Filling in the phylogenetic gaps: Induction, migration, and differentiation of neural crest cells in a squamate reptile, the veiled chameleon (Chamaeleo calyptratus)

Neural crest cells comprise a migratory progenitor cell population that differentiate into cell types such as neurons and glia of the peripheral nervous system, pigment cells, hormone secreting cells in glands, and skeletal and connective tissue in the head, thus making important contributions to most tissues and organs throughout the vertebrate body. The evolutionary appearance of neural crest cells is considered synonymous with the origin of vertebrates and their subsequent diversification and radiation. While the comparative biology of neural crest cells has been studied for a century and a half beginning with their discovery by Wilhelm His in 1868, most of our understanding of their development and function has come from a small number of species. Thus, critical gaps exist in our understanding of how neural crest cells mediate evolution and development. This is particularly true with respect to squamate reptiles (lizards, snakes, amphisbaenians), which account for approximately one-third of all living tetrapods. Here, we present veiled chameleons (Chamaeleo calyptratus) as a model system for studying neural crest cell development in squamates. Chameleons exhibit various morphological specializations associated with an arboreal lifestyle that may have been facilitated through neural crest cells acting as a conduit for evolutionary change.