Paleovirology of 'syncytins', retroviral env genes exapted for a role in placentation.
The development of the emerging field of 'paleovirology' allows biologists to reconstruct the evolutionary history of fossil endogenous retroviral sequences integrated within the genome of living organisms and has led to the retrieval of conserved, ancient retroviral genes 'exapted' by ancestral hosts to fulfil essential physiological roles, syncytin genes being undoubtedly among the most remarkable examples of such a phenomenon. Indeed, syncytins are 'new' genes encoding proteins derived from the envelope protein of endogenous retroviral elements that have been captured and domesticated on multiple occasions and independently in diverse mammalian species, through a process of convergent evolution. Knockout of syncytin genes in mice provided evidence for their absolute requirement for placenta development and embryo survival, via formation by cell-cell fusion of syncytial cell layers at the fetal-maternal interface. These genes of exogenous origin, acquired 'by chance' and yet still 'necessary' to carry out a basic function in placental mammals, may have been pivotal in the emergence of mammalian ancestors with a placenta from egg-laying animals via the capture of a founding retroviral env gene, subsequently replaced in the diverse mammalian lineages by new env-derived syncytin genes, each providing its host with a positive selective advantage.
UMR 8122, Unité des Rétrovirus Endogènes et Éléments Rétroïdes des Eucaryotes Supérieurs, CNRS, Institut Gustave Roussy, , 94805 Villejuif, France.
Christian
C
Lavialle
Guillaume
G
Cornelis
Anne
A
Dupressoir
Cécile
C
Esnault
Odile
O
Heidmann
Cécile
C
Vernochet
Thierry
T
Heidmann
D000818:Animals; D005075:Biological Evolution; D020077:Endogenous Retroviruses / Q000235:genetics / Q000502:physiology*; D005260:Female; D015686:Gene Products, env / Q000235:genetics / Q000502:physiology*; D015752:Genes, env; D016678:Genome; D006801:Humans; D051379:Mice; D010929:Placentation / Q000235:genetics / Q000502:physiology*; D011247:Pregnancy; D011257:Pregnancy Proteins / Q000235:genetics / Q000502:physiology*
D015686:Gene Products, env; D011257:Pregnancy Proteins; C405335:syncytin
cell–cell fusion; endogenous retrovirus; envelope protein; placenta; syncytin