Genetic transformation of the synaptic pattern of a motoneuron class in Caenorhabditis elegans.
Caenorhabditis elegans possesses two classes of inhibitory locomotory neurons, the DD and VD motoneurons (mns), and they form complementary components of a cross-inhibitory neuronal network innervating dorsal and ventral body muscles. The DD and VD mns (collectively called the D mns) share a number of morphological and neurochemical features, and mutations in a number of different genes disrupt both cell types in identical ways; however, the DD and VD mns have different lineal origins and different synaptic patterns. Given the number of phenotypic features shared by the D mns, it was of interest to determine what is responsible for the synaptic patterns that distinguish them. An analysis of the locomotory defect along with a genetic epistasis test suggested that unc-55 mutations alter the function of the VD but not the DD mns. Correlated with the defective locomotory behavior of unc-55 mutants was an alteration in the distribution of varicosities, structures associated with presynaptic elements, on the VD mns. The pattern of varicosities of the unc-55 VD mns resembled that of the wild-type DD mns. Moreover, the selective removal of the DD mns revealed that unc-55 VD mns had adopted a functional role appropriate for the DD mns. Thus, unc-55 appears to be involved in producing the synaptic patterns that distinguish the two D mn classes from one another; when the gene is mutated the VD and DD mns become structurally similar and functionally equivalent.
Walthall
W W
WW
Department of Biology, Georgia State University, Atlanta 30302-4010.
Plunkett
J A
JA
D000818:Animals; D001522:Behavior, Animal / Q000502:physiology; D017173:Caenorhabditis elegans / Q000235:genetics / Q000502:physiology*; D007150:Immunohistochemistry; D009043:Motor Activity / Q000502:physiology; D009046:Motor Neurons / Q000145:classification / Q000502:physiology*; D009154:Mutation; D009424:Nervous System Physiological Phenomena; D013569:Synapses / Q000502:physiology*; D014170:Transformation, Genetic