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Volvox carteri is a species of colonial green algae in the order Volvocales. It is a freshwater species with a wide distribution. The V. carteri life cycle includes a sexual phase and an asexual phase. V. carteri forms small spherical colonies, or coenobia, of 2000–6000 Chlamydomonas-type somatic cells and 12–16 large, potentially immortal reproductive cells called gonidia. While vegetative, male and female colonies are indistinguishable; however, in the sexual phase, females produce 35-45 eggs and males produce up to 50 sperm packets with 64 or 128 sperm each.
The genome of this species of algae was sequenced in 2010. Volvox carteri is a significant model organism for research into the evolution of multicellularity and organismal complexity, largely due to its simple differentiation into two cell types, versatility in controlled laboratory environments, and natural abundance.
Within V. carteri, several forms are distinguished, based on differences in asexual colonies, as well as male and female sexual colonies. One distinctive form, f. kawasakiensis, the male colonies have no somatic cells and only androgonidia (sperm packets).
Three key genes are known to play significant roles in the somatic-gonidium dichotomy: glsA (gonidialess A); regA (regenerator A); and lag (late gonidia). These genes are believed to carry out germ-soma differentiation during development in a general order:
The glsA gene contributes to asymmetric cell division that results in the designation of large cells that develop into gonidia and small cells that develop into somatic cells. Gls mutants do not experience asymmetric division, a key component for creating gonidia, and thus are composed only of somatic swimming cells.
The lag gene plays a role in specialization of gonidial initials. If mutations disable the lag gene, large cells specified by glsA will develop as somatic cells initially but then de-differentiate to become gonidia.
Determination of somatic cells is controlled by the transcription factor regA. The regA geneencodes a single 80 amino acid-long DNA-binding SAND domain that is expressed in somatic cells after embryonic development. regA acts to prevent division by inhibiting cell growth via downregulation of chloroplast biosynthesis, and represses expression of genes necessary for germ cell formation. Chlamydomonas reinhardtii, a unicellular relative of V. carteri, is known to possess genes related to regA. This suggests that the regA gene originated before proper cellular differentiation in Volvox and was likely present in an undifferentiated ancestor. In this case, the function of regA in V. carteri most likely arose due to changes in expression pattern from a temporal (environmental response) state to a spatial (developmental) state. (2025). 9789401796415 ISBN 9789401796415
Over 99% of the volume of a V. carteri colony is made up of a glycoprotein-rich extracellular matrix (ECM). Several genes involved in ECM construction and ECM proteins have been identified in V. carteri. These genes account for the expanded inner layer of the cell wall (ECM) and the count and diversity of genes encoding VMPs ( Volvox matrix metalloproteases) and pherophorins (ECM protein families).
Volvox has multiple sex-specific and sex-regulated transcripts, including MAT3, an rb-homologous tumor suppressor that displays evidence of sex-specific selection and whose alternative splicing is sexually regulated.
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