A major focus of the research currently ongoing in the lab is aimed at understanding the origin of the cellular and molecular polarities that led to the evolution of germ layer segregation and gastrulation. Towards this goal, we are using sea urchins and the cnidarian Nematostella vectensis as comparative model systems to identify the mechanisms that specify and initiate pattern formation along the animal-vegetal (AV) axis, an ancient polarity present in most animal oocytes.
We and others have shown that the Wnt signaling pathways play a critical role in initiating pattern formation along the AV axis in sea urchins and in cnidarians. However, while Wnt-mediated endomesoderm segregation and gastrulation take place in vegetal blastomeres in sea urchins (and most bilaterians), these processes occur in animal pole-derived blastomeres in cnidarians.
These and other observations have led us to propose that endoderm segregation and gastrulation evolved at the animal pole of ancient embryos by the asymmetric activation of Wnt signaling at this pole, and that the mechanisms regulation these processes were moved to the vegetal pole during bilaterian evolution.
Our current research is focused on identifying and characterizing the maternally derived egg polarities that selectively activate early Wnt signaling in sea urchins and in Nematostella, and then using that information, to begin to reconstruct the mechanisms that led to the evolution of germ layer segregation and gastrulation in metazoans.