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Description

DNA methylation, or the addition of methyl groups to cytosine bases in the dinucleotide CpG, regulates gene expression and is critical for proper development. Human proteins MECP2, MBD1, MBD2, MBD3, and MBD4 comprise a family of nuclear proteins related by the presence in each of a methyl-CpG binding domain (MBD). Each of these proteins, with the exception of MBD3, is capable of binding specifically to methylated DNA. MECP2, MBD1 and MBD2 can also repress transcription from methylated gene promoters. MBD1 has been shown to play a role in chromatin modification through interaction with the histone H3K9 methyltransferase SETDB1. Five transcript variants of the MBD1 are generated by alternative splicing resulting in protein isoforms that each contain one MBD domain, two to three cysteine-rich (CXXC) domains, and some differences in the COOH terminus. MBD1, MBD2, MBD3, and MBD4 are expressed in somatic tissues, but the expression of MBD1 and MBD2 is reduced or absent in embryonic stem cells, which are known to be deficient in MeCP1 activity.