nuclear ribosomal repeats were compared among 50 Eudorina and Pleodorina isolates and two Volvox species known to clade with Eudorina species. Of the six major subclades found, four containing Eudorina and Pleodorina illinoisensis isolates, one containing Eudorina and Pleodorina indica, and one containing Volvox gigas and V. powersii, the basal branching order remains uncertain, but the positioning of isolates known to mate was always as nearest neighbors on the terminal branches of the tree. Four hybrid clones from a cross of E. elegans with P. illinoisensis, known from chromosome counts to be products of the failure of meiosis at zygote germination, contain both parental ITS repeat regions, as expected. However, they have in addition both crossover and other variant ITS cistrons among their many repeats of ITS. Such variation is limited to terminal regions of helices, as recognized from knowledge of RNA transcript secondary structure. Proper alignment then utilizes all of the nucleotide positions; the hybrid variants appear in positions intermediate between their parents in the tree. In fact, such variants seem to be hallmarks of recent hybridization events, since they were not found in any of the other 50 isolates.

Duncan L, Bouckaert K, Yeh F, et al.

Kangaroo, a mobile element from Volvox carteri, is a member of a newly recognized third class of retrotransposons
GENETICS 162 (4): 1617-1630 DEC 2002

Abstract:
Retrotransposons play an important role in the evolution of genomic structure and function. Here we report on the characterization of a novel retrotransposon called kangaroo front the multicellular green alga, Volvox carteri. kangaroo elements are highly mobile and their expression is developmentally regulated. The), probably integrate via double-stranded, closed-circle DNA intermediates through the action of an encoded recombinase related to the X-site-specific integrase. Phylogenetic analysis indicates that kangaroo elements are closely related to other unorthodox retrotransposons including PAT (from a nematode), DIRS-1 (from Dictyostelium), and DrDIRS1 (from zebrafish). PAT and kangaroo both contain split direct repeat (SDR) termini, and here we show that DIRS-1 and DrDIRS1 elements contain terminal features structurally related to SDRs. Thus, these mobile elements appear to define a third class of retrotransposons (the DIRS1 group) that are unified by common structural features, genes, and integration mechanisms, all of which differ from those of LTR and conventional non-LTR retrotransposons.

Berthold P, Schmitt R, Mages W

An engineered Streptomyces hygroscopicus aph 7" gene mediates dominant resistance against hygromycin B in Chlamydomonas reinhardtii
PROTIST 153 (4): 401-412 DEC 2002

Abstract:
We have developed a positively selectable marker for the green alga Chlamydomonas reinhardtii using the Streptomyces hygroscopicus aminoglycoside phosphotransferase gene (aph7"). Its expression is controlled by C. reinhardtii regulatory elements, namely, the beta2-tubulin gene promoter in combination with the first intron and the 3' untranslated region of the small subunit of ribulose bisphosphate carboxylase, rbcS2. C. reinhardtii cell-wall deficient and wild-type strains were transformed at rates up to 5 x 10(-5) with two constructs, pHyg3 and pHyg4 (intron-less). Transformants selected on plates with 10 mug/ml hygromycin B exhibited diverse levels of resistance of up to 200 mug/ml that were stably maintained for at least seven months; they contained two to five copies of the construct integrated in their genomes. Transcription of the chimeric aph7" gene, correct splicing of the rbcS2 intron, and polyadenylation of the transcripts have been verified by sequencing of RT-PCR products. Average co-transformation rates using pHyg3 and a second selectable plasmid were about 11%. This advocates the hygromycin-resistance plasmid, pHyg3, as a new versatile tool for the transformation of a broad range of C. reinhardtii strains without the sustained need for using auxotrophic mutants as recipients.

Gradmann D, Ehlenbeck S, Hegemann P

Modeling light-induced currents in the eye of Chlamydomonas reinhardtii
J MEMBRANE BIOL 189 (2): 93-104 SEP 15 2002

Abstract:
Rhodopsin-mediated electrical events in green algae have been recorded in the past from the eyes of numerous micro-algae like Haematococcus pluvialis, Chlamydomonas reinhardtii and Volvox carteri. However, the electrical data gathered by suction-pipette techniques could be interpreted in qualitative terms only. Here we present two models that allow a quantitative analysis of such results: First, an electrical analog circuit for the cell in suction pipette configuration is established. Applying this model to experimental data from unilluminated cells of C. reinhardtii yields a membrane conductance of about 3 Sm-2. Furthermore, an analog circuit allows the determination of the photocurrent fraction that is recorded under experimental conditions. Second, a reaction scheme of a rhodopsin-type photocycle with an early Ca2+ conductance and a later H+ conductance is presented. The combination of both models provides good fits to light-induced currents recorded from C. reinhardtii. Finally, it allowed the calculation of the impact of each model parameter on the time courses of observable photocurrent and of inferred transmembrane voltage. The reduction of the flash-to-peak times at increasing. light intensities are explained by superposition of two kinetically distinct rhodopsins and by assuming that the Ca2+-conducting state decays faster at more positive membrane voltages.

Saliu JK

The diet of Brycinus nurse (Pisces : Characidae) from Asa Reservoir, Ilorin, Nigeria
REV BIOL TROP 50 (1): 239-243 MAR 2002

Abstract:
From November 1991 to October 1993, 980 specimens of the characid Brycinus nurse were collected from Asa reservoir to examine its diet. The diet was analyzed using the frequency of occurrence, numerical and gravimetric methods. Two hundred and sixty nine (27.45%) of the stomachs examined were empty. The fish was an omnivore feeding extensively on a wide array of plant and animal food items. These consisted of 9 families, 10 genera and 10 species. The most extensively consumed plant food item was aquatic plant parts which occurred in 63.88% of the stomachs, and accounted for 6.06% by number and 12.10% by weight while the ephemeropteran, Povilla adusta was the most dominant animal food item, occurring in 50.92% of the stomachs, and accounting for 11.98% by number and 11.86% by weight. Conversely, the least consumed plant food item was Volvox occurring in 4.49% of the stomachs and accounting for 0.18% by number and 0.35% by weight, while the fish Barbus sp. was the least consumed animal food item occurring in 0.51% of the stomachs, accounting for 0.03% by number and 1.62% by weight. New food items not previously recorded such as a watermite, Aspatharia sinuata and Barbus callipterus were found in the stomach contents. The nonspecific feeding regime of the fish and its ability to utilize different food items effectively was what accounted for the prominence and wide distribution of the fish in the lake.

Heitzer M, Hallmann A

An extracellular matrix-localized metalloproteinase with an exceptional QEXXH metal binding site prefers copper for catalytic activity
J BIOL CHEM 277 (31): 28280-28286 AUG 2 2002

Abstract:
The extracellular matrix (ECM) of the simple multicellular organism Volvox contains many region-specific morphological elements and mediates a variety of developmental and physiological responses by modification of its components. The fact that >95% of the mature organism is ECM makes Volvox suitable as a model system for ECM investigations. VMPs are a family of Volvox genes that are homologous to zinc-dependent matrix metalloproteinases (MMPs). Here we describe the identification and purification of the first VMP protein, VMP3. The 470-kDa VMP3 glycoprotein is localized within the ECM, and its biosynthesis is induced by the sex pheromone. The metal binding motif of VMP3 is QEXXH, not HEXXH as known for 1300 other metalloproteinases. VMP3 shows proteinase activity and is inhibited by EDTA or the MMP inhibitor GM 6001, but in contrast to all known proteinases, VMP3 clearly prefers copper for activity rather than zinc. The exchange from Q to H within the QEXXH motif abolishes its copper preference. The unique properties of VMP3 suggest a novel type of metalloproteinase.

Nozaki H, Takahara M, Nakazawa A, et al.

Evolution of rbcL group IA introns and intron open reading frames within the colonial Volvocales (Chlorophyceae)
MOL PHYLOGENET EVOL 23 (3): 326-338 JUN 2002

Abstract:
Mobile group I introns sometimes contain an open reading frame (ORE) possibly encoding a site-specific DNA endonuclease. However, previous phylogenetic studies have not clearly deduced the evolutionary roles of the group I intron ORFs. In this paper, we examined the phylogeny of group IA2 introns inserted in the position identical to that of the chloroplast-encoded rbcL coding region (rbcL-462 introns) and their ORFs from 13 strains of five genera (Volvox, Pleodorina, Volvulina, Astrephomene, and Gonium) of the colonial Volvocales (Chlorophyceae) and a related unicellular green alga, Vitreochlamys. The rbcL-462 introns contained an intact or degenerate ORE of various sizes except for the Gonium multicoccum rbcL-462 intron. Partial amino acid sequences of some rbcL-462 intron ORFs exhibited possible homology to the endo/excinuclease amino acid terminal domain. The distribution of the rbcL-462 introns is sporadic in the phylogenetic trees of the colonial Volvocales based on the five chloroplast exon sequences (6021 bp). Phylogenetic analyses of the conserved intron sequences resolved that the G. multicoccum rbcL-462 intron had a phylogenetic position separate from those of other colonial volvocalean rbcL-462 introns, indicating the recent horizontal transmission of the intron in the G. multicoccum lineage. However, the combined data set from conserved intron sequences and ORFs from most of the rbcL-462 introns resolved robust phylogenetic relationships of the introns that were consistent with those of the host organisms. Therefore, most of the extant rbcL-462 introns may have been vertically inherited from the common ancestor of their host organisms, whereas such introns may have been lost in other lineages during evolution of the colonial Volvocales. In addition, apparently higher synonymous substitutions than nonsynonymous substitutions in the rbcL-462 intron ORFs indicated that the ORFs might evolve under functional constraint, which could result in homing of the rbcL-462 intron in cases of spontaneous intron loss. On the other hand, the presence of intact to largely degenerate ORFs of the rbcL-462 introns within the three isolates of Gonium viridistellatum and the rare occurrence of the ORF-lacking rbcL-462 intron suggested that the ORF's might degenerate to result in the spontaneous intron loss during a very short evolutionary time following the loss of the ORF function. Thus, the sporadic distribution of the rbcL-462 introns within the colonial Volvocales can be largely explained by an equilibrium between maintenance of the introns by the intron ORF and spontaneous loss of introns when the introns do not have a functional ORE. (C) 2002 Elsevier Science (USA). All rights reserved.

Aono N, Shimizu T, Inoue T, et al.

Palindromic repetitive elements in the mitochondrial genome of Volvox
FEBS LETT 521 (1-3): 95-99 JUN 19 2002

Abstract:
Group I introns were found in the cob and cox I genes of Volvox carteri. These introns contain tandem arrays of short palindromic sequences that are related to each other. Inspection of other regions in the mtDNA revealed that similar palindromic repetitive sequences are dispersed in the non-protein coding regions of the mitochondrial genome. Analysis of the group I intron in the cob gene of another member of Volvocaceae, Volvox aureus, has shown that its sequence is highly homologous to its counterpart in V. carteri with the exception of a cluster of palindromic sequences not found in V. carteri. This indicates that the palindromic clusters were inserted into the introns after divergence of the two species, presumably due to frequent insertions of the palindromic elements during evolution of the Volvocaceae. Possible involvement of the palindromic repetitive elements in the molecular evolution of functional RNAs is discussed. (C) 2002 Published by Elsevier Science B.V. on behalf of the Federation of European Biochemical Societies.

Ender F, Godl K, Wenzl S, et al.

Evidence for autocatalytic cross-linking of hydroxyproline-rich glycoproteins during extracellular matrix assembly in volvox
PLANT CELL 14 (5): 1147-1160 MAY 2002

Abstract:
The alga Volvox carteri is one of the simplest multicellular organisms, yet it has a surprisingly complex extracellular matrix (ECM), making Volvox suitable as a model system in which to study ECM self-assembly. Here, we analyze the primary structures and post-translational modifications of two main ECM components synthesized in response to sexual induction as well as wounding. These proteins are members of the pherophorin family with as yet unknown properties. They contain polyhydroxyproline spacers as long as 500 and 2750 residues. Even the highly purified proteins retain the capacity to self-assemble and cross-link, producing an insoluble fibrous network in an apparently autocatalytic reaction. This pherophorin-based network is located within the deep zone of the ECM. A molecular genetic search for additional members of the pherophorin family indicates that at least nine different pherophorin species can be expected to serve as precursors for ECM substructures. Therefore, the highly diversified members of the pherophorin family represent region-specific morphological building blocks for ECM assembly and cross-linking.

Shimizu T, Inoue T, Shiraishi H

Cloning and characterization of novel extensin-like cDNAs that are expressed during late somatic cell phase in the green alga Volvox carteri
GENE 284 (1-2): 179-187 FEB 6 2002

Abstract:
Asexual individuals of the green alga Volvox carteri consist of two cell types, somatic and reproductive cells. The somatic cells are terminally differentiated post-mitotic cells which undergo gradual senescence leading to cell death in every generation. To understand the gene expression programs associated with senescence of somatic cells, we cloned two cDNAs, LSG1 and LSG2, that are preferentially expressed during this late developmental stage. These two cDNAs were deduced to encode Pro-rich motifs characteristic of extensin proteins that are components of the extracellular in matrix. LSG1 also resembled genes encoding plant pathogenesis-related protein 1 (PR-1), while LSG2 showed similarities with genes encoding matrix metalloproteinases, including a gamete lytic enzyme of Chlamydomonas. We also found that S9, one of the late somatic cDNAs previously cloned by Tam and Kirk (Dev. Biol. 145 (1991) 51), was deduced to encode a protein with a composition similar to LSG2. The expression of PR-1 and a matrix-metalloproteinase-encoding gene has been shown to be induced during senescence in higher plants. These results indicate that some of the late somatic genes in V. carteri are related to the senescence-associated genes in higher plants. (C) 2002 Elsevier Science B.V. All rights reserved.

Miller SM

Taming the fierce roller: an "enhanced" understanding of cellular differentiation in Volvox
BIOESSAYS 24 (1): 3-7 JAN 2002

Abstract:
Few organisms offer a better opportunity to explore the mechanisms of cellular differentiation, and their origins, than Volvox. Volvox consists of just two cell types, germ and soma, and is the most complex member of a family of green algae that includes unicellular and multicellular relatives. At the heart of the cell-fate determination program of Volvox carted is the regA gene, which encodes a putative transcriptional repressor that prevents somatic cells from expressing reproductive functions. Stark et al.((1)) have dissected the regA gene to determine how its expression is restricted to somatic cells. Their results suggest that regrA expression is controlled by multiple enhancers, the most important of which prevents transcription in reproductive cells. While these findings shed light on Volvox development, they also raise a new set of questions about the mechanisms that control the germ-soma dichotomy in this organism. (C) 2002 John Wiley Sons, Inc.

Nishii I, Kirk DL

A kinesin-like protein encoding gene, invA, is required for the cellular movements that drive inversion of Volvox embryos
MOL BIOL CELL 13: 834 NOV 2002

Stark K, Schmitt R

Genetic control of germ-soma differentiation in Volvox carteri
PROTIST 153 (2): 99-107 JUN 2002

2001

Kirk DL, Nishii I

Volvox carteri as a model for studying the genetic and cytological control of morphogenesis
DEV GROWTH DIFFER 43 (6): 621-631 DEC 2001

Abstract:
The green alga Volvox carteri has a very simple and regular adult form that arises through a short sequence of well-defined morphogenetic steps. A mature gonidium (asexual reproductive cell) initiates a stereotyped sequence of rapid cleavage divisions that will produce all of the cells found later in an adult. A predictable subset of these divisions are asymmetric and result in production of a small set of germ cells in a precise spatial pattern. Throughout cleavage, all intracellular components are held in predictable spatial relationships by a cytoskeleton of unusually regular structure, while neighboring cells are also held in fixed spatial relationships by an extensive network of cytoplasmic bridges that form as a result of incomplete cytokinesis. As a result of these two orienting mechanisms combined, dividing cells are arranged around the anterior-posterior axis of the embryo with precise rotational symmetry. These relationships are maintained by the cytoplasmic bridge system when the embryo that was inside out at the end of cleavage turns right-side out in the gastrulation-like process of inversion. Inversion is driven by a cytoskeleton-mediated sequence of cell shape changes, cellular movements and coordinated contraction. Then, by the time the cytoplasmic bridges begin to break down shortly after inversion, a preliminary framework of extracellular matrix (ECM) has been formed. The ECM traps the cells and holds them in the rotational relationships that were established during cleavage, and that must be maintained in order for the adult to be able to swim. Transposon tagging is now being used to clone and characterize the genes regulating these morphogenetic processes.

