The Rac GTPase-activating protein RotundRacGAP interferes with Drac1 and Dcdc42 signalling in Drosophila melanogaster

RhoGTPases are negatively regulated by GTPase-activating proteins (GAPs). H ere we demonstrate that Drosophila RotundRacGAP is active in vitro on Drac1 and Dcdc42 but not Drho1. Similarly, in yeast, RotundRacGAP interacts spec ifically with Drac1 and Dcdc42, as well as with their activated V12 forms, showing a particularly strong interaction with Dcdc42V12. In the fly, lower ing RotundRacGAP dosage specifically modifies eye defects induced by expres sing Drac1 or Dcdc42 but not Drho1, confirming that Drac1 and Dcdc42 are in deed in vivo targets of RotundRacGAP. Furthermore, embryonic-directed expre ssion of either RotundRacGAP, or dominant negative Drac1N17, transgenes ind uces similar defects in dorsal closure and inhibits Drac1-dependent cytoske leton assembly at the leading edge. Expression of truncated forms of Rotund RacGAP shows that the GAP domain of RotundRacGAP is essential for its funct ion. Unexpectedly, transgenes encoding Drac1N17, Dcdc42N17, or RotundRacGAP do not affect the c-Jun N-terminal kinase-dependent gene expression of dec apentaplegic and puckered, indicating that another Drac1-independent signal redundantly activates this pathway. Finally, in a situation where Drac1 is constitutively activated, RotundRacGAP greatly reduces the ectopic express ion of decapentaplegic, possibly by negatively regulating Dcdc42.