G9a also known as NG36, EHMT2 is a methyltransferase that methylates lysine residues of histone H3. G9a plays a crucial role in the regulation of gene expression through its function as a histone methyltransferase, specifically targeting histone H3 lysine 9 for methylation. This post-translational modification is vital for the repression of developmental genes and is essential for early embryogenesis, highlighting G9a′s importance in cellular differentiation and development. G9a′s ability to add methyl groups to lysine residues not only influences transcriptional regulation but also contributes to the organization of chromatin structure, thereby impacting overall genomic stability.