OCT3/4-binding sequence-dependent maintenance of the unmethylated state of CTCF-binding sequences with DNA demethylation and suppression of de novo DNA methylation in the H19 imprinted control region.

DNA demethylation and suppression of de novo DNA methylation are activities that maintain an unmethylated state. However, the strength of these two activities at the same locus has not been estimated separately. Furthermore, the association between these two activities and the unmethylated state remains unclear. Octamer-binding transcription factor-binding sequences (OBSs) and CCCTC-binding factor-binding sequences (CBSs) within the mouse H19-imprinted control region (ICR) are involved in the induction of DNA demethylation and maintenance of the unmethylated state in mouse undifferentiated embryonic cell lines. To reveal the association between the two cis-elements and the two unmethylated state maintenance activities in maintaining the unmethylated state of the ICR, we evaluated the altered DNA methylation levels at sites that were initially methylated or unmethylated using a stable transfection-based assay, and estimated the strength of the two unmethylated state maintenance activities separately via a Poisson process model that described the DNA methylation state regulatory process. Although DNA demethylation depending on OBSs affected almost the entire ICR, DNA demethylation depending on CBSs occurred near CBSs, resulting in redundant demethylation of CBS regions. Detailed analysis of the CBS4 region suggested that OBSs were required to induce unmethylated state maintenance activities, and that CBSs-dependent activities contributed, but diminished, during incubation when protection of the CBS4 region by OBSs-dependent activities was absent. Analysis via the Poisson process model indicated that the unmethylated state at the CBS4 region was maintained by OBSs-dependent suppression of de novo DNA methylation rather than DNA demethylation. We propose that the hierarchical regulation of redundant protection of the CBS region via cooperation between the two unmethylated state maintenance activities is a potential function of the ICR that effectively maintains allele-specific methylation status in the same DNA sequence.

Oct motif variants in Beckwith-Wiedemann syndrome patients disrupt maintenance of the hypomethylated state of the H19/IGF2 imprinting control region.

The methylation status of imprinting control center 1 (IC1) regulates the monoallelic transcription of H19 and Igf2 in mammalian cells. Several single nucleotide variants in Oct motifs within IC1 occur in patients with Beckwith-Wiedemann syndrome (BWS) who have hypermethylated maternal IC1. However, the importance of Oct motifs in the regulation of IC1 methylation status remains unclear. Here, we demonstrate that three variants found in BWS (BWS variants) suppress intensive induction of DNA demethylation, whereas consensus disruption of motifs unrelated to BWS only slightly affects the induction of demethylation. BWS variants reduce DNA demethylation levels and trigger the accumulation of DNA methylation downstream of the IC1 transgenes. Thus, the risk of IC1 hypermethylation is associated with inhibitory levels of Oct motif-dependent hypomethylation maintenance activities.