Glossiphoniid leech embryos, such as those of the species Helobdella triserialis, are well suited for studying cellular aspects of early development, because they are relatively large and hardy, and because their blastomeres are both experimentally accessible and individually identifiable. Thus, experimental analyses can be carried out on developmentally equivalent cells from one embryo to the next. This proposal is to continue previous analyses of various aspects of leech development, including: the role of cytoplasmic determinants in determining early cleavage; the specification of mesodermal and ectodermal cell lines; fate determining interactions between initially equipotent cells; the continuing refinement of developmental cell lineages; the influence of a transient embryonic epithelium on morphogenesis. The experiments proposed will carry out these analyses at the cellular and molecular level, by incorporating the techniques of the "reverse genetic approach" in combination with those used previously, such as microinjection of cell lineage tracers and other materials into identified embryonic cells, single cell ablation and optical microscopy.
