Fig. 6. A working model for the maintenance of opposite epigenetic states at DMRs. Methylation (M) of DNA is present on one of the parental alleles only (at many DMRs, this is the maternal allele). This methylation is recognized by MBD proteins, which recruit HDAC/chromatin-remodelling complexes to the chromatin. HDACs (filled circles) ensure deacetylation of histones and may be associated with DNMTs, which maintain the DNA methylated. MBD protein binding may also be mechanistically linked to the H3-K9 hypermethylation on this parental allele, and this could constitute a second element in the maintenance of its DNA methylation. The opposite parental allele has no DNA methylation and is not accessible to HDAC complexes and associated DNMT activities, possibly in part because of the H3-K4 methylation. H3-K4 methylation could thus prevent DNA methylation from becoming established. In contrast, HATs and K4 histone methyltransferase (HMT) have access to the chromatin and this maintains the acetylation and K4 methylation on this allele.