Sineshchekov OA, Govorunova EG

Rhodopsin receptors of phototaxis in green flagellate algae
BIOCHEMISTRY-MOSCOW+ 66 (11): 1300-1310 NOV 2001

Abstract:
Green flagellate algae are capable of the active adjustment of their swimming path according to the light direction (phototaxis). This direction is detected by a special photoreceptor apparatus consisting of the photoreceptor membrane and eyespot. Receptor photoexcitation in green flagellates triggers a cascade of rapid electrical events in the cell membrane which plays a crucial role in the signal transduction chain of phototaxis and the photophobic response. The photoreceptor current is the earliest so far detectable process in this cascade. Measurement of the photoreceptor current is at present the most suitable approach to investigation of the photoreceptor pigment in green flagellate algae, since a low receptor concentration in the cell makes application of optical and biochemical methods so far impossible. A set of physiological evidences shows that the phototaxis receptor in green flagellate algae is a unique rhodopsin-type protein. It shares common chromophore properties with retinal proteins from archaea. However, the involvement of photoelectric processes in the signal transduction chain relates it to animal visual rhodopsins. The presence of some enzymatic components of the animal visual cascade in isolated eyespot preparations might also point to this relation. A retinal-binding protein has been identified in such preparations, the amino acid sequence of which shows a certain homology to sequences of animal visual rhodopsins. However, potential function of this protein as the phototaxis receptor has been questioned in recent time.

Kaiser D

Building a multicellular organism
ANNU REV GENET 35: 103-123 2001

Abstract:
Multicellular organisms appear to have arisen from unicells numerous times. Multicellular cyanobacteria arose early in the history of life on Earth. Multicellular forms have since arisen independently in each of the kingdoms and several times in some phyla. If the step from unicellular to multicellular life was taken early and frequently, the selective advantage of multicellularity may be large. By comparing the properties of a multicellular organism with those of its putative unicellular ancestor, it may be possible to identify the selective force(s). The independent instances of multicellularity reviewed indicate that advantages in feeding and in dispersion are common. The capacity for signaling between cells accompanies the evolution of multicellularity with cell differentiation.

Fuhrmann M, Stahlberg A, Govorunova E, et al.

The abundant retinal protein of the Chlamydomonas eye is not the photoreceptor for phototaxis and photophobic responses
J CELL SCI 114 (21): 3857-3863 NOV 2001

Abstract:
The chlamyopsin gene (cop) encodes the most abundant eyespot protein in the unicellular green alga Chlamydomonas reinhardtii. This opsin-related protein (COP) binds retinal and was thought to be the photoreceptor controlling photomovement responses via a set of photoreceptor currents. Unfortunately, opsin-deficient mutants are not available and targeted disruption of non-selectable nuclear genes is not yet possible in any green alga. Here we show that intron-containing gene fragments directly linked to their intron-less antisense counterpart provide efficient post-transcriptional gene silencing (PTGS) in C. reinhardtii, thus allowing an efficient reduction of a specific gene product in a green alga. In opsin-deprived transformants, Hash-induced photoreceptor currents (PC) are left unchanged. Moreover, photophobic responses as studied by motion analysis and phototaxis tested in a light-scattering assay were indistinguishable from the responses of untransformed wild-type cells. We conclude that phototaxis and photophobic responses in C. reinhardtii are triggered by an as yet unidentified rhodopsin species.

Kirk DL

Germ-soma differentiation in Volvox
DEV BIOL 238 (2): 213-223 OCT 15 2001

Abstract:
Volvox carteri is a spherical green alga with a predominantly asexual mode of reproduction and a complete germ-soma division of labor. Its somatic cells are specialized for motility, incapable of dividing, and pro-rammed to die when only a few days old, whereas its gonidia (asexual reproductive cells) are nonmotile, specialized for growth and reproduction, and potentially immortal. When a gonidium is less than 2 days old it divides to produce a juvenile spheroid containing all of the somatic cells and gonidia that will be present in an adult of the next generation. The first visible step in germ-soma differentiation is a set of asymmetric cleavage divisions in the embryo that set apart small somatic initials from their large gonidial-initial sister cells. Three types of genes have been found to play key roles in germ-soma specification. First a set of gls genes act in the embryos to shift cell-division planes, resulting in the asymmetric divisions that set apart the large-small sister-cell pairs. Then a set of lag genes act in the large cells to prevent somatic differentiation, while the regA gene acts in the small cells to prevent reproductive development. An inducible transposon was used to tag and recover some of these and other developmentally important genes. The glsA gene encodes a chaperone-like protein that, like another chaperone that is one of its putative binding partners, is associated with the cell division apparatus, although how this leads to asymmetric division remains to be elucidated. The regA gene encodes a somatic-cell-specific nuclear protein that appears to function by repressing genes required for chloroplast biogenesis, thereby preventing somatic cells from growing enough to reproduce. Somatic-cell-specific expression of regA is controlled by three intronic enhancers. (C) 2001 Academic Press.

Shimizu T, Inoue T, Shiraishi H

A senescence-associated S-like RNase in the multicellular green alga Volvox carteri
GENE 274 (1-2): 227-235 AUG 22 2001

Abstract:
Asexual individuals of the green alga Volvox carteri consist of only two cell types. somatic and reproductive cells. The somatic cells are terminally differentiated, post-mitotic cells which undergo gradual senescence leading to cell death in every generation. To elucidate the self-degrading process of macromolecules associated with senescence, we attempted to clone an RNase whose mRNA accumulation is increased during senescence. The corresponding cDNA clone VRN1, encoding an S-like RNase of V. carteri, is the first T-2/S-like RNase to be cloned from green algae. Semi-quantitative RT-PCR analysis revealed that a relative amount of VPN1 mRNA is more than three-fold higher in the senescent somatic cells than in young somatic cells when the mRNA of ribosomal protein S18 is used as an internal standard. VRN1 mRNA is not induced by phosphate starvation, indicating that its accumulation during senescence is not due to a self-induced defect in utilizing phosphates. Similar regulation has been reported for RNS3, which encodes the S-like RNase that is induced in senescent leaves of Arabidopsis thaliana. These observations imply that VRN1 may promote RNA degradation during senescence of somatic cells in V. carteri, and that its regulation has similarity with that of certain senescence-associated RNases in higher plants. (C) 2001 Elsevier Science B.V. All rights reserved.

Hallmann A, Amon P, Godl K, et al.

Transcriptional activation by the sexual pheromone and wounding: a new gene family from Volvox encoding modular proteins with (hydroxy)proline-rich and metalloproteinase homology domains
PLANT J 26 (6): 583-593 JUN 2001

Abstract:
The green alga Volvox represents the simplest kind of multicellular organism: it is composed of only two cell types, somatic and reproductive, making it suitable as a model system. The sexual development of males and females of Volvox carteri is triggered by a sex-inducing pheromone at a concentration of < 10(-16) M. Early biochemical responses to the pheromone involve structural modifications within the extracellular matrix (ECM). By differential screenings of cDNA libraries made from mRNAs of pheromone-treated Volvox, four novel genes were identified that encode four closely related Volvox metalloproteinases that we use to define a new protein family, the VMPs. The existence of several features common to matrix glycoproteins, such as signal peptides, a (hydroxy)proline content of 12-25%, and Ser(Pro)(2-4) repeats, suggest an extracellular localization of the VMPs within the ECM. Synthesis of VMP cDNAs is triggered not only by the sex-inducing pheromone, but also by wounding, and is restricted to the somatic cell type. Sequence comparisons suggest that the VMPs are members of the MB clan of zinc-dependent matrix metalloproteinases, although the putative zinc binding site of all VMPs is QEXXHXXGXXH rather than HEXXHXXGXXH. The presence of glutamine instead of histidine in the zinc binding motif suggests a novel family, or even clan, of peptidases. Like the matrixin family of human collagenases, Volvox VMPs exhibit a modular structure: they possess a metalloproteinase homology domain and a (hydroxy)proline-rich domain, and one of them, VMP4, also has two additional domains. Metalloproteinases seem to be crucial for biochemical modifications of the ECM during development or after wounding in the lower eukaryote Volvox with only two cell types, just as in higher organisms.

Kaczanowski S, Jerzmanowski A

Evolutionary correlation between linker histones and microtubular structures
J MOL EVOL 53 (1): 19-30 JUL 2001

Abstract:
Histones of the H1 group (linker histones) are abundant components of chromatin in eukaryotes, occurring on average at one molecule per nucleosome. The recent reports on the lack of a clear phenotypic effect of knock-out mutations as well as overexpression of histone H1 genes in different organisms have seriously undermined the long-held view that linker histones are essential for the basic functions of eukaryotic cells. In an attempt to resolve the paradox of an abundant conserved protein without a clear function, we re-examined the molecular and phylogenetic data on linker histones to see if they could reveal any correlation between the features of H1 and the functional or morphological characteristics of cells or organisms. Because of an earlier demonstration that in sea urchin the chromatin-type histone HI is also found in the flagellar microtubules (Multigner et al. 1992), we focused on the correlation between the features of H1 and those of microtubular structures. A phylogenetic tree based on multiple alignment of over 100 available H1 sequences suggests that the first divergence of the globular domain of H1 (GH1) resulted in branching into separate types characteristic for plants/Dictyostelium and for animals/ascomycetes, respectively. The GH1s of these two types differ by a short region (usually 5 amino acids) placed at a specific location within the C-terminal wing subdomain of GH1. Evolutionary analysis of the diversification of H1 mRNA into cell-cycle-dependent (polyA(-)) and independent (polyA(+)) forms showed a mosaic occurrence of these two forms in plants and animals, despite the fact that the H1 proteins of plants and animals belong to two well-distinguished groups. However, among organisms from both animal and plant kingdom, only those with H1 mRNA of a polyA- type have flagellated gametes. This correlation as well as the demonstration that in Volvox carteri the accumulation of polyA- mRNA of H1 occurs concurrently with the production of new flagella (Lindauer et al. 1993), suggests a direct link between polyA- phenotype of histone H1 mRNA and flagello-genesis.

Stark K, Kirk DL, Schmitt R

Two enhancers and one silencer located in the introns of regA control somatic cell differentiation in Volvox carteri
GENE DEV 15 (11): 1449-1460 JUN 1 2001

Abstract:
The regA gene plays a central role in germ-soma differentiation of Volvox carteri by suppressing all reproductive functions in somatic cells. Here we show that the minimal promoter of regA consists of only 42 bp immediately upstream of the transcription start site, and that it contains no discernible regulatory elements. However, introns 3 and 5 are both required for regA expression in somatic cells, and intron 7 is essential for silencing regA in gonidia (asexual reproductive cells). A regA gene lacking intron 7 rescues the normal phenotype of mutant somatic cells, but also results in gonidia that reproduce only weakly and soon die out. The same phenotype is observed when a regA gene containing intron 7 is placed under control of a constitutive promoter, suggesting that the silencing activity of intron 7 is promoter specific. Intron 7 is unusual in that it contains a potential ORE that is in frame with exons 7 and 8, and some transcripts are produced in which intron 7 is retained. However, a regulatory role for the intron 7 translation product can be ruled out, because a construct in which intron 7 must be translated, and one in which it cannot be translated, both result in wild-type development of both cell types. Furthermore, intron 7 is unable to act in trans to silence regA, but is able to exert its normal effect when placed in a different location within the gene. Therefore, it appears that intron 7 functions in gonidia as a classical cell-type-specific and promoter-specific enhancer, of the inhibitory type that is often referred to as a silencer.

Babinger P, Kobl I, Mages W, et al.

A link between DNA methylation and epigenetic silencing in transgenic Volvox carteri
NUCLEIC ACIDS RES 29 (6): 1261-1271 MAR 15 2001

Abstract:
Epigenetic silencing of foreign genes introduced into plants poses an unsolved problem for transgenic technology. Here we have used the simple multicellular green alga Volvox carteri as a model to analyse the relation of DNA methylation to transgenic silencing. Volvox DNA contains on average 1.1% Ei-methylcytosine and 0.3% N6-methyladenine, as revealed by electrospray mass spectrometry and phosphoimaging of chromatographically separated P-32-labelled nucleotides. In two nuclear transformants of V.carteri, produced in 1993 by biolistic bombardment with a foreign arylsulphatase gene (C-ars), the transgene is still expressed in one (Hill 181), but not in the other (Hill 183), after an estimated 500-1000 generations. Each transformant clone contains multiple intact copies of C-ars, most of them integrated into the genome as tandem repeats. When the bisulphite genomic sequencing protocol was applied to examine two select regions of transgenic C-ars, we found that the inactivated copies (Hill 183) exhibited a high-level methylation (40%) of CpG dinucleotides, whereas the active copies (Hill 181) displayed low-level (7%) CpG methylation. These are average values from 40 PCR clones sequenced from each DNA strand in the two portions of C-ars. The observed correlation of CpG methylation and transgene inactivation in a green alga will be discussed in the light of transcriptional silencing.

Ferris PJ, Woessner JP, Waffenschmidt S, et al.

Glycosylated polyproline II rods with kinks as a structural motif in plant hydroxyproline-rich glycoproteins
BIOCHEMISTRY-US 40 (9): 2978-2987 MAR 6 2001

Abstract:
Hydroxyproline-rich glycoproteins (HRGPs) are the major proteinaceous components of higher plant walls and the predominant components of the cell wall of the green alga Chlamydomonas reinhardtii. The GPI protein, an HRGP of the C. reinhardtii wall, is shown to adopt a polyproline II helical configuration and to carry a complex array of arabinogalactoside residues, many branched, which are necessary to stabilize the helical conformation. The deduced GP1 amino acid sequence displays two Ser-Pro-rich domains, one with a repeating (SP), motif and the other with a repeating (PPSPX)(x) motif. A second cloned gene a2 also carries the PPSPX repeat, defining a novel gene family in this lineage. The SP-repeat domains of GP1 form a 100-nm shaft with a flexible kink 28 nm from the head. The gp1 gene encodes a PPPPPRPPFPANTPM sequence at the calculated kink position, generating the proposal that this insert interrupts the PPII helix, with the resultant kink exposing amino acids necessary for GP1 to bind to partner molecules. It is proposed that similar kinks in the higher plant HRGPs called extensins may play a comparable role in wall assembly.

Kirk DL

Seeking the ultimate and proximate causes of Volvox multicellularity
AM ZOOL 41 (6): 1493-1493 DEC 2001

Nishii I, Kirk DL

The invA gene of Volvox encodes a novel kinesin that is required for inversion of the embryo.
DEV BIOL 235 (1): 115 JUL 1 2001

2000

Desnitski AG

Development and reproduction of two species of the genus Volvox in a shallow temporary pool

PROTISTOLOGY 1(4): 195-198; 2000 (for pdf click here)

Kirk DL

Volvox as a model system for studying the ontogeny and phylogeny of multicellularity and cellular differentiation
J PLANT GROWTH REGUL 19 (3): 265-274 SEP 2000

Abstract:
Volvox carteri, a spherical alga with a complete division of labor between approximately 2000 biflagellate somatic cells and 16 asexual reproductive cells called gonidia, provides a very attractive system for analyzing how a molecular-genetic program for cell-autonomous cellular differentiation may be encoded within a genome. Then, when considered in combination with a group of closely related "volvocine algae" that includes unicellular Chlamydomonas plus a series of colonial forms of increasing cell number and complexity, it also provides an attractive model system for analyzing how such a program for multicellularity and cytodifferentiation may have evolved. It is proposed that the following were some of the key steps in this evolutionary pathway: (1) The Chlamydomonas cell wall was transformed into an extracellular matrix (ECM) that joined sister cells into a colonial unit. (2) Larger organisms with more abundant ECM were favored because of the role the ECM plays in storing limiting nutrients. (3) In the V. carteri lineage the ancestral biphasic "first biflagellate and then reproductive" pathway of development bt came converted to a dichotomous pathway by introduction of two kinds of cell-type-specific negative regulators: one that blocked growth and reproduction in presumptive somatic cells and one that blocked somatic development in presumptive gonidia. Progress has been made in cloning and characterizing genes that are involved in setting apart the two cell lineages of V. carteri and in subsequently controlling their dichotomous differentiation. The strengths and weaknesses of V. carteri and its relatives as a model system for studying the evolution of multicellularity are discussed.

