The segmental organization of the vertebral column is established early in embryogenesis when pairs of somites are rhythmically produced by the presomitic mesoderm (PSM). The tempo of Users may view, print, copy, and download text and data-mine the content in such documents, for the purposes of academic research, subject always to the full Conditions of use:

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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 Scincidae. Here, we performed high-throughput RNA sequencing of a placenta transcriptome and screened for the presence of retroviral genes with a full-length ORF. We identified one such gene, which we named "," 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 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.