Figure 5. Environmental cues involved in the guidance of truncal neural crest cells.

Figure 5

Environmental cues involved in the guidance of truncal neural crest cells. Schematic representations of the trunk region of chick embryos viewed transversally at three typical stages of neural crest migration : early migration (A), ventral migration through the somite (B), late migration phase (C). For each step, the position of neural crest cells and the guidance cues are indicated at the levels of rostral and caudal halves of the somite, shown on the left and right sides of the picture, respectively. Neural crest cells are depicted in dark blue and the other solid tissues in grey : ao, aorta; dmt, dermomyotome; ec, ectoderm; en, endoderm; n, notochord; nt, neural tube; s, somite; sc, sclerotome. A) At the onset of migration, neural crest cells migrate along the neural tube and rapidly reach the dorsomedial edge of the somite. Their lateral migration under the ectoderm is inhibited by ephrin-B ligands. B) As neural crest cells enter the somitic area, they are prevented to migrate farther through the sclerotome in the caudal half of the somite by a variety of repulsive molecules : sema-3A, ephrin-B and F-spondin. Such cues are not produced in the sclerotome in the rostral side of the somite, instead, positive cues stimulating migration, such as thrombospondin, are released, allowing crest cells to migrate along the developing myotome to reach the ventral side of the embryo. At this stage, neural crest cells still cannot invade the lateral pathway and stand in the so-called staging area, between the ectoderm, the neural tube and the dorsomedial aspect of the dermomyotome. C) During the last period of migration, crest cells migrating ventrally are guided toward the aorta and are forced to coalesce into the primordium of the sympathetic ganglia due to the combination of repulsive cues that prevent them migrating laterally to the limb (sema-3A), ventrally to the endoderm (slit-2) and medially to the aorta (sema-3A and Shh). Cells that accumulate along the neural tube cannot migrate farther ventrally toward the notochord due to Shh effect and, consequently they regroup into the primordium of the spinal ganglia. Conversely, in the lateral pathway, ephrin-B repulsive cues turn into stimulating factors, thereby favoring migration of the melanocyte precursors through the dermis. Repulsive cues are depicted by red arrows while cues favoring migration are indicated by green arrows. A color version of this figure is available online at http://www.Eurekah.com.

From: Neural Crest Delamination and Migration: Integrating Regulations of Cell Interactions, Locomotion, Survival and Fate

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