Cytoskeletal alterations in Dictyostelium induced by expression of human cdc42

The rho family of small G proteins has been shown to be involved in control ling actin filament dynamics in cells. To evaluate the functional overlap b etween human and Dictyostelium G proteins, we conditionally expressed const itutively active human cdc42 (V12-cdc42) in Dictyostelium cells. Upon induc tion, cells adopted a unique morphology: a flattened shape with wrinkles ru nning from the cell edge toward the center. The appearance of these wrinkle s is highly dynamic so that the cells cycle between the wrinkled and relati vely normal morphologies. Phalloidin staining indicates that the stellate w rinkles contain dense actin structures and also that numerous filopods proj ect vertically from the center of these cells. Consistent with the hypothes is that cdc42 induces actin polymerization in vivo, cells expressing V12-cd c42 show an increase in the amount of F-actin associated with the cytoskele ton. This is accompanied by an increase in the association of the actin-bin ding proteins 34-kDa bundler, ABP-120 and alpha -actinin with the cytoskele ton. In conclusion, human cdc42 has various effects on the Dictyostelium ac tin cytoskeleton consistent with a conserved role of small GTPases in contr ol of the cytoskeleton.