Effects of DNA methylation on gene expression. A: Whereas low levels of DNA methylation at gene promoters have been proposed to generate active genes through increased binding
of transcription factors, elevated DNA methylation at promoters may inhibit binding of transcription factors resulting in
inactive genes. B: DNA methylation at gene promoters may also repress gene transcription via specific proteins that bind to methylated CpGs
(methyl-CpG binding proteins, e.g., MeCP2), and these proteins may then recruit HDACs and transcriptional corepressors (e.g.,
NCoR), resulting in an altered chromatin structure and inactive genes.