The epigenome and transcriptional enhancers in the central control of reproduction

Epigenetics comprises a pivotal element in the control of mammalian reproduction both during normal development and in adaptive responses to changes in the environment. DNA and histone modifications are involved in both the tissue-specific expression of the genes encoding the key reproductive hormones, LH and FSH, as well as their re-activation at puberty which is due to increased stimulation by the hypothalamic gonadotropin-releasing hormone (GnRH). We have also shown that plasticity in the timing of pubertal onset, which is often delayed following stressful early-life events, is associated with differential DNA methylation at the Srd5a1 gene and its down-regulation in the hypothalamus. This gene encodes a steroidogenic enzyme which normally regulates GnRH levels at puberty through catalyzing the production of various neurosteroids that stimulate the GnRH neurons. Further study of these genes has pointed to the importance of regulation via distal transcriptional enhancers, which we have identified and characterized though functional analysis, H3K4me1 enrichment, ATAC-seq accessibility, chromatin conformation assays, and transcription into chromatin-associated lncRNAs. Several of these regulatory elements contain regions predicted to form G-quadruplex or i-Motif DNA structures. We have confirmed for some of these loci, using circular dichroism, that both of these structures can form in vitro, while ChIP indicates their formation in cells is affected by the cellular environment. We are currently working to identify how these DNA structures are regulated and the mechanisms through which they affect activity of their target gene promoters.