FIG. 3.

The imprinted region of the genes Igf2r (A), Peg3 (B), and Grf1 (C) are resistant to de novo methylation by overexpression of Dnmt1 in ES cells. For the Igf2r gene, we assayed an MluI site in region 2, which resulted in a maternally methylated band and a paternally unmethylated band in wild-type ES cells (42). For the Peg3 gene, a SacII site was assayed which is normally methylated on the maternal allele (25). A differentially methylated HhaI site was assayed for the Grf1 gene, which is paternally methylated in wild-type cells (34).