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PubMed2006

Enzymatically prepared RNAi libraries.

Large-scale RNA interference (RNAi) screens in mammalian cells have mainly used synthetic small interfering RNA (siRNA) or short hairpin RNA (shRNA) libraries. The RNAi triggers for both of these approaches were designed with algorithm-based predictions to identify single sequences for mRNA knockdown. Alternatives to these approaches have recently been developed using enzymatic methods. Here we describe the concepts of enzymatically prepared shRNA and siRNA libraries, and discuss their strengths and limitations.

Animals↗
PubMed2004

Synthetic dsRNA Dicer substrates enhance RNAi potency and efficacy.

RNA interference (RNAi) is the process of sequence-specific post-transcriptional gene silencing triggered by double-stranded RNAs. In attempts to identify RNAi triggers that effectively function at lower concentrations, we found that synthetic RNA duplexes 25-30 nucleotides in length can be up to 100-fold more potent than corresponding conventional 21-mer small interfering RNAs (siRNAs). Some sites that are refractory to silencing by 21-mer siRNAs can be effectively targeted by 27-mer duplexes, with silencing lasting up to 10 d. Notably, the 27-mers do not induce interferon or activate protein kinase R (PKR). The enhanced potency of the longer duplexes is attributed to the fact that they are substrates of the Dicer endonuclease, directly linking the production of siRNAs to incorporation in the RNA-induced silencing complex. These results provide an alternative strategy for eliciting RNAi-mediated target cleavage using low concentrations of synthetic RNA as substrates for cellular Dicer-mediated cleavage.

Gene Expression Regulation↗
PubMed2004

RNA interference: the molecular immune system.

Introduction of double-stranded RNA (dsRNA) into cells expressing a homologous gene triggers RNA interference (RNAi), or RNA-based gene silencing (RBGS). The dsRNA degrades corresponding host mRNA into small interfering RNAs (siRNAs) by a protein complex containing Dicer. siRNAs in turn are incorporated into the RNA-induced silencing complex (RISC) that includes helicase, RecA, and exo- and endo-nucleases as well as other proteins. Following its assembly, the RISC guides the RNA degradation machinery to the target RNAs and cleaves the cognate target RNA in a sequence-specific, siRNA-dependent manner. RNAi has now been documented in a wide variety of organisms, including plants, fungi, flies, worms, and more recently, higher mammals. In eukaryotes, dsRNA directed against a range of viruses (i.e., HIV-1, RSV, HPV, poliovirus and others) and endogenous genes can induce sequence-specific inhibition of gene expression. In invertebrates, RNAi can be efficiently triggered by either long dsRNAs or 21- to 23-nt-long siRNAs. However, in jawed vertebrates, dsRNA longer than 30 bp can induce interferon and thus trigger undesirable side effects instead of initiating RNAi. siRNAs have been shown to act as potent inducers of RNAi in cultured mammalian cells. Many investigators have suggested that siRNAs may have evolved as a normal defense against endogenous and exogenous transposons and retroelements. Through a combination of genetic and biochemical approaches, some of the mechanisms underlying RNAi have been described. Recent data in C. elegans shows that two homologs of siRNAs, microRNAs (miRNAs) and tiny noncoding RNAs (tncRNAs) are endogenously expressed. However, many aspects of RNAi-induced gene silencing, including its origins and the selective pressures which maintain it, remain undefined. Its evolutionary history may pass through the more primitive immune functions of prokaryotes involving restriction enzymes that degrade plasmid DNA molecules that enter bacterial cells. RNAi has evolved further among eukaryotes, in which its wide distribution suggests early origins. RNAi seems to be involved in a variety of regulatory and immune functions that may differ among various kingdoms and phyla. We present here proposed mechanisms by which RBGS protects the host against endogenous and exogenous transposons and retroelements. The potential for therapeutic application of RBGS technology in treating viral infections such as HIV is also discussed.

AIDS Vaccines↗
PubMed2006

Using RNAi in the clinic.

