Regulators of VC Motor Neuron Differentiation and Specification in C. elegans

The ventral cord neurons in the nematode C. elegans belong to eight distinct classes and are generated during embryonic and postembryonic development. The ventral cord class C (VCs) make up six out of eight sex-specific motor neurons found in the hermaphrodite. The aim of this work was twofold: (1) to characterize VC differentiation with molecular markers (2) to examine whether a conserved proneural factor containing a basic helix loop helix domain, HLH-3, had a function in the development of these neurons and how. First, this work establishes that the gene encoding this factor, hlh-3 is expressed during all stages of VC development revealing a newly identified role in these neurons. Second, this work demonstrates that acquisition of VC specific differentiation markers is dynamic in space and time. Characterization in the hlh-3(tm1688) deletion (null) mutant background revealed that differentiation of the VCs requires hlh-3 function. These findings also show that cell autonomous expression of hlh-3 restores VC differentiation. However, because the role of hlh-3 was primarily in one VC subclass (distal), this left an opportunity to examine regulators of the other subclass (proximal). Next, this work hypothesized that an additional regulator of VC differentiation, could be another conserved bHLH encoding gene, hlh-10. Through the characterization of VC differentiation in the absence of hlh-10 function, a repressive role was identified: two VC specific genes were negatively regulated by hlh-10, but positively regulated by hlh-3. Therefore, these findings suggested that the VC class gene, lin-11, could be regulated by these distinct bHLH containing factors. Finally, this work examined one mechanism for the regulation of lin-11 expression in VCs. By analysis of a VC enhancer element, the expression of lin-11 was shown to be repressed in non-VCs.