Figure 1: Changes in methylation state of DMRs and their impact on Igf2 and H19 expression. Upper panel. Igf2 and H19 coding regions are separated by a differentially methylated region (DMR) that is methylated (as shown by filled lollypops) on the paternal chromosome (P) and unmethylated (open lollypops) on the maternal (M) chromosome. Expression of both genes is regulated by a 3’ distal enhancer depicted in green. Methylation of the DMR on the paternal chromosome (P) prevents binding of CTCF insulator protein and allows activation of the Igf2 promoter by the distal enhancer and transcription of Igf2 mRNA from the paternal chromosome (M) (red arrow). In contrast, since the DMR is unmethylated on the maternal chromosome (M), it binds CTCF, and this prevents activation of the Igf2 promoter by the distal enhancer. As a result, only H19 mRNA is transcribed from the maternal chromosome (P) (red arrow). Normal somatic imprint observed in all somatic cells, which results, as described in Figure 1, in properly balanced expression of Igf2 from the paternal chromosome and H19 from the maternal chromosome (red arrows). Middle panel – Erasure of imprinting at the Igf2-H19 locus as seen in primordial germ cells (PGCs) and pluripotent stem cells residing post-developmentally in adult tissues (VSELs). DMRs on both the paternal (P) and maternal (M) chromosomes are engaged by the CTCF insulator protein, and thus only H19 mRNA is transcribed (red arrows), contributing to the quiescent state of cells (lacking autocrine IGF2). Lower panel – Loss of imprinting at the Igf2-H19 locus as seen in tumor cells from several types of cancer (e.g., rhabdomyosarcoma, nephroblastoma, and gastrointestinal tumors). Since both DMRs are methylated, the insulator protein CTCF cannot bind to the DNA and the distal enhancer stimulates transcription of mRNA for IGF2 from both chromosomes (red arrows). Cells that have this epigenetic change are under autocrine IGF2 stimulation.