We are studying the function of cell adhesion molecules during the development of the nervous system in Drosophila. During the previous granting period we have cloned and characterized shotgun (shg) and faint sausage ((as). shg encodes the Drosophila E-cadherin homolog, DE- cadherin; fas encodes a novel member of the superfamily of Ig-like proteins for which we will test an adhesive function as part of this proposal. Adhesion molecules, in particular classic cadherins such as E-cadherin, are centrally involved in the control of cell sorting, motility and differentiation in all animals. E-cadherin acts as a tumor suppressor gene. So far little is known about the function of cadherins during neural development; most insight has been gained from the study of vertebrate cell culture systems. Our identification of mutations in the shg/DE-cadherin gene gives us the opportunity to analyze the function of this molecule, which is expressed in the neuroectoderm and subpopulations of neurons, in whole preparations of Drosophila. It is proposed to generate a set of constructs of shg/DE-cadherin and use them to either overexpress or remove the function of this gene at defined developmental stages and in defined tissues. These manipulations will allow us to address how shg/DE-cadherin mediated adhesion is involved in the determination and migration of neuronal progenitors, axonal pathfinding, and synaptogenesis. We will further use our constructs, in both embryos and Drosophila 52 cells, to analyze the role of phosphorylation of the cadherin/catenin complex (CCC) in cell adhesion in the Drosophila system. Our preliminary data suggest that the membrane bound tyrosine kinase DER (Drosophila homolog of the EGF receptor) phosphorylates the CCC, since loss"""""""" of DER function causes a phenotype that closely resembles the phenotype resulting from E-cadherin overexpression. We will investigate whether DER directly binds to the CCC (as has been shown in vertebrate cell lines) and whether its activation leads to phosphorylation of shg/DE-cadherin and/or catenins. We believe that our analysis of shg/DE-cadherin in Drosophila will further our understanding of the function of classic cadherins in general. The possibility that the CCC is an immediate target of EGFR activity in Drosophila would widen our understanding of the function of growth factors in embryonic development.
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