Hallmann A, Kirk DL

The developmentally regulated ECM glycoprotein ISG plays an essential role in organizing the ECM and orienting the cells of Volvox
J CELL SCI 113 (24): 4605-4617 DEC 2000

Abstract:
Volvox is one of the simplest multicellular organisms with only two cell types, yet it has a surprisingly complex extracellular matrix (ECM) containing many region-specific morphological components, making Volvox suitable as a model system for ECM investigations. ECM deposition begins shortly after inversion, which is the process by which the embryo turns itself right-side-out at the end of embryogenesis. It was previously shown that the gene encoding an ECM glycoprotein called ISG is transcribed very transiently during inversion. Here we show that the developmentally controlled ISG accumulates at the bases of the flagella right after inversion, before any morphologically recognizable ECM structures have yet developed. Later, ISG is abundant in the 'flagellar hillocks' that encircle the basal ends of all flagella, and in the adjacent 'boundary zone' that delimits the spheroid. Transgenic Volvox were generated which express a truncated form of ISG, These transgenics exhibit a severely disorganized ECM within which the cells are embedded in a highly chaotic manner that precludes motility, A synthetic version of the C-terminal decapeptide of ISG has a similar disorganizing effect, but only when it is applied during or shortly after inversion. We postulate that ISG plays a critical role in morphogenesis and acts as a key organizer of ECM architecture; at the very beginning of ECM formation ISG establishes an essential initial framework that both holds the somatic cells in an adaptive orientation and acts as the scaffold upon which the rest of the ECM can be properly assembled, assuring that somatic cells of post-inversion spheroids are held in orientations and locations that makes adaptive swimming behavior possible.

Goodwin PH, Li J, Jin SM

Evidence for sulfate derepression of an arylsulfatase gene of Colletotrichum gloeosporioides f. sp malvae during infection of round-leaved mallow, Malva pusilla
PHYSIOL MOL PLANT P 57 (4): 169-176 OCT 2000

Abstract:
An arylsulfatase gene, cgars, was cloned from Colletotrichum gloeosporioides f. sp. malvae (Cgm), a hemibiotrophic plant pathogenic fungus that causes anthlacnose disease of round-leaved mallow (Malva pusilla). The clone of cgars showed high amino acid sequence identity to ass-1(+), an arylsulfatase gene of Neurospora crassa. Arylsulfatase genes have been shown to be good reporter genes for detecting available sulfur levels in a variety of microorganisms. Expression of cgars was determined by relative RT-PCR, in which gars expression levels were compared to those of actA, a constitutively expressed actin gene of Cgm, following coamplification. In culture, expression of gars was found to be repressed by methionine as has been demonstrated for ars-1(+). In host leaf tissue, cgars expression was relatively higher than actA during penetration, similar to actA during biotrophic growth and then progressively lower than actA during necrotrophic growth. These results show that the availability of host sulfur differs depending upon the stage of infection. (C) 2000 Academic Press.

Nozaki H, Misawa K, Kajita T, et al.

Origin and evolution of the colonial Volvocales (Chlorophyceae) as inferred from multiple, chloroplast gene sequences
MOL PHYLOGENET EVOL 17 (2): 256-268 NOV 2000

Abstract:
A combined data set of DNA sequences (6021 bp) from five protein-coding genes of the chloroplast genome (rbcL, atpB, psaA, psaB, and psbC genes) were analyzed for 42 strains representing 30 species of the colonial Volvocales (Volvox and its relatives) and 5 related species of green algae to deduce robust phylogenetic relationships within the colonial green flagellates. The 4-celled family Tetrabaenaceae was robustly resolved as the most basal group within the colonial Volvocales. The sequence data also suggested that all five volvocacean genera with 32 or more cells in a vegetative colony (all four of the anisogamous/oogamous genera, Eudorina, Platydorina, Pleodorina, and Volvox, plus the isogamous genus Yamagishiella) constituted a large monophyletic group, in which 2 Pleodorina species were positioned distally to 3 species of Volvox. Therefore, most of the evolution of the colonial Volvocales appears to constitute a gradual progression in colonial complexity and in types of sexual reproduction, as in the traditional volvocine lineage hypothesis, although reverse evolution must be considered for the origin of certain species of Pleodorina. Data presented here also provide robust support for a monophyletic family Goniaceae consisting of two genera: Gonium and Astrephomene. (C) 2000 Academic Press.

Sekimoto H

Intercellular communication during sexual reproduction of Closterium (Conjugatophyceae)
J PLANT RES 113 (1111): 343-352 SEP 2000

Abstract:
Processes of intercellular communication during sexual reproduction of conjugating green algae Closterium were reviewed. In the case of Closterium peracerosum-strigosum-littorale complex, two sex-specific pheromones and their receptors were involved in sexual reproduction. These pheromones were glycoproteins and the expression of corresponding genes was critically regulated by the sex and environmental conditions. In the case of Closterium ehrenbergii, chemotactic and sexual cell division-inducing activities for mating-type plus cells were detected and characterized. Although many processes remain to be elucidated, the present results will be helpful for understanding not only the mode of sexual reproduction in Closterium but also the variety of intercellular communication in the plant kingdom especially during sexual reproduction.

Kerszberg M

The survival of slow reproducers
J THEOR BIOL 206 (1): 81-89 SEP 7 2000

Abstract:
Multicellularity, and the attendant segregation of the germ line, entails the loss of reproductive capacity by the soma: in Volvox carteri, less than 1 cell in 100 contributes to the next generation. However, compensatory advantages are unlikely to be very large (Koufopanou & Bell, 1993. Proc. R. Soc. Lond. (B) 254, 107-113). Somewhat similarly, sex implies the generation of males, hence a dramatic reproductive slowdown (Barton & Charlesworth, 1998. Science 281, 1986-1990); yet, a compensating (two-fold) advantage of sex has not been found. Here, I try to evaluate the actual cost of maintaining slow reproductive cycles, namely cycles that necessitate the production of "dead end" units such as somatic cells or males. In a quantitative model for the competition of individuals with different, heritable reproductive rates, this cost turns out to be unexpectedly small, and may even sometimes become irrelevant. The bases for this are made fairly clear: thus, when all enjoy high fecundity (e.g. a long reproductive life) the handicap of a slower reproduction vanishes; alternatively, a slight separation of ecological niches may be sufficient for survival of slower but otherwise unchanged reproducers; and finally, inherent to slow reproduction is a low rate of destabilizing genetic change. These facts are largely independent of the formal model details, and are supported by direct computer simulations. They give a quantitative basis for analysing the evolution and prevalence of slow life cycles. The implications of these findings for the evolution of multicellularity are briefly discussed. (C) 2000 Academic Press.

Matveev V, Matveeva L, Jones GJ

Relative impacts of Daphnia grazing and direct stimulation by fish on phytoplankton abundance in mesocosm communities
FRESHWATER BIOL 44 (3): 375-385 JUL 2000

Abstract:
1. Planktivorous fish were hypothesised to influence the abundance of algal biomass in lakes by changing zooplankton grazing, affecting zooplankton nutrient recycling and by direct recycling of nutrients to phytoplankton. The relative roles of direct fish effects vs. zooplankton grazing were tested in mesocosm experiments by adding to natural communities large grazing zooplankton (Daphnia carinata) and small planktivorous fish (mosquitofish or juveniles of Australian golden perch).

2. The addition of Daphnia to natural communities reduced the numbers of all phytoplankton less than 30 mu m in size, but did not affect total biomass of phytoplankton as large Volvox colonies predominated.

3. The addition of Daphnia also reduced the abundance of some small (Moina, Bosmina, Keratella) and large (adult Boeckella) zooplankton, suggesting competitive interactions within zooplankton.

4. The addition of mosquitofish to communities containing Daphnia further reduced the abundance of some small zooplankton (Moina, Keratella), but increased the numbers of Daphnia and adult Boeckella. In spite of the likely increase in grazing due to Daphnia, the abundance of total phytoplankton and dominant alga Volvox did not decline in the presence of mosquitofish but was maintained at a significantly higher level than in control.

5. The addition of juveniles of golden perch to communities containing Daphnia reduced the abundance of small zooplankton (Moina), increased the abundance of large zooplankton (adult Boeckella) but had no significant effect on Daphnia and total phytoplankton abundance.

6. The results of the present study suggest that some planktivorous fish can promote the growth of phytoplankton in a direct way, probably by recycling nutrients, and even in the presence of large grazers. However, the manifestation of the direct effect of fish can vary with fish species.

Suzuki L, Woessner JP, Uchida H, et al.

Zygote-specific protein with hydroxyproline-rich glycoprotein domains and lectin-like domains involved in the assembly of the cell wall of Chlamydomonas reinhardtii (Chlorophyta)
J PHYCOL 36 (3): 571-583 JUN 2000

Abstract:
The cell wall of Chlamydomonas reinhardtii zygotes, which forms rapidly after the fusion of wall-free gametes, provides a tractable system for studying the properties and assembly of hydroxyproline-rich glycoproteins, the major proteinaceous components of green algal and plant cell walls. We report the cloning of the zsp2 gene and the analysis of its ZSP-2 product, a 58.9 kDa poly-peptide that is synthesized exclusively by zygotes, The protein contains two (SP), repeats, establishing it as a member of the cell wall hydroxyproline-rich glycoproteins family. It also contains a 4-fold iteration of an amino acid sequence centered around cysteine residues, a configuration found in both plant and animal lectins, Furthermore, we report four observations on pellicle composition and production, First, cell-free preparations of the pellicle matrix are rich in hydroxyproline, arabinose, and galactose and contain bundles of very long fibrils, Second, glutathione blocks pellicle formation and results in the accumulation of long fibrils in the growth medium. Third, antibody to ZSP-8 also blocks pellicle formation, Fourth, ZSP-2 immunolocalizes to the boundary between the outer layers of the wall proper and the pellicle matrix. These observations are consistent with the possibility that the Cys-rich (glutathione-sensitive) lectin-like domains of ZSP-2 may bind to sugar residues on the long fibrils and anchor

Sumper M, Nink J, Wenzl S

Self-assembly and cross-linking of Volvox extracellular matrix glycoproteins are specifically inhibited by Ellman's reagent
EUR J BIOCHEM 267 (8): 2334-2339 APR 2000

Abstract:
A major impediment to the biochemical characterization of extracellular matrices from algae (as well as higher plants) is the extensive covalent cross-linking that exists in the matrix, rendering most components insoluble and resistant to conventional extraction procedures. In the multicellular green alga Volvox, biogenesis of the extracellular matrix (ECM) is initiated immediately after the process of embryonic inversion. At this stage of development, the sulfhydryl reagent 5,5'-dithio-bis(2-nitrobenzoic acid), known as Ellman's reagent, interferes in a highly specific manner with ECM biogenesis. Treated post-inversion embryos are no longer able to assemble an intact ECM and consequently dissociate into a suspension of single cells. Dissociated cells remain viable and continue to secrete ECM proteins into the growth medium, as documented by the identification of several members of the pherophorin family. Cross-linked ECM polymers such as sulfated surface glycoprotein 185 remain in a soluble state. Thus, treatment with Ellman's reagent opens a simple approach for the isolation and characterization of otherwise inaccessible monomeric precursors.

Wittstock U, Fischer M, Svendsen I, et al.

Cloning and characterization of two, cDNAs encoding sulfatases in the Roman snail, Helix pomatia
IUBMB LIFE 49 (1): 71-76 JAN 2000

Abstract:
The sulfatase from the snail Helix pomatia is widely used for analytical applications. We have investigated the content of sulfatases in H, pomatia, using a biochemical and a molecular approach. A 112-kDa protein from the intestinal juice of H. pomatia comigrated with sulfatase activity when chromatographed on Sephacryl S300 and concanavalin A-Sepharose. The N-terminal amino acid sequence of the protein was similar to one of three sulfatase motifs defined by sequence alignment of known sulfatases, Degenerate primers designed from the motifs and the N-terminal amino acid sequence obtained were used to generate PCR fragments and to isolate both a full-length and a 3'-truncated cDNA encoding H, pomatia sulfatases, designated SULF1 and SULF2, SULF1 consists of 503 amino acids and shows 53-55% identity to the mammalian arylsulfatase B, The amino acid sequence deduced from the 878-bp SULF2 cDNA fragment is 55% identical with SULF1, Both SULF1 and SULF2 contain the cysteine residue conserved in the active site of many sulfatases, which is known to be posttranslationally modified into formylglycine in eukaryotic sulfatases, However, the SULF1 and SULF2 cDNAs do not code for the protein purified. This indicates the presence of at least three sulfatase genes in H. pomatia.

Kirk DL, Miller SM

Embryonic polarity, asymmetric division,and cell fate determination in Volvox.
DEV BIOL 222 (1): 24 JUN 1 2000

1999

Meissner M, Stark K, Cresnar B, et al.

Volvox germline-specific genes that are putative targets of RegA repression encode chloroplast proteins
CURR GENET 36 (6): 363-370 DEC 1999

Abstract:
In Volvox carteri, regA acts as a master gene to suppress all germ cell functions in somatic cells. Its product, RegA, has features of a transcriptional repressor. Here we report cDNA sequences representing 15 nuclear genes with properties expected of RegA targets: they are expressed strongly in germ cells and in regA(-), but not regA(+), somatic cells. Two of them encode polypeptides with no recognizable features, but ten (like three previously sequenced ones) encode chloroplast proteins of known function, and the remaining three encode putative chloroplast proteins of unknown function. This suggests that RegA blocks reproductive development in somatic cells by preventing chloroplast biogenesis, thereby making it impossible for the cells to grow enough to reproduce

Ender F, Hallmann A, Amon P, et al.

Response to the sexual pheromone and wounding in the green alga Volvox: Induction of an extracellular glycoprotein consisting almost exclusively of hydroxyproline
J BIOL CHEM 274 (49): 35023-35028 DEC 3 1999

Abstract:
The extracellular matrix (ECM) of Volvox is modified during development or in response to external stimuli, like the sex-inducing pheromone. It has recently been demonstrated that a number of genes triggered by the sex-inducing pheromone are also inducible by wounding. By differential screening of a cDNA library, a novel gene was identified that is transcribed in response to the pheromone. Its gene product was characterized as an ECM glycoprotein with a striking feature: it exhibits a hydroxyproline content of 68% and therefore is an extreme member of the family of hydroxyproline-rich glycoproteins (HRGPs), HRGPs are known as constituents of higher plant ECMs and seem to function as structural barriers in defense responses. The Volvox HRGP is also found to be inducible by wounding. This indicates that the wound response scenarios of higher plants and multicellular green algae may be evolutionary related.

Kirk DL

Evolution of multicellularity in the volvocine algae
CURR OPIN PLANT BIOL 2 (6): 496-501 DEC 1999

Abstract:
Recent studies reveal that relationships among the volvocine algae are more complex than was previously believed. Nevertheless, this group still appears to provide an unrivaled opportunity to analyze an evolutionary pathway leading from unicellularity (Chlamydomonas) to multicellularity with division of labor (volvox). Significant progress in this regard was made in the past year when two genes playing key roles in volvox cellular differentiation were cloned, and clues were uncovered regarding their mechanisms of action.

Coleman AW

Phylogenetic analysis of "Volvocacae" for comparative genetic studies
P NATL ACAD SCI USA 96 (24): 13892-13897 NOV 23 1999

Abstract:
Sequence analysis based on multiple isolates representing essentially all genera and species of the classic family Volvocaeae has clarified their phylogenetic relationships. Cloned internal transcribed spacer sequences (ITS-1. and ITS-2, flanking the 5.8S gene of the nuclear ribosomal gene cistrons) were aligned, guided by ITS transcript secondary structural features, and subjected to parsimony and neighbor joining distance analysis. Results confirm the notion of a single common ancestor, and Chlamydomonas reinharditii alone among all sequenced green unicells is most similar. interbreeding isolates were nearest neighbors on the evolutionary tree in all cases. Some taxa, at whatever level, prove to be clades by sequence comparisons, but others provide striking exceptions. The morphological species Pandorina morum, known to be widespread and diverse in mating pairs, was found to encompass all of the isolates of the four species of Volvulina. Platydorina appears to have originated early and not to fall within the genus Eudorina, with which it can sometimes be confused by morphology. The four species of Pleodorina appear variously associated with Eudorina examples. Although the species of Volvox are each clades, the genus Volvox is not The conclusions confirm and extend prior, more limited, studies on nuclear SSU and LSU rDNA genes and plastid-encoded rbcL and atpB. The phylogenetic tree suggests which classical taxonomic characters are most misleading and provides a framework for molecular studies of the cell cycle-related and other alterations that have engendered diversity in both vegetative and sexual colony patterns in this classical family.

Funke RP, Kovar JL, Logsdon JM, et al.

