Global identification of functional microRNA-mRNA interactions in Drosophila
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ABSTRACT: MicroRNAs (miRNAs) are key mediators of post-transcriptional gene expression silencing. So far, no comprehensive experimental annotation of functional miRNA target sites exists in Drosophila. To close this gap, we generated the first transcriptome-wide in vivo map of miRNA-mRNA interactions in Drosophila melanogaster, making use of single nucleotide resolution in Argonaute1 (AGO1) crosslinking and immunoprecipitation (CLIP) data. Absolute quantification of cellular miRNA levels presents the miRNA pool in Drosophila cell lines to be more diverse than previously reported. Benchmarking two CLIP approaches, we identify a similar predictive potential to unambiguously assign thousands of miRNA-mRNA pairs from AGO1 interaction data at unprecedented depth, achieving higher signal-to-noise ratios than with computational methods alone. Quantitative RNA-Seq and sub-codon resolution ribosomal footprinting data upon AGO1 depletion enabled the determination of miRNA-mediated effects on target expression and translation. We thus provide the first comprehensive resource of miRNA target sites and their quantitative functional impact in Drosophila.
Project description:In Arabidopsis thaliana, ARGONAUTE1 (AGO1) plays a central role in microRNA (miRNA) and small interfering RNA (siRNA)-mediated silencing. Nuclear AGO1 is loaded with miRNAs and exported to the cytosol where it associates to the rough ER to conduct miRNA-mediated translational repression, mRNA cleavage and biogenesis of phased siRNAs. These latter, as well as other cytosolic siRNAs, are loaded into cytosolic AGO1, but in which compartment this happens is not known. Moreover, the effect of stress on AGO1 localization is still unclear. Here, we show that heat stress (HS) promotes AGO1 protein accumulation, which co-localize with components of the siRNA bodies and of stress granules (SGs). AGO1 does not need SGS3, a key component of siRNA bodies, to efficiently form condensates during HS. Instead, we found that the still poorly characterized N-terminal Poly-Q domain of AGO1, which contains a prion-like domain, is sufficient to undergo phase separation. Moreover, an exposure of 1 hour to HS only moderately affected AGO1 loading by miRNAs and target cleavage, suggesting that its localization in condensates protects AGO1 rather than promote its activity in reprograming gene expressing during stress. Collectively, our work shed new light on the impact of high temperature on a main effector of RNA silencing in plants.
Project description:In flies, small silencing RNAs are sorted between Argonaute1 (Ago1), the central protein component of the microRNA (miRNA) pathway, and Argonaute2 (Ago2), which mediates RNA interference. Extensive double-stranded character—as is found in small interfering RNAs (siRNAs)—directs duplexes into Ago2, whereas central mismatches, like those found in miRNA/miRNA* duplexes, direct duplexes into Ago1. Central to this sorting decision is the affinity of the small RNA duplex for the Dcr-2/R2D2 heterodimer, which loads small RNAs into Ago2. Here, we show that while most Drosophila miRNAs are bound to Ago1, miRNA* strands accumulate bound to Ago2. Like siRNA loading, efficient loading of miRNA* strands in Ago2 favors duplexes with a paired central region and requires both Dcr-2 and R2D2. Those miRNA and miRNA* sequences bound to Ago2, like siRNAs diced in vivo from long double-stranded RNA, typically begin with cytidine, whereas Ago1-bound miRNA and miRNA* disproportionately begin with uridine. Consequently, some pre-miRNA generate two or more isoforms from the same side of the stem that differentially partition between Ago1 and Ago2. Our findings provide the first genome-wide test for the idea that Drosophila small RNAs are sorted between Ago1 and Ago2 according to their duplex structure and the identity of their first nucleotide.
Project description:RNA silencing is a conserved mechanism in eukaryotes and is involved in development, heterochromatin maintenance and defense against viruses. In plants, ARGONAUTE1 (AGO1) protein plays a central role in both microRNA (miRNA) and small interfering RNA (siRNA)-directed silencing and its expression is regulated at multiple levels. Here, we report that the F-box protein FBW2 targets proteolysis of AGO1 by a CDC48-mediated mechanism. We found that FBW2 assembles an SCF complex that recognizes the MID-PIWI domain of AGO1 and requires its C-terminal domain containing a GW motif for AGO1 turnover. We showed that FBW2 has a preference for the unloaded and for some mutated forms of AGO1 protein. While FBW2 loss of function does not lead to strong growth or developmental defects, it significantly increases RNA silencing activity. Interestingly, under conditions in which small RNA production or accumulation is affected, the failure to degrade AGO1 in fbw2 mutants becomes more deleterious for the plant. Hence, we showed that the non-degradable AGO1 protein assembles high molecular complexes and binds illegitimate small RNA leading to the cleavage of new target genes that belong to stress responses and cellular metabolic processes. Therefore, the control of AGO1 homeostasis by ubiquitin ligases, plays an important quality control to avoid off-target cleavage.
