In Rac1V12.Scer\UAS.T:Hsap\MYC; Scer\GAL4elav.PLu embryos, severe outgrowth defects are seen in peripheral motor axons. For example, segmental nerve (SN)a and SNb motor axons (abdominal posterior fascicle) completely fail to emerge from the CNS, while intersegmental nerve (ISN) axons (anterior fascicle) fail to extend out of the CNS in 93% of the cases.