Endogenous retroviruses

inherited retrovirus encoded in an organism's genome

Syncytin-1 also known as enverin is a protein found in humans and other primates that is encoded by the ERVW-1 gene (endogenous retrovirus group W envelope member 1). Syncytin-1 is a cell-cell fusion protein whose function is best characterized in placental development. The placenta in turn aids in embryo attachment to the uterus and establishment of a nutrient supply.

Syncytin-2 also known as endogenous retrovirus group FRD member 1 is a protein that in humans is encoded by ERVFRD-1 gene. It is a member of the HERV-FRD family of endogenous retroviral elements. The human ERVFRD-1 gene is located on chromosome 6. Both Syncytin-2 and Syncytin-1 are encoded by ENV genes and were first identified in a human placenta. Specifically, Syncytin-2 was observed in the cytoplasmic membrane of primary trophoblast cells in the placenta.