Small interfering RNA production by enzymatic engineering of DNA (SPEED).
ABSTRACT: Small interfering RNAs (siRNAs) potently silence expression of target genes. In principle siRNA libraries can be used to perform effective genome-scale functional genetic screens in mammalian cells, but their development has been hampered by the need to chemically synthesize thousands of oligonucleotides and to incorporate them into expression vectors. We have developed a technology to efficiently convert a double-stranded cDNA library into a retroviral siRNA library in which 21-base siRNAs are produced in infected cells at high levels and efficiently block expression of their target genes. The key steps are the generation of random cDNA fragments that are fused to a hairpin linker, cleavage with the MmeI endonuclease that creates 20- to 21-bp cDNA fragments, conversion to a double-stranded DNA that contains two copies of the cDNA insert in a head-to-head palindrome, and insertion of the construct downstream of a polymerase III promoter. We constructed a siRNA library with 3 x 10(6) clones from a mouse embryo cDNA library; siRNAs were found against many different genes; and multiple siRNAs can be generated from a single mRNA. We further showed that specific siRNAs were efficiently produced in stably infected mammalian cells and resulted in significant and specific reduction of their target mRNAs. Because no prior knowledge about target transcripts is needed, a cDNA-derived siRNA library will generate siRNAs against unknown transcripts and genes. Finally, cDNA-derived siRNA libraries can be readily generated from any cell type or species, enabling genome-wide functional screens in many biological systems.
Project description:The use of small interfering RNAs (siRNAs) to silence target gene expression has greatly facilitated mammalian genetic analysis by generating loss-of-function mutants. In recent years, high-throughput, genome-wide screening of siRNA libraries has emerged as a viable approach. Two different methods have been used to generate short hairpin RNA (shRNA) libraries; one is to use chemically synthesized oligonucleotides, and the other is to convert complementary DNAs (cDNAs) into shRNA cassettes enzymatically. The high cost of chemical synthesis and the low efficiency of the enzymatic approach have hampered the widespread use of screening with shRNA libraries.We report here an improved method for constructing genome-wide shRNA libraries enzymatically. The method includes steps of cDNA fragmentation and endonuclease MmeI digestion to generate 19-bp fragments, capping the 19-bp cDNA fragments with a hairpin oligonucleotide, and amplification of the hairpin structures by PCR. The PCR step converts hairpins into double-stranded DNAs that contain head-to-head cDNA fragments that can be cloned into a vector downstream of a Pol III promoter.This method can readily be used to generate shRNA libraries from a small amount of mRNA and thus can be used to create cell- or tissue-specific libraries.
Project description:A number of groups have developed libraries of siRNAs to identify genes through functional genomics. While these studies have validated the approach of making functional RNAi libraries to understand fundamental cellular mechanisms, they require information and knowledge of existing sequences since the RNAi sequences are generated synthetically. An alternative strategy would be to create an RNAi library from cDNA. Unfortunately, the complexity of such a library of siRNAs would make screening difficult. To reduce the complexity, longer dsRNAs could be used; however, concerns of induction of the interferon response and off-target effects of long dsRNAs have prevented their use. As a first step in creating such libraries, long dsRNA was expressed in mammalian cells. The 250 nt dsRNAs were capable of efficiently silencing a luciferase reporter gene that was stably transfected in MDA-MB-231 cells without inducing the interferon response or off-target effects any more than reported for siRNAs. In addition, a long dsRNA expressed in the same cell line was capable of silencing endogenous c-met expression and inhibited cell migration, whereas the dsRNA against luciferase had no effect on c-met or cell migration. The studies suggest that large dsRNA libraries are feasible and that functional selection of genes will be possible.
Project description:We have develped a novel method of making siRNAs (named pro-siRNA for prokaryotic siRNA). To evaluate off-targeting of pro-siRNA, we compared the mRNA expression profiles of HeLa-d1EGFP cells transfected with 4 nM EGFP siRNAs and pro-siRNAs by microarray. We used microarray to study the off-target effect of siRNAs in the HeLa-d1EGFP cell line. After transfection of siRNAs for 24 hrs, RNA were extracted using Trizol. Deep sequencing libraries were generated using the NEBNext Ultra RNA Library Prep Kit for Illumina (NEB #E7530).
Project description:RNA interference (RNAi) libraries screens have become widely used for small RNA (sRNA) therapeutic targets development. However, conventional enzymatically libraries, typically prepared using the type 2 restriction enzyme MmeI, produce sRNAs between 18 and 20?bp, much shorter than the usual lengths of 19-23?bp. Here we develop a size unbiased representative enzymatically generated RNAi (SURER) library, which employs type 3 restriction modification enzyme EcoP15I to produce sRNAs ranging from 19 to 23?bp using a group of rationally designed linkers, which can completely mimic the length of sRNAs naturally generated by Dicer enzyme in living cells, and the screening results of SURER libraries showed high recombination rate and knockdown efficiency. SURER library provides a useful tool for RNAi therapeutics screening in a fast and simple way.
