Publication Date:
2015-01-20
Description:
Syncytinsare genes of retroviral origin captured by eutherian mammals, with a role in placentation. Here we show that some marsupials—which are the closest living relatives to eutherian mammals, although they diverged from the latter ∼190 Mya—also possess asyncytingene. The gene identified in the South American marsupial opossum and dubbedsyncytin-Opo1has all of the characteristic features of a bona fidesyncytingene: It is fusogenic in an ex vivo cell–cell fusion assay; it is specifically expressed in the short-lived placenta at the level of the syncytial feto–maternal interface; and it is conserved in a functional state in a series ofMonodelphisspecies. We further identify a nonfusogenic retroviral envelope gene that has been conserved for 〉80 My of evolution among all marsupials (including the opossum and the Australian tammar wallaby), with evidence for purifying selection and conservation of a canonical immunosuppressive domain, but with only limited expression in the placenta. This unusual captured gene, together with a third class of envelope genes from recently endogenized retroviruses—displaying strong expression in the uterine glands where retroviral particles can be detected—plausibly correspond to the different evolutionary statuses of a captured retroviral envelope gene, with onlysyncytin-Opo1being the present-day bona fidesyncytinactive in the opossum and related species. This study would accordingly recapitulate the natural history ofsyncytinexaptation and evolution in a single species, and definitely extends the presence of such genes to all major placental mammalian clades.
Print ISSN:
0027-8424
Electronic ISSN:
1091-6490
Topics:
Biology
,
Medicine
,
Natural Sciences in General
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