Project description:In flies, small silencing RNAs are sorted between Argonaute1 (Ago1), the central protein component of the microRNA (miRNA) pathway, and Argonaute2 (Ago2), which mediates RNA interference. Extensive double-stranded characterM-bM-^@M-^Tas is found in small interfering RNAs (siRNAs)M-bM-^@M-^Tdirects duplexes into Ago2, whereas central mismatches, like those found in miRNA/miRNA* duplexes, direct duplexes into Ago1. Central to this sorting decision is the affinity of the small RNA duplex for the Dcr-2/R2D2 heterodimer, which loads small RNAs into Ago2. Here, we show that while most Drosophila miRNAs are bound to Ago1, miRNA* strands accumulate bound to Ago2. Like siRNA loading, efficient loading of miRNA* strands in Ago2 favors duplexes with a paired central region and requires both Dcr-2 and R2D2. Those miRNA and miRNA* sequences bound to Ago2, like siRNAs diced in vivo from long double-stranded RNA, typically begin with cytidine, whereas Ago1-bound miRNA and miRNA* disproportionately begin with uridine. Consequently, some pre-miRNA generate two or more isoforms from the same side of the stem that differentially partition between Ago1 and Ago2. Our findings provide the first genome-wide test for the idea that Drosophila small RNAs are sorted between Ago1 and Ago2 according to their duplex structure and the identity of their first nucleotide. Sequencing of small RNAs (either total small RNAs or Ago1-associated small RNAs) in wild-type, dcr-2 and r2d2 mutant flies. Small RNA sequencing, Small RNAs (18-29 nt long), Size selection (18 to 30 nt).
Project description:ARGONAUTE1 (AGO1) binds directly to small regulatory RNA and is a key effector protein of post-transcriptional gene silencing mediated by microRNA (miRNA) and small interfering RNA (siRNA). The formation of an RNA induced silencing complex (RISC) of AGO1 and small RNA requires the function of the Heat Shock Protein 70/90 chaperone system. Some functions of AGO1 occur in association with endomembranes, in particular the rough endoplasmic reticulum (rER), but proteins interacting with AGO1 in membrane fractions remain unidentified. In this study, we show that the farnesylated Heat Shock Protein 40 homologs, J2 and J3, associate with AGO1 in membrane fractions in a manner that involves protein farnesylation. We also show that three changes in AGO1 function are detectable in mutants in protein farnesylation and J2/J3. First, perturbations of the HSP40/70/90 pathway by mutation of j3, hsp90 and farnesyl transferase affect the amounts of AGO1 associated with membranes. Second, miRNA association with membrane-bound AGO1, and with membrane-bound polysomes is increased in farnesyl transferase and farnesylationdeficient J2/J3 mutants. Third, silencing by non-cell autonomously acting short interfering RNAs (siRNAs) is impaired. These observations highlight the involvement of farnesylated J2/J3 in small RNA-mediated gene regulation, and suggest that the importance of chaperone-AGO1 interaction is not limited to the RISC assembly process.
Project description:MicroRNAs (miRNAs) are endogenous noncoding small RNAs with important roles in many biological pathways; their generation and activity are under precise regulation. Emerging evidence suggests that miRNA pathways are precisely modulated with controls at the level of transcription, processing, and stability, with miRNA deregulation linked with diseases and neurodegenerative disorders. In the Drosophila miRNA biogenesis pathway, long primary miRNA transcripts undergo sequential cleavage to release the embedded miRNAs. Mature miRNAs are then loaded into Argonaute1 (Ago1) within the RNA-induced silencing complex (RISC). Intriguingly, we found that Drosophila miR-34 displays multiple isoforms that differ at the 3′ end, suggesting a novel biogenesis mechanism involving 3′ end processing. To define the cellular factors responsible, we performed an RNA interference (RNAi) screen and identified a putative 3′→5′ exoribonuclease CG9247/nibbler essential for the generation of the smaller isoforms of miR-34. Nibbler (Nbr) interacts with Ago1 and processes miR-34 within RISC. Deep sequencing analysis revealed a larger set of multi-isoform miRNAs that are controlled by nibbler. These findings suggest that Nbr-mediated 3′ end processing represents a critical step in miRNA maturation that impacts miRNA diversity.
