During gastrulation the embryo undergoes a dramatic reorganization, as massive morphogenetic movements and tissue differentiation result in the formation of patterned structures arrayed along the body axis. The cells that participate in morphogenesis at the gastrula stage must presumably "read out" information regarding their position along the axes of the forming embryo, and use that information as they produce patterned structures. Dr. Harden's laboratory has focused on pattern formation during gastrulation in a seemingly simple system, the sea urchin embryo, in order to discover general rules that all embryos use to produce patterned structures during gastrulation. Using experimental approaches that are unique to this system, we have found that mesenchyme cells in that sea urchin embryo form patterned structures in response to spatially localized target information in the ectoderm or underlying basal lamina. This proposal is aimed at gaining a greater understanding of these target recognition events, using molecular biology, computer-enhanced imaging techniques, and classical embryology. Specifically, this proposal seeks to answer the following questions: (1) What is the nature of the interaction between cells and their targets? (2) When and how do these targets arise during development? (3) What is the molecular nature of these targets? Our long term goal is to understand the rules that cells use to interact with one another in a coordinated fashion to transform the structure of the embryo during gastrulation.
