摘要
Cell-cell fusion is essential for many physiological events such as egg-sperm fertilization, muscle differentiation, viral entry, and placental development. The envelope genes of human endogenous retrovirus (HERV)-W and -FRD, named syncytin-1 and -2, are primarily expressed in placenta and mediate trophoblastic fusion for formation of the multinucleated syncytiotrophoblast layer, which is essential for fetal growth. Recently, envelope genes of retroviral origin encoding fusogenic proteins have also been identified from the genomes of other mammals. These novel envelope genes, named mouse syncytin-A and -B, rabbit syncytin-Ory1, and sheep enJSRV envelope, are required for placental development and trophoblastic fusion. Although syncytins are critical for placental development, abnormal expression of syncytins is associated with placental disorders, cancers, and neurological diseases. Here we provide a general description of the biological functions of syncytins and the regulation of syncytin gene expression at the molecular level. In addition, the pathological functions of syncytins are also discussed. © Springer Science+Business Media B.V. 2011.