Genome-wide CRISPR guide RNA design and specificity analysis with GuideScan2
Ontology highlight
ABSTRACT:
ORGANISM(S): Mus musculus Homo sapiens
PROVIDER: GSE285667 | GEO | 2025/01/08
REPOSITORIES: GEO
Similar Datasets
Project description:Background: The CRISPR/Cas9 toolbox has recently been expanded to include approaches for modulating gene expression. To successfully build on this work, and apply it for answering biological questions, it is important to establish it in a broad range of circumstances. Genome-scale CRISPR interference (CRISPRi) has been used in human cells lines, however the rules for designing effective guide RNAs (gRNAs) in different organisms are not well known. We sought to determine rules that determine gRNA effectiveness at transcriptional repression in Saccharomyces cerevisiae. Results: We created an inducible single plasmid CRISPRi system for gene repression in yeast, and used it to analyze fitness effects of gRNAs under 18 small molecule treatments. Our approach correctly identified previously-described chemical-genetic interactions, as well as a new mechanism of suppressing fluconazole toxicity by repression of the ERG25 gene. Assessment of multiple target loci across treatments allowed us to determine generalizable features associated with gRNA efficacy. Guides that target regions with low nucleosome occupancy and high chromatin accessibility were clearly more effective. We also found the best region to target gRNAs was between the transcription start site (TSS) and 200bp upstream of the TSS. Finally, unlike nuclease-proficient Cas9 in human cells, point mutations were tolerated equally well by truncated (18 nt specificity sequence) and full length (20 nt) gRNAs, however, 18 nt gRNAs were generally less potent than full length gRNAs. Conclusions: Our results establish a powerful functional genomics screening method, provide rules for designing effective gRNAs for gene repression, and show that 18 nt and 20 nt gRNAs exhibit similar tolerance to mismatches in the target sequence. These findings will enable effective library design and genome-wide screening in many genetic backgrounds. An expression construct was created for inducible CRISPRi in yeast. Key features include ORFs expressing dCas9-Mxi1 and the tetracycline repressor (TetR), as well as a tetracycline inducible gRNA locus containing the RPR1 promoter with a TetO site, a NotI site for cloning new gRNA specificity sequences, and the constant part of the gRNA. When yeast containing this plasmid are grown in the absence of anhydrotetracycline (ATc) TetR binds the gRNA promoter and prevents PolIII from binding and transcribing the gRNA. This in turn prevents dCas9-Mxi1 from binding the target site. In the presence of ATc, TetR dissociates and gRNA is expressed, allowing dCas9-Mxi1 to bind its target locus, and repress gene expression. gRNA libraries were cloned into this construct and transformed into yeast to create pools. Experiments were conducted in which yeast pools were grown in inducing (+ATc) and non-inducing conditions (-ATc) in the presence of different drugs. After multiple generations of growth in these conditions, yeast plasmids were minipreped and the gRNA locus was PCRed and sequenced via MiSeq. Counts of each gRNA were compared in different conditions.
2016-01-18 | E-GEOD-71490 | biostudies-arrayexpress
Project description:Type VI CRISPR enzymes are RNA-targeting proteins with nuclease activity that enable specific and robust target gene knockdown without altering the genome. To define rules for the design of Cas13d guide RNAs, we conducted massively parallel screens targeting messenger RNAs of a green fluorescent protein transgene, and CD46, CD55 and CD71 cell-surface proteins in human cells. In total, we measured the activity of 24,460 gRNAs with and without mismatches relative to the target sequences. Knockdown efficacy is driven by gRNA-specific features and target site context. Single mismatches generally reduce knockdown to a modest degree, but spacer nucleotides 15–21 are largely intolerant of target site mismatches. We developed a computational model to identify optimal gRNAs and confirm their generalizability testing 3,979 guides targeting mRNAs of 48 endogenous genes. We show that Cas13 can be used in forward transcriptomic pooled screens and, using our model, predict optimized Cas13 gRNAs for all protein-coding transcripts in the human genome.
