Nck2 is essential for limb trajectory selection by spinal motor axons

Background: The development of a functioning nervous system requires precise assembly of neuronal connections, which can be achieved by the guidance of axonal growth cones to their proper targets. How axons are guided by signals transmitted to the cytoskeleton through cell surface-expressed guidance receptors remains unclear. We investigated the function of Nck2 adaptor protein as an essential guidance intermediary in the context of spinal lateral motor column (LMC) motor axon trajectory into the limb. Results: Nck2 mRNA and protein are preferentially expressed in the medial subgroups of chick LMC neurons during axon trajectory into the limb. Nck2 loss- and gain-of-function in LMC neurons using in ovo electroporation perturb LMC axon trajectory selection demonstrating an essential role of Nck2 in motor axon guidance. We also showed that Nck2 knockdown and overexpression perturb the growth preference of LMC neurites against ephrins in vitro and Eph-mediated redirection of LMC axons in vivo. Finally, the significant changes of LMC neurite growth preference against ephrins in the context of Nck2 and α2-chimaerin loss- and gain-of-function implicated Nck2 function to modulate α2-chimaerin activity. Conclusions: Here, we showed that Nck2 is required for Eph-mediated axon trajectory selection from spinal motor neurons through possible interaction with α2-chimaerin. Developmental Dynamics 247:1043-1056, 2018.