Facial motor neuron migration advances.

During development, the migration of specific neuronal subtypes is required for the correct establishment of neural circuits. In mice and zebrafish, facial branchiomotor (FBM) neurons undergo a tangential migration from rhombomere 4 caudally through the hindbrain. Recent advances in the field have capitalized on genetic studies in zebrafish and mouse, and high-resolution time-lapse imaging in zebrafish. Planar cell polarity signaling has emerged as a critical conserved factor in FBM neuron migration, functioning both within the neurons and their environment. In zebrafish, migration depends on specialized 'pioneer' neurons to lead follower FBM neurons through the hindbrain, and on interactions with structural components including pre-laid axon tracts and the basement membrane. Despite fundamental conservation, species-specific differences in migration mechanisms are being uncovered.