Volvox carteri, the 'fierce roller', is a
multicellular chlorophyte alga, closely related to the single-celled Chlamydomonas
reinhardtii. Volvox normally reproduces as an asexual
haploid, but can be induced to undergo sexual differentiation and reproduction.
The 48-hour life cycle allows easy laboratory culture and includes an embryogenesis
program that features many of the hallmarks of animal and plant development.
These features include embryonic axis formation, asymmetric cell division,
a gastrulation-like inversion, and differentiation of germ and somatic
cells. The ~2000 somatic cells in a Volvox spheroid are biflagellate and
adapted for motility, while the ~16 large germ cells contained within the
spheroid are non-motile and specialized for growth and reproduction. Volvox embryogensis generates the coordinated arrangement of somatic flagella
and photosensing eye spots needed for the organism's characteristic forward
The draft sequence of the Volvox genome
will provide fascinating insights into the evolution of multicellularity
in the green algal lineage and beyond. Moreover, the Volvocales, the
family that includes single-celled
Chlamydomonas (whose genome sequence is already available) and Volvox,
also includes several multicellular or colonial species with intermediate
cell numbers and less complex developmental programming. Comparative
genomic studies within this group promises further insights into the
origin and evolution of multicellularity in eukaryotes.
Genomic Analysis of Organismal Complexity in the Multicellular Green Alga Volvox carteri Science 9 July 2010