Identification of a Novel PNMA-MS1 Gene in Marsupials Suggests the LTR retrotransposon-derived PNMAGenes Evolved Differently in Marsupials

Twomajor gene families derived fromTy3/Gypsy long terminal repeat (LTR) retrotransposonswere recently identified in mammals. The sushi-ichi retrotransposon homologue (SIRH) family comprises 12 genes: 11 in eutherians including Peg10 and Peg11/Rtl1 that have essential roles in the eutherian placenta and 1 that is marsupial specific. Fifteen and 12 genes were reported in the second gene family, para-neoplastic antigen MA (PNMA), in humans and mice, respectively, although their biological functions and evolutionary history remain largely unknown.Here,we identified twonovel candidatePNMA genes,PNMA-MS1 and-MS2 inmarsu-pials. Like all eutherian-specific PNMA genes, they exhibit the highest homology to a Gypsy12_DR (DR,Danio rerio) Gag protein. PNMA-MS1 is conserved in both Australian and South American marsupial species, the tammar wallaby and grey short-tailed opossum. However, no PNMA-MS1 orthologuewas found in eutherians, monotremesornon-mammalianvertebrates.PNMA-MS1wasexpressedintheovary,mammaryglandandbrain during development and growth in the tammar, suggesting that PNMA-MS1 may have acquired a marsupial-specific function.However,PNMA-MS2 seemstobeapseudogene.Theabsenceofmarsupialorthologuesofeu