Overexpression of RnRacGAP in Drosophila melanogaster deregulates cytoskeletal organisation in cellularising embryos and induces discrete imaginal phenotypes

RacGAP proteins have been shown to down-regulate members of the Rho/Rac subfamily, small GTPases controlling actin network organisation. Only one RacGAP protein, RnRacGAP, has been identified in Drosophila. To examine RnRacGAP function, we generated transgenic strains expressing RnRacGAP under the control of the heat-shock promoter hsp70. In cellularising embryos, ectopic RnRacGAP induces lethality, associated with radical cell-shape changes, apical F-actin delocalisation, and inhibition of basal actin polymerisation. Overexpression of RnRacGAP in pupae induces a number of phenotypes with distinct critical periods of induction. These include wing shape and margin changes, wing vein defects, disorientation of wing hairs and thoracic bristles, and abdominal segment fusion. Thus, changes in cell shape/adhesion and reorganisation of the actin network are sensitive to overexpression of RnRacGAP throughout development in Drosophila.