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DNA methylation



DNA methylation is a chemical modification by a methyl group on cytosines at the CpG sequences of DNA. When a region that regulates gene expression (a promoter region) is methylated, the gene cannot be expressed (Fig. 1). DNA methylation status is precisely maintained after DNA replication (Fig. 2), and is a stable epigenetic mark (Ushijima et al., 2003).

DNA methylation is essential for development in higher organisms such as humans. In addition to specification of cellular types, DNA methylation is deeply involved in other biological phenomena, such as differential use of genes in a parent-of-origin-specific manner (genomic imprinting) and inactivation of one of the two X chromosomes in females (X chromosome inactivation). Furthermore, aberrant patterns of DNA methylation are observed in human diseases such as cancer.

Fig. 1. Inactivation of a gene by DNA methylation.
Fig. 1. Inactivation of a gene by DNA methylation.
When a promoter region is methylated, the gene cannot be expressed.


Fig. 2. Maintenance of DNA methylation status
Fig. 2. Maintenance of DNA methylation status
When cells divide, DNA is replicated. Although the newly synthesized DNA strands are unmethylated, DNA methyltransferase 1 (DNMT1) precisely maintains the DNA methylation status.