Project description:Systematic genetic perturbation screening in human cells remains technically challenging. Typically, large libraries of chemically synthesized siRNA oligonucleotides are used, each designed to degrade a specific cellular mRNA via the RNA interference (RNAi) mechanism. Here, we report on data from three genome-wide siRNA screens, conducted to uncover host factors required for infection of human cells by two bacterial and one viral pathogen. We find that the majority of phenotypic effects of siRNAs are unrelated to the intended "on-target" mechanism, defined by full complementarity of the 21-nt siRNA sequence to a target mRNA. Instead, phenotypes are largely dictated by "off-target" effects resulting from partial complementarity of siRNAs to multiple mRNAs via the "seed" region (i.e., nucleotides 2-8), reminiscent of the way specificity is determined for endogenous microRNAs. Quantitative analysis enabled the prediction of seeds that strongly and specifically block infection, independent of the intended on-target effect. This prediction was confirmed experimentally by designing oligos that do not have any on-target sequence match at all, yet can strongly reproduce the predicted phenotypes. Our results suggest that published RNAi screens have primarily, and unintentionally, screened the sequence space of microRNA seeds instead of the intended on-target space of protein-coding genes. This helps to explain why previously published RNAi screens have exhibited relatively little overlap. Our analysis suggests a possible way of identifying "seed reagents" for controlling phenotypes of interest and establishes a general strategy for extracting valuable untapped information from past and future RNAi screens.
Project description:RNA-seq has been widely adopted as a gene-expression measurement tool due to the detail, resolution, and sensitivity of transcript characterization that the technique provides. Here we present two transposon-based methods that efficiently construct high-quality RNA-seq libraries. We first describe a method that creates RNA-seq libraries for Illumina sequencing from double-stranded cDNA with only two enzymatic reactions. We generated high-quality RNA-seq libraries from as little as 10 pg of mRNA (?1 ng of total RNA) with this approach. We also present a strand-specific RNA-seq library construction protocol that combines transposon-based library construction with uracil DNA glycosylase and endonuclease VIII to specifically degrade the second strand constructed during cDNA synthesis. The directional RNA-seq libraries maintain the same quality as the nondirectional libraries, while showing a high degree of strand specificity, such that 99.5% of reads map to the expected genomic strand. Each transposon-based library construction method performed well when compared with standard RNA-seq library construction methods with regard to complexity of the libraries, correlation between biological replicates, and the percentage of reads that align to the genome as well as exons. Our results show that high-quality RNA-seq libraries can be constructed efficiently and in an automatable fashion using transposition technology.
Project description:We determined the genome-wide digital gene expression (DGE) profiles of primary acute lymphoblastic leukemia (ALL) cells from 28 patients and fractionated blood cells from healthy blood donors taking advantage of “second generation” sequencing technology. The patients included in the study represent distinct subtypes of B-cell precursor (BCP) ALL and T-cell lineage ALL (T-ALL) and the controls are fractionated CD19+ and CD3+ cells. Gene expression analysis of 28 ALL patient samples with different immunophenotypic backgrounds including T-ALL (n=4) and patients with BCP ALL with diverse cytogenetic backgrounds: High Hyperploidy (HeH) (n=10), t(9;22) BCR-ABL1 (n=3), t(12;21) ETV6-RUNX1 (n=4), dic(9;20) (n=3), t(1;19)TCF3-PBX1, MLL/11q23 (n=1) and undefined/non-recurrent aberrations (n=1). Fractionated b-cells (CD19+) and t-cells (CD3+) isolated from peripheral blood of healthy donors were used as controls. Sequencing libraries were prepared from 1 µg of total RNA using reagents from the NlaIII Digital Gene Expression Tag Profiling kit (Illumina Inc, San Diego, CA, USA). mRNA was captured on magnetic oligo(dT) beads and reverse transcribed into double-stranded cDNA. The cDNA was cleaved using the restriction enzyme NlaIII. An adapter sequence containing the recognition sequence for the restriction enzyme MmeI was ligated to the NlaIII cleavage sites. The adapter-ligated cDNA was digested with MmeI to release the cDNA from the magnetic bead, while leaving 17 base-pairs of sequence in the fragment. The fragments were dephosphorylated and purified by phenol-chloroform. A second adapter was ligated at the MmeI cleavage sites. The adapter-ligated cDNA fragments were amplified by PCR, and the PCR products were purified on a 6% polyacrylamide gel. The ~96 base pair PCR products were excised from the gel and eluted overnight, followed by ethanol precipitation and re-suspension. Purified libraries were quality controlled and quantified on a Bioanalyzer using DNA 1000 series or High Sensitivity chips. The DGE libraries were diluted to a 10 nM concentration and sequenced on one lane of an Illumina GAII or GAIIx for 18 cycles.
