In the sea urchin embryo there are five territories of invariant lineage - the prospective aboral ectoderm, the prospective oral ectoderm the vegetal plate, the skeletogenic mesenchyme and the small micromeres. In addition to a unique pattern of gene expression, these territories are defined by individual cell lineage histories and generation of distinct cell types. The lineages forming these territories are completely segregated from each other by the 6th cleavage and spatially restricted gene expression begins one or two divisions later. In all the territories except the skeletogenic mesenchyme, the founder cells that are the progenitors of each territory achieve unique patterns of gene expression by means of intracellular interactions with other cells. The following studies are designed to determine the lineage and fate of founder cells for specific cell types within territories; to investigate the specific functional significance of interactions with neighboring cells in establishing certain of the territories; and to test the role of major signal transduction systems in the specification of territories and cell types. The proposed experiments fall into the following categories: 1. Vegetal plate and neuronal lineage tracing with caged flourescein- dextran. 2. Cell lineage and cell interaction studied by means of cell ablation. 3. Molecular characterization of abnormal phenotypes derived from introduction of a foreign serotonin ligand- receptor system. 4. Developmental consequences of ectopic stimulation of the PI signal transduction system in specific blastomeres of known lineage (using the serotonin receptor). 5. The effects of elevated levels of second messengers in whole embryos and individual blastomeres. 6. Developmental effects of the expression of foreign receptor kinases in whole embryos and individual cells.
