English: Summary of the pathways in motor neurons implicated in mediating a BC cell derived repellent signal that stops somal migration. Boundary cap cells (yellow) located at the MEP express repellent signals (red) that act either directly on motor neuron cell bodies or retrogradely via their axons to disengage somal migration from axon extension. Our data suggest that these signals comprise a combination of class 3 semaphorins and Sema6A (red). Plexin-A2 (purple) expressed by the motor neurons can function as a dual receptor for class 3 and class 6 semaphorins, the former in conjunction with Npn-2 (blue). In this scheme, MICAL3 (green), by linking Plexin-A to the cytoskeleton, is a key downstream mediator of the somal stabilising signal. As a result of cytoskeletal re-organisation, the force (green arrow) exerted from the axonal growth cone that leads to somal translocation in migrating neurons is disrupted. Bron et al. Neural Development 2007 2:21 doi:10.1186/1749-8104-2-21