DROSOPHILA RAC1 CONTROLS MOTOR AXON GUIDANCE

Previous genetic studies of intersegmental nerve b development have id entified several cell-surface proteins required for correct axon guida nce to appropriate target muscles. Here we provide evidence that the s mall GTPase Drac1 also plays a key role in this guidance process. Neur onal expression of the dominant negative mutation Drac1(N17) causes ax ons to bypass and extend beyond normal synaptic partners. This phenoty pe is consistently reproduced by pharmacological blockade of actin ass embly. Genetic interactions between Drac1(N17) and the receptor-tyrosi ne phosphatase Dlar suggest that intersegmental nerve b guidance requi res the integration of multiple, convergent signals.