Expression of endogenous retroviruses in pre-implantation stages of bovine embryo

Endogenous retroviruses (ERVs) are involved in cellular proliferation, pluripotency, tissue-specific remodelling and regulation of developmental processes. These elements are transcriptionally active in mouse and human pre-implantation embryos. Empirical evidence indicates that regulatory networks involved with ERV transcripts are responsible for pluripotency and totipotency at certain stages of mouse and human pre-implantation development. Yet, the expression in pre-implantation bovine embryo remains unidentified. To determine whether two members of bovine endogenous retroviruses, BERV-K1 and BERV-K2, are expressed in the pre-implantation bovine embryo, each embryonic stage developed in vitro and was subjected to RNA release, reverse transcription and quantitative PCR. We found that BERV-K1 and BERV-K2 are expressed throughout different stages of pre-implantation development. The higher level of expression was detected in embryonic blastomeres with totipotent/pluripotent status (two-cell to 16-cell stages), while the more differentiated blastocyst stage showed significantly lower levels of ERVs expression. These findings suggest a possible role for endogenous retroviruses in the establishment of totipotent and pluripotent states in pre-implantation bovine embryo, similar to functions which have been suggested for these elements in human and mouse embryos.