Formation of the neural crest
Truly the cells of the neural crest (stage 9) represent a fourth embryonic germinal layer that exhibits a partially segmented organization and is involved in the genesis of the peripheral nervous system (neurons as well as glial cells of the sympathetic, parasympathetic and sensory systems).
During the closure of the neural tube the nerve cells multiply in the transition region between the neuroectoderm and ectoderm as the result of an interaction between these two tissues. At the same time, these neurons detach themselves from the association and migrate into the depths
- A
- Neural plate
- B
- Neural groove
- 1
- Superficial ectoderm
- 2
- Neural groove
- 3
- Cells of the future neural crest
Begin of the neurulation in the neck area with suggested neural groove.
The arrows indicate the direction of the folding.
Orange represents the cells of the future neural crest.
- Superficial ectoderm
- Neural folds
- Cells of the neural crest in the process of migrating
(neural tube stage, stage 11)
- 4
- Neuroepithelium
- 5
- Central canal
- 6
- Neural tube
Formation of the neural groove and of the neural tube proceeding from the neural plate:
cell collections (orange) detach themselves from the edges of the neural plate in order to form the neural crest. After leaving the neuroepithelium the cells lose their cohesive properties.
NB: Note: in the neural tube stage the neural epithelium is multi-layered (not shown for reasons of clarity).
The cells of the neural crest exhibit a noteworthy ability for migration and a phenotypical diversity. Numerous and various types of cells originate from them
- 1a
- Bipolar neuroblast
- 1b
- A bipolarer neuroblast in the process of differentiation
- 1c
- Pseudounipolar spinal ganglion cell
- 2a
- Unipolar neuroblast
- 2b
- Multipolar neuron of a sympathetic ganglion
- 2c
- Chromaffin cell in the adrenal medulla
- 3a
- Glioblast
- 3b
- Schwann’s cell
- 3c
- Satellite cell
- 4a
- Mesenchym cell
- 4b
- Leptomeningeal cell (arachnoidea and pia mater)
- 4c
- Cell of the mesectoderm
- 5a
- Melanoblast (pigment cell)
- 5b
- Melanocyte
- A
- Neural crest
- B
- Neural tube (mantel zone)
- C
- Mesenchym
- D
- Neural tube (ependym)
From the neural crest stem the neuroblasts of the peripheral nervous system, the glioblasts of the peripheral glia, the chromaffin cells of the adrenal medulla, the melanoblasts, the cells of the mesectoderm of the head region and the cells of the leptomeninx.
The migration of neural crest cells is in a close relationship to the disappearance of the N-CAM and cadherin formed from the neural tube as well as the appearing of membrane integrin. The molecules of the TGF-β family appear to trigger the migration of the neural crest cells in that they modify their adhesion properties at the level of the extracellular matrix (fibronectin, laminin, collagen). Indeed, these cells bind themselves via specific membrane receptors (integrin) at molecules of the extracellular matrix (fibronectin and laminin) in order to move. The end of the cell migration occurs together with a renewed expression of cadherin and N-CAM that mediate the cells' adhesion.
Studies have shown the significance of the molecules of the BMPs, FGFs, Wnts families and retinoic acid in the induction of the neural crest. For its part SHH should prevent the spread of the neural crest cells by activating integrin β1.