12. Neural Crest Cells

So far, we have followed the journey of cells in the central nervous system. However, if you have a sharp eye, you may have noticed that we have NOT addressed neural crest cells, even though like neurons and epidermis cells, are derived from the ectoderm!

To be fair, we haven't talked about it because it doesn't make up any part of the central nervous system, only the peripheral nervous system--but that doesn't mean it's not important! For one, neural crest cells make up the cranial nervous in our faces. Disturbances in neural crest cell formation and migration can result in cleft palate, Hirschsprung's disease (disease affecting the colon and gut), cancer, and others.

So, where do neural crest cells come from? Around the formation of the neural tube. They actually migrate away from particular adherence points (remember those?) as the neurula is folding into the neural tube:

This process of neural crest cell migration is called the epithelial to mesenchymal transition (EMT for short). On the molecular level, EMT marks a signal that leads to the downregulation of E-cadherin and upregulation of N-cadherin, as well as an upregulation of integrins, which makes the to-be neural crest cells more motile. If it helps, remember that the premigratory neural crest cells express a transcription factor called slug, which makes the neural crest cells move away from the folding neural tube.

Neural crest cells guide their own migration in several ways through signaling. We will not go into them in detail; however, it might be helpful to know that neural crest cells can form little cliques, in which they travel in different groups to go to different places and form different parts. Similar to axon growth cones, chemoattraction tells neural crest cells where exactly to go.

Neural crest cells are considered multipotent stem cells, and their final cell types, much like neurons, vary along the A-P axis. We will not be going over this specific patterning for neural crest cells at the moment.