Project description:5’-isomiRs expand the repertoire of miRNA targets. However, how they are generated is not well understood. Here, we showed that, for some miRNAs in mammalian cells, 5’-isomiRs are generated by alternative Dicer processing by using miRNA offset RNAs (moRs) to determine Drosha cleavage sites in cells. In addition, we showed that in miR-203, alternative Dicer processing is regulated by a conserved sliding-bulge structure at the Dicer processing site, which allows the pre-miRNA molecule to fold into two different structures that are processed differently by Dicer. So far no RNA motif that slides to change conformation and alter a protein–RNA interaction has been reported. Thus, our study revealed a novel RNA motif that regulates 5’-isomiR generation in some miRNAs. It might also contribute to regulating protein–RNA interactions in other biological processes, since it takes only one point mutation to generate the sliding bulge, and there are a large number of different RNAs in the cell.
Project description:5’-isomiRs expand the repertoire of miRNA targets. However, how they are generated is not well understood. Here, we showed that, for some miRNAs in mammalian cells, 5’-isomiRs are generated by alternative Dicer processing by using miRNA offset RNAs (moRs) to determine Drosha cleavage sites in cells. In addition, we showed that in miR-203, alternative Dicer processing is regulated by a conserved sliding-bulge structure at the Dicer processing site, which allows the pre-miRNA molecule to fold into two different structures that are processed differently by Dicer. So far no RNA motif that slides to change conformation and alter a protein–RNA interaction has been reported. Thus, our study revealed a novel RNA motif that regulates 5’-isomiR generation in some miRNAs. It might also contribute to regulating protein–RNA interactions in other biological processes, since it takes only one point mutation to generate the sliding bulge, and there are a large number of different RNAs in the cell.
Project description:A sliding-bulge structure at the Dicer processing site of pre-miRNA regulates alternative Dicer processing to generate 5’-isomiRs (pre-miR-203)
Project description:Short-hairpin RNA (shRNA)-induced RNAi is used for biological discovery and therapeutics. Dicer, whose normal role is to liberate endogenous miRNAs from their precursors, processes shRNAs into different biologically active siRNAs, affecting their efficacy and potential for off-targeting. We found that in cells, Dicer induced imprecise cleavage events around the expected sites based on the previously described 5'/3'-counting rules. These promiscuous non-canonical cleavages were abrogated when the cleavage site was positioned 2 nt from a bulge or loop. Interestingly, we observed that the ~1/3 of mammalian endogenous pre-miRNAs that contained such structures were more precisely processed by Dicer. Implementing a new "loop-counting rule", we designed potent anti-HCV shRNAs with substantially reduced off-target effects. Our results suggest that Dicer recognizes the loop/bulge structure in addition to the ends of shRNAs/pre-miRNAs for accurate processing. This has important implications for both miRNA processing and future design of shRNAs for RNAi-based genetic screens and therapies.
Project description:Short-hairpin RNA (shRNA)-induced RNAi is used for biological discovery and therapeutics. Dicer, whose normal role is to liberate endogenous miRNAs from their precursors, processes shRNAs into different biologically active siRNAs, affecting their efficacy and potential for off-targeting. We found that in cells, Dicer induced imprecise cleavage events around the expected sites based on the previously described 5'/3'-counting rules. These promiscuous non-canonical cleavages were abrogated when the cleavage site was positioned 2 nt from a bulge or loop. Interestingly, we observed that the ~1/3 of mammalian endogenous pre-miRNAs that contained such structures were more precisely processed by Dicer. Implementing a new "loop-counting rule", we designed potent anti-HCV shRNAs with substantially reduced off-target effects. Our results suggest that Dicer recognizes the loop/bulge structure in addition to the ends of shRNAs/pre-miRNAs for accurate processing. This has important implications for both miRNA processing and future design of shRNAs for RNAi-based genetic screens and therapies. Various shRNAs were expressed in Cell and processed by the RNase III enzyme Dicer. The profiles of the siRNA products were generated by deep sequencing with or without the Ago2-IP.
