Methylation dynamics of IG-DMR and Gtl2-DMR during murine embryonic and placental development.

The Dlk1-Dio3 imprinted domain on mouse chromosome 12 contains IG-DMR and Gtl2-DMR, whose methylation patterns are established in the germline and after fertilization, respectively. In this study, we determine that acquisition of DNA methylation at the paternal allele of the Gtl2-DMR is initiated after the blastocyst stage and completed by embryonic day 6.5, and that Gtl2 (approved symbol: Meg3) is monoallelically expressed from the maternal allele as early as the blastocyst. Therefore, DNA methylation at the Gtl2-DMR is not a prerequisite for the imprinted expression of Gtl2, which may be involved in the control of proliferation and differentiation of cells during early gestation. We also reveal that a subregion of the IG-DMR exhibits tissue-specific differences in allelic methylation patterns. These results add to the growing body of knowledge elucidating the mechanism whereby parent-of-origin-dependent DNA methylation at the IG-DMR leads to the imprinted expression of the Dlk1-Dio3 cluster.