Nucleus-encoded, plastid-targeted acetolactate synthase genes in two closely related chlorophytes, Chlamydomonas reinhardtii and Volvox carteri: phylogenetic origins and recent insertion of introns
MOL GEN GENET 262 (1): 12-21 AUG 1999

Abstract:
Acetolactate synthase (ALS catalyzes the first committed step in the synthesis of branched-chain amino acids. In green plants and fungi, ALS is encoded by a nuclear gene whose product is targeted to plastids (in plants) or to mitochondria tin fungi). In red algae, the gene is plastid-encoded. We have determined the complete sequence of nucleus-encoded ALS genes from the green algae Chlamydomonas reinhardtii and Volvox carteri. Phylogenetic analyses of the ALS gene family indicate that the ALS genes of green algae and plants are closely related, sharing a recent common ancestor. Furthermore, although these genes are clearly of eubacterial origin, a relationship to the ALS genes of red algae and cyanobacteria (endosymbiotic precursors of plastids) is only weakly indicated. The algal ALS genes are distinguished from their homologs in higher plants by the fact that they are interrupted by numerous spliceosomal introns; plant ALS genes completely lack introns. The restricted phylogenetic distribution of these introns suggests that they were inserted recently, after the divergence of these green algae from plants. Two introns in the Volvox ALS gene, not found in the Chlamydomonas gene, are positioned precisely at sites which resemble "proto-splice" sequences in the Chlamydomonas gene.

Kobayashi K, Koyanagi R, Matsumoto M, et al.

Switching from asexual to sexual reproduction in the planarian Dugesia ryukyuensis: Bioassay system and basic description of sexualizing process
ZOOL SCI 16 (2): 291-298 APR 1999

Abstract:
An assay system has been established for the sexual induction in the OH strain, an exclusively fissiparous (asexual) strain, of Dugesia ryukyuensis by feeding them with sexually matured worms of Bdellocephala brunnea, an exclusively oviparous (sexual) species. In this assay system, asexual worms gradually differentiated sexual organs, namely the ovary, testis, genital pore and yolk gland in this order, and eventually mated and laid cocoons filled with fertilized eggs. Although the OH strain worms were believed not to have any sexual organs, a pair of undeveloped ovaries with a few oogonia were detected by an intensive histological search. Along with the progression of sexualization, five distinct stages were histologically recognized: In the first stage, the ovaries became larger enough to be externally apparent; oocytes appeared first at stage 2; the primordial testes emerged at stage 3; a genital pore opened, yolk gland primordia developed and spermatocytes appeared at stage 4; and finally at stage 5 matured spermatozoa and yolk glands were formed. Worms in stages 1 and 2 but not in later stages returned asexual if feeding on B, brunnea was interrupted. Furthermore, when the worms at stage 3 onwards were cut posterior to the ovaries, all the tail regenerants developed eventually into fully sexualized worms. Taking these results in account, we have concluded that the process of sexualization has a point-of-no-return between stages 2 and 3. It is likely also that the testes, even the primordia, play an important role in the maintenance and development of sexuality.

Hoops HJ, Brighton MC, Stickles SM, et al.

A test of two possible mechanisms for phototactic steering in Volvox carteri (Chlorophyceae)
J PHYCOL 35 (3): 539-547 JUN 1999

Abstract:
We tested two competing models that could explain how differential flagellar activity leads to phototactic turning in spheroids of Volvox carteri f, weismannia (Powers) Iyengar. In one model, turning results from the flagella of anterior cells in the lighted and shadowed hemispheres beating at different frequencies. In a competing model, turning results from a change in beat direction in these flagella. Both models successfully explain phototactic steering under constant illumination, but they make different predictions when colonies are exposed to abrupt changes in light intensity. If turning is due to control of flagellar beat frequency, both progression and rotation rates will change in the same direction and with similar magnitudes. If spheroid turning is due to a change in flagellar beat direction, a decreased rate of progression will accompany an increased rate of rotation and vice versa. We used video-microscopy to observe the behavior of positively phototactic V. carteri spheroids exposed to 10x step-up and step-down stimuli. After a step-up stimulus, spheroids slow their progression and rotation by equal amounts, No significant changes are reported in these parameters after the reciprocal step-down response. These observations are consistent with the variable flagellar frequency model and inconsistent with the variable flagellar direction model for phototactic turning. Switching the direction of Light stimulus by 180 degrees results in reorientation of positively phototactic spheroids, The kinetics of this reorientation did not precisely match the predictions of either model.

Nishii I, Ogihara S

Actomyosin contraction of the posterior hemisphere is required for inversion of the Volvox embryo
DEVELOPMENT 126 (10): 2117-2127 MAY 1999

Abstract:
During inversion of a Volvox embryo, a series of cell shape changes causes the multicellular sheet to bend outward, and propagation of the bend from the anterior to the posterior pole eventually results in an inside-out spherical sheet of cells. We use fluorescent and electron microscopy to study the behavior of the cytoskeleton in cells undergoing shape changes. Microtubules are aligned parallel to the cell's long axis and become elongated in the bend. Myosin and actin filaments are arrayed perinuclearly before inversion. In inversion, actin and myosin are located in a subnuclear position throughout the uninverted region but this localization is gradually lost towards the bend. Actomyosin inhibitors cause enlargement of the embryo. The bend propagation is inhibited halfway and, as a consequence, the posterior hemisphere remains uninverted. The arrested posterior hemisphere will resume and complete inversion even in the presence of an actomyosin inhibitor if the anterior hemisphere is removed microsurgically. We conclude that the principal role of actomyosin in inversion is to cause a compaction of the posterior hemisphere; unless the equatorial diameter of the embryo is reduced in this manner, it is too large to pass through the opening defined by the already-inverted anterior hemisphere.

Huey RB, Berrigan D, Gilchrist GW, et al.

Testing the adaptive significance of acclimation: A strong inference approach
AM ZOOL 39 (2): 323-336 APR 1999

Abstract:
Acclimation is a common phenotypic response to environmental change. Acclimation is often thought to enhance performance and thus to be adaptive. This view has recently been formalized as the "Beneficial Acclimation Hypothesis" and predicts that individuals acclimated to one environment perform better in that environment than do individuals acclimated to a different environment. Although Beneficial Acclimation is appealing and widely supported, recent studies with E. coli and Drosophila have challenged its general validity. Although these challenges could be dismissed as mere exceptions, they encourage a re-evaluation of the adaptive significance of acclimation. Our philosophical approach differs from that of most previous studies of acclimation, in which the prediction derived from a Beneficial Acclimation perspective (e.g., heat tolerance is positively correlated with acclimation temperature) is tested against the null hypothesis ("single hypothesis approach"). Instead, we follow Huey and Berrigan (1996) in advocating a strong inference approach (sensu Platt, 1964), which recognizes that Beneficial Acclimation is actually one of a set of competing hypotheses that make different predictions as to how developmental temperature influences the thermal sensitivity of adults ("developmental acclimation"). Using this perspective, Huey and Berrigan proposed a factorial experimental design (3 developmental by 3 adult temperatures) designed to discriminate among all competing hypotheses. We now derive a formal statistical model (ANOVA with orthogonal polynomial contrasts) for this experimental design and use it to evaluate simultaneously the relative impact of each competing hypothesis. We then apply this model to several case studies (Drosophila, Volvox, Trichogramma), and we review also a recent study with E. coli. The influence of Beneficial Acclimation is supported (albeit often weakly) in most cases. Nevertheless, other hypotheses (especially the Optimal Developmental Temperature Hypothesis) often have a greater impact. Even so, however, Beneficial Acclimation usually predicts relative performance at extreme test temperatures. We conclude that, although rumors of its death are premature, Beneficial Acclimation cannot be viewed as the dominant expectation, at least with regard to developmental temperature acclimation. Moreover, our findings reinforce the view that a strong inference approach provides a more comprehensive portrait of complex biological responses than do single-hypothesis approaches.

Hallmann A

Enzymes in the extracellular matrix of Volvox: an inducible, calcium-dependent phosphatase with a modular composition
J BIOL CHEM 274 (3): 1691-1697 JAN 15 1999

Abstract:
The volvocine algae provide the unique opportunity for exploring development of an extracellular matrix. Volvox is the most advanced member of this family and represents the simplest multicellular organism, with differentiated cells, a complete division of labor, and a complex extracellular matrix, which serves structural and enzymatic functions. In Volvox carteri a glycosylated extracellular phosphatase was identified, which is partially released from the extracellular matrix into the growth medium. The phosphatase is synthesized in response to inorganic phosphate starvation and is strictly to inorganic phosphate starvation and is strictly calcium-dependent. The metalloenzyme has been purified to homogeneity and characterized. Its gene and cDNA have been cloned. Comparisons of genomic and cDNA sequences revealed an extremely intron-rich gene (32 introns), With an apparent molecular mass of 160 kDa the Volvox extracellular phosphatase is the largest phosphatase cloned, with no sequence similarity to any other phosphatase. This enzyme exhibits a modular composition. There are two large domains and a small one. The large domains are highly homologous to each other and therefore most likely originated from gene duplication and fusion. At least one EF-hand motif for calcium binding was identified in this extracellular protein Volvox extracellular phosphatase is the first calcium-dependent extracellular phosphatase to be cloned.

Rodriguez H, Haring MA, Beck CF

Molecular characterization of two light-induced, gamete-specific genes from Chlamydomonas reinhardtii that encode hydroxyproline-rich proteins
MOL GEN GENET 261 (2): 267-274 MAR 1999

Abstract:
Gametic differentiation in Chlamydomonas reinhardtii is a two-step process, which is controlled by the sequential action of the two extrinsic signals, nitrogen starvation and blue light. The gamete-specific genes GAS28 and GAS29 are expressed in the late phase of gametogenesis. Their light-induced expression is restricted to cells that have completed the first, nitrogen starvation-activated, phase of differentiation. A comparison of the two genes revealed striking similarities as well as differences. Their most prominent shared feature is an extended sequence homology of over 90% in their 5'-untranslated regions, suggesting a role in translational regulation. GAS28 and GAS29 both encode hydroxyproline-rich proteins (HRGPs) of very similar sizes that exhibit typical features of volvocalean cell wall constituents. GAS28 shows a high degree of homology with the Volvox pherophorin gene family, suggesting a relationship between these genes.

Bischoff F, Molendijk A, Rajendrakumar CSV, et al.

GTP binding proteins in plants
CELL MOL LIFE SCI 55 (2): 233-256 FEB 1999

Abstract:
GTP-binding proteins are found in all organisms. They are important switches that cycle between an active and an inactive state, ensuring vectorial flow of information on the expense of guanosine triphosphate (GTP). In this review, we discuss current progress in the molecular characterization and functional analysis of plant genes encoding heterotrimeric and small GTPases. An up-to-date list in eluding all cloned plant GTPase genes is given and a systematic classification is proposed.

Kirk MM, Stark K, Miller SM, et al.

regA, a Volvox gene that plays a central role in germ-soma differentiation, encodes a novel regulatory protein
DEVELOPMENT 126 (4): 639-647 Feb 1999

Abstract:
Volvox has two cell types: mortal somatic cells and immortal germ cells. Here we describe the transposon-tagging, cloning and characterization of regA, which plays a central role as a master regulatory gene in Volvox germsoma differentiation by suppressing reproductive activities in somatic cells. The 12.5 kb regA transcription unit generates a 6,725 nucleotide mRNA that appears at the beginning of somatic cell differentiation, and that encodes a 111 kDa RegA protein that localizes to the nucleus, and has an unusual abundance of alanine, glutamine and proline, This is a compositional feature shared by functional domains of many 'active' repressors, These findings are consistent with the hypothesis that RegA acts in somatic cells to repress transcription of genes required for growth and reproduction, including 13 genes whose products are required for chloroplast biogenesis.

Miller SM, Kirk DL

glsA, a Volvox gene required for asymmetric division and germ cell specification, encodes a chaperone-like protein
DEVELOPMENT 126 (4): 649-658 FEB 1999

Abstract:
The gls genes of Volvox are required for the asymmetric divisions that set apart cells of the germ and somatic lineages during embryogenesis. Here we used transposon tagging to clone glsA, and then showed that it is expressed maximally in asymmetrically dividing embryos, and that it encodes a 748-amino acid protein with two potential protein-binding domains. Site-directed mutagenesis of one of these, the J domain (by which Hsp40-class chaperones bind to and activate specific Hsp70 partners) abolishes the capacity of glsA to rescue mutants. Based on this and other considerations, including the fact that the GlsA protein is associated with the mitotic spindle, we discuss how it might function, in conjunction with an Hsp70-type partner, to shift the division plane in asymmetrically dividing cells.

Nozaki H, Ohta N, Takano H, et al.

Reexamination of phylogenetic relationships within the colonial Volvocales (Chlorophyta): An analysis of atpB and rbcL gene sequences
J PHYCOL 35 (1): 104-112 FEB 1999

Abstract:
The chloroplast-encoded atpB gene was sequenced from 33 strains representing 28 species of the colonial Volvocales (the Volvocaceae and its relatives) to reexamine phylogenetic relationships as previously deduced by morphological data and rbcL gene sequence data.1128 base pairs in the coding regions of the atpB gene were analyzed by MP, NJ, and ML analyses, Although supported with relatively low bootstrap values (75% and 65% in the NJ and ML analyses, respectively), three anisogamous/oogamous volvocacean genera-Eudorina, Pleodorina, and Volvox, excluding the section Volvox(= Euvolvox, illegitimate name), constituted a large monophyletic group (Eudorina group), Outside the Eudorina group, a robust Lineage composed of three species of Volvox sect, Volvox was resolved as in the rbcL gene trees, rejecting the hypothesis of the previous cladistic analysis based on morphological data that the genus Volvox is monophyletic, In addition, the NJ and ML trees suggested that Eudorina is a non-monophyletic genus as inferred from the morphological data and rbcL gene sequences. Although phylogenetic status of the genus Gonium is ambiguous in the rbcL gene trees and the paraphyly of this genus is resolved in the cladistic analysis based on morphological data, the atpB gene sequence data suggest monophyly of Gonium with relatively low bootstrap values (56-61%) in the NJ and ML trees. On the basis of the combined sequence data (2256 base pairs) from atpB and rbcL genes, Gonium was resolved as a robust monophyletic genus in the NJ and ML trees (with 68-86% bootstrap values), and Eudorina elegans Ehrenberg represented a paraphyletic species positioned most basally within the Eudorina group, However, phylogenetic status and relationships of the families of the colonial Volvocales were still almost ambiguous even in the combined analysis.

Braun FJ, Hegemann P

Two light-activated conductances in the eye of the green alga Volvox carteri
BIOPHYS J 76 (3): 1668-1678 MAR 1999

Abstract:
Photoreceptor currents of the multicellular green alga Volvox carteri were analyzed using a dissolver mutant. The photocurrents are restricted to the eyespot region of somatic cells. Photocurrents are detectable from intact cells and excised eyes. The rhodopsin action spectrum suggests that the currents are induced by Volvox rhodopsin. Flash-induced photocurrents are a composition of a fast Ca2+-carried current (P-F) and a slower current (P-S), which is carried by H+. P-F is a high-intensity response that appears with a delay of less than 50 mu s after flash. The stimulus-response curve of its initial rise is fit by a single exponential and parallels the rhodopsin bleaching. These two observations suggest that the responsible channel is closely connected to the rhodopsin, both forming a tight complex. At low flash energies P-S is dominating. The current delay increases up to 10 ms, and the P-S amplitude saturates when only a few percent of the rhodopsin is bleached. The data are in favor of a second signaling system, which includes a signal transducer mediating between rhodopsin and the channel. We present a model of how different modes of signal transduction are accomplished in this alga under different light conditions.

Hallmann A, Rappel A

Genetic engineering of the multicellular green alga Volvox: a modified and multiplied bacterial antibiotic resistance gene as a dominant selectable marker
PLANT J 17 (1): 99-109 JAN 1999

Abstract:
The green alga Volvox represents the simplest multicellular organism: Volvox is composed of only two cell types, somatic and reproductive. Volvox, therefore, is an attractive model system for studying various aspects of multicellularity. With the biolistic nuclear transformation of Volvox carteri, the powerful molecular genetic manipulation of this organism has been established, but applications have been restricted to an auxotrophic mutant serving as the DNA recipient. Therefore, a dominant selectable marker working in all strains and mutants of this organism is required. Among several gene constructs tested, the most advantageous results were obtained with a chimeric gene composed of the coding sequence of the bacterial ble gene, conferring resistance to the antibiotic zeocin, modified with insertions of two endogenous introns from the Volvox arylsulfatase gene and fused to 5' and 3' untranslated regions from the Volvox beta 2-tubulin gene. In the most suitable plasmid used, the gene dosage was increased 16-fold by a technique that allows exponential multiplication of a DNA fragment. Go-transformation of this plasmid and a non-selectable plasmid allowed the identification of zeocin resistant transformants with nuclear integration of both selectable and non-selectable plasmids. Stable expression of the ble gene and of genes from several non-selectable plasmids is demonstrated. The modified ble gene provides the first dominant marker for transformation of both wild-type and mutant strains of Volvox.

