Expression of endogenous retrovirus-like transcripts in bovine trophoblastic cells

Abstract Endogenous retrovirus envelope elements are considered to participate in trophoblastic cell fusion and multinucleate cell formation in humans, mice, and sheep. However, there is limited information about their roles in the ruminant placenta. Objectives We explore and identify the endogenous retrovirus envelope element genes expressed in bovine trophoblasts. Methods The NCBI UniGene database (Build #97 Bos taurus ) was screened by in silico analysis. After cloning endogenous retrovirus envelope element-like transcript (ERVE), expression profiles were analyzed with quantitative RT-PCR and in situ hybrizaidation. Results Two UniGene clusters, UniGene ID: Bt.68042 and Bt.85243, were detected, and ERVE-A gene was cloned. Weak expression of this gene was first detected on Day 20 of gestation, and the intensity of its expression increased up to Day 70 of gestation. The intensity of its expression was maintained throughout gestation in the placenta, and its specific expression in trophoblastic binucleate cells was confirmed by in situ hybridization. Conclusions bERVE-A has a similar sequence to human syncytin-1, although it lacks an intact envelope sequence, and is specifically expressed in binucleate cells. This is the first evidence that endogenous retrovirus envelope element genes are expressed in bovine binucleate cells.