Understanding fundamental mechanisms goving axon outgrowth and guidance can inform the development of therapeutic strategies to restore neuronal function damaged though injury or disease.Axons navigate the extracellular environment by responding to guidance cues that bind to cell surface recep tors to relay information intracellularly via Rho GTPase family members,including the Rac GTPases.Rac GTPases act as master switches to regulate diverse signalling pathways to control the actin cytoskeleton-a major driver of axon outgrowth.However,scant evidence exists concing how different domains within Rac GTPases regulate specific neurodevelopmental events,such as axon outgrowth and guidance.