Fabry S, Kohler A, Coleman AW

Intraspecies analysis: Comparison of ITS sequence data and gene intron sequence data with breeding data for a worldwide collection of Gonium pectorale
J MOL EVOL 48 (1): 94-101 JAN 1999

Abstract:
The morphologically uniform species Gonium pectorale is a colonial green flagellate of worldwide distribution. The affinities of 25 isolates from 18 sites on five continents were assessed by both DNA sequence comparisons and sexual compatibility. Complete sequences were obtained (i) for the internal transcribed spacer ITS-1 and ITS-2 regions of ribosomal DNA and (ii) for each of three single-copy spliceosomal introns, two in a small G protein and one in the actin gene. ITS sequences appeared to homogenize sufficiently rapidly to behave as a single copy gene. Intron sequence differences between isolates in this species reached nucleotide substitution saturation, while ITS sequences did not. Parsimony and evolutionary distance analysis of the two types of DNA data gave essentially the same tree conformation. By all these criteria, the group of G. pectorale isolates fell into two main clades, A and B. Clade A, with isolates from four continents, was comprised of four subclades of quite closely related isolates, plus one strain of ambiguous affinity. Clade B was comprised of two subclades represented by South African and South American isolates, respectively; thus, only subclades of clade B showed geographical localization. With respect to mating, all isolates except one homothallic strain and one apparently sterile strain fell into either one or the other of two mating types. Pairings in all possible combinations revealed that isolates from the same site formed abundant zygotes, which germinated to produce new, sexually active organisms. Zygotes were also formed in many pairings of other combinations, including crosses of clade A with clade B organisms, but none of the latter produced viable germlings. The ability to mate and produce viable progeny that were themselves capable of sexual reproduction was restricted to members of subclades established on the basis of DNA sequence similarities. Thus, the grades of difference in both nuclear intron sequences and rDNA ITS sequences paralleled those observed in the sexual analysis.

Miller SM, Kirk DL

glsA, a Volvox gene required for asymmetric division and germ cell specification, encode a chaperone-like protein that co-localizes with the mitotic spindle
MOL BIOL CELL 10: 2265 Suppl. S NOV 1999

1998

Gonzalez MA, Gomez PI, Montoya R

Comparison of PCR-RFLP analysis of the ITS region with morphological criteria of various strains of Dunaliella
J APPL PHYCOL 10 (6): 573-580 1998

Abstract:
The genus Dunaliella comprises 28 species defined primarily by morphological and physiological criteria, which vary considerably depending on growth conditions. Concomitantly, the taxonomic status of various species is uncertain. To confirm the taxonomic identity and to better understand the relationship within Dunaliella, seven taxa (D. salina, D. bardawil, D. tertiolecta, D. parva, D. viridis, D. lateralis, D. peircei) were compared using RFLP analysis of the nuclear rDNA repeats, specifically the internal transcribed spacer regions, including the 5.8S rRNA gene. Volvox aureus was used as an outgroup. A single ITS PCR amplification product was obtained for each taxon. An ITS fragment of ca. 640 bp was present in all the taxa within the subgenus Dunaliella, except for D. salina CCMP 1303 (ca. 540 bp) and D. lateralis (subgenus Pascheria) (ca. 600 bp). A cluster analysis based on the presence or absence of bands generated by digestion of the PCR product with 8 restriction endonucleases (DpnI, HhaI, EcoRI, PVuII, TaqI, HaeIII, MspI, StyI) revealed no correlation between the genetic relationship inferred from the ITS-RFLP data and the morpho-physiological attributes used for taxonomy. In addition, differences in morphology, physiology and in the length and restriction fragment patterns of the ITS region of D. salina CCMP 1303 suggest that this strain does not belong to Dunaliella.

Kobl I, Kirk DL, Schmitt R

Quantitative PCR data falsify the chromosomal endoreduplication hypothesis for Volvox carteri (Volvocales, Chlorophyta)
J PHYCOL 34 (6): 981-988 DEC 1998

Abstract:
Two conflicting hypotheses for chromosome replication in the Volvocaceae, one postulating multiple rounds of replication prior to cell division (endoreduplication) and the other claiming a canonical sequence of one round of nuclear DNA replication preceding each cell division, have been tested experimentally. Competitive PCR of the single-copy actin gene (target) of Volvox carteri f. nagariensis Iyengar and a shortened gene version (competitor) containing the same primer binding sites were used to assess the genome equivalents present in a given number of cells. Determining the molar ratio of the PCR products generated from target DNA (extracted from a known number of cells) acid defined numbers of competitor molecules revealed that Volvox embryos between the one- and 16-cell stages possess an average of between one and two-but never more than two-copies of the actin gene. This led us to conclude that the number of genome equivalents per nucleus in dividing Volvox embryos varies only between one and two and that, unlike the case predicted by endoredduplication, the nuclear genome undergoes only one round of replication prior to each cell division.

Sekimoto H, Fukumoto R, Dohmae N, et al.

Molecular cloning of a novel sex pheromone responsible for the release of a different sex pheromone in Closterium peracerosum-strigosum-littorale complex
PLANT CELL PHYSIOL 39 (11): 1169-1175 NOV 1998

Abstract:
A sex pheromone, protoplast-release-inducing protein (PR-IP) inducer, of the Closterium peracerosum-strigosum-littorale complex is known to induce the release of PR-IF, from mating-type plus (mtf) cells during sexual reproduction. The purified PR-IF inducer was treated with trypsin to obtain internal peptides for determination of partial amino acid sequences. Using these sequences, oligonucleotides were synthesized and used as primers for the combined reverse transcription-PCR, A 296 bp cDNA fragment was amplified, permitting the cloning of corresponding full length cDNA (CpPI; Closterium peracerosum-strigosum-littorale complex PR-IF inducer). The deduced amino acid sequence of CpPI encodes a protein of 212 amino acid residues of M-r 23,071 whereas portion of the peptide secreted is predicted to have 142 amino acid residues of M-r 15,717 and shows no significant similarity with known proteins. The predicted protein has three possible consensus sequences for asparagine-linked glycosylation site. The CpPI gene was expressed when mating-type minus (mt(-)) cells were incubated at a low cell density in the light. Nitrogen deprivation from the medium enhances expression of the CpPI gene. An analysis by genomic Southern hybridization revealed that the cDNA probe hybridized to several DNA fragments obtained from both the genome of mt(-) and mt(+) cells. However, in mt- cells, transcripts for the PR-IF inducer could not be detected by Northern hybridization.

Schirmer A, Kolter R

Computational analysis of bacterial sulfatases and their modifying enzymes
CHEM BIOL 5 (8): R181-R186 AUG 1998

Abstract:
The sequence analysis of enzymes that might modify bacterial sulfatases should be useful in the task of identifying the human sulfatase-modifying homologs enzymes that are defective in the rare inherited disease multi sulfatase deficiency.

Gladyshev MI, Sushchik NN, Kalachova GS, et al.

The effect of algal blooms on the disappearance of phenol in a small forest pond
WATER RES 32 (9): 2769-2775 SEP 1998

Abstract:
Using experimental microecosystems the kinetics of phenol disappearance in small forest pond waters (Siberia, Russia) in the summer of 1995-96 were investigated. Despite of high variability of components of the ecosystem (plankton biomass and species composition) and two pronounced "blooms" of green algae Volvox aureus the same kinetics of the disappearance took place over the investigated period. Half-lives of the pollutant depended on water temperature only. A comparison of the self-purification of the pond with that of the Krasnoyarsk reservoir, "blooming" with blue-greens was carried out. Half-lives in the pond were significantly lower than that in the reservoir. During the periods of "blooms" of the green algae in the pond the concentrations of inorganic nutrients were comparatively high and the phenol-degrading bacteria likely were not limited by these nutrients, in contrast to the periods of "bloom" of the blue-green algae in the reservoir. (C) 1998 Elsevier Science Ltd. All rights reserved.

von Figura K, Schmidt B, Selmer T, et al.

A novel protein modification generating an aldehyde group in sulfatases: its role in catalysis and disease
BIOESSAYS 20 (6): 505-510 JUN 1998

Abstract:
In multiple sulfatase deficiency, a rare human lysosomal storage disorder, all known sulfatases are synthesized as catalytically poorly active polypeptides. Analysis of the latter has shown that they lack a protein modification that was detected in all members of the sulfatase family. This novel protein modification generates a 2-amino-3-oxopropanoic acid (C alpha-formylglycine) residue by oxidation of the thiol group of a cysteine that is conserved among all eukaryotic sulfatases, The oxidation occurs in the endoplasmic reticulum at a stage when the nascent polypeptide is not yet folded. The aldehyde is part of the catalytic site and is likely to act as an aldehyde hydrate. One of the geminal hydroxyl groups accepts the sulfate during sulfate ester cleavage leading to the formation of a covalently sulfated enzyme intermediate. The other hydroxyl is required for the subsequent elimination of the sulfate and regeneration of the aldehyde group. In some prokaryotic members of the sulfatase gene family, the DNA sequence predicts a serine residue, and not a cysteine, Analysis of one of these prokaryotic sulfatases, however, revealed the presence of the C alpha-formylglycine indicating that the aldehyde group is essential for all members of the sulfatase family and that it can be generated from either cysteine or serine, (C) 1998 John Wiley & Sons, Inc.

Arai S, Takahashi H, Takano H, et al.

Isolation, characterization, and chromosome mapping of an actin gene from the primitive green alga, Nannochloris bacillaris (Chorophyceae)
J PHYCOL 34 (3): 477-485 JUN 1998

Abstract:
Historically, the genus Nannochloris has been classified using the morphology of cell division, although the mechanics of division remain relatively poorly understood. Nannochloris bacillaris reproduces by binary fission. Microscopic observation with fluorescein isothiocyanate-phaloloidin showed that actin filaments localized near the nucleus and appeared as a ring- or beltlike structure in the septum-forming area in the middle of the cell during cell division. In primitive unicellular Chlorophyta such as N. bacillaris, actin is also thought to play important roles in nuclear migration and cell division. The N. bacillaris actin gene has three exons and two introns defined by two exon-intron junctions with splice site consensus sequences. The two introns are located at codons specifying amino acids 3/4 and 47/48. One of these, intron position 3/4, is conserved in the actin gene of Saccharomyces cerevisiae. The actin gene product was predicted to be 378 amino acids long with an estimated molecular weight of 42 kDa. There is only one copy of the actin gene in the N. bacillaris genome. Nannochloris bacillaris has 14 chromosomes that range in size from 230 kb to 3000 kb, and the total size of the genome was estimated to be 20.3 Mb. The actin gene is on either chromosome XI or XII. In a phylogenetic tree based on the actin gene sequence, N. bacillaris diverged before the divergence of Volvox, Chlamydomonas, and higher plants, and very shortly after the radiation of the Rhodophyta.

Amon P, Haas E, Sumper M

The sex-inducing pheromone and wounding trigger the same set of genes in the multicellular green alga Volvox
PLANT CELL 10 (5): 781-789 MAY 1998

Abstract:
The sex-inducing pheromone of the multicellular green alga Volvox carteri is a glycoprotein that triggers development of males and females at a concentration <10(-16) M. By differential screening of a cDNA library, two novel genes were identified that are transcribed under the control of this pheromone. Unexpectedly, one gene product was characterized as a lysozyme/chitinase, and the other gene product was shown to encode a polypeptide with a striking modular composition. This polypeptide has a cysteine protease domain separated by an extensin-like module from three repeats of a chitin binding domain. In higher plants, similar protein families are known to play an important role in defense against fungi. Indeed, we found that the same set of genes triggered by the sexual pheromone was also inducible in V. carteri by wounding.

Hallmann A, Godl K, Wenzl S, et al.

The highly efficient sex-inducing pheromone system of Volvox
TRENDS MICROBIOL 6 (5): 185-189 MAY 1998

Abstract:
The green alga Volvox is one of the simplest multicellular organisms and is capable of both asexual and sexual reproduction. Sexual development is initiated by a glycoprotein pheromone that acts at a concentration below 10(-16) M. The extracellular matrix (ECM) appears to play a key role in signal amplification: several ECM proteins contain a domain with homology to the sex-inducing pheromone.

El-Naggar MEE, Shaaban-Dessouki SA, Abdel-Hamid MI, et al.

Studies on the phytoplankton populations and physico-chemical conditions of treated sewage discharged into Lake Manzala in Egypt
MICROBIOLOGICA 21 (2): 183-196 APR 1998

Abstract:
Over a full year, the phytoplankton populations and physico-chemical conditions of treated sewage discharged into Lake Manzala in Egypt were investigated. Sixty-seven species of algae were identified, 18 Cyanophyta (Cyanobacteria), 19 Chlorophyta, 21 Bacillariophyta, 6 Euglenophyta, 2 Cryptophyta and one species Pyrrhophyta. Nitzschia (6 spp.), Scenedesmus (6 spp.), Navicula (4 spp.), Oscillatoria (4 spp.) and Euglena (4 spp.) were the most common genera.

A remarkable seasonal variation in species composition and standing crop of the phytoplankton populations was noted during the study. The total phytoplankton standing crop appeared to be mainly dependent on the growth of certain species viz., Oscillatoria chalybea, O. princepes, O. tenuis, Microcystis aeruginosa, Anabaena constricta (Cyanophyta), Nitzschia obtusa, Bacillaria paradoxa, Cocconeis placentula, Cyclotella meneghiniana (Bacillariophyta), Pandorina morum, Volvox sp. (Chlorophyta) and Phacus curvicauda (Euglenophyta). The continuous presence of Anabaena constricta and Nitzschia palea was recorded in the treated sewage. The least represented algal divisions were Pyrrhophyta and Cryptophyta, both in terms of quality and quantity.The data indicate that the secondary effluents were unstable in their chemical features and grossly polluted. Therefore, the treatment systems must treat the discharged sewage to a tertiary level before discharging into Lake Manzala.

Corrette-Bennett J, Rosenberg M, Przybylska M, et al.

Positional cloning without a genome map: Using 'Targeted RFLP Subtraction' to isolate dense markers tightly linked to the regA locus of Volvox carteri
NUCLEIC ACIDS RES 26 (7): 1812-1818 APR 1 1998

Abstract:
The ability to isolate genes defined by mutant phenotypes has fueled the rapid progress in understanding basic biological mechanisms and the causes of inherited diseases. Positional cloning, a commonly used method for isolating genes corresponding to mutations, is most efficiently applied to the small number of model organisms for which high resolution genetic maps exist. We demonstrate a new and generally applicable positional cloning method that obviates the need for a genetic map. The technique is based on Restriction Fragment Length Polymorphism (RFLP) Subtraction, a method that isolates RFLP markers spanning an entire genome, The new method, Targeted RFLP Subtraction (TRS), isolates markers from a specific region by combining RFLP Subtraction with a phenotypic pooling strategy. We used TRS to directly isolate dense markers tightly linked to the regA gene of the eukaryotic green alga Volvox, As a generally applicable method for saturating a small targeted region with DNA markers, TRS should facilitate gene isolation from diverse organisms and accelerate the process of physically mapping specific regions in preparation for sequence analysis.

ten Lohuis MR, Miller DJ

Genetic transformation of dinoflagellates (Amphidinium and Symbiodinium): expression of GUS in microalgae using heterologous promoterconstructs
PLANT J 13 (3): 427-435 FEB 1998

Abstract:
Genetic transformation of two dinoflagellates (Amphidinium sp., Symbiodinium microadriaticum) was achieved using plasmid constructs containing the neomycin phosphotransferase gene (nptll) fused to the Agrobacterium nos promoter, or the hygromycin B phosphotransferase gene (hpt) fused to the bidirectional Agrobacterium p1'2' promoter. Gene transfer into intact (walled) dinoflagellate cells was achieved by agitation in the presence of silicon carbide (SiCa) whiskers. Transformation rates of 5-24 transformants per 10(7) cells were obtained. Southern hybridization of transformants revealed stable integration of multiple copies of the constructs. Activity of integrated copies of the beta-glucoronidase (GUS) reporter gene coupled to the cauliflower mosaic virus 35S promotor or the p1'2' promoter was confirmed both histochemically and fluorometrically. This is the first report of successful application bf heterologous and widely used promoter and reporter genes in microalgae, and is the first demonstration of transformation of a dinoflagellate. There appear to be no substantial barriers to transformation of Amphidinium and Symbiodinium, which must now be considered as the first of the dinoflagellate genera accessible to genetic manipulation.

