Scales, scutes, and embryonic origins of the vertebrate dermal skeleton

Abstract

The story of vertebrate origins is one of novel cell types and shifting germ layer fates—and at the center of this story lies the neural crest. Neural crest cells are a population of stem-like cells that are specified within the dorsal neural tube of vertebrate embryos and that migrate widely throughout the body, giving rise to an array of neuronal and glial, neuroendocrine, pigment, connective tissue, and skeletal cell types (1). While there are hints of neural crest-like cells or “latent” neural crest homologues (2) in nonvertebrate chordates (3), the neural crest exhibits germ layer-scale developmental potential in vertebrate animals and gives rise to many defining features of the vertebrate body plan (4, 5). Importantly, however, in the most widely studied vertebrate lineages, the neural crest does not do everything, everywhere, all at once—rather, there is axial regionalization of the neural crest into cranial, vagal, trunk, and sacral domains, with each exhibiting restricted fate potential and giving rise to distinct derivatives (6). It therefore follows that to understand the origin and early evolution of vertebrates, it is important to consider not only the origin of the neural crest itself but also the evolution of its fate along the embryonic axis. In this issue, Stundl et al. report a paradigm-shifting discovery of trunk neural crest contribution to the postcranial dermal skeleton in fishes that challenges current models of neural crest axial regionalization and evolution (7).