Project description:Although many in vitro studies have helped us understand how Dicer-2 is able to discriminate between different dsRNA substrate termini, much less is known about how this translates to the in vivo recognition of viral dsRNA. Indeed, Dicer-2 associates with several dsRNA-binding proteins (dsRBPs), which can modify its specificity for a substrate, however it remains unknown how Dicer-2 is able to recognize the protected termini of viral dsRNAs. Therefore, in order to study how the ribonucleoprotein network of Dicer-2 impacts antiviral immunity, we used an IP-MS approach to identify interactants of several fly lines expressing different versions of GFP:Dicer-2. By combining the global analysis of the Dicer-2 interactome with different line-specific analyses, we were able to both obtain a global overview of the partners of Dicer-2 in vivo, and study how this interactome was modulated by different factors such as the infection and/or the presence of different point mutations on the helicase or RNase III domains of GFP:Dicer-2. This allowed the identification of several new Dicer-2 interactants as well as new pro- and antiviral factors that had an impact on DCV infection. In addition, this work provides a resource composed of several candidates, available to the scientific community that can now be investigated further to gain a better understanding of the proteins involved in Dicer-2-mediated antiviral RNAi.
Project description:Cytoplasmic polyadenylation is a mechanism to promote mRNA translation in a wide variety of biological contexts.The conserved RNA-binding protein family CPEB has been shown to mediate canonical cytoplasmic polyadenylation of target transcripts. We have previously reported evidence for RNA-interference factor Dicer-2 as a component of a non-canonical complex, that operates independent of CPEB in Drosophila. In this study, we investigate Dicer-2 mRNA targets and protein co-factors in cytoplasmic polyadenylation. Using RIP‐Seq analysis we identify hundreds of potential Dicer-2 target transcripts, ~60% of which were previously found as targets of the cytoplasmic poly(A) polymerase Wispy, suggesting widespread roles of Dicer-2 in cytoplasmic polyadenylation. Large-scale immunoprecipitation and mass spectrometry revealed Ataxin-2 and Twenty-four among the high-confidence interactors of Dicer-2. Complex analyses indicated that both factors form an RNA‐independent complex with Dicer‐2, and mediate interactions of Dicer‐2 with Wispy. Functional poly(A)‐test analyses showed that Twenty‐four and Ataxin-2 are required for cytoplasmic polyadenylation of a subset of Dicer‐2 targets. Our results reveal components of a novel cytoplasmic polyadenylation complex that operates during Drosophila early embryogenesis.
Project description:A variety of small RNAs, including the Dicer-dependent miRNAs and the Dicer-independent Piwi-interacting RNAs, associate with Argonaute family proteins to regulate gene expression in diverse cellular processes. These two species of small RNA have not been found in fungi. Here, by analyzing small RNA associated with the Neurospora Argonaute protein QDE-2, we show that diverse pathways generate miRNA-like small RNAs (milRNAs) and Dicer-independent small interfering RNAs (disiRNAs) in this filamentous fungus. Surprisingly, milRNAs are produced by at least four different mechanisms that use a distinct combination of factors, including Dicers, QDE-2, the exonuclease QIP and an RNAse III domain-containing protein MRPL3. In contrast, disiRNAs originate from loci producing overlapping sense and antisense transcripts, and do not require the known RNAi components for their production. Taken together, these results uncover several pathways for small RNA production in filamentous fungi, shedding light on the diversity and evolutionary origins of eukaryotic small RNAs.
Project description:Bats are reservoirs for many viruses that frequently cause epidemics in humans and animals. It is thus critical to better understand their immune system and mechanisms of antiviral immunity. Despite an increasing number of studies, much is still unknown about the molecular mechanisms that govern bat-virus interactions, especially given the large diversity of bat species. Dicer is a conserved ribonuclease with multiple activities that can modulate antiviral immunity, including the detection of viral RNA as part of the RNA interference (RNAi) pathway, the maturation of micro RNAs, and the direct inhibition of innate immunity in mouse and human cells. In view of these complex activities of Dicer, we tested its antiviral activity in Myotis myotis nasal epithelial cells. Surprisingly, we did not see strong evidence of RNAi in these cells, but instead saw a proviral effect of Dicer for two alphaviruses, Sindbis and Semliki forest virus. We also observed a striking relocalization of Dicer to cytoplasmic foci upon infection with these viruses, which did not occur in the several human cell lines we tested. These foci contained dsRNA and viral plus strand RNA, suggesting that they are sites of viral replication. Finally, we found that factors specific to M. myotis cells are needed for Dicer relocalization. Overall, we propose that Dicer can play different roles in different bat species and/or cell types, and is being repurposed by alphaviruses to promote viral replication.