RNA interference (RNAi) is a biological process that controls gene silencing in all living cells. Targeting the RNAi system represents a novel therapeutic strategy that has the ability to intercede with multiple disease-related genes and so target many human diseases. Recently, the design of small interfering RNA (siRNA)-selective compounds has become more straightforward because of the significant progress made in predictive modeling. Exciting new data show that siRNA blocks gene function in vivo, suggesting that it has potential as a therapeutic approach for humans. This article highlights recent advances in siRNA research and discusses the aims of the pharmaceutical and biotechnology industries to progress siRNA compounds into the clinical. In the fight against disease, the use of RNAi is a powerful new tactic that adds to the arsenal of small-molecule inhibitors and antibody-blocking approaches.

Animals↗
PubMed2004

The RNA-induced silencing complex is a Mg2+-dependent endonuclease.

In the Drosophila and mammalian RNA interference (RNAi) pathways, target RNA destruction is catalyzed by the siRNA-guided, RNA-induced silencing complex (RISC). RISC has been proposed to be an siRNA-directed endonuclease, catalyzing cleavage of a single phosphodiester bond on the RNA target. Although 5' cleavage products are readily detected for RNAi in vitro, only 3' cleavage products have been observed in vivo. Proof that RISC acts as an endonuclease requires detection of both 5' and 3' cleavage products in a single experimental system. Here, we show that siRNA-programmed RISC generates both 5' and 3' cleavage products in vitro; cleavage requires Mg(2+), but not Ca(2+), and the cleavage product termini suggest a role for Mg(2+) in catalysis. Moreover, a single phosphorothioate in place of the scissile phosphate blocks cleavage; the phosphorothioate effect can be rescued by the thiophilic cation Mn(2+), but not by Ca(2+) or Mg(2+). We propose that during catalysis, a Mg(2+) ion is bound to the RNA substrate through a nonbridging oxygen of the scissile phosphate. The mechanism of endonucleolytic cleavage is not consistent with the mechanisms of the previously identified RISC nuclease, Tudor-SN. Thus, the RISC-component that mediates endonucleolytic cleavage of the target RNA remains to be identified.

Animals↗
PubMed2006

Gene expression: long-term gene silencing by RNAi.

Small RNA molecules participate in a variety of activities in the cell: in a process known as RNA interference (RNAi), double-stranded RNA triggers the degradation of messenger RNA that has a matching sequence; the small RNA intermediates of this process can also modify gene expression in the nucleus. Here we show that a single episode of RNAi in the nematode Caenorhabditis elegans can induce transcriptional silencing effects that are inherited indefinitely in the absence of the original trigger. Our findings may prove useful in the ongoing development of RNAi to treat disease.

Animals↗
PubMed2006

Analysis of short RNAs in the malaria parasite and its red blood cell host.

RNA interference (RNAi) is an RNA degradation process that involves short, double-stranded RNAs (dsRNA) as sequence specificity factors. The natural function of the RNAi machinery is to generate endogenous short double-stranded RNAs to regulate gene expression. It has been shown that treatment of Plasmodium falciparum, the etiologic agent of malaria, with dsRNA induces degradation of the corresponding microRNA (miRNA), yet typical RNAi-associated genes have not been identifiable in the parasite genome. To clarify this discrepancy we set out to clone short RNAs from P. falciparum-infected red blood cells and from purified parasites. We did not find any short RNA that was not a rRNA or tRNA fragment. Indeed, only known human miRNAs were isolated in parasite preparations indicating that very few if any short RNAs exist in P. falciparum. This suggests a different mechanism than classical RNAi in observations of dsRNA-mediated degradation. Of the human miRNAs identified, the human miRNA mir-451 accumulates at a very high level in both infected and healthy red blood cells. Interestingly, mir-451 was not detectable in a series of immortalised cell lines representing progenitor stages of all major blood lineages, suggesting that mir-451 may play a role in the differentiation of erythroid cells.

Animals↗
PubMed2002

Confirming specificity of RNAi in mammalian cells.

