Collective migration in complex environments: The case of the trunk neural crest

The neural crest is a highly invasive, multipotent embryonic cell population common to all vertebrates. Neural crest cells migrate all along the anteroposterior axis of the vertebrate embryos, crossing complex microenvironments during their journey and eventually halting their migration to give rise to a variety of derivatives. At cranial levels, neural crest cells originate cartilage and bone of the skull and face, cranial ganglia and glia and pigment cells. In contrast, neural crest of the trunk is unable to form ectomesenchymal tissues such as cartilage and bone, but instead contributes to the cardiac outflow tract, enteric neurons, sensory and sympathetic neurons, Schwann cells and pigment across the vertebrate trunk. Defects in neural crest formation and migration can result in an array of birth defects and childhood malignancies collectively known as neurocristopathies, and investigation of the mechanisms underlying neural crest migration has significant clinical relevance. Considerable progress has been made in recent years in our understanding of the principles underlying collective cell migration of cranial neural crest cells. However, the extracellular environment trunk neural crest traverse in vivo is radically different from that experienced by cranial neural crest cells. Here, we review collective cell migration, fate specification and current in vivo and in vitro models of trunk neural crest migration under the lens of the complex interaction of this extraordinary cell population with its complex tissue environment.