title: Comparative phylogenetic analysis reveals multiple non-imprinted isoforms of opossum Dlk1.
abstract: Imprinted genes are monoallelically expressed in a parent-of-origin manner and were previously identified in both marsupials and eutherians, but not in monotremes. Phylogenetic comparison of imprinted domains is a powerful tool for investigating the molecular and adaptive evolution of this unique gene regulatory mechanism. Herein, we report that multiple transcripts of Dlk1 (Delta, Drosophila, Homolog-like 1) are expressed in the opossum, but none are imprinted. Thus, we provide the first example of a reciprocally imprinted gene domain in which imprinting evolved in a common ancestor to eutherian rather than therian mammals. Moreover, the reciprocally imprinted Meg3 (Maternally Expressed Gene 3), found downstream of Dlk1 in eutherian mammals, is absent in the opossum. We propose that the Meg3 sequence integrated into the eutherian Dlk1 domain via a LINE-1 element and that Dlk1 became imprinted in eutherian mammals only after this downstream integration. These findings clearly demonstrate that imprinted genes did not all evolve before the divergence of marsupials and eutherians.
authors.affiliation: Department of Radiation Oncology, Duke University Medical Center, Durham, North Carolina 27710, USA.
authors.forename: Jennifer R
authors.initials: JR
authors.lastname: Weidman
authors.forename: Kristin A
authors.initials: KA
authors.lastname: Maloney
authors.forename: Randy L
authors.initials: RL
authors.lastname: Jirtle
mesh_terms: D000818:Animals; D019143:Evolution, Molecular; D016678:Genome; D018392:Genomic Imprinting; D007335:Insulin-Like Growth Factor II; D036341:Intercellular Signaling Peptides and Proteins; D008565:Membrane Proteins / Q000235:genetics*; D009893:Opossums / Q000235:genetics*; D009928:Organ Specificity; D010802:Phylogeny; D020033:Protein Isoforms / Q000235:genetics; D017434:Protein Structure, Tertiary; D011506:Proteins / Q000235:genetics; D012097:Repressor Proteins / Q000235:genetics*
chemical_list: C035170:IGF2 protein, human; D036341:Intercellular Signaling Peptides and Proteins; D008565:Membrane Proteins; D020033:Protein Isoforms; D011506:Proteins; D012097:Repressor Proteins; D007335:Insulin-Like Growth Factor II