Bivalent chromatin are segments of DNA, bound to histone proteins, that have both repressing and activating epigenetic regulators in the same region.
[2] Bivalent chromatin domains are normally associated with promoters of transcription factor genes that are expressed at low levels.
[1][3] Bivalent domains have also been found to play a role in developmental regulation in pluripotent embryonic stems cells, gene imprinting and cancer.
[2] H3K4me3 and H3K27me3 marks found on the bivalent domains regulate whether or not an embryonic stem cell differentiates or remains unspecified (pluripotent state).
[2] Although this mark represses the lineage control genes, it does keep them ready for activation upon differentiation.
[2] Having the activating H3K4me3 mark protects genes from being silenced permanently by repelling transcription repressors and blocking repressive DNA methylation.