Riding the crest to get a head: neural crest evolution in vertebrates
Megan L. Martik, Marianne Bronner‐Fraser
Abstract
In their seminal 1983 paper, Gans and Northcutt proposed that evolution of the vertebrate ‘new head’ was made possible by the advent of the neural crest and cranial placodes. The neural crest is a stem cell population that arises adjacent to the forming CNS and contributes to important cell types, including components of the peripheral nervous system and craniofacial skeleton and elements of the cardiovascular system. In the past few years, the new head hypothesis has been challenged by the discovery in invertebrate chordates of cells with some, but not all, characteristics of vertebrate neural crest cells. Here, we discuss recent findings regarding how neural crest cells may have evolved during the course of deuterostome evolution. The results suggest that there was progressive addition of cell types to the repertoire of neural crest derivatives throughout vertebrate evolution. Novel genomic tools have enabled higher resolution insight into neural crest evolution, from both a cellular and a gene regulatory perspective. Together, these data provide clues regarding the ancestral neural crest state and how the neural crest continues to evolve to contribute to the success of vertebrates as efficient predators. The 'new head' hypothesis proposes that the advent of the neural crest and cranial placodes was crucial for the evolution of vertebrates. In this Review, Martik and Bronner discuss this hypothesis and how emerging data about gene regulatory networks in neural crest-like cell types in invertebrate chordates are providing insights into neural crest evolution.