Expression of C-type viral particles at implantation in the marmoset monkey

Type C RNA retroviral particles have been observed budding from the plasma membrane of syncytiotrophoblast during a study of embryo implantation in the common marmoset (Callithrix jacchus). These viral particles appear in profusion at the interface of syncytiotrophoblast with cytotrophoblast. They appear to be a non-infective, endogenous viral component of the host genome, although the precise role of the C-type virus in this context is unclear at present. Such viral particles have been reported previously from studies of human term placenta; however, this is the first report indicating that expression of viral particles occurs at the earliest stages of embryo implantation.