Hox genes, neural crest cells and branchial arch patterning

Proper craniofacial development requires the orchestrated integration of mu ltiple specialized tissue interactions. Recent analyses suggest that cranio facial development is not dependent upon neural crest pre-programming as pr eviously thought but is regulated by a more complex integration of cell and tissue interactions. In the absence of neural crest cells it is still poss ible to obtain normal arch patterning indicating that neural crest is not r esponsible for patterning all of arch development. The mesoderm, endoderm a nd surface ectoderm tissues play a role in the patterning of the branchial arches, and there is now strong evidence that Hoxa2 acts as a selector gene for the pathways that govern second arch structures.