H3K9me23

H3K9me23 is not a standard term in histone biology. It likely refers to methylation of lysine 9 on histone H3 with two or three methyl groups, i.e., H3K9me2 and H3K9me3. The well-established marks are H3K9me2 and H3K9me3, both associated with repressed chromatin states and heterochromatin formation. H3K9me2 is enriched at pericentromeric and repetitive regions and serves as a platform for heterochromatin protein 1 (HP1) docking; H3K9me3 is found at constitutive heterochromatin and plays roles in development and genome stability.

Methyltransferases such as SUV39H1/H2 and SETDB1 deposit H3K9me3, while G9a (EHMT2) and GLP (EHMT1) primarily generate H3K9me1/2. Demethylases including the JMJD2 (KDM4) family and KDM3 (JMJD1) family remove methyl groups from H3K9me2/1 and H3K9me3. Readers like HP1 proteins recognize H3K9me2/3 and promote chromatin compaction, contributing to transcriptional silencing and heterochromatin formation.

Biological function centers on stabilizing heterochromatin, silencing transposable elements, and regulating gene expression during development and differentiation. These marks interact with other epigenetic layers, including DNA methylation, to coordinate genome regulation and integrity.

Clinical relevance includes observed alterations of H3K9me2/3 in cancer, aging, and several neurological disorders, where dysregulation can contribute to transcriptional changes and genomic instability. Detection and mapping typically rely on ChIP-seq with antibodies specific for H3K9me2 or H3K9me3, with careful consideration of antibody specificity.

Nomenclature note: H3K9me23 is not widely used; standard terms are H3K9me2 and H3K9me3.