Epigenetic regulation refers to reversible chemical and structural changes to DNA and chromatin that alter gene activity without changing the DNA sequence. These mechanisms allow cells with identical genomes to adopt distinct identities and respond dynamically to internal and external signals.

Key epigenetic marks include DNA methylation, primarily the addition of methyl groups to cytosine bases in CpG dinucleotides, and a wide array of post translational histone modifications such as acetylation, methylation, phosphorylation and ubiquitination. DNA methylation is often associated with gene silencing, especially when present in promoter regions, while methylation patterns in gene bodies and enhancers can have more complex roles. Histone acetylation generally correlates with open chromatin and active transcription, whereas certain histone methylation marks are linked either to activation or repression depending on their position.

These marks are interpreted by specialized protein complexes that remodel chromatin structure, recruiting transcriptional machinery or blocking its access. Epigenetic states are established during development, helping specify cell lineages, and are stably maintained through cell division by maintenance enzymes that copy patterns after DNA replication.

Epigenetic mechanisms integrate environmental cues such as diet, toxins, stress and inflammation, thereby connecting external conditions to long term changes in gene expression. Disruption of epigenetic regulation contributes to cancer, neurodevelopmental and psychiatric disorders, metabolic disease and immune dysfunction, often through aberrant methylation patterns or misregulated histone modifiers.

Because epigenetic changes are reversible, they are attractive therapeutic targets. Inhibitors of DNA methyltransferases and histone deacetylases are already in clinical use, and newer strategies aim to modulate specific chromatin states with higher precision.