Meeting Abstract

47.2  Sunday, Jan. 5 10:30  Gastrulation and the fate of the blastopore in the snail Crepidula fornicata LYONS, D/C*; PERRY, K; HENRY, J/Q; Duke University; University of Illinois, Urbana-Champaign dcl.duke@gmail.com

Gastrulation is a critical morphogenetic process in metazoan development by which presumptive endoderm and mesoderm cells become internalized. Modes of gastrulation (e.g., ingression, invagination, epiboly) are particularly diverse among the bilaterian protostomes. However, lophotrochozoan gastrulation has been studied in very few species, despite its importance for understanding the evolution of this process. Here we summarize results from an investigation of gastrulation mechanisms in the snail Crepidula fornicata, a model system for development among lophotrochozoans. First we characterized the epibolic spreading of the micromere cap as it envelops the mesentoblast and other endodermal cells. These data allow us to directly compare epiboly between Crepidula and other clades. A controversial aspect of gastrulation is the fate of the blastopore (the site of endoderm formation). While in most deuterostomes the blastopore becomes the anus, in protostomes the blastopore can be the site of anus or mouth formation. In some species it has been argued that the blastopore gives rise to both mouth and anus. However, lineage tracing is necessary to confirm the fate of cells rimming the blastopore, as cell rearrangement there is highly dynamic. Live imaging and lineage tracing showed definitively that the cells ringing the blastopore (derived from 2a-c and 3a-d micromeres) form the mouth in Crepidula. The anus is derived from the 2d lineage that generates a remote clone located at the posterior end of the embryo and never contributes to the blastopore. These data provide the necessary framework for ongoing investigations into the molecular basis of gastrulation and fate specification of mouth and anal tissues, which are essential for understanding basic origins of metazoan body plans.