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Proc Natl Acad Sci U S A. 2017 Dec 19;114(51):E10991-E11000. doi: 10.1073/pnas.1714590114. Epub 2017 Nov 21.

An endogenous retroviral envelope syncytin and its cognate receptor identified in the viviparous placental Mabuya lizard.

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Unité Physiologie et Pathologie Moléculaires des Rétrovirus Endogènes et Infectieux, CNRS UMR 9196, Gustave Roussy, Villejuif, F-94805, France.
UMR 9196, Université Paris-Sud, Orsay, F-91405, France.
Laboratorio de Biologia Reproductiva de Vertebrados, Escuela de Biologia, Universidad Industrial de Santander, 680002 Bucaramanga, Colombia.
Plateforme de Bioinformatique, INSERM US23/CNRS UMS3655, Gustave Roussy, Villejuif, F-94805, France.
Institut de Systématique, Evolution, Biodiversité, Muséum National d'Histoire Naturelle, CNRS UPMC EPHE, Sorbonne Universités, Paris, F-75005, France.
Unité Physiologie et Pathologie Moléculaires des Rétrovirus Endogènes et Infectieux, CNRS UMR 9196, Gustave Roussy, Villejuif, F-94805, France;


Syncytins are envelope genes from endogenous retroviruses that have been captured during evolution for a function in placentation. They have been found in all placental mammals in which they have been searched, including marsupials. Placental structures are not restricted to mammals but also emerged in some other vertebrates, most frequently in lizards, such as the viviparous Mabuya Scincidae. Here, we performed high-throughput RNA sequencing of a Mabuya placenta transcriptome and screened for the presence of retroviral env genes with a full-length ORF. We identified one such gene, which we named "syncytin-Mab1," that has all the characteristics expected for a syncytin gene. It encodes a membrane-bound envelope protein with fusogenic activity ex vivo, is expressed at the placental level as revealed by in situ hybridization and immunohistochemistry, and is conserved in all Mabuya species tested, spanning over 25 My of evolution. Its cognate receptor, required for its fusogenic activity, was searched for by a screening assay using the GeneBridge4 human/Chinese hamster radiation hybrid panel and found to be the MPZL1 gene, previously identified in mammals as a signal-transducing transmembrane protein involved in cell migration. Together, these results show that syncytin capture is not restricted to placental mammals, but can also take place in the rare nonmammalian vertebrates in which a viviparous placentotrophic mode of reproduction emerged. It suggests that similar molecular tools have been used for the convergent evolution of placentation in independently evolved and highly distant vertebrates.


endogenous retrovirus; envelope protein; placenta; receptor; syncytin

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