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Neural Crest Cells and Axonal Specificity
Noncanonical Wnt signaling is critical for activating the small Rho GTPases in premigratory neural crest cells. These Rho GTPases function to (1) facilitate the expression of Foxd3 and the Snail family genes and (2) establish the cytoskeletal conditions for migration by promoting actin polymerization into microfilaments and the attachment of these microfilaments to focal adhesions in the cell membrane (Hall 1998; De Calisto et al. 2005).
The crest cells cannot leave the neural tube as long as they are tightly connected to one another. Snail has been shown to directly downregulate the expression of cadherin-6B and the tight junction proteins that bind epithelial cells together (see Figure 15.9). In zebrafish, Cadherin-6 is transiently maintained only at the apical end of the delaminating cell, which allows RhoA to construct the actomyosin contractile fibers for apical constriction and the commencement of delamination and migration (Clay and Halloran 2014). After migration, neural crest cells re-express cadherins, as demonstrated where they aggregate to form the dorsal root and sympathetic ganglia (Takeichi 1988; Akitaya and Bronner-Fraser 1992; Coles et al. 2007).
Literature Cited
Akitaya, T. and M. Bronner-Fraser. 1992. Expression of cell adhesion molecules during initiation and cessation of neural crest cell migration. Dev. Dynam. 194: 12–20.
PubMed Link
Clay, M. R. and M. C. Halloran. 2014. Cadherin 6 promotes neural crest cell detachment via F-actin regulation and influences active Rho distribution during epithelial-to-mesenchymal transition. Development 141: 2506–2515.
PubMed Link
Coles, E. G., L. A. Taneyhill and M. Bronner-Fraser. 2007. A critical role for Cadherin6B in regulating avian neural crest emigration. Dev. Biol. 312: 533–544.
PubMed Link
De Calisto, J., C. Araya, L. Marchant, C. F. Riaz and R. Mayor. 2005. Essential role of noncanonical Wnt signalling in neural crest migration. Development 132: 2587–2597.
PubMed Link
Hall, A. 1998. The Rho GTPases and the actin cytoskeleton. Science 279: 509–514.
PubMed Link
Takeichi, M. 1988. The cadherins: Cell-cell adhesion molecules controlling animal morphogenesis. Development 102: 639–656.
PubMed Link
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