http://jcb.rupress.org/content/202/5/725.full
Back to TopAbstract
Many neurons resemble other cells in
developing embryos in migrating long distances before they
differentiate. However, despite
shared basic machinery, neurons differ from other
migrating cells. Most dramatically, migrating neurons have a long and
dynamic
leading process, and may extend an axon from the
rear while they migrate. Neurons must coordinate the extension and
branching
of their leading processes, cell movement with axon
specification and extension, switching between actin and microtubule
motors,
and attachment and recycling of diverse adhesion
proteins. New research is needed to fully understand how migration of
such
morphologically complicated cells is coordinated
over space and time.
Nervous systems are the organs through which
animals perceive, interpret, and respond to the world around them. They
consist
of specialized, electrically active cells connected
together in networks. Essentially, all nervous systems develop by four
main stages: the proliferation of progenitors in an
epithelium, the specification of neurons and glia, the growth and
guidance
of axons and dendrites, and the development and
refinement of electrical and chemical synapses. However, some more
complex
nervous systems, including those of vertebrates, have
another stage in which newly specified neurons migrate before they
differentiate
and form synapses. Some migrations cover long
distances—up to thousands of cell diameters—and follow complex routes,
changing
direction at landmarks along the way (a key to the
major migratory routes, terminology, and abbreviations is provided in Box 1 and Fig. 1).
Because they migrate, neurons from different proliferative zones, and
correspondingly distinct lineages and genetic programs,
are able to position close to each other and
communicate, potentially increasing efficiency. In addition, different
types
of neurons arrive at a particular location at
different times during development, so circuits are established in a
specific
order. For these reasons, it is generally thought that
neuron migrations facilitate circuit formation and improve nervous
system function, although this hypothesis has not been
critically tested by the appropriate mutation studies.
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