Functional characterization of the bovine foamy virus miRNA expression cassette and its dumbbell-shaped pri-miRNA
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Foamy viruses are unconventional and complex retroviruses distinct from the other members of the Retroviridae family. Currently, no disease has been firmly linked to persistent foamy virus infection of their cognate host including simians, bovines, felines, and equines or upon zoonotic transmission of different simian foamy viruses to humans. Bovine and simian foamy viruses have been recently shown to encode a RNA polymerase-III-driven micro RNA cluster which likely modulates and regulates host–virus interactions at different levels. Using sub-genomic bovine foamy virus micro RNA expression plasmids and dual luciferase reporter assays as readout, the requirements for expression and processing of the bovine foamy virus micro RNAs have been analyzed. Here, we report that the minimal BFV micro RNA cassette is significantly weaker than a U6 promoter-based construct and strongly suppressed by flanking sequences. The primary micro RNA sequence can be manipulated and chimerized as long as the dumbbell-like folding of the primary micro RNA is maintained. Since more subtle changes are associated with reduced functionality, the overall structure and shape, but possibly individual elements and residues also, are important for the expression and processing of the bovine foamy virus micro RNAs.
KeywordsBovine foamy virus MiRNA BFV Spumaretrovirus Gene expression and regulation
We thank the Baden-Württemberg Stiftung for financing these studies by the research Grant SID 49. We thank Bryan Cullen, Duke University, Durham, USA for thoughful discussions, Dirk Grimm, BioQuant, Heidelberg, Germany for providing the U6 promoter-containing plasmid pBS–U6-GFP plasmid and the German Cancer Research Center Core Facility Genomics and Proteomics for sequencing of miRNAs.
WC performed and analyzed the experiments, AH and AH-W evaluated sequencing data and conducted pri-miRNA structural analyses, and ML designed and supervised the study and wrote the manuscript. All authors read and approved the final manuscript.
The funding bodies played no role in the study design, data collection or analysis, or writing of the manuscript.
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Conflict of interest
The authors declare that there are no conflicts of interest.
This article does not include any studies with human participants or animals performed by any of the authors.
Not applicable as no human participants are involved.