Role of the target in the pathfinding of facial visceral motor axons

Axon navigation depends, in part, on guidance cues emanating from the targe t. We have investigated the possible role of the target in the pathfinding of visceral motor axons to cranial parasympathetic ganglia. Mice homozygous for a tau-LacZ transgene targeted in the Phox2a locus lack the sphenopalat ine ganglion, which is the normal target of visceral motor axons of the fac ial nerve. We found that in these mutants, facial visceral motor axon pathf inding was disrupted, and some axons were misrouted to an alternative paras ympathetic ganglion. Moreover, the absence of correct facial visceral motor pathways was concomitant with defects in the pathfinding of rostrally-proj ecting sympathetic axons.