The neuronal architecture of Xenopus retinal ganglion cells is sculpted byrho-family GTPases in vivo

Dendritogenesis, axonogenesis, pathfinding, and target recognition are all affected in distinct ways when Xenopus retinal ganglion cells (RGCs) are tr ansfected with constitutively active (ca), wild-type (wt), and dominant neg ative (dn) Rho-family GTPases in vivo. Dendritogenesis required Rac1 and Cd c42 activity. Moreover, ca-Rac1 caused dendrite hyperproliferation. Axonoge nesis, in contrast, was inhibited by ca-Rac1. This phenotype was partially rescued by the coexpression of dn cyclin-dependent kinase (Cdk5), a propose d effector of Rac1, suggesting that Rac1 activity must be regulated tightly for normal axonogenesis. Growth cone morphology was particularly sensitive to dn-RhoA and wt-Cdc42 constructs. These also caused targeting errors, su ch as tectal bypass, suggesting that cytoskeletal rearrangements are involv ed in target recognition and are transduced by these pathways.