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The C. elegans nervous system consists
of only 302 neurons and 56 glial-like cells. The 302 neurons are of
118 distinct classes, based upon morphology, neurotransmitter content
and connectivity. The complete reconstruction of the C. elegans
nervous system from serial section electron micrographs defined a
wiring diagram with about 5000 chemical synapses, 2000 neuromuscular
junctions and 600 gap junctions. The neurotransmitters used by C.
elegans are generally the same as those used by other animals:
acetylcholine is the major excitatory neurotransmitter, and GABA is
the major inhibitory neurotransmitter; glutamate, serotonin, dopamine,
octopamine (an invertebrate counterpart of norepinephrine) and various
neuropeptides are also active. Because the complete cell lineage of
C. elegans has been described, we know the developmental origin
of every neuron and the precise lineal relationships among neurons
of different types. We have identified and characterized many genes
responsible for many aspects of nervous system development, including
the acquisition of neuronal identity, neuronal cell migration, axonal
outgrowth and neurotransmitter expression. Among the genes we found
to control axonal outgrowth are genes that encode components of a
DCC/netrin pathway, modifiers of the actin cytoskeleton, and several
novel proteins. We have recently focused on a subset of the genes
involved in axonal outgrowth that also function to effect other cell-shape
changes, including changes in cell-corpse engulfment and cell migration.
These genes encode members of the Rac/Rho GTPase family and regulators
of the activities of these G proteins.
Electron micrographs and line drawings
comparing the ventral nerve cords of the (A/B) wild type and a (C/D)
ced-10; mig-2 double mutant, which is defective in two of the
three C. elegans Rac genes and in which many axons are displaced
or missing. (N, nucleus; M, muscle; red dots, axons)
Publications:
Neural Development
Abstracts:
Neural Development
The Horvitz Lab
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