RNA interference (RNAi) is a process of sequence-specific gene silencing. Recent advances in the understanding of RNAi have provided practical tools to silence gene expression in mammalian cells, opening new possibilities for studying the functions of genes and proteins. It is important to ensure that an observed effect of RNAi is due to silencing of the intended target. Indeed, it is possible that an siRNA may silence more than one messenger RNA that is homologous in the region complementary to the siRNA. Considering that we know little about how RNAi works in mammalian cells, other artifacts may be yet to be recognized. Thus, we suggest approaches to rescue the effect of RNAi by ectopically expressing the protein of interest. These approaches involve introducing silent mutations into the complementary DNA of the protein and targeting RNAi to the untranslated regions of the gene.

3' Untranslated Regions↗
PubMed2006

Conversion of pre-RISC to holo-RISC by Ago2 during assembly of RNAi complexes.

In the Drosophila RNA interference (RNAi) pathway, small interfering RNAs (siRNAs) direct Argonaute2 (Ago2), an endonuclease, within the RNA-induced silencing complex (RISC) to cleave complementary mRNA targets. In vitro studies have shown that, for each siRNA duplex, RISC retains only one strand, the guide, and releases the other, the passenger, to form a holo-RISC complex. Here, we have isolated a new Ago2 mutant allele and provide, for the first time, in vivo evidence that endogenous Ago2 slicer activity is important to mount an RNAi response in Drosophila. We demonstrate in vivo that efficient removal of the passenger strand from RISC requires the cleavage activity of Ago2. We have also identified a new intermediate complex in the RISC assembly pathway, pre-RISC, in which Ago2 is stably bound to double-stranded siRNA.

Alleles↗
PubMed2006

FlyRNAi: the Drosophila RNAi screening center database.

RNA interference (RNAi) has become a powerful tool for genetic screening in Drosophila. At the Drosophila RNAi Screening Center (DRSC), we are using a library of over 21,000 double-stranded RNAs targeting known and predicted genes in Drosophila. This library is available for the use of visiting scientists wishing to perform full-genome RNAi screens. The data generated from these screens are collected in the DRSC database (http://flyRNAi.org/cgi-bin/RNAi_screens.pl) in a flexible format for the convenience of the scientist and for archiving data. The long-term goal of this database is to provide annotations for as many of the uncharacterized genes in Drosophila as possible. Data from published screens are available to the public through a highly configurable interface that allows detailed examination of the data and provides access to a number of other databases and bioinformatics tools.

Animals↗
PubMed2003

High-throughput selection of effective RNAi probes for gene silencing.

RNA interference (RNAi) is a process of sequence-specific posttranscriptional gene silencing mediated by double-stranded RNA. RNAi has recently emerged as a powerful genetic tool to analyze gene function in mammalian cells. The power of this method is limited however, by the uncertainty in predicting the efficacy of small interfering RNAs (siRNAs) in silencing a gene. This has imposed serious limitations not only for small-scale but also for high-throughput RNAi screening initiatives in mammalian systems. We have developed a reliable and quantitative approach for the rapid and efficient identification of the most effective siRNA against any gene. The efficacy of siRNA sequences is monitored by their ability to reduce the expression of cognate target-reporter fusions with easily quantified readouts. Finally, using micro array-based cell transfections, we demonstrate an unlimited potential of this approach in high-throughput screens for identifying effective siRNA probes for silencing genes in mammalian systems. This approach is likely to have implications in the use of RNAi as a reverse genetic tool for analyzing mammalian gene function on a genome-wide scale.

Animals↗
PubMed2001

RNAi as random degradative PCR: siRNA primers convert mRNA into dsRNAs that are degraded to generate new siRNAs.

In posttranscriptional gene silencing (PTGS), "quelling," and RNA interference (RNAi), 21-25 nucleotide RNA fragments are produced from the initiating dsRNA. These short interfering RNAs (siRNAs) mediate RNAi by an unknown mechanism. Here, we show that GFP and Pp-Luc siRNAs, isolated from a protein complex in Drosophila embryo extract, target mRNA degradation in vitro. Most importantly, these siRNAs, as well as a synthetic 21-nucleotide duplex GFP siRNA, serve as primers to transform the target mRNA into dsRNA. The nascent dsRNA is degraded to eliminate the incorporated target mRNA while generating new siRNAs in a cycle of dsRNA synthesis and degradation. Evidence is presented that mRNA-dependent siRNA incorporation to form dsRNA is carried out by an RNA-dependent RNA polymerase activity (RdRP).