Project description:High-throughput siRNA screens were only recently applied to cell factories to identify novel engineering targets which are able to boost cells towards desired phenotypes. While siRNA libraries exist for model organisms such as mice, no CHO-specific library is publicly available, hindering the application of this technique to CHO cells. The optimization of these cells is of special interest, as they are the main host for the production of therapeutic proteins. Here, we performed a cross-species approach by applying a mouse whole-genome siRNA library to CHO cells, optimized the protocol for suspension cultured cells, as this is the industrial practice for CHO cells, and developed an in silico method to identify functioning siRNAs, which also revealed the limitations of using cross-species libraries. With this method, we were able to identify several genes that, upon knockdown, enhanced the total productivity in the primary screen. A second screen validated two of these genes, Rad21 and Chd4, whose knockdown was tested in additional CHO cell lines, confirming the induced high productivity phenotype, but also demonstrating the cell line/clone specificity of engineering effects.
Project description:We employed next generation sequencing to examine whether knocking down the steroid receptor RNA activator (SRA) gene significantly affect the expression levels of certain genes in MCF-7 cells. MCF-7 cells were transfected with either a pool of four non-target control siRNAs or a pool of four SRA siRNAs for 32 hrs. 157 million reads were generated from triplicate samples of the control group; 151 million reads were generated from triplicate samples of the SRA knockdown group. Six genes were identified as significantly changed in the expression levels with the cutoff of q value ≤ 0.05, fold change ≤ 0.5 or ≥ 2, and reads per kilobase per million mapped reads (RPKM) ≥ 1. However, except for SRA itself, the other five genes were shown by real-time PCR to be only affected by one siRNA in the SRA siRNA pool. Further analysis of this dataset with different cuttoff setting may reveal true SRA-regulated genes in MCF-7. MCF-7 cells were cultured in high glucose DMEM with 10% fetal bovine serum, 2 mM Glutamax-1, 100 units/ml penicillin and 100 μg/ml streptomycin. ON-TARGETplus SMARTpool for human SRA (Thermo Scientific, L-027192-00-0005) was used to knockdown SRA (siSRA) and ON-TARGETplus Non-targeting Pool Thermo Scientific, D-001810-10-05) was used as a negative control (siCtrl). A total of 25 nM siRNA was transfected in 6-well dishes using Lipofectamine™ RNAiMAX Reagent (Life Technologies, Invitrogen) following the manufacturer’s recommendations. Polyadenylated RNA was purified from the cells 32 hrs after transfection. cDNA libraries were prepared and double-stranded cDNA was fragmented using DNase I according to Illumina specifications, prior to adaptor ligation. Sequencing libraries were amplified and sequenced using an Illumina HiSeq 2000 sequencer.
Project description:BACKGROUND:RNA interference (RNAi) screens have been used to identify novel components of signal-transduction pathways in a variety of organisms. We performed a small interfering (si)RNA screen for novel members of the transforming growth factor (TGF)-? pathway in a human keratinocyte cell line. The TGF-? pathway is integral to mammalian cell proliferation and survival, and aberrant TGF-? responses have been strongly implicated in cancer. RESULTS:We assayed how strongly single siRNAs targeting each of 6,000 genes affect the nuclear translocation of a green fluorescent protein (GFP)-SMAD2 reporter fusion protein. Surprisingly, we found no novel TGF-? pathway members, but we did find dominant off-target effects. All siRNA hits, whatever their intended direct target, reduced the mRNA levels of two known upstream pathway components, the TGF-? receptors 1 and 2 (TGFBR1 and TGFBR2), via micro (mi)RNA-like off-target effects. The scale of these off-target effects was remarkable, with at least 1% of the sequences in the unbiased siRNA library having measurable off-target effects on one of these two genes. It seems that relatively minor reductions of message levels via off-target effects can have dominant effects on an assay, if the pathway output is very dose-sensitive to levels of particular pathway components. In search of mechanistic details, we identified multiple miRNA-like sequence characteristics that correlated with the off-target effects. Based on these results, we identified miR-20a, miR-34a and miR-373 as miRNAs that inhibit TGFBR2 expression. CONCLUSIONS:Our findings point to potential improvements for miRNA/siRNA target prediction methods, and suggest that the type II TGF-? receptor is regulated by multiple miRNAs. We also conclude that the risk of obtaining misleading results in siRNA screens using large libraries with single-assay readout is substantial. Control and rescue experiments are essential in the interpretation of such screens, and improvements to the methods to reduce or predict RNAi off-target effects would be beneficial.