Project description:We have used genome editing to generate inactivating deletion mutations in all three copies of the dicer (hdcr) gene present in the human cell line 293T. As previously shown in murine ES cells lacking Dicer function, hDcr-deficient 293T cells are severely impaired for the production of mature microRNAs (miRNAs). Nevertheless, RNA-induced silencing complexes (RISCs) present in these hDcr-deficient cells are readily programmed by transfected, synthetic miRNA duplexes to repress mRNAs bearing either fully or partially complementary targets, including targets bearing incomplete seed homology to the introduced miRNA. Using these hDcr-deficient 293T cells, we demonstrate that human pre-miRNA processing can be effectively rescued by ectopic expression of the Drosophila Dicer 1 protein, but only in the presence of the PB isoform of Loquacious (Loqs-PB), the fly homolog of the hDcr co-factor TRBP. In contrast, Drosophila Dicer 2, even in the presence of its co-factors Loqs-PD and R2D2, was unable to support human pre-miRNA processing. Interestingly, although ectopic Drosophila Dicer 1/Loqs-PB or hDcr both rescued pre-miRNA processing effectively in these hDcr-deficient cells, there were significant differences in the ratio of the miRNA isoforms that were produced, especially in the case of miR-30 family members, and we also noted differences in the relative expression level of miRNAs versus passenger strands for a subset of human miRNAs. These data demonstrate that the mechanisms underlying the accurate processing of pre-miRNAs are largely, but not entirely, conserved between mammalian and insect cells. Series includes three datasets of total small RNA reads from wild type and Dicer negative 293T cells. Also included are total small RNA reads of the Dicer-negative cell line NoDice(4-25) transfected with a vector expressing human Dicer, Drosophila Dicer1, or mock transfected. RISC-associated small RNAs identified by ribonucleoprotein immunoprecipitation (RIP-Seq) in wild type 293T, Dicer-negative NoDice(4-25) line, and NoDice(4-25) transfected with either hsa-miR-155 or kshv-miR-K12-11 miRNA duplexes. The final data series are PAR-CLIP libraries which identified microRNA targets in untransfected NoDice(4-25) cells and NoDice(4-25) cells transfected with either hsa-miR-92a, hsa-miR-155, kshv-miR-K12-11 miRNA duplexes
Project description:Biogenesis of canonical microRNAs (miRNAs) involves multiple steps: nuclear processing of primary miRNA (pri-miRNA) by DROSHA, nuclear export of precursor miRNA (pre-miRNA) by Exportin 5 (XPO5), and cytoplasmic processing of pre-miRNA by DICER. To gain a deeper understanding of the contribution of each of these maturation steps, we deleted DROSHA, XPO5, and DICER in the same human cell line, and analyzed their effects on miRNA biogenesis. Canonical miRNA production was completely abolished in DROSHA-deleted cells while we detected a few DROSHA-independent miRNAs including three previously unidentified noncanonical miRNAs (miR-7706, miR-3615, and miR-1254). In contrast to DROSHA knockout, many canonical miRNAs were still detected without DICER albeit at markedly reduced levels. In the absence of DICER, pre-miRNAs are loaded directly onto AGO and trimmed at the 3â² end, yielding miRNAs from the 5â² strand (5p miRNAs). Interestingly, in XPO5 knockout cells, most miRNAs are affected only modestly, suggesting that XPO5 is necessary but not critical for miRNA maturation. Our study demonstrates an essential role of DROSHA and an important contribution of DICER in the canonical miRNA pathway, and reveals that the function of XPO5 can be complemented by alternative mechanisms. Thus, this study allows us to understand differential contributions of key biogenesis factors, and provides with valuable resources for miRNA research. Two independent sequencing experiments (set 1 and set 2, respectively) were performed using 9 samples.
Project description:Biogenesis of canonical microRNAs (miRNAs) involves multiple steps: nuclear processing of primary miRNA (pri-miRNA) by DROSHA, nuclear export of precursor miRNA (pre-miRNA) by Exportin 5 (XPO5), and cytoplasmic processing of pre-miRNA by DICER. To gain a deeper understanding of the contribution of each of these maturation steps, we deleted DROSHA, XPO5, and DICER in the same human cell line, and analyzed their effects on miRNA biogenesis. Canonical miRNA production was completely abolished in DROSHA-deleted cells while we detected a few DROSHA-independent miRNAs including three previously unidentified noncanonical miRNAs (miR-7706, miR-3615, and miR-1254). In contrast to DROSHA knockout, many canonical miRNAs were still detected without DICER albeit at markedly reduced levels. In the absence of DICER, pre-miRNAs are loaded directly onto AGO and trimmed at the 3′ end, yielding miRNAs from the 5′ strand (5p miRNAs). Interestingly, in XPO5 knockout cells, most miRNAs are affected only modestly, suggesting that XPO5 is necessary but not critical for miRNA maturation. Our study demonstrates an essential role of DROSHA and an important contribution of DICER in the canonical miRNA pathway, and reveals that the function of XPO5 can be complemented by alternative mechanisms. Thus, this study allows us to understand differential contributions of key biogenesis factors, and provides with valuable resources for miRNA research.