MYOBLAST CITY, THE DROSOPHILA HOMOLOG OF DOCK180 CED-5, IS REQUIRED IN A RAC SIGNALING PATHWAY UTILIZED FOR MULTIPLE DEVELOPMENTAL PROCESSES/

The Rac and Cdc42 GTPases share several regulators and effecters, yet perform distinct biological functions. The factors determining such sp ecificity in vivo have not been identified. In a mutational screen in Drosophila to identify Rac-specific signaling components, we isolated 11 alleles of myoblast city (mbc). mbc mutant embryos exhibit defects in dorsal closure, myogenesis, and neural development. DOCK180, the ma mmalian homolog of Mbc, associates with Rac, but not Cdc42, in a nucle otide-independent manner. These results suggest that Mbc is a specific upstream regulator of Rac activity that mediates several morphogeneti c processes in Drosophila embryogenesis.