Dupressoir Anne, Heidmann Thierry
Unité des rétrovirus endogènes et éléments rétroïdes des eucaryotes supérieurs, UMR 8122 CNRS, Institut Gustave Roussy, 39, rue Camille Desmoulins, 94805 Villejuif, France.
Med Sci (Paris). 2011 Feb;27(2):163-9. doi: 10.1051/medsci/2011272163. Epub 2011 Mar 8.
In the past, germline infections by retroviruses have led to vertical transmission of "endogenized" retroviruses. Escaping genetic drift, some of the viral genes have been conserved until now because of beneficial effects on their host. Here we present the syncytin genes that encode envelope proteins from endogenous retroviruses. Syncytins have inherited fusogenic properties from their infectious ancestor and are specifically expressed in the placenta. Both properties have suggested their involvement in the formation of the syncytiotrophoblast, a multinucleated layer that mediates feto-maternal exchanges in the placenta. The capture of syncytin genes occurred on several independent occasions during evolution of mammals. Knock-out experiments of syncytins in the mouse definitively confirmed the role of these genes in placentation. Finally, a second function for syncytins, i.e. an immunosuppressive activity, could contribute to materno-fetal immune tolerance. This constitutes a remarkable example of convergent evolution where the properties of retroviral envelope genes are subverted to play a major physiological role.
过去，逆转录病毒的种系感染导致了“内源性”逆转录病毒的垂直传播。由于对宿主具有有益作用，一些病毒基因逃脱了遗传漂变，至今仍得以保留。在此，我们展示了编码内源性逆转录病毒包膜蛋白的合胞素基因。合胞素从其具有感染性的祖先那里继承了融合特性，并在胎盘中特异性表达。这两种特性表明它们参与了合体滋养层的形成，合体滋养层是介导胎盘母婴物质交换的多核层。在哺乳动物进化过程中，合胞素基因的捕获发生过几次独立事件。在小鼠中对合胞素进行的基因敲除实验明确证实了这些基因在胎盘形成中的作用。最后，合胞素的第二个功能，即免疫抑制活性，可能有助于母胎免疫耐受。这构成了趋同进化的一个显著例子，即逆转录病毒包膜基因的特性被转而发挥主要的生理作用。
