Biology Reference
In-Depth Information
DISPERSA
L OF CELLS FROM ONE SITE TO THE REST OF
THE BODY
One of the most spectacular demonstrations of cell migration in development is provided
by the vertebrate neural crest. The neural crest arises from the dorsal-most zone of the neural
tube (presumptive brain and spinal cord) (
Figure 7.5
), and it gives rise to a multitude of cell
types in locations often far removed from the neural tube itself. The face, for example, is
produced primarily from neural crest cells that migrate around from the dorsal zone of
the cranial neural tube and produce craniofacial mesenchyme; this mesenchyme subse-
quently differentiates into cartilage, bones, teeth, glial cells, neurons and connective tissues.
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Crest from the neck region migrates to colonize the gut to produce the enteric nervous
system.
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In the trunk region of birds and mammals, the neural crest follows two main migra-
tion routes: one a dorsolateral route that runs outside the somites and under the epidermis,
the other a ventral route that takes it through the sclerotomes of the anterior halves of each
somite
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(
Figure 7.5
). Some cells remain in the sclerotomes and aggregate together to form the
dorsal root ganglia, which process sensory information from the periphery and relay it to the
spinal cord. Others settle more ventrally to produce the sympathetic nervous system and the
inner parts of the adrenal gland. The cells that migrate between the outside of the somites and
the skin give rise mainly to melanocytes, responsible for the pigmentation of the skin. The
vast range of tissues produced by the migratory crest cells is so important to vertebrate devel-
opment that one commentator has suggested that the crest be regarded as a fourth germ layer
(to be added to the traditional three of endoderm, mesoderm and ectoderm).
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FIGURE 7.5
Principal migration routes of the neural crest within the trunk of the embryo.
MIGRATION BY CELL PROCESSES
Development of the nervous system requires migration both of whole cells and of cell
processes. Many neurons of the peripheral nervous system arise from migratory cells of
the neural crest, but even when these cells have found their ultimate location and settled
down to differentiate, directed locomotion continues as cell processes emerge and navigate