Animals↗
PubMed2005

Transforming growth factor {beta} (TGF-{beta})-Smad target gene protein tyrosine phosphatase receptor type kappa is required for TGF-{beta} function.

Transforming growth factor beta (TGF-beta) inhibits proliferation and promotes cell migration. In TGF-beta-treated MCF10A mammary epithelial cells overexpressing HER2 and by chromatin immunoprecipitation, we identified novel Smad targets including protein tyrosine phosphatase receptor type kappa (PTPRK). TGF-beta up-regulated PTPRK mRNA and RPTPkappa (receptor type protein tyrosine phosphatase kappa, the protein product encoded by the PTPRK gene) protein in tumor and nontumor mammary cells; HER2 overexpression down-regulated its expression. RNA interference (RNAi) of PTPRK accelerated cell cycle progression, enhanced response to epidermal growth factor (EGF), and abrogated TGF-beta-mediated antimitogenesis. Endogenous RPTPkappa associated with EGF receptor and HER2, resulting in suppression of basal and ErbB ligand-induced proliferation and receptor phosphorylation. In MCF10A/HER2 cells, TGF-beta enhanced cell motility, FAK phosphorylation, F-actin assembly, and focal adhesion formation and inhibited RhoA activity. These responses were abolished when RPTPkappa was eliminated by RNA interference (RNAi). In cells expressing RPTPkappa RNAi, phosphorylation of Src at Tyr527 was increased and (activating) phosphorylation of Src at Tyr416 was reduced. These data suggest that (i) RPTPkappa positively regulates Src; (ii) HER2 signaling and TGF-beta-induced RPTPkappa converge at Src, providing an adequate input for activation of FAK and increased cell motility and adhesion; and (iii) RPTPkappa is required for both the antiproliferative and the promigratory effects of TGF-beta.

Actins↗
PubMed2026

Development of a Droplet-Based RNA Interference Feeding Assay for Neonates of the Citrus Root Weevil Diaprepes abbreviatus.

The citrus root weevil, Diaprepes abbreviatus, is an economically important pest of citrus and ornamental crops whose subterranean larval feeding damages roots and predisposes plants to secondary pathogen infection. Development of efficient RNA interference (RNAi) delivery methods for early larval stages is essential for functional genomics studies and the evaluation of RNAi-based pest management strategies. In this study, we developed a droplet-based feeding assay for oral delivery of double-stranded RNA (dsRNA) to neonates of D. abbreviatus using chitin synthase 2 (DaCHS2) as a model RNAi target to validate the assay. Feeding solutions containing dsRNA were supplemented with sucrose and bromophenol blue dye, with bromophenol blue used to visually confirm ingestion. Across three independent biological replicates, all neonates exposed to DaCHS2-dsRNA, GFP-dsRNA, and water control droplets were confirmed to have ingested the feeding solution (45/45 neonates per treatment; 100% feeding success). Oral delivery of dsRNA targeting DaCHS2 reduced transcript abundance and was associated with developmental abnormalities and mortality, including incomplete molting, abnormal pigmentation, cuticular deformities, defective pupation, and malformed adults. Regression analysis demonstrated moderate and significant relationship between dsRNA concentration and neonate mortality and developmental abnormalities. RT-qPCR further confirmed reduced DaCHS2 transcript abundance following oral dsRNA exposure. The developed assay provides a simple, reproducible, and minimally invasive proof-of-concept platform for oral dsRNA delivery to D. abbreviatus neonates. The assay requires only small dsRNA volumes, provides visual confirmation of ingestion, and may facilitate laboratory-based screening of additional RNAi target genes in D. abbreviatus and other coleopteran pests.

