The novel Rho-family GTPase Rif regulates coordinated actin-based membranerearrangements

Small GTPases of the Rho family have a critical role in controlling cell mo rphology, motility and adhesion through dynamic regulation of the actin cyt oskeleton [1,2], individual Rho GTPases have been shown to regulate distinc t components of the cytoskeletal architecture; RhoA stimulates the bundling of actin filaments into stress fibres [3], Rac reorganises actin to produc e membrane sheets or lamellipodia [4] and Cdc42 causes the formation of thi n, actin-rich surface projections called filopodia [5]. We have isolated a new Rho-family GTPase, Rif (Rho in filopodia), and shown that it represents an alternative signalling route to the generation of filopodial structures . Coordinated regulation of Rho-family GTPases can be used to generate more complicated actin rearrangements, such as those underlying cell migration [6], In addition to inducing filopodia, Rif functions cooperatively with Cd c42 and Rac to generate additional structures, increasing the diversity of actin-based morphology.