Fig. 8

The evolution of the IGF2R imprinted domain and the intragenic DMR. A Schematic diagram of the tammar IGF2R imprinted domain and mouse Igf2r imprinted domain. The IGF2R DMR is located in intron 12 in the tammar whereas the eutherian IGF2R DMR is located in the promoter and intron 2. Red-coloured boxes and blue-coloured boxes represent maternally expressed genes and paternally expressed genes, respectively. White and grey-coloured boxes represent non-imprinted and silenced genes, respectively. Arrows indicate the direction of transcription. There are three scenarios for the evolution of IGF2R DMR and SLC22A3 imprinting in therian mammals. A Transposition of the IGF2R DMR in marsupials. In this case, the IGF2R DMR evolved in the common ancestor of therian mammals and the DMR acts as an ICR to establish epigenetic silencing of SLC22A2 and SLC22A3 as in mice. Even after the transposition, the SLC22A3 imprinting but not SLC22A2 was positively maintained in marsupial lineage. B Transposition of the IGF2R DMR in eutherians. In this case, the IGF2R DMR evolved in the common ancestor of therian mammals and the DMR acts as an ICR to establish epigenetic silencing of SLC22A3 as in the tammar. After the transposition, the SLC22A2 imprinting evolved in eutherian lineage. C Independent acquisition of the IGF2R DMR in each mammalian lineage. In this case, the evolution of SLC22A3 imprinting would have accompanied the de novo acquisition of IGF2R DMR in each mammalian lineage. Yellow and red lines indicate that SLC22A2 imprinting and SLC22A3 imprinting, respectively