The Caenorhabditis elegans genome contains three rac-like genes,
ced-10,
mig-2, and
rac-2. We report that
ced-10,
mig-2 and
rac-2 act redundantly in axon pathfinding: inactivating one gene had little effect, but inactivating two or more genes perturbed both axon outgrowth and guidance.
mig-2 and
ced-10 also have redundant functions in some cell migrations. By contrast,
ced-10 is uniquely required for cell-corpse phagocytosis, and
mig-2 and
rac-2 have only subtle roles in this process. Rac activators are also used differentially. The UNC-73 Trio Rac GTP exchange factor affected all Rac pathways in axon pathfinding and cell migration but did not affect cell-corpse phagocytosis. CED-5 DOCK180, which acts with CED-10 Rac in cell-corpse phagocytosis, acted with MIG-2 but not CED-10 in axon pathfinding. Thus, distinct regulatory proteins modulate Rac activation and function in different developmental processes.