Miller SM, Kirk DL

glsA, a Volvox gene required for asymmetric division and germ cell specification encodes a chaperone-like protein
MOL BIOL CELL 9: 1694 Suppl. S NOV 1998

Bell G

Volvox - Molecular-genetic origins of multicellularity and cellular differentiation
SCIENCE 282 (5387): 248-248 OCT 9 1998

Sumper M, Hallmann A

Biochemistry of the extracellular matrix of Volvox
INT REV CYTOL 180: 51-85 1998

1997

Kirk DL

The genetic program for germ-soma differentiation in Volvox
ANNU REV GENET 31: 359-380 1997

Abstract:
Volvox carteri possesses only two cell types: mortal somatic cells and potentially immortal asexual reproductive cells called gonidia. Mutational analysis indicates that three categories of genes play central roles in programming this germ-soma division of labor: First the gls genes function during embryogenesis to cause asymmetric divisions that produce large and small cells. Then the lag genes act in the large cells (gonidial initials) to repress functions required for somatic development while the regA locus acts in the small cells (somatic initials) to repress functions required for reproductive development. Transposon tagging and DNA transformation have recently been used to recover and characterize the glsA and regA genes, and the sequences of these genes lead to testable hypotheses about how they play their roles in germ-soma differentiation.

Kroger N, Lehmann G, Rachel R, et al.

Characterization of a 200-kDa diatom protein that is specifically associated with a silica-based substructure of the cell wall
EUR J BIOCHEM 250 (1): 99-105 NOV 15 1997

Abstract:
The cell wall of a diatom is made up of a silica-based scaffold and organic macromolecules. Proteins located in the cell wall are believed to control morphogenesis of the species-specific silica structures of the scaffold. However, data that correlate distinct silica elements and specific proteins within the diatom cell wall have not been reported. Here, the cell wall protein HEP2OO (200-kDa HE-extractable protein) from the diatom Cylindrotheca fusiformis is identified and characterized. HEP200 is tightly associated with a substructure of the silica scaffold. It is a member of a new protein family, of which two more members are identified. Each member displays the same bipartite structure. The N-terminal part consists of a variable number of a repeated sequence motif (PSCD domain), whereas the C-terminal part is unique, Immunolocalization experiments revealed the arrangement of different proteins within the cell wall. Frustulins, a previously described group of glycoproteins, constitute the outer coat of the cell wall and exhibit a ubiquitous distribution. In contrast, HEP200 is specifically located at a subset of about six silica strips in intact cell walls, shielded by frustulins. This study therefore identifies a diatom cell wall protein (HEP200) that is associated with a distinct substructure of the silica scaffold.

Kurvari V

Cell wall biogenesis in Chlamydomonas: molecular characterization of a novel protein whose expression is up-regulated during matrix formation
MOL GEN GENET 256 (5): 572-580 NOV 1997

Abstract:
In the unicellular eukaryote Chlamydomonas, disruption of cell-matrix interactions by treatment with a periplasmic matrix metalloproteinase, g-lysin, activates a signal transduction pathway that results in the rapid synthesis and secretion of matrix molecules, followed by their assembly into a new matrix. I have identified and partially characterized several cDNA clones for transcripts that are dramatically up-regulated following treatment of cells with g-lysin. Here I report the complete nucleotide sequence and preliminary characterization of a matrix-related molecule termed Mrp47. The cDNA clone for Mrp47 contained an insert of 2.5 kb, corresponding to a transcript of 3.0 kb that is encoded by a single-copy gene. Sequence analysis indicated that Mrp47 cDNA contains an open reading frame (ORF) that encodes a 46-kDa polypeptide. The putative polypeptide is unusually rich in the amino acids proline, alanine and serine, with prolines clustered together in a 30-amino acid N-terminal region and a 80-amino acid C-terminal region. Further analysis of the predicted amino acid sequence suggested that Mrp47 is likely to be a secreted glycoprotein. Southern hybridization analysis indicated that Mrp47 is encoded by a single-copy gene in the Chlamydomonas genome. Database searches suggested that Mrp47 shows homology to other proline-rich proteins including a surface glycoprotein in Volvox and verprolin from yeast.

Hoops HJ

Motility in the colonial and multicellular Volvocales: structure, function, and evolution
PROTOPLASMA 199 (3-4): 99-112 1997

Abstract:
The colonial Volvocales are often said to be composed of Chlamydomonas-like cells, but there are substantial differences in motility and flagellar apparatus construction between the unicellular forms and the individual members of a colony or spheroid. These changes appear to be required for effective organismal motion and might possibly limit the rate at which new colonial forms evolve from unicellular ones. The flagellar-beat envelopes in colonial members are modified such that they beat in the same direction and in parallel planes with their effective strokes at right angles to the cellular anterior-posterior axis. These changes result from a series of developmental events of the flagellar apparatus of the colonial forms while the colony is still an embryo. Differences in the flagellar-apparatus structure in the members of the Goniaceae and Volvocaceae are not obviously correlated with the traditional placement of these algae in a simple volvocine lineage. Effective colonial motion clearly requires precise positioning and rotational orientation of the cells within the colony. Almost any arrangement where the cells are placed with rotational symmetry within the colony results in colonial progression with rotation. Such rotational symmetry is present from the time of embryogenesis. The mechanism that leads to organismal steering in behavioral responses (e.g., phototaxis) must likewise differ between colonial and unicellular forms. Ln at least some cases, this appears to result from changes in beat frequency in some parts of the spheroid, but changes in beat direction cannot be ruled out for all forms.

Hegemann P

Vision in microalgae
PLANTA 203 (3): 265-274 NOV 1997

Abstract:
Flagellate green algae such as Chlamydomonas and related genera are guided by their eyes to places where light conditions are optimal for photosynthetic growth. These eyes constitute the simplest and most common visual system found in nature. The eyes contain optics, photoreceptors and the elementary components of a signal-transduction chain. Rhodopsin serves as the photoreceptor, as it does in animal vision. Upon light stimulation, its all-trans-retinal chromophore isomerizes into 13-cis and activates a photoreceptor channel which leads to a rapid Ca2+ influx into the eyespot region. At low light levels, the depolarization activates small flagellar currents which induce in both flagella small but slightly different beating changes resulting in distinct directional changes. In continuous light, Ca2+ fluxes serve as the molecular basis for phototaxis. In response to flashes of higher energy the larger photoreceptor currents trigger a massive Ca2+ influx into the flagella which causes the well-known phobic response. The identification of proteins contributing to this signalling system has just begun with the isolation and cloning of the opsins from Chlamydomonas and Volvox. These plant opsins are highly charged, are not typical seven-helix receptors, and are believed to form a protein complex with the photoreceptor channel. In Spermatozopsis, a G-protein has been found which interacts either directly with the rhodopsin or with the rhodopsin-ion channel complex. By using insertional mutagenesis, genes coding for proteins that are involved in signalling have been tagged. One of them is connected to the flagellar channel and crucial for the flagellar action potential. Elucidation of photoreception in flagellated algae will provide deeper insight into the development of visual systems, starting from single-celled organisms and moving up through higher animals.

Nozaki H, Ito M, Uchida H, et al.

Phylogenetic analysis of Eudorina species (Valvocaceae, Chlorophyta) based on rbcL gene sequences
J PHYCOL 33 (5): 859-863 OCT 1997

Abstract:
Species and varieties in the genus Eudorina Ehrenberg (Volvocaceae, Chlorophyta) were evaluated on the basis of phylogenetic analyses of the large subunit of ribulose-1,5-bisphosphate carboxylase/oxygenase (rbcL) gene sequence from 14 strains of four Eudorina species, as well as from nine species of Pleodorina and Volvox. The sequence data suggested that 10 of the 14 Eudorina strains form three separate and robust monophyletic groups within the nonmonophyletic genus Eudorina. The first group comprises ail three strains off. unicocca G. M. Smith; the second group consists of one of the E, elegans Ehrenberg var elegans strains, the E. cylindrica Korshikov strain, and both E. illinoisensis (Kofoid) Pascher strains; and the third group consists of two monoecious varieties off, elegans [two strains of E. elegans var synoica Goldstein and one strain of E. elegans var. carteri (G. hi. Smith) Goldstein]. In addition, E. illinoisensis represents a poly- or paraphyletic species within the second group. The remaining four strains, all of which are assigned to E. elegans var. elegans, are nonmonophyletic. Although their position in the phylogenetic trees is more or less ambiguous, they are ancestral to other taxa ill the large anisogamous/oogamous monophyletic group including Eudorina, Pleodorina, and Volvox (except for sect. Volvox). Thus, the four Eudorina groups resolved in the present molecular phylogeny do not correspond with the species concepts of Eudorina based on vegetative morphology, but they do reflect the results Of the previous intercrossing experiments and modes of monoecious and dioecious sexual reproduction.

Dierks T, Schmidt B, VonFigura K

Conversion of cysteine to formylglycine: A protein modification in the endoplasmic reticulum
P NATL ACAD SCI USA 94 (22): 11963-11968 OCT 28 1997

Abstract:
In sulfatases a C-alpha-formylglycine residue is found at a position where their cDNA sequences predict a cysteine residue. In multiple sulfatase deficiency, an inherited lysosomal storage disorder, catalytically inactive sulfatases are synthesized which retain the cysteine residue, indicating that the C,-formylglycine residue is required for sulfatase activity. Using in vitro translation in the absence or presence of transport competent microsomes we found that newly synthesized sulfatase polypeptides carry a cysteine residue and that the oxidation of its thiol group to an aldehyde is catalyzed in the endoplasmic reticulum. A linear sequence of 16 residues surrounding the Cys-69 in arylsulfatase A is sufficient to direct the oxidation, This novel protein modification occurs after or at a late stage of cotranslational protein translocation into the endoplasmic reticulum when the polypeptide is not yet folded to its native structure.

Hallmann A, Rappel A, Sumper M

Gene replacement by homologous recombination in the multicellular green alga Volvox carteri
P NATL ACAD SCI USA 94 (14): 7469-7474 JUL 8 1997

Abstract:
With only two different cell types, the haploid green alga Volvox represents the simplest multicellular model system. To facilitate genetic investigations in this organism, the occurrence of homologous recombination events was investigated with the intent of developing methods for gene replacement and gene disruption. First, homologous recombination between two plasmids was demonstrated by using overlapping nonfunctional fragments of a recombinant arylsulfatase gene (tubulin promoter/arylsulfatase gene). After bombardment of Volvox reproductive cells with DNA-coated gold microprojectiles, transformants expressing arylsulfatase constitutively were recovered, indicating the presence of the machinery for homologous recombination in Volvox. Second, a well characterized loss-of-function mutation in the nuclear nitrate reductase gene (nitA) with a single G --> A nucleotide exchange in a 5'-splice site was chosen as a target for gene replacement. Gene replacement by homologous recombination was observed with a reasonably high frequency only if the replacement vector containing parts of the functional nitrate reductase gene contained only a few nucleotide exchanges. The ratio of homologous to random integration events ranged between 1:10 and 1:50, i.e., homologous recombination occurs frequently enough in Volvox to apply the powerful tool of gene disruption for functional studies of novel genes.

Raven JA

Multiple origins of plasmodesmata
EUR J PHYCOL 32 (2): 95-101 MAY 1997

Abstract:
Plasmodesmata in photosynthetic eukaryotes are found in all embryophytes, in many members of the Chlorophyta, and in the Phaeophyceae. The Phaeophyceae and the Chlorophyta clearly developed cell walls and multicellularity independently, sc that (in the absence of lateral gene transfer) plasmodesmata evolved independently in these groups. The minimum number of independent origins of plasmodesmata in the Chlorophyta based on molecular phylogenies is two (Chlorophyceae sensu late, Charophyceae sensu late). Other intercellular connections in members of the Chlorophyta (Ctenocladus, Smithsoniella, Volvox) are structurally very different from true plasmodesmata. Recently published taxonomies of the Chlorophyta have five classes (Chlorophyceae, Oedegoniophyceae, Trentepohliophyceae, Klebsormidiophyceae and Charophyceae sensu stricto) with plasmodesmata out of a total of thirteen. However, it is by no means clear that these classes all acquired plasmodesmata independently.

Nozaki H, Ito M, Sano R, et al.

Phylogenetic analysis of Yamagishiella and Platydorina (Volvocaceae, Chlorophyta) based on rbcL gene sequences
J PHYCOL 33 (2): 272-278 APR 1997

Abstract:
Yamagishiella, based on Pandorina unicocca Rayburn et Starr is distinguished from Eudorina by its isogamous sexual reproduction, whereas Platydorina exhibits anisogamous sexual reproduction. In the present study, rue sequenced the large subunit of ribulose-1,5-bisphosphate carboxylase/oxygenase (rbcL) genes from five Japanese and North American strains of Y. unicocca (Rayburn et Stair) Nozaki, true Platydorina caudata Kofoid strains, and two strains of Eudorina unicocca G. M. Smith, as well as eight related colonial and unicellular species. Phylogenetic trees were constructed based on these sequence data and on previously published rbcL gene sequences from 23 volvocalean species in order to deduce phylogenetic relationships within the colonial Volvocales, with particular regard to the phylogenetic positions and status of the genera Yamagishiella and Platydorina. Two robust monophyletic groups of the anisogamous/oogamous volvocacean species were resolved in the maximum-parsimony tree as well as in the neighbor-joining distance tree. One of the two groups comprises three species of Volvox section Volvox, whereas the other is composed of other sections of Volvox as well as of all the species of Eudorina and Pleodorina. Platydorina, however, was positioned outside these two monophyletic groups. Therefore, derivation of the Platydorina lineage may be earlier than that of such anisogamous/oogamous groups, or origin of ''anisogamy with sperm, packets'' in Platydorina may De independent of sperm packet evolution in Eudorina, Pleodorina, and Volvox. It was also resolved with high bootstrap values that all of the Y. unicocca strains form a monophyletic group positioned outside the large monophyletic group including Eudorina and Pleodorina. These reject the possibility of the reverse evolution of isogamy from anisogamy to give rise to Yamagishiella within the lineage of Eudorina.

Liss M, Kirk DL, Beyser K, et al.

Intron sequences provide a tool for high-resolution phylogenetic analysis of volvocine algae
CURR GENET 31 (3): 214-227 MAR 1997

Abstract:
Three nuclear spliceosomal introns in conserved locations were amplified and sequenced from 28 strains representing 14 species and 4 genera of volvocalean green algae. Data derived from the three different introns yielded congruent results in nearly all cases. In pairwise comparisons, a spectrum of taxon-specific sequence differences ranging from complete identity to no significant similarity was observed, with the most distantly related organisms lacking any conserved elements apart from exon-intron boundaries and a pyrimidine-rich stretch near the 3' splice site. A metric (SI50), providing a measure of the degree of similarity of any pair of intron sequences, was defined and used to calculate phylogenetic distances between organisms whose introns displayed statistically significant similarities. The rate of sequences divergence in the introns was great enough to provide useful information about relationships among different geographical isolates of a single species, but in most cases was too great to provide reliable guides to relationships above the species level. A substitution rate of approximately 3 x 10(-8) per intron position per year was estimated, which is about 150-fold higher than in nuclear genes encoding rRNA and about 10-fold higher than the synonymous substitution rate in protein-coding regions. Thus, these homologous introns not only provide useful information about intraspecific phylogenetic relationships, but also illustrate the concept that different parts of a gene may be subject to extremely different intensities of selection. The intron data generated here (1) reliably resolve for the first;time the relationships among the five most extensively studied strains of Volvox, (2) reveal that two other Volvox species may be more closely related than had previously been suspected, (3) confirm prior evidence that particular isolates of Eudorina elegans and Pleodorina illinoisensis appear to be sibling taxa, and (4) contribute to the resolution of several hitherto unsettled issues in Chlamydomonas taxonomy.

Godl K, Hallmann A, Wenzl S, et al.

Differential targeting of closely related ECM glycoproteins: The pherophorin family from Volvox
EMBO J 16 (1): 25-34 JAN 2 1997

Abstract:
The alga Volvox carteri represents one of the simplest multicellular organisms. Its extracellular matrix (ECM) is modified under developmental control, e.g. under the influence of the sex-inducing pheromone that triggers development of males and females at a concentration below 10(-16) M. A novel ECM glycoprotein (pherophorin-S) synthesized in response to this pheromone was identified and characterized. Although being a typical member of the pherophorins, which are identified by a C-terminal domain with sequence homology to the sex-inducing pheromone, pherophorin-S exhibits a completely novel set of properties. In contrast to the other members of the family, which are found as part of the insoluble ECM structures of the cellular zone, pherophorin-S is targeted to the cell-free interior of the spherical organism and remains in a soluble state. A main structural difference is the presence of a polyhydroxyproline spacer in pherophorin-S that is linked to a saccharide containing a phosphodiester bridge between two arabinose residues. Sequence comparisons indicate that the self-assembling proteins that create the main parts of the complex Volvox ECM have evolved from a common ancestral gene.

