Taming the fierce roller: an "enhanced" understanding of cellular differentiation in Volvox

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 carteri is the regA gene, which encodes a putative transcriptional repressor that prevents somatic cells from expressing reproductive functions. Stark et al. have dissected the regA gene to determine how its expression is restricted to somatic cells. Their results suggest that regA 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.