Mechanisms of Differentiation

Abstract

Neural crest cells do not self-differentiate. Instead they diversify into particular cell types following interactions with other cells, extracellular matrices, growth factors, and/or hormones. These differentiative signals may be encountered in the premigratory environment in the neural tube, while neural crest cells are migrating, or after they arrive at their final site. I have already touched on how pharyngeal endoderm, either alone or with dorsal mesoderm and/or ectoderm, elicits chondrogenesis from visceral arch mesenchyme in amphibians and possibly also in lampreys (chapters 4 and 5), and how oral epithelium interacts with dental mesenchyme to initiate odontoblast differentiation and deposition of dentine during tooth development in amphibians and mammals (Chapter 8). When do neural crest cells become committed for particular cell fates? In this chapter I consider whether either pre- or postmigratory cranial or trunk neural crest cells are comprised of subpopulations of cells, and whether commitment occurs early during embryonic development or only at the time of interaction(s) with the environmental cues that evoke differentiation. I then provide overviews of the evidence supporting inductive specification of neural crest cells, discuss inductive interactions and epigenetic cascades in craniofacial development, and discuss neural crest cells as inhibitors of inductions involving non-neural-crest cells.¹