Neural crest migration: patterns, phases and signals.

The neural crest is a migratory, multipotent cell type that forms a vast array of vertebrate structures including the craniofacial skeleton and peripheral nervous system (Le Douarin and Kalcheim, 1999). Abnormalities in the ability of neural crest cells to reach precise target sites cause myriad birth defects. Unraveling the mechanisms that generate neural crest migratory patterns is essential to understanding how molecular signals sculpt the migration, morphogenesis, and differentiation of structures during development. Furthermore, neural crest migration resembles cancer metastasis, and insights into the programmed invasion of a highly migratory cell type may yield clues into the unprogrammed events during cancer. Neural crest cells emerge from the dorsal neural tube (orange line) in a rostrocaudal progression, so that neural crest development ismore advanced in the head than in the trunk (“Developmental Age” arrow). Neural crest cells invade surrounding tissues along stereotypical pathways (grey), exhibiting three distinct phases in their migratory behaviors (side bar). This idealized embryo illustrates the patterns, phases, and signals of cranial and trunk neural crest migration in a condensed format (Gammill and Roffers-Agarwal, 2010; Kulesa et al., 2010).