Project description:In Arabidopsis thaliana, ARGONAUTE1 (AGO1) plays a central role in microRNA (miRNA) and small interfering RNA (siRNA)-mediated silencing. Nuclear AGO1 is loaded with miRNAs and exported to the cytosol where it associates to the rough ER to conduct miRNA-mediated translational repression, mRNA cleavage and biogenesis of phased siRNAs. These latter, as well as other cytosolic siRNAs, are loaded into cytosolic AGO1, but in which compartment this happens is not known. Moreover, the effect of stress on AGO1 localization is still unclear. Here, we show that heat stress (HS) promotes AGO1 protein accumulation, which co-localizes with components of the siRNA bodies and of stress granules (SGs). AGO1 does not need SGS3, a key component of siRNA bodies, to efficiently form condensates during HS. Instead, we found that the still poorly characterized N-terminal Poly-Q domain of AGO1, which contains a prion-like domain, is sufficient to undergo phase separation. Moreover, an exposure of 1 hour to HS only moderately affected AGO1 loading by miRNAs and target cleavage, suggesting that its localization in condensates protects AGO1 rather than promoting its activity in reprograming gene expression during stress. Collectively, our work shed new light on the impact of high temperatures on the main effector of RNA silencing in plants.
Project description:In Arabidopsis thaliana, ARGONAUTE1 (AGO1) plays a central role in microRNA (miRNA) and small interfering RNA (siRNA)-mediated silencing. Nuclear AGO1 is loaded with miRNAs and exported to the cytosol where it associates to the rough ER to conduct miRNA-mediated translational repression, mRNA cleavage and biogenesis of phased siRNAs. These latter, as well as other cytosolic siRNAs, are loaded into cytosolic AGO1, but in which compartment this happens is not known. Moreover, the effect of stress on AGO1 localization is still unclear. Here, we show that heat stress (HS) promotes AGO1 protein accumulation, which co-localizes with components of the siRNA bodies and of stress granules (SGs). AGO1 does not need SGS3, a key component of siRNA bodies, to efficiently form condensates during HS. Instead, we found that the still poorly characterized N-terminal Poly-Q domain of AGO1, which contains a prion-like domain, is sufficient to undergo phase separation. Moreover, an exposure of 1 hour to HS only moderately affected AGO1 loading by miRNAs and target cleavage, suggesting that its localization in condensates protects AGO1 rather than promoting its activity in reprograming gene expression during stress. Collectively, our work shed new light on the impact of high temperatures on the main effector of RNA silencing in plants.
Project description:In Arabidopsis thaliana, ARGONAUTE1 (AGO1) plays a central role in microRNA (miRNA) and small interfering RNA (siRNA)-mediated silencing. Nuclear AGO1 is loaded with miRNAs and exported to the cytosol where it associates to the rough ER to conduct miRNA-mediated translational repression, mRNA cleavage and biogenesis of phased siRNAs. These latter, as well as other cytosolic siRNAs, are loaded into cytosolic AGO1, but in which compartment this happens is not known. Moreover, the effect of stress on AGO1 localization is still unclear. Here, we show that heat stress (HS) promotes AGO1 protein accumulation, which co-localizes with components of the siRNA bodies and of stress granules (SGs). AGO1 does not need SGS3, a key component of siRNA bodies, to efficiently form condensates during HS. Instead, we found that the still poorly characterized N-terminal Poly-Q domain of AGO1, which contains a prion-like domain, is sufficient to undergo phase separation. Moreover, an exposure of 1 hour to HS only moderately affected AGO1 loading by miRNAs and target cleavage, suggesting that its localization in condensates protects AGO1 rather than promoting its activity in reprograming gene expression during stress. Collectively, our work shed new light on the impact of high temperatures on the main effector of RNA silencing in plants.
Project description:Plant microRNAs undergo stepwise-nuclear maturation before engaging cytosolic sequence-complementary transcripts in association with the silencing-effector protein ARGONAUTE1(AGO1). How plant miRNAs translocate to the cytosol remains mysterious as does their cellular loading site(s) into AGO1. Here, we show that the N-termini of plant AGO1s contain a nuclear-localization (NLS) and nuclear-export signal (NES), which, in Arabidopsis thaliana (At) enables AtAGO1 nucleo-cytosolic shuttling in a Leptomycin-B-inhibited manner, diagnostic of CRM1(Expo1)/NES-dependent nuclear export. Nuclear-only AtAGO1 contains the same 2’O-methylated miRNA cohort as its nucleo-cytosolic counterpart, but specifically interacts with the miRNA loading-chaperone HSP90. AtAGO1 nucleo-cytosolic shuttling is required for mature miRNA translocation and for miRNA-mediated silencing. We propose that plant miRNAs are matured, methylated, loaded into AGO1 in the nucleus, and exported cytoplasmically as AGO1:miRNA complexes in a CRM1(Expo1)/NES-dependent manner.