Rho family small GTPases are Ras-related small GTPases that regulate cytoskeletal organization, motility, trafficking, and cell migration. Numerous studies have shown that Rho GTPase signaling pathways contribute to proper neuronal axon pathfinding and migration in C. elegans. There are 7 Rho GTPases in C. elegans: RHO-1 (RhoA), CDC-42 (Cdc-42), CED-10 (Rac1), RAC-2 (Rac1), MIG-2 (RhoG), and the atypical Cdc-42-like molecules CHW-1 (Chp/Wrch-1), and CRP-1 (putative TC10, TCL). Despite extensive knowledge of Rho/Cdc-42/Rac GTPases, little is known about the contribution of the C. elegans atypical Cdc-42-like family members CHW-1 and CRP-1 to axon pathfinding and neuronal migration. CHW-1 is similar to both Chp (Wrch-2, RhoV) and Wrch-1 (RhoU), while CRP-1 is similar to both TC10 (RhoQ) and TCL (RhoJ). CHW-1 and CRP-1 are predicted to, or have been shown to display altered GDP/GTP cycling characteristics (Jenna et al., 2005). CHW-1 contains an alanine instead of the conserved glycine at the 12 position (using Ras numbering), which is predicted to be a partially activating mutation. CRP-1 resembles TC10 and TCL, and like these GTPases, CRP-1 also shows altered GDP/GTP binding characteristics (Neudauer et al., 1998; Vignal et al., 2000; Jenna et al., 2005). To test the roles of CHW-1 and CRP-1 in axon pathfinding and cell migration, we assayed the PDE axons and the migrations of the Q descendants AQR and PQR in
chw-1(
ok697) and
crp-1(
ok685) mutants. We found that loss of
chw-1 or
crp-1 alone resulted in only modest pathfinding defects in PDE neurons, similar to
cdc-42(
gk388). However loss of both
cdc-42 and
chw-1 or
chw-1 and
crp-1 resulted in synergistic increases in PDE axon pathfinding defects. These results suggest that, similar to the Rac-like GTPases CED-10 and MIG-2 (Lundquist et al., 2001), the Cdc-42-family GTPases CDC-42, CHW-1, and CRP-1 act redundantly in axon pathfinding. Preliminary studies indicate that loss of either
chw-1 or
crp-1 result in modest defects in AQR migration, suggesting that they might redundantly control cell migration as well. As a complementary approach, we plan to drive the expression of mutant versions of CHW-1 and CRP-1 in the PDE neurons and AQR/PQR to determine the effects of overactivity, similar to studies on the Rac GTPases (Struckhoff and Lundquist, 2003). Preliminary results indicate that expression of a mutant CHW-1 transgene predicted to have increased GTPase activity disrupted neuronal morphology. Taken together, these data provide preliminary evidence for a role of the atypical Cdc-42-like GTPases CHW-1 and CRP-1 in axon pathfinding and neuronal migration.