Forge Capsule

Epigenetics: DNA Methylation, Histone Modification, and Gene Silencing

Epigenetics: heritable changes in gene expression without DNA sequence changes. DNA methylation: 5-methylcytosine (5mC) at CpG sites. CpG islands: promoter regions with high CpG density — methylation → silencing. DNMT1 (maintenance), DNMT3a/3b (de novo). TET enzymes: oxidize 5mC → 5hmC → demethylation. Histone modifications: H3K4me3 (active promoters), H3K27me3 (repression, Polycomb), H3K9me3 (heterochromatin), H3K27ac (active enhancers). Histone acetyltransferases (HATs) vs deacetylases (HDACs). Chromatin remodelers: SWI/SNF, ISWI, NuRD. Bivalent domains: H3K4me3 + H3K27me3 in stem cells (poised genes). Imprinting: parent-of-origin gene expression (IGF2/H19). X-inactivation (XIST lncRNA). Forge: epigenetics c...