To this end, the authors depleted the siRNA pathway Dicer protein, Dicer-2, as well as the miRNA biogenesis factors Drosha and Dicer-1 from shrimp, and then challenged the shrimp with WSSV. While the levels of vp28-siRNA were unaffected in Drosha- and Dicer-1-depleted animals, knockdown of Dicer-2 abolished vp28-siRNA accumulation. The authors also detected vp28-siRNA in the cytoplasm of wild type infected cells using RNA-FISH, but not in Dicer-2-depleted animals. Therefore, the siRNA pathway component Dicer-2, but not

the miRNA pathway components Drosha or Dicer-1, is required for vp28-siRNA biogenesis in WSSV-infected shrimp. To investigate Selleck CHIR-99021 whether the vsiRNA functions in the Bortezomib solubility dmso context of RISC, Huang and Zhang [20] used an electrophoretic mobility shift assay to demonstrate that synthetic vp28-siRNA interacts with Ago2, but not Ago1, while a control siRNA specifically interacts with Ago1 rather than Ago2. These results suggest that vp28-siRNAs produced during infection are incorporated into an Ago2-containing RISC. However, additional studies, such as immunoprecipitation and sequencing of Ago2-bound small RNAs from infected shrimp, are necessary

to verify this conclusion. It will be essential to determine whether depletion of Ago2 renders shrimp more susceptible to virus infection, since this would demonstrate a role for both the biogenesis and effector steps of the RNAi pathway in antiviral defense. Arguably the most important discovery of Huang and Zhang [20] is their finding that Dicer-2 is required for antiviral defense against WSSV. Depletion of either Dicer-2 or its product, vp28-siRNA, rendered the shrimp more susceptible to WSSV infection, as evidenced by the replication of WSSV being enhanced more than tenfold at 24 and 48 h postinfection in these animals. These results clearly implicate the biogenesis step of the shrimp RNAi pathway in suppressing DNA viral infection in vivo. The work of Huang and Zhang [20] raises several important

questions that will likely guide acetylcholine future efforts to characterize anti-viral responses against DNA viruses. Regarding the biogenesis of vsiRNAs, it is clear that one particular vsiRNA, vp28-siRNA, is generated during WSSV infection, and that it is potently anti-viral. How can one particular vsiRNA provide so much protection? Are other vsiRNAs produced during infection? What are the viral precursors that give rise to these small RNAs? Moreover, how do dsDNA viruses differ from RNA viruses in their recognition and processing by the cell? As mentioned previously, in insects, DNA virus-derived siRNAs can be produced from bidirectional transcription [15] or from structured single-stranded RNAs [16] (Fig. 1A).