1996

Stratmann J, Paputsoglu G, Oertel W

Differentiation of Ulva mutabilis (Chlorophyta) gametangia and gamete release are controlled by extracellular inhibitors
J PHYCOL 32 (6): 1009-1021 DEC 1996

Abstract:
Blade cells of Ulva mutabilis Foyn (Chlorophyta) excrete regulatory factors into their cell walls and into the environment. These factors are essential for the maintenance of the vegetative state. ''Sporulation inhibitor-1a'' (SI-1a) is a glycoprotein that was isolated from the culture medium of axenic Ulva growing as an undifferentiated callus. This protein was unusually stable to denaturing treatments and showed an extremely high apparent molecular mass (M(r)) of 1-4 X 10(7) daltons estimated by size exclusion chromatography. The glycosylation was not essential for activity. SI-1a suppressed gametogenesis completely at concentrations lower than 10(-14) M. When Ulva developed normally in the presence of their symbiotic bacteria, smaller forms of SI-1 accumulated in the medium (10(4) - 10(6) daltons). Sporulation inhibitors of the same size spectrum and with similar properties were also extracted from crude cell walls of nonaxenic Ulva. A class of different nonprotein sporulation inhibitors (SI-2) of very low M(r) and yet unknown structure was isolated from the inner space between the two blade cell layers. Excretion of all SI-1 forms decreased with maturation of the thallus, whereas the overally concentration of SI-2 in the thallus stayed constant throughout the life cycle. The SI-2 affected different Ulva species whereas SI-1 was species-specific. Gametogenesis was induced upon removal of both sporulation inhibitors from small single-layered fragments of mature blades. After a ''determination phase'' of 23-46 h, dependent on the time of induction within the cell cycle, the cells became irreversibly committed to differentiation and were no longer susceptible to SI-1 or SI-2. Subsequently, during a 28-h ''differentiation phase,'' 16 progametes were formed by synchronous genome doublings and cell divisions and differentiated into mature gametes. These became motile and were released from the gametangia when the concentration of a ''swarming inhibitor'' of low M(r), excreted mainly during the ''determination phase,'' declined below a threshold concentration. The biochemical properties of these regulatory factors and their effects on gametogenesis and gamete release are described.

Ichimura T

Genome rearrangement and speciation in freshwater algae
HYDROBIOLOGIA 336 (1-3): 1-17 OCT 25 1996

Abstract:
Speciation problems are reviewed in the context of biogeography of fresh-water algae. Currently accepted species concept in phycology is based on morphological characters, and according to this concept, most freshwater algal species are considered cosmopolitan. This implies whether they have a highly efficient means of dispersal or their morphological characters are very static through a long evolutionary time. Recent studies of reproductive isolation show that some biological species of fresh-water algae are not so static or may not have such a high power of dispersal means, though some are indeed very static in morphological characters. The life cycle of most freshwater algae is composed of a vegetative cycle of growth and reproduction and a sexual cycle of gametic fusion and meiosis in the zygote, which forms a dormant spore-like structure. Since any freshwater habitat is ephemeral in terms of evolutionary time scale, each species has a capacity of forming germlings from a dormant cell in order to recycle its life history. The genome of freshwater algae, therefore, contains various coadapted gene systems, at least two, for the vegetative and for the sexual cycle. Homothallism and heterothallism are two contrasting mating systems that represent two opposing ways of life to harmonize antagonism between the vegetative stage of growth and reproduction and the sexual and dormant stage. Geographic and ecological distribution, polyploidy, and sex determination are discussed in conjunction with sexual and postzygotic isolating mechanisms.

Nozaki H

Morphology and evolution of sexual reproduction in the Volvocaceae (Chlorophyta)
J PLANT RES 109 (1095): 353-361 SEP 1996

Abstract:
Morphological features of sexual reproduction in the Volvocaceae are reviewed, focusing particularly on gametic union and zygote germination. Both of the two conjugating gametes of the isogamous genera Pandorina, Volvulina and Yamagishiella bear a tubular mating structure (mating papilla), and plasmogamy is initiated by union of the papillae tips. On zygote germination, a single biflagellate gone cell is released from the zygote wall. Although all the anisogamous and oogamous genera of the Volvocaceae produce ''sperm packets'' during gametogenesis and a single gone cell at zygote germination, some difference can be recognized in the male gametes. The male gametes of Eudorina bear a tubular cytoplasmic protuberance (putative mating papilla) near the base of the flagella, whereas such a structure recognized at the light microscopic level is not evident in Pleodorina and Volvox, Evolution of the sexual reproduction characteristics of volvocacean algae is discussed on the basis of recent cladistic analysis of morphological data as well as of the ribosomal (r) RNA phylogeny and large subunit of the ribulose-1,5-biphosphate carboxylase/oxygenase(rbcL) gene trees.

Beyser K, Fabry S

Identification and characterization of a lower plant Ypt/Rab guanosine dissociation inhibitor (GDI)
FEBS LETT 396 (2-3): 298-304 NOV 4 1996

Abstract:
The cDNA encoding a Ypt/Rab guanosine dissociation inhibitor (Ypt-GDI) was isolated from the multicellular green alga Volvox carteri, representing the first complete plant gdi gene described. The gdiV1 gene occurs as a single copy in the algal genome, indicating that its product regulates all YptV proteins from Volvox. The derived GDI protein (GDIV1p) shows high similarity to animal and fungal GDIs. A specific antibody developed against GDIV1p detected the protein throughout the whole Volvox life-cycle. GDIV1p was localized in the cytoplasm and in the algal flagellum. This is in line with earlier findings of a dual localization of Ypt proteins both in the cell body and in the motility organelle, and indicates a novel role of the GDI/Ypt system, possibly in intraflagellar transport.

Choi G, Przybylska M, Straus D

Three abundant germ line-specific transcripts in Volvox carteri encode photosynthetic proteins
CURR GENET 30 (4): 347-355 SEP 1996

Abstract:
Volvox carteri is a multicellular eukaryotic green alga composed of about 2000 cells of only two differentiated types: somatic and germ line. To understand how embryonic cells are assigned either to somatic or germ line fates, we are investigating the regulation of transcripts that are abundant in only one cell type. Here we report the identity of three

transcripts that are coordinately expressed at high levels in germ line cells but not in somatic cells. Surprisingly, all three transcripts encode photosynthetic chloroplast proteins (light-harvesting complex protein. oxygen-evolving enhancer protein 3, and ferredoxin-NADP(+) reductase) that are transcribed from nuclear genes. We discuss why these mRNAs might be required at high levels in germ line cells and present a hypothesis, suggested by our results, on the evolution of cell specialization in the Volvocales.

Ortega MA, DiazGuerra M, Sastre L

Actin gene structure in two Artemia species, A-franciscana and A-parthenogenetica
J MOL EVOL 43 (3): 224-235 SEP 1996

Abstract:
Genomic clones coding for actin have been isolated from two species of the crustacean Artemia, A. parthenogenetica and A. franciscana. The Act211 isoform gene was isolated from A. parthenogenetica, and the two other isoform genes, Act302 and Act403, were isolated from A. franciscana. The comparison of the nucleotide sequence of genomic and cDNA clones showed an interspecific divergence of 4% in translated and 6.1% in untranslated regions. However, the establishment of the partial structure of the Act211 gene in A. franciscana and of the Act302 gene in A. parthenogenetica suggests their similarity in the two species. The Act211 gene is divided into four exons, the Act302 gene into six exons, and the Act403 gene into seven exons. The three genes have introns in the 5' untranslated region and between codons 41 and 42. The Act211 and 403 genes have one common intron in codon 168. The Act302 and 403 genes have common introns between codons 121-122, 246-247, and within codon 301. While introns in the 5' untranslated region and between codons 41-42 and 121-122 are present in many organisms, the introns in positions 168 and 246-247 had only been found previously in actin genes from the nematode Onchocerca volvulus and the green alga Volvox carterii, respectively. The intron in position 301 had not been reported before. The transcription initiation sites of these three genes as well as the nucleotide sequences of the promoter regions have been also determined.

Huber H, Beyser K, Fabry S

Small G proteins of two green algae are localized to exocytic compartments and to flagella
PLANT MOL BIOL 31 (2): 279-293 MAY 1996

Abstract:
The Ypt/Rab proteins are small GTPases, which belong to the Ras superfamily and have been shown to be involved in endo- and exocytosis in mammalian cells and yeast. Using affinity-purified antibodies specific for four Ypt proteins, namely Ypt1p, Ypt4p, Ypt5p and Ypt6p, of the multicellular green alga Volvox carteri (YptVp) and its close unicellular relative Chlamydomonas reinhardtii (YptCp), we examined the abundance of the corresponding antigens during the asexual life cycle of Volvox, and their intracellular localization. The YptV proteins were found in all stages throughout the asexual life cycle and are tightly associated with intracellular membranes. Indirect immunofluorescence revealed that YptV4p, YptV5p and YptV6p are present in perinuclear regions of the cell, indicating an association with the Golgi region. Golgi localization of YptV4p and YptV6p in Volvox was confirmed by immunogold electron microscopy. In contrast, we found Ypt1p associated with the contractile vacuole in both V. carteri and C. reinhardtii. Furthermore, the YptV proteins were also detected along the entire length of the flagella of somatic Volvox cells. This flagellar location was substantiated by western blot analysis of extracts prepared from isolated flagella of both algae. While localization to exocytic compartments is in agreement with the established Ypt/Rab function in intracellular vesicle transport of eukaryotic cells, presence in the algal flagellum is the first hint of a possible role for small G proteins also in motility organelles.

Ferris PJ, Woessner JP, Goodenough UW

A sex recognition glycoprotein is encoded by the plus mating-type gene fus1 of Chlamydomonas reinhardtii
MOL BIOL CELL 7 (8): 1235-1248 AUG 1996

Abstract:
Sexual fusion between plus and minus gametes of the unicellular green alga Chlamydomonas reinhardtii entails adhesion between plus-specific and minus-specific ''fringe'' proteins displayed on the plasma membrane of gametic mating structures. We report the identification of the gene (fus1) encoding the plus fringe glycoprotein, which resides in a unique domain of the mating-type plus (mt(+)) locus, and which was identified by transposon insertions in three fusion-defective mutant strains. Transformation with fus1(+) restores fringe and fusion competence to these mutants and to the pseudo-plus mutant imp11 mt(-), defective in minus differentiation. The fus1 gene is remarkable in lacking the codon bias found in all other nuclear genes of C. reinhardtii.

Gruber H, Kirzinger SH, Schmitt R

Expression of the Volvox gene encoding nitrate reductase: Mutation-dependent activation of cryptic splice sites and intron-enhanced gene expression from a cDNA
PLANT MOL BIOL 31 (1): 1-12 APR 1996

Abstract:
Use of the nitrate reductase encoding gene (nitA) as selection marker has facilitated the successful nuclear transformation of Volvox carteri. The Volvox nitA gene contains 10 introns. A stable nitA mutation in the Volvox recipient strain 153-81 resides in a G-to-A transition of the first nucleotide in the 5' splice site of nitA intron 2. This mutation resulted in at least three non-functional splice variants, namely: (1) intron 2 was not spliced at all; (2) a cryptic 5' splice site 60 nt upstream or (3) a cryptic 5' splice site 16 nt downstream of the mutation were activated and used for splicing. When we used nitA cDNA (pVcNR13) for transformation of V. carteri 153-81, a low efficiency of about 5 x 10(-5) transformants per reproductive cell was observed. Re-integration of either intron 1 (pVcNR15) or introns 9 and 10 (pVcNR16) in the transforming cDNA increased transformation rates to 5 x 10(-4). In parallel, pVcNR15-transformed Volvox exhibited growth rates that were 100-fold increased over the pVcNR13-transformed alga. This intron-enhancement of nitA gene expression appears to be associated with post-transcriptional processing and 'channelling' of the message. These data suggest an important role of splicing for gene expression in V. carteri.

Agrawal SC, Sharma UK

Chemical and biological properties of culture filtrates of Westiellopsis prolifica and Chaetophora attenuata
ISRAEL J PLANT SCI 44 (1): 43-48 1996

Abstract:
Westiellopsis prolifica Janet and Chaetophora attenunta Hazen cultures released sugars (glucose, fructose, and sucrose), organic acids (oxaloacetic acid and oxalic acid), amino acids, and protein. W. prolifica cultures released the amino acids glycine, serine, cystine, glutamic acid, aspartic acid, and cc-alanine, while C. attenuata cultures released glycine, serine, aspartic acid, and cr-alanine. W. prolifica and C. attenuata cultures of all ages released more extracellular protein than total free amino acids. Cultures of C. attenuata released more protein than cultures of the same age of W. prolifica. The filtrates from old cultures of W. prolifica and C. attenunta decreased the total chlorophyll content of all algae tested, totally suppressed conjugation in Spirogyra decimina and zoospore formation in C. attenuata, and drastically decreased spore germination in W. prolifica, thus producing stressful conditions affecting the growth and reproduction of these and other algae.

Selmer T, Hallmann A, Schmidt B, et al.

The evolutionary conservation of a novel protein modification, the conversion of cysteine to serinesemialdehyde in arylsulfatase from Volvox carteri
EUR J BIOCHEM 238 (2): 341-345 JUN 1 1996

Abstract:
A novel post-translational protein modification has recently been described in two human sulfatases, by which a cysteine is replaced by a serinesemialdehyde (2-amino-3-oxopropionic acid) residue [Schmidt, B., Selmer, T., Ingendoh, A. & von Figura, K. (1995) Cell 82, 271-278]. This cysteine is conserved among all known eukaryotic sulfatases. Here we report the presence of this modification in arylsulfatase from the green alga Volvox carteri. The evolutionary conservation of this novel protein modification between sulfatases of V. carteri and man lends further support to the assumption that this modification is required for the catalytic activity of sulfatases and may be present in all sulfatases of eukaryotic origin.

Sugase Y, Hirono M, Kindle KL, et al.

Cloning and characterization of the actin-encoding gene of Chlamydomonas reinhardtii
GENE 168 (1): 117-121 FEB 2 1996

Abstract:
The genomic and complementary DNA sequences were determined for the unique actin-encoding gene in Chlamydomonas reinhardtii (Cr). The deduced amino acid (aa) sequence of this actin was similar to most known actin sequences, with the highest identity (98.1%) being with that of Volvox carteri actin. The Cr actin-encoding gene has one intron in the 5'-untranslated region and eight introns in the coding region. The latter eight introns occur at the same positions as those in the V. casteri actin-encoding gene. The 5'-upstream region contains four short stretches of sequence similar to the so-called 'tub box', a characteristic sequence proposed to be responsible for the regulation of synthesis of various axonemal proteins upon deflagellation and during the cell cycle, Southern blot analysis indicated that the Cr genome has only a single actin-encoding gene. An antibody specific for the 11-aa peptide corresponding to the N-terminal sequence of this actin was found to react with a 43-kDa protein associated with flagellar inner-arm dynein. These findings indicate that a single actin functions in both the cytoplasm and flagella of this organism.

Fabry S, Beyser K

YptV2p, a membrane-associated small G protein abundant during embryogenesis in the green alga Volvox carteri
PROTOPLASMA 190 (1-2): 79-87 1996

Abstract:
The multicellular fresh-water alga Volvox carteri contains at least six small G protein-encoding genes (ypt genes) whose products are probably involved in intracellular vesicle transport. Four of them, YptV1, YptV3, YptV4, and YptV5, have been isolated and characterized previously. Here we report the cloning of yptV2 cDNA, the production of recombinant His-tagged YptV2p protein (reYptV2p) in E. coli, and the analysis of its GTPase activity and intracellular localization. YptV2p is predominantly present in dividing Volvox embryos. It is a membrane-associated protein which is localized to the cell periphery (plasma membrane or plasma-membrane-associated vesicles), probably by a lipid moiety. Purified, E. coli-expressed YptV2p binds GTP specifically, and has a typically low intrinsic GTPase activity (k(cat) = 0.004/min), which is enhanced by a GTPase activating protein activity present in Volvox. Our observations suggest a role of YptV2p in secretion, with a peak during the rapid cleavages of the Volvox embryo.

Hallmann A, Sumper M

The Chlorella hexose H+ symporter is a useful selectable marker and biochemical reagent when expressed in Volvox
P NATL ACAD SCI USA 93 (2): 669-673 JAN 23 1996

Abstract:
The multicellular obligately photoautotrophic alga Volvox is composed of only two types of cells, somatic and reproductive, Therefore, Volvox provides the simplest model system for the study of multicellularity. Metabolic labeling experiments using radioactive precursors are crucial for the detection of stage- and cell-type-specific proteins, glycoproteins, lipids, and carbohydrates. However, wild-type Volvox lacks import systems for sugars or amino acids. To circumvent this problem, the hexose/H+ symporter (HUP1) gene from the unicellular alga Chlorella was placed under the control of the constitutive Volvox beta-tubulin promoter. The corresponding transgenic Volvox strain synthesized the sugar transporter in a functional state and was able to efficiently incorporate C-14 from labeled glucose or glucosamine. Sensitivity toward the toxic glucose/mannose analogue 2-deoxyglucose increased by orders of magnitude in transformants. Thus we report the successful transformation of Volvox with a gene of heterologous origin. The chimeric gene may be selected for in either a positive or a negative manner, because transformants exhibit both prolonged survival in the dark in the presence of glucose and greatly increased sensitivity to the toxic sugar 2-deoxyglucose. The former trait may make the gene useful as a dominant selectable marker for use in transformation studies, whereas the latter trait may make it useful in development of a gene-targeting system.

