Neural crest cell plasticity. size matters.

Patterning and morphogenesis of neural crest-derived tissues within a developing vertebrate embryo rely on a complex balance between signals acquired by neural crest cells in the neuroepithelium during their formation and signals from the tissues that the neural crest cells contact during their migration. Axial identity of hindbrain neural crest is controlled by a combinatorial pattern of Hox gene expression. Cellular interactions that pattern neural crest involve signals from the same key molecular families that regulate other aspects of patterning and morphogenesis within a developing embryo, namely the BMP, SHH and FGF pathways. The developmental program that regulates neural crest cell fate is both plastic and fixed. As a cohort of interacting cells, neural crest cells carry information that directs the axial pattern and species-specific morphology of the head and face. As individual cells, neural crest cells are responsive to signals from each other as well as from non-neural crest tissues in the environment. General rules and fundamental mechanisms have been important for the conservation of basic patterning of neural crest, but exceptions are notable and relevant. The key to furthering our understanding of important processes such as craniofacial development will require a better characterization of the molecular determinants of the endoderm, ectoderm and mesoderm and the effects that these molecules have on neural crest cell development.