Meg3-DMR, not the Meg3 gene, regulates imprinting of the Dlk1-Dio3 locus

The imprinted delta like 1 homolog (DLK1) - thyroxine deiodinase type III (DIO3) locus regulates development and growth. Its imprinting regulation involves two differentially methylated regions (DMRs), intergenic-DMR (IG-DMR) and maternally expressed gene 3-DMR (Meg3-DMR). In mice, a maternal deletion of the IG-DMR leads to LOI in the locus, proving that the IG-DMR is a cis-acting imprinting control region of the locus. However, the Meg3-DMR overlaps with the promoter, exon 1 and intron 1 of the Meg3 gene. Because deletion of the Meg3-DMR inactivates the Meg3 gene, their roles in imprinting regulation of Meg3-DMR mice is unknown. Therefore, we generated two mouse models: Meg3(Delta(1-4)) and Meg3(Delta(2-4)), respectively targeting exons 1-4 and exons 2-4 of the Meg3 gene. A maternal deletion of Meg3(Delta(1-4)) caused embryonic death and LOI in both embryos and placentas, but did not affect methylation status of the IG-DMR. In contrast, mice carrying a maternal deletion of Meg3(Delta(2-4)) were born normally and did not have LOI. These data indicate that it is the Meg3-DMR, not the Meg3 gene, which regulates imprinting of the Dlk1-Dio3 locus.