Nishii I, Ogihara S

Role of actomyosin in multicellular deformation: Inversion of Volvox embryos.
MOL BIOL CELL 7: 2219-2219 Suppl. S DEC 1996

Girardin HM, Pelletier JA, Jovanovic L, et al.

Translational control during the development of Volvox.
MOL BIOL CELL 7: 624-624 Suppl. S DEC 1996

1995

Nozaki H, Itoh M, Sano R, et al.

Phylogenetic relationships within the colonial volvocales (Chlorophyta) inferred from rbcL gene sequence data
J PHYCOL 31 (6): 970-979 DEC 1995

Abstract:
The chloroplast-encoded large subunit of the ribulose-1, 5-bisphosphate carboxylase/oxygenase (rbcL) gene was sequenced from 20 species of the colonial Volvocales (the Volvacaceae, Goniaceae, and Tetrabaenaceae) in order to elucidate phylogenetic relationships within the colonial Volvocales. Eleven hundred twenty-eight base pairs In the coding regions of the (rbcL) gene were analyzed by the neighbor-joining (NJ) method using three kinds of distance estimations, as well as by the maximum parsimony (MP) method. A large group comprising all the anisogamous and oogamous volvocacean species was resolved in the MP tree as well as in the NJ trees based on overall and synonymous substitutions. In all the trees constructed, Basichlamys and Tetrabaena (Tetrabaenaceae) constituted a very robust phylogenetic group. Although not supported by high bootstrap values, the MP tree and the NJ tree based on nonsynonymous substitutions indicated that the Tetrabaenaceae is the sister group to the large group comprising the Volvocaceae and the Goniaceae. In addition, the present analysis strongly suggested that Pandorina and Astrephomene are monophyletic genera whereas Eudorina is nonmonophyletic. These results are essentially consistent with the results of the recent cladistic analyses of morphological data. However, the monophyly of the Volvocaceae previously supported by four morphological synapomorphies is found only in the NJ tree based on nonsynonymous substitutions (with very low bootstrap values). The genus Volvox was clearly resolved as a polyphyletic group with V. rousseletii Pocock separated from other species of volvox in the rbcL gene comparisons, although this genus represents a monophyletic group in the previous morphological analyses. Furthermore, none of the rbcL gene trees supported the monophyly of the Goniaceae; Astrephomene was placed in various phylogenetic positions.

Memon A, Hwang SB, Deshpande N, et al.

Novel aspects of the regulation of a cDNA (Arf1) from Chlamydomonas with high sequence identity to animal ADP-ribosylation factor 1
PLANT MOL BIOL 29 (3): 567-577 NOV 1995

Abstract:
ADP-ribosylation factor (ARF) is a highly conserved, low molecular mass (ca. 21 kDa) GTP-binding protein that has been implicated in vesicle trafficking and signal transduction in yeast and mammalian cells. However, little is known of ARF in plant systems. A putative ARF polypeptide was identifed in subcellular fractions of the green alga Chlamydomonas reinhardtii, based on [P-32]GTP binding and immunoblot assays. A cDNA clone was isolated from Chlamydomonas (Arfl), which encodes a 20.7 kDa protein with 90% identity to human ARF1. Northern blot analyses showed that levels of Arfl mRNA are highly regulated during 12 h/12 h light/dark (LD) cycles. A biphasic pattern of expression was observed: a transient peak of Arfl mRNA occurred at the onset of the light period, which was followed ca. 12 h later by a more prominent peak in the early to mid-dark period. When LD-synchronized cells were shifted to continuous darkness, the dark-specific peak of Arfl mRNA persisted, indicative of a circadian rhythm. The increase in Arfl mRNA at the,beginning of the light period, however, was shown to be light-dependent, and, moreover, dependent on photosynthesis, since it was prevented by DCMU. We conclude that the biphasic pattern of Arfl mRNA accumulation during LD cycles is due to regulation by two different factors, light (which requires photosynthesis) and the circadian clock. Thus, these studies identify a novel pattern of expression for a GTP-binding protein gene.

Imaizumi M, Doida Y

Cyclic AMP is a signal for repression of differentiation into gametes in Micrasterias thomasiana var notata
PLANT SCI 112 (1): 33-42 NOV 24 1995

Abstract:
This study investigates the effects of adenosine 3':5'-cyclic monophosphate (cAMP) and several chemicals which elevate the intracellular level of cAMP on the induction of zygote formation in Micrasterias thomasiana var. notata. When added at a concentration of 0.5-3 mM, cAMP repressed the induction of zygotes and simultaneously promoted cell proliferation, although at a concentration of 0.1 mM it merely delayed the initiation of zygote induction. Methylxanthines caffeine (0.05-1 mM) and theophylline (0.05-1 mM), forskolin (10 mu M), which is a potent activator of adenylate cyclase, and a membrane-permeable cAMP analog, 8-bromo cAMP (0.1-3 mM), also repressed the induction of zygotes and simultaneously promoted cell proliferation. In contrast, another cAMP analog used in this study, N-6,O-2'-dibutyryl cAMP (2-3 mM), repressed the induction of zygotes but did not cause promotion of cell proliferation. This analog also specifically blocked the cell division directly involved with gamete formation. The results obtained suggest that intracellular cAMP may function as a signal which simultaneously represses zygote induction and causes proliferation of cells in Micrasterias.

DESNITSKI AG

On the origin of Metazoa
ZH OBSHCH BIOL 56 (5): 629-631 SEP-OCT 1995

Abstract:
Under consideration is a new version of the phagocytella conception. It is suggested to consider blastea not a particular organism but a morphologically variable taxon of mixotrophic flagellates. Some of its subtaxa might have made a transition to the true heterotrophy, thus having become direct metazoan ancestors.

WALTHER Z, HALL JL

The uni chromosome of chalmydomonas – histone genes and nucleosome structure.
NUCLEIC ACIDS RES 23 (18): 3756-3763 SEP 25 1995

Abstract:
The uni linkage group (ULG) of Chlamydomonas reinhardtii contains many genes involved in the basal body-flagellar system, Recent evidence suggests that the corresponding uni chromosome is located in close proximity to the basal body complex. In the course of studies into its molecular organization, we have found a cluster of four histone genes on the ULG. The genes are arranged as divergently-transcribed pairs: H3-H4 and H2B-H2A. Genomic sequencing reveals that these genes lack introns and contain characteristic 3' palindromes similar to those of animals, The predicted amino acid sequences are highly conserved across species, with greatest similarities to the histone genes of Volvox. Southern analysis shows that each histone gene is present in 15-20 copies in Chlamydomonas and suggests a dispersed genomic organization. Northern analysis of mitotically-synchronized cells shows that, like the replication-dependent histones of higher eukaryotes, Chlamydomonas histone genes are expressed during S-phase. Using a gene-specific probe on Northern blots, we provide evidence that the ULG H4 gene is regulated in the same manner as other Chlamydomonas histone genes. Finally, micrococcal nuclease protection experiments show that the uni chromosome itself associates with histone proteins and displays a conventional nucleosomal banding pattern.

FABRY S, MULLER K, LINDAUER A, et al.

THE ORGANIZATION STRUCTURE AND REGULATORY ELEMENTS OF CHLAMYDOMONAS HISTONE GENES REVEAL FEATURES LINKING PLANT AND ANIMAL GENES
CURR GENET 28 (4): 333-345 SEP 1995

Abstract:
The genome of the green alga Chlamydomonas reinhardtii contains approximately 15 gene clusters of the nucleosomal (or core) histone H2A, H2B, H3 and H4 genes and at least one histone H1 gene. Seven non-allelic histone gene loci were isolated from a genomic library, physically mapped, and the nucleotide sequences of three isotypes of each core histone gene species and one linked H1 gene determined. The core histone genes are organized in clusters of H2A-H2B and H3-H4 pairs, in which each gene pair shows outwardly divergent transcription from a short (< 300 bp) intercistronic region. These intercistronic regions contain typically conserved promoter elements, namely a TATA-box and the three motifs TGGCCAGG(G/C)-CGAG, CGTTGACC and CGGTTG. Different from the genes of higher plants, but like those of animals and the related alga Volvox, the 3' untranslated regions contain no poly A signal, but a palindromic sequence (3' palindrome) essential for mRNA processing is present. One single H1 gene was found in close linkage to a H2A-H2B pair. The H1 upstream region contains the octameric promoter element GGTTGACC (also found upstream of the core histone genes) and two specific sequence motifs that are shared only with the Volvox H1 promoters. This suggests differential transcription of the H1 and the core histone genes. The H1 gene is interrupted by two introns. Unlike Volvox H3 genes, the three sequenced H3 isoforms are intron-free. Primer-directed PCR of genomic DNA demonstrated, however, that at least 8 of the about 15 H3 genes do contain one intron at a conserved position. In synchronized C. reinhardtii cells, H4 mRNA levels (representative of all core histone mRNAs) peak during cell division, suggesting strict replication-dependent gene control. The derived peptide sequences place C. reinhardtii core histones closer to plants than to animals, except that the H2A histones are more animal-like. The peptide sequence of histone H1 is closely related to the V. carteri VH1-II (66% identity). Organization of the core histone gene in pairs, and non-polyadenylation of mRNAs are features shared with animals, whereas peptide sequences and enhancer elements are shared with higher plants, assigning the volvocalean histone genes a position intermediate between animals and plants.

DESNITSKI AG

A REVIEW ON THE EVOLUTION OF DEVELOPMENT IN VOLVOX - MORPHOLOGICAL AND PHYSIOLOGICAL-ASPECTS
EUR J PROTISTOL 31 (3): 241-247 AUG 25 1995

Abstract:
This paper presents a morphophysiological concept of the evolution of Volvox development. We use published data concerning differences in size of the mature gonidia, rates of their division and peculiarities in segregation of somatic and reproductive cell lines. Based on this, four programmes (types) of asexual development of Volvox are recognized, and the evolutionary relationships among these programmes (but not among any concrete species of Volvox) are elucidated. The first developmental programme (Volvox powersii - V. pocockiae) is clearly primitive for the genus. This programme is characterized by ancestral features: large gonidia, division is fast, and there is no unequal (asymmetric) division into two cellular types. The second developmental programme(V. carteri), the third programme (V. tertius) and the fourth programme (V. aureus) are all derived, but constitute different phylogenetic trends. They each have some derived features: the second programme involves asymmetric division, the third programm involves slow division, while the fourth programme involves small gonidia and slow division. The evolutionary concept is supplemented by data on sexual reproduction in various species of Volvox.

GODL K, HALLMANN A, RAPPEL A, et al.

PHEROPHORINS - A FAMILY OF EXTRACELLULAR-MATRIX GLYCOPROTEINS FROM VOLVOX STRUCTURALLY RELATED TO THE SEX-INDUCING PHEROMONE
PLANTA 196 (4): 781-787 JUL 1995

Abstract:
Pherophorins are extracellular matrix (ECM) glycoproteins from Volvox that share homology with the sex-inducing pheromone. A novel pherophorin (pherophorin III) was characterized both with respect to expression pattern and proteolytic processing in vivo. Furthermore, it was shown that the pherophorins represent a protein family of ECM glycoproteins exhibiting a modular composition: their N-terminally located domain is a homolog of a domain found in the ECM glycoprotein SSG 185. Together with SSG 185, pherophorin I is a main component of the cellular zone within the ECM. The Volvox genome contains a tandem arrangement of genes encoding pherophorin II-related polypeptides. Inhibition of proteolytic processing of pherophorin II and III in vivo appears to result in the suppression of sexual induction.

DIETMAIER W, FABRY S, HUBER H, et al.

ANALYSIS OF A FAMILY OF YPT GENES AND THEIR PRODUCTS FROM CHLAMYDOMONAS-REINHARDTII
GENE 158 (1): 41-50 MAY 26 19

Abstract:
Small G-proteins encoded by the ras-like ypt genes are ubiquitous in eukaryotic cells. They have been shown to play an essential role in membrane vesicle transport. We have isolated four ypt genes, yptC1, yptC4, yptC5 and yptC6, from Chlamydomonas reinhardtii (Cr) genomic and cDNA libraries. Three of them, yptC1, yptC4 and yptC5, are close homologues of ypt genes previously found in the multicellular alga Volvox carteri (Vc), the fourth, yptC6, is new. Each yptC gene is present as a single copy in the genome. Comparisons of genomic and cDNA sequences revealed that the coding regions are interrupted by five (yptC5), six (yptC6), seven (yptC4) and eight (yptC1) introns, respectively. Cr ypt genes and the closely related Vc ypt genes have identical exon-intron structures, but the corresponding intron sequences are completely different. Polyadenylation is signalled by UAUAA, UGUAG and UGUAA. The deduced amino acid (aa) sequence of YptC6 exhibited 79% identity with HRab2; YptC1, YptC4 and YptC5 exhibited over 90% identity with their Vc homologues. Primary structures of the 9-aa 'effector domain' and the contiguous 'helix3-loop7' motif (approx. 30 aa) are 'diagnostic' features for functional assignment. Recombinant YptC proteins, overproduced in Escherichia coli and purified to near homogeneity, displayed strong and specific binding of GTP, but not of GMP or ATP. The four Cr Ypt proteins showed immunochemical cross reactions to their Vc counterparts. Moreover, Western blots demonstrated at least six types of Ypt in both Cr and Vc, suggesting that these Ypt are used for household functions responsible for vesicle transport rather than for cellular differentiation.

VOIGT J, VOGELER HP, KONIG WA, et al.

CHAOTROPE-SOLUBLE CELL-WALL GLYCOPROTEINS OF VOLVOX AND SOME MEMBERS OF THE ZYGNEMATOPHYCEAE IMMUNOLOGICALLY RELATED TO THE 150 KDA CELL-WALL GLYCOPROTEIN OF CHLAMYDOMONAS-REINHARDTII
MICROBIOL RES 150 (2): 129-137 MAY 1995

Abstract:
As previously described, the cell wall of Chlamydomonas reinhardtii contains several chaotrope-soluble glycoproteins with similar sugar compositions, but considerably different proportions of hydroxyproline. All these hydroxyproline-containing cell wall glycoproteins are recognized by a polyclonal antibody raised against the purified '150 kDa' cell wall glycoprotein of Chlamydomonas reinhardtii. This antibody also cross-reacts with some polypeptides present in the LiCl-extracts from intact cells of Spirotaenia erythrocephala, Spirotaenia obscura, Volvox aureus, and Volvox globator as revealed by Western blot analyses. Therefore, an Ige fraction of this particular antibody coupled to CNBr-activated Sepharose was used to isolate the immunologically related polypeptides extracted by aqueous LiCl from intact cells or cell wall preparations of different green algae belonging to the Volvocales or to the Zygnematophycene. Different and more or less complex polypeptide patterns were observed by comparative SDS-PAGE analyses of the polypeptide fractions isolated by immunoaffinity chromatography from extracts of Chlamydamonas reinhardtii, Volvox aureus, Micrasterias rotata, Gonatozygon brebissonii and Netrium digitus, respectively, whereas the corresponding fraction prepared from Spirotaenia erythrocephala contained a predominant '160 kDa' component. Amino acid and sugar analyses revealed that all these polypeptide fractions contained hydroxyproline (1.0-4.5 mol%) and the same sugars as the Chlamydomonas cell wall glycoproteins. However, the relative amounts of these sugars (arabinose, galactose, glucose, mannose and xylose) were found to be rather different. The highest proportion of hydroxyproline (4.5 mol%) and the highest ratio of arabinose:galactose (4.75:1) were determined for the glycoprotein fraction isolated from Spirotaenia erythrocephala indicating that at least the predominant '160 kDa' component is an intrinsic cell wall glycoprotein containing hydroxyproline and oligo-arabinosyl side chains. All the polypeptide fractions isolated from the other green algae obviously also contained chaotropesoluble cell wall glycoproteins as revealed by the presence of arabinose and hydroxyproline. These findings show that all the investigated green algae contain chaotrope-soluble cell wall glycoproteins immunologically related to the '150 kDa' cell wall glycoprotein of Chlamydomonas reinhardtii.