Comparative analysis of Reoviridae reverse genetics methods

Effective methods to engineer the segmented, double-stranded RNA genomes of Reoviridae viruses have only recently been developed. Mammalian orthoreoviruses (MRV) and bluetongue virus (BTV) can be recovered from entirely recombinant reagents, significantly improving the capacity to study the replication, pathogenesis, and transmission of these viruses. Conversely, rotaviruses (RVs), which are the major etiological agent of severe gastroenteritis in infants and children, have thus far only been modified using single-segment replacement methods. Reoviridae reverse genetics techniques universally rely on site-specific initiation of transcription by T7 RNA polymerase to generate the authentic 5' end of recombinant RNA segments, but they vary in how the RNAs are introduced into cells: recombinant BTV is recovered by transfection of in vitro transcribed RNAs, whereas recombinant MRV and RV RNAs are transcribed intracellularly from transfected plasmid cDNAs. Additionally, several parameters have been identified in each system that are essential for recombinant virus recovery. Generating recombinant BTV requires the use of 5' capped RNAs and is enhanced by multiple rounds of RNA transfection, suggesting that translation of viral proteins is likely the rate-limiting step. For RV, the efficiency of recovery is almost entirely dependent on the strength of the selection mechanism used to isolate the single-segment recombinant RV from the unmodified helper virus. The reverse genetics methods for BTV and RV are presented and compared to the previously described MRV methods. Analysis and comparison of each method suggest several key lines of research that might lead to a reverse genetics system for RV, analogous to those used for MRV and BTV.