Quantitative characterization of the 
locomotory behavior of unc-55 mutants in the
nematode Caenorhabditis elegans

Locomotion in Caenorhabditis elegans is a behavior that has been amenable to genetic and cellular dissection. The synaptic patterns connecting interneurons, motoneurons, and muscles that drive locomotion have been determined for wild-type animals. These cellular networks cause the animals to move forward or backward in a snake-like fashion in which dorsal and ventral muscle produce oscillatory contractile body waves. Currently, more than one hundred uncoordinated (unc) mutants in C. elegans have been isolated and the severity of uncoordination ranges from complete paralysis to very subtle alterations in these networks. A subset of the unc mutants produce asymmetric locomotion due to alterations in the synaptic patterns of individual classes of motoneurons. The identification of genes involved in determining synaptic specificity could provide insight into mechanisms responsible for assembling neuronal circuits.

As a prelude to analyzing mutants that exhibit asymmetric locomotory patterns and objective measure comparing the magnitude of the dorsal and ventral contractile waves was devised. This measurement provides a sensitive means for detecting asymmetric locomotion in C. elegans.

unc-55 mutants produce an asymmetric pattern of locomotion due to an alteration in the synaptic pattern in a subset of motoneurons. The measurement described above was used to examine the locomotory defects in several unc-55 alleles. The results of the analysis revealed that allele specific differences exists in the severity of uncoordination and has allowed a more thorough genetic characterization of the mutants.