Human α cells demonstrate a higher number of bivalently marked genes than β and exocrine cells.
(A) Here, α cells display more bivalently marked loci than β and exocrine cells. Nearly half of the genes bivalently marked in α cells carry a monovalent mark in β cells (purple and dark blue portion of the far left bar corresponding to H3K4me3 and H3K27me3 marks in β cells, respectively). (B) 406 genes are marked bivalently in β cells, but monovalently by H3K4me3 in α cells, and gene ontology analysis for these genes shows 3 modestly enriched categories: regulation (reg.) of RNA metabolic process, regulation of transcription, and transcription. (C) Genes marked bivalently in α cells, but monovalently by H3K27me3 in β cells, are significantly enriched for developmental processes. For detailed GO analysis see Supplemental Table 6. (D) Comparison of transcriptional regulators marked bivalently in hESC (22) to the histone modification signatures of human α and β cells reveals a higher overlap between α cells and hESCs (44%, right pie chart) than between β cells and hESC (26%, left pie chart). Many of the genes marked bivalently both in α cells and hESCs carry the repressive mark in β cells (43%, dark blue portion of inset).