Neural crest cell fate: to be or not to be prespecified

Abstract

The neural crest, the intriguing cell population that gives rise to a panoply of derivatives in the vertebrate embryo including the mesenchymal structures in the head, melanocytes and most of the peripheral nervous system still proves to be an important yet enigmatic developmental cell population to study, with applications in stem cell biology, cancer biology and clinical medicine. Albeit our knowledge base is rich due to a strong history of experimentation, the fact that we have yet to decipher so many key aspects of neural crest cell (NCC) behavior speaks to the challenging complexity of this transient yet vital cell population. With the advent of new fluorescent tracing techniques, we have reexamined the migratory behaviors and ultimate fate of ventrally migrating avian NCCs within a late wave of emigration and identified a subpopulation of lineally restricted NCCs who migrate to the contralateral dorsal root ganglia (DRG) and therein give rise to mitotically active progenitor cells that ultimately produce the majority of the nociceptive sensory neurons in the DRG. These data provide evidence for the fate prespecification of subsets of NCCs while still resident in the neural tube.

Figure 1

Schematic of the two waves of neurogenesis in the chick dorsal root ganglia (DRG). The first wave (St. 15–18) is generated from neural crest cells (NCCs) that migrate ipsilaterally and differentiate in the inner core of what will be the DRG. The second wave (St. 19–26) is derived from NCCs that migrate both ipsilaterally and contrallaterally between St. 19–22: the cells that migrate ipsilaterally (blue) delaminate from the more lateral regions of the dorsal neural tube and tend to migrate directly into the inner core of the DRG. A second population (green) that tends to delaminate from the very medial region of the dorsal neural tube includes cells that migrate both ipsilaterally and contralaterally. This medially-derived population of NCCs localize to the DRG perimeter where they remain in the cell cycle and become the major source of mitotically-active progenitor cells for the second wave of neurogenesis and for glial cells in the DRG (*indicates neurons). A few neurons derived from the perimeter progenitor cells are indicated. These cells are TrkA⁺ neurons. The green neurons on the left side are meant to represent derivatives of contralaterally migrating NCCs that delaminated from the right side of the medial roof plate of the neural tube.