Neural crest
Semaphorin-neuropilin repulsive signaling works synergistically with EphB signaling to guide neural crest cells down the rostral half of somites in mice. In chick embryos, semaphorin acts in the cephalic region to guide neural crest cells through the pharyngeal arches. On top of repulsive repulsive signaling, neural crest cells express β1and α4 integrins which allows for binding and guided interaction with collagen, laminin, and fibronectin of the extracellular matrix as they travel. Additionally, crest cells have intrinsic contact inhibition with one another while freely invading tissues of different origin such as mesoderm. Neural crest cells that migrate through the rostral half of somites differentiate into sensory and sympathetic neurons of the peripheral nervous system. The other main route neural crest cells take is dorsolaterally between the epidermis and the dermamyotome. Cells migrating through this path differentiate into pigment cells of the dermis. Further neural crest cell differentiation and specification into their final cell type is biased by their spatiotemporal subjection to morphogenic cues such as BMP, Wnt, FGF, Hox, and Notch.