H3K4me1 distribution at promoters predicts the poised epigenetic state

Post-translational modifications on histone tails are closely correlated to transcriptional states. One such modification is monomethylation on lysine 4 of histone 3(H3K4me1), a mark that has been linked to enhancers. Identifying regions enriched for H3K4me1 and depleted in H3K4me3, or regions enriched for both H3K4me1 and H3K27ac, has proven to be a feasible enhancer discovery method. At the same time, not all H3K4me1-enriched regions correspond to enhancers. H3K4me1 marks also exist at promoters, which implies that the H3K4me1 modification may have a context-dependent role in regulating transcription. We report distinct patterns of H3K4me1 that predict transcriptional regulatory states at promoters in germ cells and ESCs. We examined ChIP-seq data for H3K4me1, H3K4me3, H3K27me3, and H3K27ac in mouse and human male germ cells, and found that H3K4me1 peak density around the transcription start sites (TSS) exhibits either a broad bimodal profile or a narrower unimodal profile centered at the TSS. We then examined the position of the H3K4me1 marks relative to H3K4me3, and found that unimodal H3K4me1 directly at the TSS predicts a poised (H3K4me1/H3K27me3 bivalent) state of chromatin, while bimodal H3K4me1 flanking the TSS predicts an active state. We conclude that unimodal H3K4me1 centered on the TSS is a characteristic feature of the poised epigenetic state in ESCs and germ cells. Note: H3K4me1 and H3K27ac data are included in this GEO accession; H3K4me3 and H3K27me3 were released in GSE68507. ChIP-seq for H3K4me1 and H3K27ac in spermatogenic cells (pachytene spermatocytes and round spermatids) from adult mouse and human.