2020-01-30 | GSE142675 | GEO
Project description:Background: The CRISPR/Cas9 toolbox has recently been expanded to include approaches for modulating gene expression. To successfully build on this work, and apply it for answering biological questions, it is important to establish it in a broad range of circumstances. Genome-scale CRISPR interference (CRISPRi) has been used in human cells lines, however the rules for designing effective guide RNAs (gRNAs) in different organisms are not well known. We sought to determine rules that determine gRNA effectiveness at transcriptional repression in Saccharomyces cerevisiae. Results: We created an inducible single plasmid CRISPRi system for gene repression in yeast, and used it to analyze fitness effects of gRNAs under 18 small molecule treatments. Our approach correctly identified previously-described chemical-genetic interactions, as well as a new mechanism of suppressing fluconazole toxicity by repression of the ERG25 gene. Assessment of multiple target loci across treatments allowed us to determine generalizable features associated with gRNA efficacy. Guides that target regions with low nucleosome occupancy and high chromatin accessibility were clearly more effective. We also found the best region to target gRNAs was between the transcription start site (TSS) and 200bp upstream of the TSS. Finally, unlike nuclease-proficient Cas9 in human cells, point mutations were tolerated equally well by truncated (18 nt specificity sequence) and full length (20 nt) gRNAs, however, 18 nt gRNAs were generally less potent than full length gRNAs. Conclusions: Our results establish a powerful functional genomics screening method, provide rules for designing effective gRNAs for gene repression, and show that 18 nt and 20 nt gRNAs exhibit similar tolerance to mismatches in the target sequence. These findings will enable effective library design and genome-wide screening in many genetic backgrounds.
2016-01-18 | GSE71490 | GEO
Project description:Alternative splicing is an essential mechanism for diversifying proteins, with different mature RNA isoforms producing different proteins with potentially distinct functions. Two major challenges in characterizing the cellular function of isoforms are the lack of both experimental methods to specifically and efficiently modulate isoform expression and computational tools for complex experimental design. To address these gaps, we developed and methodically tested a strategy which pairs the RNA-targeting CRISPR/Cas13d system with guide RNAs (gRNAs) that overlap exon-exon junctions in the mature RNA. We perform a high-throughput essentiality screen, numerous qPCR assays, and PacBio long read sequencing to affirm that our strategy works to specifically target the unique junctions of isoforms to robustly knockdown their RNA. In parallel, we provide computational tools for experimental design and screen analysis. Considering all possible splice junctions in current GENCODE annotations and our predictions of gRNA efficacy, we estimate that this strategy can target 94% of all human isoforms, including 29,238 protein-coding and 9,638 lncRNA isoforms that are specifically targetable with a gRNA spanning a unique splice junction.
2023-09-13 | GSE242105 | GEO
Project description:Alternative splicing is an essential mechanism for diversifying proteins, with different mature RNA isoforms producing different proteins with potentially distinct functions. Two major challenges in characterizing the cellular function of isoforms are the lack of both experimental methods to specifically and efficiently modulate isoform expression and computational tools for complex experimental design. To address these gaps, we developed and methodically tested a strategy which pairs the RNA-targeting CRISPR/Cas13d system with guide RNAs (gRNAs) that overlap exon-exon junctions in the mature RNA. We perform a high-throughput essentiality screen, numerous qPCR assays, and PacBio long read sequencing to affirm that our strategy works to specifically target the unique junctions of isoforms to robustly knockdown their RNA. In parallel, we provide computational tools for experimental design and screen analysis. Considering all possible splice junctions in current GENCODE annotations and our predictions of gRNA efficacy, we estimate that this strategy can target 94% of all human isoforms, including 29,238 protein-coding and 9,638 lncRNA isoforms that are specifically targetable with a gRNA spanning a unique splice junction.
2023-09-13 | GSE242104 | GEO
Project description:Alternative splicing is an essential mechanism for diversifying proteins, with different mature RNA isoforms producing different proteins with potentially distinct functions. Two major challenges in characterizing the cellular function of isoforms are the lack of both experimental methods to specifically and efficiently modulate isoform expression and computational tools for complex experimental design. To address these gaps, we developed and methodically tested a strategy which pairs the RNA-targeting CRISPR/Cas13d system with guide RNAs (gRNAs) that overlap exon-exon junctions in the mature RNA. We perform a high-throughput essentiality screen, numerous qPCR assays, and PacBio long read sequencing to affirm that our strategy works to specifically target the unique junctions of isoforms to robustly knockdown their RNA. In parallel, we provide computational tools for experimental design and screen analysis. Considering all possible splice junctions in current GENCODE annotations and our predictions of gRNA efficacy, we estimate that this strategy can target 94% of all human isoforms, including 29,238 protein-coding and 9,638 lncRNA isoforms that are specifically targetable with a gRNA spanning a unique splice junction.
2023-09-13 | GSE242106 | GEO
Project description:Novel single cell RNA-seq analysis combined with CRISPR screens enables the high- throughput characterization of transcriptional changes caused by genetic perturbations. Dedicated software to annotate CRISPR guide RNA (gRNA) libraries and associate them with single cell transcriptomes are however lacking. Here, we generated a CRISPR droplet sequencing dataset. We demonstrate that the current default tool fails to detect mutant gRNAs. We therefore developed GiRAFR, a pysam-based software tool to characterize intact and mutant gRNAs. We show that mutant gRNAs are dysfunctional, and failure to detect and annotate them leads to an inflated estimate of the number of untransformed cells as well as an underestimated multiplet frequency. These findings are mirrored in publicly available datasets, where we find that up to 34 % of cells are transduced with a mutant gRNA. Applying GiRAFR hence stands to improve the annotation and quality of single cell CRISPR screens.
