Increased plasticity of genomic imprinting of Dlk1 in brain is due to genetic and epigenetic factors

The expression of six imprinted genes (Dlk1, Gtl2, Igf2r, Kcnq1, Nnat, and Peg1) was examined in brains of 21 mice derived from N₂ × N₂ intercrosses between C57BL/6 and MOLF/Ei strains. Imprinting of Igf2r, Kcnq1, Gtl2, and Dlk1 varied among individuals. As three of these genes are implicated in cell–cell signaling or cell–environment interactions, variation in their imprinting may influence a wide range of biological processes from cell differentiation to behavior. To elucidate the mechanisms underlying the interindividual imprinting variation in the brain, we focused our effort on the paternally expressed gene Dlk1. We investigated expression of Dlk1 in the brains of animals from N₉ and N₁₀ backcrosses and found that reactivation of the normally silent maternal Dlk1 allele in the N₉ and N₁₀ mice occurred less often than in N₂ × N₂ animals. Our data suggest that trans-acting genetic factors of MOLF/Ei origin facilitate the reactivation of the normally silent maternal allele of Dlk1. We mapped one of these factors to the proximal part of Chr 7. The results of bisulfite sequencing methylation analysis show that reactivation of the maternal allele was also associated with hypermethylation of the intragenic differentially methylated region (IG DMR), which is the imprinting control region for the Dlk1–Gtl2 domain. Thus, the imprinting status of Dlk1 in the brain depends upon trans-acting genetic influences and correlates with the methylation status of a specific subregion of the IG DMR.The GenBank accession numbers for sequences described in this article are AY644388–644394.