Characterization of putative effector proteins for the small GTPase Dcdc42 in Drosophila. B. Zahedi , K. Sem , B. Xu , N. Harden. Mol. Biol. and Biochem., Simon Fraser University, Burnaby, BC, Canada.

   The Rho subfamily of small GTPases are key regulators of the actin cytoskeleton and have important roles in the determination of cell morphology and motility. We are interested in characterizing the roles of these small GTPases during Drosophila development. As part of our efforts we have been characterizing effectors for Drosophila Cdc42 (Dcdc42), a member of the Rho subfamily. We have identified a Drosophila homologue of the mammalian protein CIP4. CIP4 was originally isolated as a binder of activated Cdc42. DCIP4 shows 38% overall identity to CIP4, and the two proteins share a variety of domains, including an SH3 motif. We are currently characterizing loss-of-function mutations in DCIP4 and addressing its role in Dcdc42 signaling. We have also been characterizing DACK, a member of a family of nonreceptor tyrosine kinases that are likely Cdc42 effectors. We will present evidence that DACK is a component of Dcdc42 signaling during dorsal closure of the embryo.