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Jenna Dare
Of the 302 neurons in C. elegans, 113 are motor neurons, which control locomatory behavior. This is
known as crawling on solid surfaces, and swimming or thrashing in liquid or on semi-solid surfaces. 75
of these 113 motor neurons innervate 79 body wall muscles posterior to the head and are divided into 8
classes: 6 excitatory cholinergic motorneurons and 2 inhibitory GABAergic motorneurons. The two Dtype GABAergic motorneurons make up a cross-inhibitory network that contributes to the C. elegans
locomotion. This cross-inhibitory network is comprised of neurons along the nerve cords, which
innervate and inhibit muscle groups on opposing sides of the worm. As a cholinergic motorneuron
activates a muscle group on the ventral nerve cord, a GABAergic motorneuron then inhibits the
opposing muscle group on the dorsal nerve cord. For C. elegans to maintain sinuous and symmetrical
movement, there must be balance between activation and inhibition of these muscle groups.
There are two D-type motorneurons, DD and VD, dorsal and ventral respectively. There are 6 DD
motorneurons, with postsynaptic processes on the ventral nerve cord and presynaptic processes on the
dorsal nerve cord. This allows for transmission of information to flow from the ventral to the dorsal
side. Conversely, the 13 VD motorneurons contain postsynaptic processes on the dorsal nerve cord and
presynaptic processes on the ventral nerve cord, which allows for information transmission from dorsal
to ventral side. The two D-type motorneuron classes work together to form the cross-inhibitory
network to maintain balanced locomotion. Though similar in morphology, these D-type motorneurons
differ in their synaptic patterns and resulting phenotypic behaviors. Responsible for these phenotypic
differences are differing genes present in the motorneurons. A large family of genes found to contribute
to locomotion is appropriately named Uncoordinated, as mutations within these genes cause an
uncoordinated locomatory phenotype in the nematode.
References:
1. G. Shan and W. Walthall, 2005. Convergent genetic programs regulate similarities and
differences between related motor neuron classes in Caenorhabditis elegans. Developmental
Biology 280 494-503.
2. Dare, J, 2009. . Identifying Cofactors and Partners for the Nuclear Receptor UNC-55.
Wormclub, Emory University
3. Wormatlas, 2009.
http://www.wormatlas.org/neurons/Individual%20Neurons/DDframeset.html,
4. Wormatlas, 2009.
http://www.wormatlas.org/neurons/Individual%20Neurons/VDframeset.html
5. Wormbase.org http://wormbase.org/db/ontology/anatomy?name=dd1