HLH-3, a basic helix-loop-helix (bHLH) protein in C. elegans, is a member of the Achaete/Scute family of transcription factors [1]. The expression of HLH-3 is sexually dimorphic. We have published the characterization of the expression pattern and function of
hlh-3 in hermaphrodites.
hlh-3(lof) mutant hermaphrodites are egg-laying defective (Egl). The Egl phenotype is a result of abnormal late differentiation of the hermaphrodite specific neurons (HSN). In
hlh-3 mutants the HSNs are non functional [1]. This report presents our characterization of the expression and possible site of function of
hlh-3 in the male nervous system. HLH-3 has already been implicated in the specification of the male linker cells. In
hlh-3 mutant males, the linker cells are absent, which result in an abnormal gonad phenotype [2]. To investigate the function of
hlh-3 in males, we performed male mating assays for three null
hlh-3 mutant alleles,
hlh-3(
bc248),
hlh-3(
tm1688) and
hlh-3(
q805). Our preliminary data suggests a defect in male mating behavior, specifically the inability to locate the vulva. Many males did not insert their spicules into the vulva slit. Additionally, the time from initial contact with hermaphrodites to spicule insertion was longer in mutant males when compared to wild type males. Thus, we hypothesized that
hlh-3 may have a functional role in HOA, HOB, or PCS neurons, which are neurons required for general and precise vulva location, respectively. To test this hypothesis we characterized the expression of
hlh-3::gfp in
him-5 males expressing a translational fusion construct of the
hlh-3 promoter and coding sequence fused to gfp. We found that expression was robust in tail neurons. To determine the identity of the tail neurons expressing
hlh-3, we carried out a 5-HT staining experiment. Others have shown that neurons in the right preanal ganglion are serotonergic [3]. The cell bodies of the hook neurons are located in the preanal ganglion, which suggests that the HOA and HOB neurons may be serotonergic and HLH-3::GFP positive. Our observations that
hlh-3 mutants are less likely to locate the vulva when compared to control males and execute more turns around the hermaphrodite than wildtype males, suggests that
hlh-3 may play a role in the HOA and HOB neurons. We are interested in analyzing further whether
hlh-3 has a role in the differentiation or function of these cells as well as regulating the function of other neurons involved in male mating behaviors. 1. Doonan et. al., 2008. Mechanisms of Development, 125:883-893 2. Ngan Lam et. al., International C. elegans Worm Meeting, 2009 3. Loer et. al., 1993. The Journal of Neuroscience, 13(12): 5407-5417