The LTR of endogenous retrovirus ev21 retains promoter activity and exhibits tissue specific transcription in chicken

Endogenous viruses integrate into the host genome and influence the expression of neighboring genes through their long terminal repeats (LTRs). In this study, we analyzed the promoter, enhancer and transcriptional activities of the chicken endogenous retrovirus ev21 LTR. The LTR was cloned into pGL3-basic and pGL3-promoter luciferase vectors in forward and reverse orientation separately. The luciferase activities were detected respectively in chicken embryonic fibroblast cell, human embryonic kidney cell line, human lung carcinoma cell line, Chinese hamster ovary cell line, and murine melanoma cell line. Relative luciferase activity analysis indicated that the ev21 LTR retained bi-directional promoter activity but no detectable enhancer activity in these cells. The constructs containing the LTR and F1 region show stronger promoter activity than the constructs containing only LTR. The transcriptional pattern of ev21 LTR varied in tissues of late feathering White Leghorn chicken at post-hatch day one. Skin exhibits the highest expression in the tissues examed. Collectively, our results indicate that the ev21 LTR exhibits tissue-type specific expression in White Leghorn chicken, and it also have regulatory potential.