Conservation of Dnmt1o cytosine methyltransferase in the marsupial Monodelphis domestica

Imprinted genes have been identified in both eutherian mammals and in marsupials. In eutherian species, there is a conservation of the imprinting process, both in terms of the genes imprinted and the epigenetic inheritance mechanism. In the mouse, the inheritance of gametic methylation patterns depends on an oocyte-derived isoform of the Dnmt1 (cytosine-5) -methyltransferase protein, Dnmt1o, which functions during preimplantation development to maintain methylation patterns on imprinted alleles. To determine if this component of genomic imprinting is also found in marsupials, Dnmt1 isoforms were examined in somatic cells and germ cells of the South American opossum Monodelphis domestica. There is a Dnmt1o protein in Monodelphis oocytes that is synthesized, as in the mouse, from a different transcript than the somatic Dnmt1 protein. Thus, an essential component of imprinting in eutherian mammals is found in a marsupial species, suggesting that marsupials and eutherian mammals imprint their genes with the same methylation-dependent mechanism.