Animals↗
PubMed2004

RNA interference and double-stranded-RNA-activated pathways.

RNAi (RNA interference) has become a powerful tool to determine gene function. Different methods of expressing the short ds (double-stranded) RNA intermediates required for interference in mammalian systems have been developed, including the introduction of si (short interfering) RNAs by direct transfection or driven from transfected plasmids or lentiviral vectors encoding sh (short hairpin) RNAs. Although RNAi relies upon a high degree of specificity, recent findings suggest that off-target non-specific effects can be encountered. We found that transfection of siRNAs can results in an interferon-mediated activation of the JAK/STAT (Janus kinase/signal transducer and activator of transcription) pathway and global up-regulation of interferon-stimulated genes. This effect is mediated in part by the dsRNA-dependent protein kinase PKR, as this kinase is activated by the 21 bp siRNA, and is required in response to the siRNAs. However, the transcription factor IRF3 (interferon-regulatory factor 3) is also activated by siRNA as a primary response, resulting in the stimulation of genes independent of an interferon response. In cells deficient in IRF3, this response is blunted, but can be restored by re-introduction of IRF3. Thus siRNAs induce complex signalling responses in target cells, leading to effects beyond the selective silencing of specific genes.

Animals↗
PubMed2004

A link between mRNA turnover and RNA interference in Arabidopsis.

In RNA interference (RNAi), double-stranded RNA (dsRNA) triggers degradation of homologous messenger RNA. In many organisms, RNA-dependent RNA polymerase (RdRp) is required to initiate or amplify RNAi, but the substrate for dsRNA synthesis in vivo is not known. Here, we show that RdRp-dependent transgene silencing in Arabidopsis was caused by mutation of XRN4, which is a ribonuclease (RNase) implicated in mRNA turnover by means of decapping and 5'-3' exonucleolysis. When both XRN4 and the RdRp were mutated, the plants accumulated decapped transgene mRNA. We propose that mRNAs lacking a cap structure become exposed to RdRp to initiate or maintain RNAi.

Animals↗
PubMed2003

RNA interference in mammalian cells by chemically-modified RNA.

RNA interference (RNAi) is proving to be a robust and versatile technique for controlling gene expression in mammalian cells. To fully realize its potential in vivo, however, it may be necessary to introduce chemical modifications to optimize potency, stability, and pharmacokinetic properties. Here, we test the effects of chemical modifications on RNA stability and inhibition of gene expression. We find that RNA duplexes containing either phosphodiester or varying numbers of phosphorothioate linkages are remarkably stable during prolonged incubations in serum. Treatment of cells with RNA duplexes containing phosphorothioate linkages leads to selective inhibition of gene expression. RNAi also tolerates the introduction of 2'-deoxy-2'-fluorouridine or locked nucleic acid (LNA) nucleotides. Introduction of LNA nucleotides also substantially increases the thermal stability of modified RNA duplexes without compromising the efficiency of RNAi. These results suggest that inhibition of gene expression by RNAi is compatible with a broad spectrum of chemical modifications to the duplex, affording a wide range of useful options for probing the mechanism of RNAi and for improving RNA interference in vivo.

Blotting, Western↗
PubMed2006

[Gene silencing RNAi technology: possible application to therapy].

RNA interference (RNAi), i.e. gene silencing, or gene expression down-regulation is the process whereby a double-stranded RNA (dsRNA) induces the homology-dependent degradation of cognate messenger RNA (mRNA). When dsRNA is introduced into cells, an RNA-induced silencing complex (RISC) is assembled. RISC serves as cellular machinery that is responsible for the specific mRNA degradation. This process results in the subsequent reduction of the specific protein translated from appropriate mRNA. Short RNA duplexes (21 nucleotide), called small interfering RNA (siRNA), have become the major tool for induction of gene silencing. With the human genome mapped and sequenced, attempts are currently being made to manipulate the expression of genes involved in viral diseases, carcinogenesis and other disorders with the aim of developing novel therapies.

Chromosome Mapping↗