Neural Development and Crest Migration

BMP and Wnt signaling pathways determine the three main areas of the neuroepithelium: the surface ectoderm, neural tube, and premigratory neural crest. These regions are identified by their unique adhesion proteins: E-cadherin (surface ectoderm), N-cadherin (neural tube), and cadherin-6B (premigratory neural crest).

The premigratory neural crest cells exhibit high BMP levels and moderate Wnt levels, leading to the expression of Snail-2 protein. Snail-2 represses the expression of N-cadherin and E-cadherin, allowing these cells to detach from their original location.

Cadherin-6B, present on the apical half of premigratory neural crest cells, activates RhoA and actomyosin contractile fibers, causing apical constriction and initiating delamination. This process allows the neural crest cells to detach from the neural tube and start their migration.

Noncanonical Wnt signaling controls the directionality of migrating neural crest cells by regulating the activity of RhoA and Rac1 proteins. RhoA (red) and Rac1 (yellow) are responsible for extending and retracting cellular protrusions, guiding the cells along their migratory path.

When neural crest cells encounter each other, they exhibit contact inhibition of locomotion, causing them to halt their migration, change direction, and disperse. This behavior occurs because contact depolymerizes the cytoskeleton of the cells, inhibiting protrusive activity along the contact point and promoting new protrusions away from the point of contact.