Deletion of a putative HDA-1 binding site in the hlh-2 promoter eliminates expression in C. elegans dorsal uterine cells

The helix-loop-helix transcription factor hlh-2 (E/Daughterless) has been shown to play an important role in regulating cell fate patterning, cell cycle, and basement membrane invasion in the context of the development of the C. elegans somatic gonad. Here, using CRISPR/Cas9 genome engineering, we generated a new hlh-2 allele (hlh-2(Δ-1303-702)) in the endogenous, GFP-tagged hlh-2 locus. This allele represents a deletion of a 601 bp region in the hlh-2 promoter that contains a putative binding site of the histone deacetylase hda-1 (HDAC) according to publicly available ChIP-sequencing data. Strikingly, we find that HLH-2 expression is virtually absent in the dorsal uterine cells of hlh-2(Δ-1303-702) animals compared to wild type controls. Levels of HLH-2 in the anchor cell and ventral uterine cells are only modestly reduced in the mutant; however, this does not seem to be functionally significant based on the lack of relevant phenotypes and expression levels of a downstream gene, NHR-67 (TLX/Tailless/NR2E1), in these cells. Taken together, these results support growing evidence that HDACs can potentially positively regulate transcription and provide a new reagent for studying hlh-2 regulation.