The fascinating world of neural crest cells

Abstract

Neural crest cells are a multipotent, stem cell-like population that have fascinated scientists for generations. First described by Wilhem His in 1868, Santiago Ramón y Cajal termed them " pre-ganglionic cells, " understanding that the cells from the dorsal neural tube populate the dorsal root ganglia. Neural crest cells arise at the border between the neural and non-neural ecto-derm. As cells express the cascade of transcriptional regulators, neural crest cells become specified and it is at this point that they undergo an epithelial-mesenchymal transition (EMT) and migrate away from the neural tube. Once migratory, they follow two main paths: a dorsal lateral pathway between the epidermis and mesoderm and a ventral pathway through the somites. Their migratory tracks are lined with attractive cues and the boundaries contain repulsive cues that direct their migration to the correct targets. Cell-cell interactions between migratory cells also play an important role in directed cell migration. Neural crest give rise to a plethora of different derivatives and, depending on their migratory path, they can become melano-cytes, neurons and glia of the peripheral nervous system, smooth muscle of the arch arteries and proximal outflow track of the heart, and in the head, cartilage and bones of the face. It is this diver-sity that has led some investigators to call them stem cells. The neural crest has been termed the " fourth " germ layer because of the timing and importance of their development and the number of diverse cell types it produces. Evolutionarily, neural crest cells are thought to have driven the transition from the jawless to jawed vertebrates, allowing for predation and the explosion of this lineage. Understanding the migratory processes of neural crest cells will provide key insights into evolution, development and pathogenesis, as well as more general processes, such as cancer cell metastasis. This special focus series offers an insightful look at different aspects of the molecular and cellular mechanisms of neural crest cell specification and migration in a variety of species. The papers in this issue provide overviews of cranial, cardiac and trunk neu-ral crest migration at the cellular level to provide a comprehen-sive view of how neural crest cells migrate. While many aspects of their migration are similar, there are differences that may be significant for future studies. The first review by Alfandari and colleagues focuses on cranial neural crest migration in Xenopus laevis emphasizing cell adhesion in the regulation of cell migra-tion. Cadherin-11-based interactions maintain adhesion between neural crest cells, while Integrins, Syndecan-4, Cadherin-11 and