Background: Development is an epigenetic regulation dependent event. As one pretranscriptional
regulator, bivalent histone modifications were observed to be involved in development
recently. It is believed that histone methylation potentially takes charge of cell fate determination and
differentiation. The synchronous existence of functionally opposite histone marks at transcript start
sequence (TSS) is defined as “Bivalency”, which mainly mark development related genes. H3K4me3
and H3K27me3, the prominent histone methylations of bivalency, are implicated in transcriptional activation
and transcriptional repression respectively. The delicate balance between H3K4me3 and
H3K27me3 produces diverse chromatin architectures, resulting in different transcription states of
downstream genes: “poised”, “activated” or “repressed”.
Objective: In order to explore the developmental role of bivalent histone modification and the underlying
mechanism, we did systematic review and rigorous assessment about relative literatures.
Result: Bivalent histone modifications are considered to set up genes for activation during lineage commitment
by H3K4me3 and repress lineage control genes to maintain pluripotency by H3K27me3.
Summarily, bivalency in stem cells keeps stemness via poising differentiation relevant genes. After
receiving developmental signals, the balance between “gene activation” and “gene repression” is broken,
which turns genes transcription state from “poised” effect to switch on or switch off effect, thus
initiates irreversible and spontaneous differentiation procedures.
Conclusion: Bivalent histone modifications and the associated histone-modifying complexes safeguard
proper and robust differentiation of stem cells, thus playing an essential role in development.