Neurotrophic factor NT-3 displays a non-canonical cell guidance signaling function for cephalic neural crest cells.

Chemotactic cell migration is triggered by extracellular concentration gradients of molecules segregated by target fields. Neural crest cells (NCCs), paradigmatic as an accurately moving cell population, undergo wide dispersion along multiple pathways, invading with precision defined sites of the embryo to differentiate into many derivatives. This report addresses the involvement of NT-3 in early colonization by cephalic NCCs invading the optic vesicle region. The results of in vitro and in vivo approaches showed that NCCs migrate directionally up an NT-3 concentration gradient. We also demonstrated the expression of NT-3 in the ocular region as well as their functional TrkB, TrkC and p75 receptors on cephalic NCCs. On whole-mount embryo, a perturbed distribution of NCCs colonizing the optic vesicle target field was shown after morpholino cancelation of cephalic NT-3 or TrkC receptor on NCCs, as well as in situ blocking of TrkC receptor of mesencephalic NCCs by specific antibody released from inserted microbeads. The present results strongly suggest that, among other complementary cell guidance factor(s), the chemotactic response of NCCs toward the ocular region NT-3 gradient is essential for spatiotemporal cell orientation, amplifying the functional scope of this neurotrophic factor as a molecular guide for the embryo cells, besides its well-known canonical functions.