5-Methylcytosine (5-mC) (D3S2Z) Rabbit mAb #28692

Methylation of DNA at cytosine residues is a heritable, epigenetic modification that is critical for proper regulation of gene expression, genomic imprinting, and mammalian development (1,2). 5-methylcytosine is a repressive epigenetic mark established de novo by two enzymes, DNMT3a and DNMT3b, and is maintained by DNMT1 (3, 4). 5-methylcytosine was originally thought to be passively depleted during DNA replication. However, subsequent studies have shown that Ten-Eleven Translocation (TET) proteins TET1, TET2, and TET3 can catalyze the oxidation of methylated cytosine to 5-hydroxymethylcytosine (5-hmC) (5). Additionally, TET proteins can further oxidize 5-hmC to form 5-formylcytosine (5-fC) and 5-carboxylcytosine (5-caC), both of which are excised by thymine-DNA glycosylase (TDG), effectively linking cytosine oxidation to the base excision repair pathway and supporting active cytosine demethylation (6,7).
Normally DNA methylation occurs in a bimodal fashion, such that CpG dinucleotides are largely methylated across the genome, except in short stretches of CpG-rich sequences associated with gene promoters, known as CpG-islands, where methylation is virtually absent (8). Cancer cell genomes often undergo global hypomethylation, while CpG-islands become hypermethylated, causing their associated promoters to become repressed (9). There is evidence that a number of aberrantly hypermethylated CpG-islands found in carcinomas occur at tumor suppressor genes such as RB1, MLH1, and BRCA1 (10).