2023-09-29 | GSE216040 | GEO
Project description:Recent technological developments in single-cell RNA-seq CRISPR screens enable high-throughput investigation of the genome. Through transduction of a gRNA library to a cell population followed by transcriptomic profiling by scRNA-seq, it is possible to characterize the effects of thousands of genomic perturbations on global gene expression. A major source of noise in scRNA-seq CRISPR screens are ambient gRNAs, which are contaminating gRNAs that likely originate from other cells. If not properly filtered, ambient gRNAs can result in an excess of false positive gRNA assignments. Here, we utilize CRISPR barnyard assays to characterize ambient gRNA noise in single-cell CRISPR screens. We use these datasets to develop and train CLEANSER, a mixture model that identifies and filters ambient gRNA noise. This model takes advantage of the bimodal distribution between native and ambient gRNAs and includes both gRNA and cell-specific normalization parameters, correcting for confounding technical factors that affect individual gRNAs and cells. The output of CLEANSER is the probability that a gRNA-cell assignment is in the native distribution over the ambient distribution. We find that ambient gRNA filtering methods impact differential gene expression analysis outcomes and that CLEANSER outperforms alternate approaches by increasing gRNA-cell assignment accuracy.
2024-10-08 | GSE272457 | GEO
Project description:Recent technological developments in single-cell RNA-seq CRISPR screens enable high-throughput investigation of the genome. Through transduction of a gRNA library to a cell population followed by transcriptomic profiling by scRNA-seq, it is possible to characterize the effects of thousands of genomic perturbations on global gene expression. A major source of noise in scRNA-seq CRISPR screens are ambient gRNAs, which are contaminating gRNAs that likely originate from other cells. If not properly filtered, ambient gRNAs can result in an excess of false positive gRNA assignments. Here, we utilize CRISPR barnyard assays to characterize ambient gRNA noise in single-cell CRISPR screens. We use these datasets to develop and train CLEANSER, a mixture model that identifies and filters ambient gRNA noise. This model takes advantage of the bimodal distribution between native and ambient gRNAs and includes both gRNA and cell-specific normalization parameters, correcting for confounding technical factors that affect individual gRNAs and cells. The output of CLEANSER is the probability that a gRNA-cell assignment is in the native distribution over the ambient distribution. We find that ambient gRNA filtering methods impact differential gene expression analysis outcomes and that CLEANSER outperforms alternate approaches by increasing gRNA-cell assignment accuracy.
2024-10-08 | GSE272454 | GEO
Project description:Cas9, a CRISPR RNA-guided nuclease, has been rapidly adopted as a tool for biochemical and genetic manipulation of DNA. Although Cas9 offers remarkable specificity and versatility for genome manipulation, mis-targeted events occur. To extend the understanding of Cas9 target::homology requirements, we compared mismatch tolerance for a specific Cas9::gRNA complex in vitro and in vivo (in Saccharomyces cerevisiae). A variety of truncated and full-length gRNAs (with 17, 18, and 20 nucleotides of complementarity sequence) were used. In each case, we observed notable differences between in vitro and in vivo Cas9 cleavage specificity profiles, with a more stringent effect of mismatches on activity seen in vivo. Increased specificity of the 18 nt complementarity truncated gRNA was evident in vivo, but not in vitro. Overall, this study highlights differences in the specificity of Cas9 cleavage between controlled in vitro conditions and complex and chromatinized in vivo conditions. We adapted a previous high throughput sequencing approach (doi: 10.1093/nar/gku1102) to assess the effects of single base variants in vivo. We used a polymorphic random variant library matched to a specific trigger sequence (for which we used a segment from the C. elegans unc-22 gene, previously designated âunc-22Aâ (doi: 10.1093/nar/gku1102). Cas9 in vivo and in vitro assays were carried out with four different gRNAs incorporating sequence from the unc-22A trigger segment. The four segments incorporate 17 nt, 18 nt, 20 nt, and 20+G nt of unc-22A complementarity respectively. The retention is calculated based on PMID: 25399416. File names denote the experiment-> gRNAname_gRNAlength_(invitro or invivo)_(incubation or induction time)_IlluminaRunID.dat The files contain all normalized sequences in column one with their calculated retentions in column 2.
2016-06-10 | E-GEOD-79667 | biostudies-arrayexpress