One of the most important processes in morphogenesis is gastrulation, the means by which cells that will establish the internal germ layers of an organism move from the surface to the interior of the embryo. C. elegans is an excellent model organism to dissect the links between cell fate specification and morphogenesis because the time between cell fate specification and the earliest morphogenetic event (gastrulation) is very short.
  
Gastrulation begins in C. elegans with the ingression of two endodermal precursor cells (E cells). Our lab has previously shown that ingressing E cells undergo a myosin-driven apical constriction, activated by myosin regulatory light chain phosphorylation, which is dependent on Wnt signaling. Interestingly, Wnt signaling also specifies the endodermal fate of the E cells.
  
We are working to determine whether the mechanism used by the endodermal lineage applies to mesodermal and germline internalization, with the goal of identifying how cell fate specification controls morphogenesis in a variety of cells. C. elegans is unusual among model animal systems in that gastrulation involves repeated ingressions of small numbers of cells. This allows us to study several distinct examples of how well-studied cell fate specification mechanisms can control the cytoskeletal mechanisms that drive morphogenetic movements of cells. For example, E cell ingression occurs when there are two endodermal precursors; however, ingression of the mesodermal cells in C. elegans begins when there are sixteen MS cells, and the mechanism behind this ingression is not well characterized. Preliminary results from us and others have found that the MS cells ingress in pairs and myosin accumulates at the surface of these cells during this time. In addition, myosin also accumulates at the surface of ingressing germline cells. However, while the basic mechanism behind E cell, MS cell, and germline ingressions may be similar, their ingressions must be controlled differently, perhaps tied to the specifications of their cell fates. Experiments are ongoing to determine if Wnt pathway proteins are involved in MS and germline cell ingression, how and when these cells are polarized, and which transcription factors are acting upstream of gastrulation.