HLH-29 regulates ovulation in C. elegans by targeting genes in the inositol triphosphate signaling pathway

Abstract

SummaryThe reproductive cycle in the nematode Caenorhabditis elegans depends in part on the ability of the mature oocyte to ovulate into the spermatheca, fuse with the sperm during fertilization, and then exit the spermatheca as a fertilized egg. This cycle requires the integration of signals between the germ cells and the somatic gonad and relies heavily on the precise control of inositol 1,4,5 triphosphate (IP3)levels. The HLH-29 protein, one of five Hairy/Enhancer of Split (HES) homologs in C. elegans, was previously shown to affect development of the somatic gonad. Here we show that HLH-29 expression in the adult spermatheca is strongly localized to the distal spermatheca valve and to the spermatheca-uterine valve, and that loss of hlh-29 activity interferes with oocyte entry into and egg exit from the spermatheca. We show that HLH-29 can regulate the transcriptional activity of the IP3 signaling pathway genes ppk-1, ipp-5, and plc-1 and provide evidence that hlh-29 acts in a genetic pathway with each of these genes. We propose that the HES-like protein HLH-29 acts in the spermatheca of larval and adult animals to effectively increase IP3 levels during the reproductive cycle.

Genome-Wide Microarrray Analysis Reveals Roles for the REF-1 Family Member HLH-29 in Ferritin Synthesis and Peroxide Stress Response

“…**RT-qPCR results for these genes were previously published [22].ΔThese genes correlate with previously predicted targets of homodimeric HLH-29 [48].…”

“…Of these, 250 genes were up-regulated and 34 genes were down-regulated (Table S1). HLH-29 dependent expression for five of the genes was previously reported [22], and we used RT-qPCR to confirm that expression of 21 additional genes was significantly affected in hlh-29 mutants (Table 1). We found that expression of all of the tested genes was significantly affected in hlh-29 mutants, and that the direction of regulation (up-regulated versus down-regulated) was the same for 20 out of the 26 tested genes.…”

“…Our previous work indicated that HLH-29 is expressed throughout the C. elegans lifespan, and that aberrant hlh-29 expression affects hermaphrodite development and reproduction [21], [22]. We wished to identify the post-embryonic targets of hlh-29 , and so we used late larval stage (L4)/young-adult animals that were fertile and producing gametes, but were not yet producing fertilized embryos.…”

“…In larval and adult animals, HLH-29 is expressed in chemosensory neurons, intestines, spermatheca, and vulva muscles, and has been shown to affect fat accumulation, reproduction, and brood size [21], [22]. Here, we have identified genes in the HLH-29 post-embryonic regulatory network.…”

“…Ectopic expression of hlh-29 has also been shown to partially rescue the intestinal asymmetry defects associated with mutations in ref-1 [17]. More recently, HLH-29 has been found to act within the IP 3 signaling pathway to regulate the ability of oocytes and fertilized eggs to enter and exit the spermatheca, respectively [22], a finding which underscores the importance of the REF-1 family proteins in regulating both embryonic and post-embryonic events. Candidate target genes for HLH-29 have been identified based on the individual DNA binding site selectivity of homodimeric protein [48]; functional annotation of those genes suggests HES-like roles for HLH-29 in regulating embryonic and larval development, growth, cell fate specification, and reproductive behaviors.…”