Epigenetics and DNA Methylation

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Epigenetics

CpG Islands

Histone Code

Genomic Imprinting

Epigenetics

Histone Modification

Chromatin Immunoprecipitation

DNA Methylation and DNA Methyltransferases

DNA methylation patterns are known to be established by a complex interplay of at least three independent DNA methyltransferases: DNMT1, DNMT3A and DNMT3B. Homozygous loss of any of the three currently known mammalian DNMTs, which includes DNMT1, 3a, and 3b, has been described to be lethal in mice (Li et al., 1992).

DNMT1 is the most abundant methyltransferase in somatic cells (Robertson et al., 1999), localizes to replication foci (Leonhardt et al., 1992), has a 10-40-fold preference for hemimethylated DNA (Pradhan et al., 1999), and interacts with the proliferating cell nuclear antigen (PCNA) (Chuang et al., 1997). It is thought to be the enzyme responsible for copying methylation patterns after DNA replication, and therefore is often referred to as the ‘maintenance' methyltransferase (Robertson and Wolffe, 2000A). DNMT1 is essential for proper embryonic development, imprinting and X-inactivation (Li et al., 1992; Li et al., 1993; Beard et al.,1995).