Characterization of the placenta-specific EnvV2-Fca soluble protein derived from endogenous retrovirus

Endogenous retroviruses (ERVs) are remnants of ancestral viruses in the host genome. Here, we identified the expression of a defective retroviral env gene belonging to the ERV group V member 2 Env (EnvV2) in Felis catus (EnvV2-Fca), which was specifically detected in the placental trophoblast syncytiotrophobic layer. EnV2-Fca was expressed as a secreted protein in cultured cells. Genetic analyses indicated that EnvV2 genes are widely present in vertebrate, and are under purifying selection among carnivores, suggesting a potential benefit for the host. Notably, this study suggests that birds, bats, and rodents carrying EnvV2 may play significant roles as intermediate vectors in spreading or cross-transmitting viruses among species. Overall, our findings provide valuable insights into the evolution of ERV in vertebrate hosts.