One of the most remarkable attributes of developmentally complex organisms is that they start life as a single cell but ultimately produce many different cell types. The generation of cellular diversity can be driven by intrinsic factors, whereby asymmetries are established in the pre-divisional cell and daughters are quantitatively and/or qualitatively different at birth, or it can be driven by extrinsic factors that signal equivalent daughters to develop differently.

Our laboratory investigates cell-intrinsic mechanisms of differentiation, using a simple model, the green alga Volvox carteri. V. carteri has many attributes to recommend it for such studies, including the following: (1) it possesses just two cell types, germ and soma, and hence displays the simplest type of division of labor; (2) it reproduces rapidly, with each adult generating ~16 new asexual progeny in just two days; (3) mutants defective for cell differentiation are easy to isolate, because V. carteri is genetically haploid; and  (4) cloning and molecular analysis of genes regulating cellular differentiation in V. carteri has been facilitated by the development of many tools, including a sequenced genome. Current work in our lab focuses on genes required to set aside progenitors of the two cell types during embryogenesis, and on genes required for the maintenance of the somatic cell fate.

V. carteri is closely related to extant taxa that are even simpler than it is, including unicellular Chlamydomonas reinhardtii, which is also a tractable model organism. Since V. carteri has been diverging from these species for only ~1/10th the time that animals and land plants have been evolving from their respective closest unicellular cousins, these green algae comprise an especially promising system for analyzing the evolution of developmental complexity.  Accordingly, we are using genes that are required for cellular differentiation in V. carteri to trace the molecular genetic origins of cell-fate determination in the family of green algae to which it and C. reinhardtii belong.