Assessment of epigenetic contributions to sexually-dimorphic Kiss1 expression in the anteroventral periventricular nucleus of mice.

The Kiss1 gene, which encodes kisspeptin and is critical for reproduction, is sexually differentiated in the hypothalamic anteroventral periventricular (AVPV)/rostral periventricular (PeN) nuclei. Specifically, female rodents have higher AVPV/PeN Kiss1 expression than males, but how this Kiss1 sex difference is induced in early development is poorly understood. Here, we explored the contribution of epigenetic mechanisms to the establishment of the AVPV/PeN Kiss1 sex difference, focusing on histone deacetylation and DNA methylation. First, we utilized postnatal pharmacological blockade of histone deacetylation and analyzed Kiss1 expression in the AVPV/PeN. Postnatal disruption of histone deacetylase modestly increased AVPV Kiss1 cell number in both sexes but did not alter the Kiss1 sex difference. Next, we assessed whether the level of CpG methylation, which can influence transcription factor binding and gene expression, in the murine Kiss1 gene differs between males and females. We found significant sex differences in methylation at several CpG sites in the putative promoter and first intron of the Kiss1 gene in the AVPV/PeN, but not in the arcuate (which lacks adult Kiss1 sex differences), suggesting that differential methylation of the Kiss1 gene may influence sexually-dimorphic Kiss1 expression in the AVPV/PeN. Transgenic impairment of methyl CpG-binding protein-2 function did not eliminate the Kiss1 sex difference, indicating that other methylation factors are involved. Interestingly, CpG methylation in the AVPV/PeN was lower in males than females, suggesting that transcriptional repressors may contribute to the AVPV/PeN Kiss1 sex difference, a possibility supported by in silico identification of putative repressor binding sites near some of the sexually-dimorphic CpG.