Characterization of the Long Terminal Repeat of the Endogenous Retrovirus-derived microRNAs in the Olive Flounder.

Endogenous retroviruses (ERVs) have been identified at different copy numbers in various organisms. The long terminal repeat (LTR) element of an ERV has the capacity to exert regulatory influence as both a promoter and enhancer of cellular genes. Here, we describe olive flounder (OF)-ERV9, derived from chromosome 9 of the olive flounder. OF-ERV9-LTR provide binding sites for various transcription factors and showed enhancer activity. The OF-ERV9-LTR demonstrates high sequence similarity with the 3' untranslated region (UTR) of various genes that also contain seed sequences (TGTTTTG) that bind the LTR-derived microRNA(miRNA), OF-miRNA-307. Additionally, OF-miRNA-307 collaborates with transcription factors located in OF-ERV9-LTR to regulate gene expression. Taken together, our data facilitates a greater understanding of the molecular function of OF-ERV families and suggests that OF-miRNA-307 may act as a super-enhancer miRNA regulating gene activity.