Fig. 7.

Kalirin-induced neuronal fiber outgrowth is mediated by RhoG. A–D, Constitutively active Rho GTPases (Rac1-Q61L, RhoA-Q62L, Cdc42-Q61L, and Rho G12V; all at 200 ng/μl) were microinjected, and the neurons were examined 48 hr later. Only the microinjection of the active RhoG G12V induced the fiber outgrowth phenotype resembling that observed for Kalirin or kalGEF1.E–G, Coinjection of neurons with kalGEF1 (50 ng/μl) and the RhoG competitive inhibitor RhoG F37A (F; 200 ng/μl) or RhoGIP122, a RhoG-GTP binding protein (G; 200 ng/μl), either diminished or blocked, respectively, the fiber outgrowth phenotype observed for kalGEF1 alone (E); the cells were photographed 48 hr after injection. H–J, RhoG F37A expression also blocked Kalirin-12-induced fiber outgrowth. RhoG F37A fluorescence (H; EGFP, green) andmyc-epitope staining for Kalirin-12 (I; Cy3, red) are merged in J; new fiber extensions were never observed despite high levels ofmyc-expression. Scale bar, 50 μm.