CHARACTERIZATION OF RHO GTPASE FAMILY HOMOLOGS IN DROSOPHILA-MELANOGASTER - OVEREXPRESSING RHO1 IN RETINAL CELLS CAUSES A LATE DEVELOPMENTAL DEFECT

The rho family of GTPases has been implicated in regulating changes in cell morphology in response to extracellular signals. We have cloned three widely expressed members of this family from Drosophila melanoga ster; a rho homologue (Rho1) and two rac homologues (Rad and Rac2). Fl ies harbouring a Rho1 transgene that is specifically expressed in the eye exhibit a dramatic dose dependent disruption of normal eye develop ment. Flies bearing at least two copies of the transgene display a sev ere rough eye phenotype characterized by missing secondary and tertiar y pigment cells, a substantial reduction in the number of photorecepto r cells and a grossly abnormal morphology of the rhabdomeres. Cell fat e determination in the imaginal disc occurs normally and abnormalities become manifest late in pupariation, coincident with the phase when t he cells undergo major morphological changes. This phenotype is modifi ed by mutations at several other loci that have been implicated in sig nal transduction, but not by mutations in ras pathway components.