Induction of ovine trophoblast cell fusion by fematrin‐1 in vitro

Endogenous retroviruses present in the genomes take a specific role in placental formation in various vertebrates, including bovine and sheep. Fematrin-1, which is the envelope (Env) protein of bovine endogenous retrovirus found in bovine placenta, is involved in the formation of fetomaternal hybrid cells in cattle placenta. This study was conducted to clarify whether fematrin-1 possesses fusogenic activity in trophoblast cells. Another question is whether Env proteins only have species-specific activity or not. For this, fematrin-1 gene was transfected in ovine trophoblast cells, and we examined fusogenic activity with Cos-7 cells. Although fematrin-1 fusogenic activity was detected in both neutral and acidic pH conditions, acidic condition significantly enhanced it. These activities were rather weaker than those of vesicular stomatitis virus G protein as a positive control. However, the ratio of fematrin-1 and vesicular stomatitis virus G protein fusion index was confirmed similar to those in the previous reports. Some fusion cells showed multinucleate cells. These results imply that fematrin-1 is involved in the formation of trophoblast hybrid cells even in different species trophoblastic cells.