CELL-TYPE-SPECIFIC ROLES FOR CDC42, RAC, AND RHOL IN DROSOPHILA OOGENESIS

The Rho subfamily of GTPases has been shown to regulate cellular morph ology. We report the discovery of a new member of the Rho family, name d RhoL, which is equally similar to Rac, Rho, and Cdc42. Expression of a dominant-negative RhoL transgene in the Drosophila ovary caused nur se cells to collapse and fuse together. Mutant forms of Cdc42 mimicked this effect. Expression of constitutively active RhoL led to nurse ce ll subcortical actin breakdown and disruption of nurse cell-follicle c ell contacts, followed by germ cell apoptosis. In contrast, Rac activi ty was specifically required for migration of a subset of follicle cel ls called border cells. All three activities were necessary for normal transfer of nurse cell cytoplasm to the oocyte. These results suggest that Rho protein activities have cell type-specific effects on morpho genesis.