The molecular mechanisms of early development in the sea urchin must be interpreted in terms of the embryonic cell lineage. The purpose of this investigation is to further explore the role of cell lineage relationships in the development of sea urchin embryos and larvae. A multiple approach is taken: 1) Building on the existing, partially completed database, some studies will address unsolved problems in the lineage of the S. purpuratus embryo by further defining the lineage and specification within the definitive vegetal plate, by determining more completely the fate of the eight small micromeres, and by describing the origins of the neuroblasts; 2) To describe lineage changes in regulative development, a group of experiments will compare normal lineage patterns with the lineage of cells in isolated animal caps treated with LiCl or fused with micromeres and will compare normal lineage patterns with those of meridional quarter embryos, and 3) To provide descriptions of lineage and specification in the morphogenesis of the juvenile echinoderm, the expression of histospecific marker genes in the rudiment of S. purpuratus larvae will be investigated by in situ hybridization. %%% A fundamental problem in developmental biology is how the various cell types found in an adult are derived from a single fertilized egg. This study will trace the cell fates of founder cells from very early divisions after fertilization to their ultimate form in a larvae. It will also explore the factors which determine the fate of those cells.
