The Rho family of small GTPases function in many morphogenetic processes that shape an embryo. Their activity is partly modulated by RhoGAP proteins,which switch RhoGTPases to an inactive state. By searching for genes that regulate Drosophila embryo morphogenesis, Denholm et al. have discovered that the crossveinless-c (cv-c) gene encodes a RhoGAP that is expressed in, and is required by, multiple embryonic tissues undergoing morphogenesis, such as the Malpighian tubules (MpTs) and the epidermis during dorsal closure (see p. 2389). Genetic interactions between cv-c and RhoGTPase mutants indicate that the small GTPases, Rho1, Rac1 and Rac2, are Cv-c substrates. The authors' loss-and gain-of-function studies reveal that Cv-c regulates actin cytoskeleton dynamics during MpT convergent extension movements. From these and other data,they conclude that Cv-c functions to organise the actin cytoskeleton in tissues undergoing morphgenesis by regulating the activity of specific RhoGTPases.