Asymmetric DNA methylation of CpG dyads is a feature of secondary DMRs associated with the Dlk1 / Gtl2 imprinting cluster in mouse

• Published in: Epigenetics & chromatin 2017-06, Vol.10 (1), p.31-31, Article 31
• Main Authors: Guntrum, Megan, Vlasova, Ekaterina, Davis, Tamara L
• Format: Article
• Language: English
• Subjects: 5-Hydroxymethylcytosine; Animals; Bisulfite; CpG islands; CpG Islands - genetics; Demethylation; Deoxyribonucleic acid; DNA; DNA - genetics; DNA methylation; DNA Methylation - genetics; Embryonic Development - genetics; Epigenetics; Fertilization; Gametes; Gametic DMR; Gene expression; Gene regulation; Genomes; Genomic imprinting; Genomic Imprinting - genetics; Genomics; Gtl2; Hypotheses; Immunoglobulins; Intercellular Signaling Peptides and Proteins - genetics; Mammals; Methylation; Mice; Mutagenesis; Preadipocyte factor 1; RNA, Long Noncoding - genetics; Somatic cells; Somatic DMR; Stem cells
• ISSN: 1756-8935; 1756-8935
• DOI: 10.1186/s13072-017-0138-0

Differential DNA methylation plays a critical role in the regulation of imprinted genes. The differentially methylated state of the imprinting control region is inherited via the gametes at fertilization, and is stably maintained in somatic cells throughout development, influencing the expression of genes across the imprinting cluster. In contrast, DNA methylation patterns are more labile at secondary differentially methylated regions which are established at imprinted loci during post-implantation development. To investigate the nature of these more variably methylated secondary differentially methylated regions, we adopted a hairpin linker bisulfite mutagenesis approach to examine CpG dyad methylation at differentially methylated regions associated with the murine imprinting cluster on both complementary strands. We observed homomethylation at greater than 90% of the methylated CpG dyads at the IG-DMR, which serves as the imprinting control element. In contrast, homomethylation was only observed at 67-78% of the methylated CpG dyads at the secondary differentially methylated regions; the remaining 22-33% of methylated CpG dyads exhibited hemimethylation. We propose that this high degree of hemimethylation could explain the variability in DNA methylation patterns at secondary differentially methylated regions associated with imprinted loci. We further suggest that the presence of 5-hydroxymethylation at secondary differentially methylated regions may result in hemimethylation and methylation variability as a result of passive and/or active demethylation mechanisms.