Project description:In mammals, early resistance to viruses relies on interferons, which protect differentiated but not stem cells from viral replication. Many other organisms rely instead on RNA interference (RNAi) mediated by a specialised Dicer protein that cleaves viral double stranded RNA. Whether RNAi also contributes to mammalian antiviral immunity remains controversial. Here we identify an isoform of Dicer, named antiviral Dicer (aviD), that protects tissue stem cells from RNA viruses, including Zika virus and SARS-CoV-2, by dicing viral double-stranded RNA to orchestrate antiviral RNAi. Our work sheds light on the molecular regulation of antiviral RNAi in mammalian innate immunity in which different cell-intrinsic antiviral pathways are tailored to the differentiation status of cells.
Project description:In mammals, early resistance to viruses relies on interferons, which protect differentiated cells but not stem cells from viral replication. Many other organisms rely instead on RNA interference (RNAi) mediated by a specialized Dicer protein that cleaves viral double-stranded RNA. Whether RNAi also contributes to mammalian antiviral immunity remains controversial. We identified an isoform of Dicer, named antiviral Dicer (aviD), that protects tissue stem cells from RNA viruses-including Zika virus and severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2)-by dicing viral double-stranded RNA to orchestrate antiviral RNAi. Our work sheds light on the molecular regulation of antiviral RNAi in mammalian innate immunity, in which different cell-intrinsic antiviral pathways can be tailored to the differentiation status of cells.
Project description:Drosophila Dicer-1 produces microRNAs (miRNAs) from pre-miRNA, whereas Dicer-2 generates small interfering RNAs (siRNAs) from long dsRNA. loquacious (loqs) encodes three Dicer partner proteins, Loqs-PA, Loqs-PB, and, Loqs-PD, generated by alternative splicing. To understand the function of each Loqs isoform, we constructed loqs isoform-specific rescue flies. Loqs-PD promotes siRNA production in vivo by Dicer-2. Loqs-PA or Loqs-PB is required for viability, but the proteins are not fully redundant: Loqs-PB is required to produce a specific subset of miRNAs. Surprisingly, Loqs-PB tunes the product size cleaved by Dicer-1 from pre-miR-307a, generating a longer miRNA isoform with a distinct seed sequence and target specificity. The mouse and human Dicer-binding partner TRBP, a homolog of Loqs-PB, similarly tunes the site of pre-miR-132 cleavage by mammalian Dicer. Thus, Dicer-binding partner proteins can change the choice of cleavage site by Dicer, producing miRNAs with different target specificities than those that would be made by Dicer alone.
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:Mammals have one Dicer gene required for biogenesis of small RNAs in microRNA (miRNA) and RNA interference (RNAi) pathways. Yet, endogenous RNAi is highly active in oocytes but not in somatic cells. Here, we provide a mechanistical explanation for high RNAi activity in mouse oocytes. The main Dicer isoform in oocytes is transcribed from an intronic MT-C retrotransposon, which functions as a promoter of an oocyte-specific Dicer isoform (denoted DicerO). DicerO lacks an N-terminal helicase domain and has a higher cleavage activity than the full-length Dicer from somatic cells. DicerO can rescue the miRNA pathway and, in addition, it efficiently produces small RNAs from long dsRNA substrates. Thus, control of endogenous RNAi activity in mice occurs via alternative Dicer isoform and the phylogenetic origin of DicerO demonstrates evolutionary plasticity of RNA silencing pathways.
Project description:Drosophila Dicer-1 produces microRNAs (miRNAs) from pre-miRNA, whereas Dicer-2 generates small interfering RNAs (siRNAs) from long dsRNA. loquacious (loqs) encodes three Dicer partner proteins, Loqs-PA, Loqs-PB, and, Loqs-PD, generated by alternative splicing. To understand the function of each Loqs isoform, we constructed loqs isoform-specific rescue flies. Loqs-PD promotes siRNA production in vivo by Dicer-2. Loqs-PA or Loqs-PB is required for viability, but the proteins are not fully redundant: Loqs-PB is required to produce a specific subset of miRNAs. Surprisingly, Loqs-PB tunes the product size cleaved by Dicer-1 from pre-miR-307a, generating a longer miRNA isoform with a distinct seed sequence and target specificity. The mouse and human Dicer-binding partner TRBP, a homolog of Loqs-PB, similarly tunes the site of pre-miR-132 cleavage by mammalian Dicer. Thus, Dicer-binding partner proteins can change the choice of cleavage site by Dicer, producing miRNAs with different target specificities than those that would be made by Dicer alone. Examination of Dicer-binding proteins on small RNA profiles of female fly heads, fly ovaries, mouse embryonic fibroblasts, and mouse tail fibroblasts.
Project description:Mammals have one Dicer gene required for biogenesis of small RNAs in microRNA (miRNA) and RNA interference (RNAi) pathways. Yet, endogenous RNAi is highly active in oocytes but not in somatic cells. Here, we provide a mechanistical explanation for high RNAi activity in mouse oocytes. The main Dicer isoform in oocytes is transcribed from an intronic MT-C retrotransposon, which functions as a promoter of an oocyte-specific Dicer isoform (denoted DicerO). DicerO lacks an N-terminal helicase domain and has a higher cleavage activity than the full-length Dicer from somatic cells. DicerO can rescue the miRNA pathway and, in addition, it efficiently produces small RNAs from long dsRNA substrates. Thus, control of endogenous RNAi activity in mice occurs via alternative Dicer isoform and the phylogenetic origin of DicerO demonstrates evolutionary plasticity of RNA silencing pathways. NIH3T3 cells or mouse embryonic stem cells expressing oocyte-specific or somatic form of Dicer were transiently transfected with a plasmid expressing long double-stranded RNA (within the 3'-UTR of EGFP reporter) or left without transfection for controls.
Project description:DICER has a well-characterized role in the processing of microRNAs (miRNAs) and small interfering RNAs (siRNA) that are important for post-transcriptional gene regulation. Emerging evidence suggests that DICER also has several non-canonical functions beyond miRNA/siRNA biogenesis, for example in transcriptional gene silencing at the chromatin level, as well as in RNA degradation and maintenance of genomic integrity. We have shown that the function of DICER in germ cells is essential for normal spermatogenesis; male mice lacking DICER in postnatal male germ cells are infertile due to severe defects in haploid differentiation. To better understand the function of DICER in male germ cells, we immunoprecipitated DICER from juvenile mouse testes and performed mass spectrometric analysis to identify DICER-interacting proteins.
Project description:Dicer is an essential ribonuclease involved in the biogenesis of miRNA. Previous studies have reported that Dicer is dysregulated in multiple types of cancers. To investigate the downstream phosphoproteome of Dicer, we carried out phosphotyrosine profiling of the liver of Dicer knockout of mice. We employed antibody-based enrichment of phosphotyrosine containing peptides coupled with spike-in SILAC-based quantitation. Over 400 phosphoisites were identified in each condition while 290 phosphosites were quantitated in common. Amongst these, several key signaling molecules like receptor tyrosine kinase MET, MET, PDGFR, EPHA2, EPHB4 and IGF1R/INSR were hyperphosphorylated. Also, non-receptor tyrosine kinases of Src family and their downstream effector signaling partners including IRS2 and STAT3were found to be hyperphosphorylated. Our study indicates that there is significant alteration in the signaling pathways upon ablation of Dicer.
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.