Project description:The innate immune response against viruses mainly involves type I interferon (IFN) in mammalian cells. The exact contribution of the RNA silencing machinery remains to be established, but several recent studies indicate that the type III ribonuclease DICER can generate viral siRNAs in specific conditions. In addition, it has been proposed that type I IFN and RNA silencing could be mutually exclusive responses. In order to decipher the implication of DICER during infection of human cells with the Sindbis virus, we determined its interactome by immunoprecipitation and mass spectrometry analysis. Our results show that human DICER specifically interacts with several double-stranded RNA binding proteins and helicases during viral infection. In particular, proteins such as DHX9, ADAR-1 and the protein kinase PKR are enriched with DICER in virus-infected cells. We validated the importance of the helicase domain of DICER in its interaction with PKR and showed that it has functional consequences for the cellular response to viral infection.
Project description:Background: RNA silencing pathways play critical roles in gene regulation, virus infection, and transposon control. RNA interference (RNAi) is mediated by small interfering RNAs (siRNAs), which are liberated from double stranded (ds) RNA precursors by Dicer and direct the RNA-induced silencing complex (RISC) to target transcripts. Recent efforts have uncovered important principles governing small RNA (smRNA) sorting into RISC, yet mechanisms defining substrate selection by Dicer proteins remain uncharacterized. Methodology: To better characterize Dicer-2 substrates in Drosophila, we examined the antiviral RNAi response, which generates virus-derived siRNAs from viral RNA. Using high-throughput sequencing, we found that diverse viruses were uniquely targeted; substrates included dsRNA replication intermediates and intramolecular RNA stem loops. smRNA distribution patterns from viral and synthetic dsRNA precursors were highly reproducible, and machine learning techniques identified characteristics of precursor molecules and smRNA duplexes important in determining relative smRNA abundance. Significance: To our knowledge, this study provides the first description of the rules governing Dicer-2 substrate selection, which has important implications for exogenous RNA silencing technologies and the development of smRNA-based antiviral therapeutics.
Project description:<p>Viral studies of Drosophila melanogaster typically involve virus injection with a small needle, causing post-injury a wounding/wound healing response, in addition to the effects of viral infection. However, the metabolic response to the needle injury is understudied, and many viral investigations neglect potential effects of this response. Furthermore, the wMel strain of the endosymbiont bacterium Wolbachia pipientis provides anti-viral protection in Drosophila. Here we used NMR-based metabolomics to characterise the acute wounding response in Drosophila and the relationship between wound healing and the Wolbachia strain wMel. The most notable response to wounding was found on the initial day of injury and lessened with time in both uninfected and Wolbachia infected flies. Metabolic changes in injured flies revealed evidence of inflammation, Warburg-like metabolism and the melanisation immune response as a response to wounding. In addition, at five days post injury Wolbachia infected injured flies were metabolically more similar to the uninjured flies than uninfected injured flies were at the same time point, indicating a positive interaction between Wolbachia infection and wound healing. This study is the first metabolomic characterisation of the wound response in Drosophila and its findings are crucial to the metabolic interpretation of viral experiments in Drosophila in both past and future studies.</p>
Project description:RNAi, a gene-silencing pathway triggered by double-stranded RNA, is conserved in diverse eukaryotic species but has been lost in the model budding yeast, Saccharomyces cerevisiae. We report that RNAi is present in other budding-yeast species, including Saccharomyces castellii and Candida albicans. These species use noncanonical Dicer proteins to generate siRNAs, which mostly correspond to transposable elements and Y´ subtelomeric repeats. In S. castellii, RNAi mutants are viable but have excess Y´ mRNA levels. In S. cerevisiae, introducing Dicer and Argonaute of S. castellii restores RNAi, and the reconstituted pathway silences endogenous retrotransposons. These results identify a novel class of Dicer proteins, bring the tool of RNAi to the study of budding yeasts, and bring the tools of budding yeast to the study of RNAi.