scholarly journals Crossing enhanced and high fidelity SpCas9 nucleases to optimize specificity and cleavage

2017 ◽  
Author(s):  
Péter István Kulcsér ◽  
András Tálas ◽  
Krisztina Huszár ◽  
Zoltán Ligeti ◽  
Eszter Tóth ◽  
...  
Keyword(s):  
Dna Binding ◽  
Streptococcus Pyogenes ◽  
High Fidelity ◽  
Prediction Tools ◽  
Target Activity ◽  
Target Effects

AbstractBackgroundThe propensity for off-target activity of Streptococcus pyogenes Cas9 (SpCas9) has been considerably decreased by rationally engineered variants with increased fidelity (eSpCas9; SpCas9-HF1). However, a subset of targets still generate considerable off-target effects. To deal specifically with these targets, we generated new "Highly enhanced Fidelity" nuclease variants (HeFSpCas9s) containing mutations from both eSpCas9 and SpCas9-HF1 and examined these improved nuclease variants side-by-side, to decipher the factors that affect their specificities and to determine the optimal nuclease for applications sensitive to off-target effects.ResultsThese three increased-fidelity nucleases can routinely be used only with perfectly matching 20 nucleotide-long spacers; a matching 5' G extension being more detrimental to their activities than a mismatching one. HeFSpCas9s exhibit substantially improved specificity specifically for those targets for which eSpCas9 and SpCas9-HF1 have higher off-target propensity. There is also a ranking among the targets by their cleavability and off-target effects manifested by the increased fidelity nucleases. Furthermore, we show that the mutations in these variants may diminish the cleavage, but not the DNA-binding, of SpCas9s.ConclusionsNo single nuclease variant shows generally superior fidelity; instead, for highest specificity cleavage, each target needs to be matched with an appropriate high fidelity nuclease. We provide here a framework for generating new nuclease variants for targets that currently have no matching optimal nuclease, and offer a simple mean for identifying the optimal nuclease for targets in the absence of accurate target-ranking prediction tools.

scholarly journals Improving the specificity of adenine base editor using high-fidelity Cas9

2019 ◽  
Author(s):  
Ruisha Hong ◽  
Sidi Ma ◽  
Feng Wang
Keyword(s):  
Gene Therapy ◽  
Streptococcus Pyogenes ◽  
Genomic Dna ◽  
High Fidelity ◽  
Wild Type ◽  
Sequencing Data ◽  
Deep Sequencing Data ◽  
Target Sites ◽  
Target Activity ◽  
Adenine Base

ABSTRACTAdenine base editor (ABE) mediates the conversion of A to G in genomic DNA. In human, approximately 47.8% of known pathogenic SNPs can be corrected by A to G conversion, indicating that ABE have tremendous potential in gene therapy. However, the off-target activity of ABE limits its clinical application. ABE off-target activity in DNA is depended on the bonding of Streptococcus pyogenes Cas9 (SpCas9) on off-target sites [1, 2]. Therefore, using high-fidelity Cas9 should be able to improve the specificity of ABE. Based on this, we replaced the wild-type SpCas9 in ABE7.10 with four high-fidelity Cas9s to improve its specificity. The analysis of target deep sequencing data demonstrate that the specificity of e-ABE is substantially improved compared to conventional ABE7.10 in four test sites. But the broad editing window of ABE hampers its application, ABE needs to be optimized to get variants with narrow editing window.

scholarly journals Cas12a is a dynamic and precise RNA-guided nuclease without off-target activity on λ-DNA

2021 ◽  
Author(s):  
Bijoya Paul ◽  
Loic Chaubet ◽  
Emma Verver ◽  
Guillermo Montoya
Keyword(s):  
Dna Binding ◽  
Genome Editing ◽  
Optical Tweezers ◽  
Target Site ◽  
Target Dna ◽  
Multiple Binding ◽  
Target Sites ◽  
Dna Binding And Cleavage ◽  
Target Activity ◽  
Insight Into

Cas12a is an RNA-guided endonuclease that is emerging as a powerful genome-editing tool. Here we combined optical tweezers with fluorescence to monitor Cas12a binding onto λ-DNA, providing insight into its DNA binding and cleavage mechanisms. At low forces Cas12a binds DNA specifically with two off-target sites, while at higher forces numerous binding events appear driven by the mechanical distortion of the DNA and partial matches to the crRNA. Despite the multiple binding events, cleavage is only observed on the target site at low forces, when the DNA is flexible. Activity assays show that the preferential off-target sites are not cleaved, and the λ-DNA is severed at the target site. This precision is also observed in Cas12a variants where the specific dsDNA and the unspecific ssDNA cleavage are dissociated or nick the target DNA. We propose that Cas12a and its variants are precise endonucleases that efficiently scan the DNA for its target but only cleave the selected site in the λ-DNA.

scholarly journals Ultra-deep sequencing reveals no evidence of oncogenic mutations or enrichment by ex vivo CRISPR/Cas9 genome editing in human hematopoietic stem and progenitor cells

2021 ◽  
Author(s):  
M. Kyle Cromer ◽  
Valentin V. Barsan ◽  
Erich Jaeger ◽  
Mengchi Wang ◽  
Jessica P. Hampton ◽  
...  
Keyword(s):  
Genome Editing ◽  
Deep Sequencing ◽  
Limit Of Detection ◽  
Ex Vivo ◽  
High Fidelity ◽  
Seed Region ◽  
Hematopoietic Stem ◽  
Oncogenic Mutations ◽  
Ex Vivo Culture ◽  
Target Activity

As CRISPR-based therapies enter the clinic, evaluation of the safety remains a critical and still active area of study. While whole genome sequencing is an unbiased method for identifying somatic mutations introduced by ex vivo culture and genome editing, this methodology is unable to attain sufficient read depth to detect extremely low frequency events that could result in clonal expansion. As a solution, we utilized an exon capture panel to facilitate ultra-deep sequencing of >500 tumor suppressors and oncogenes most frequently altered in human cancer. We used this panel to investigate whether transient delivery of high-fidelity Cas9 protein targeted to three different loci (using guide RNAs (gRNAs) corresponding to sites at AAVS1, HBB, and ZFPM2) at day 4 and day 10 timepoints post-editing resulted in the introduction or enrichment of oncogenic mutations. In three separate primary human HSPC donors, we identified a mean of 1,488 variants per Cas9 treatment (at <0.07% limit of detection). After filtering to remove germline and/or synonymous changes, a mean of 3.3 variants remained per condition, which were further reduced to six total mutations after removing variants in unedited treatments. Of these, four variants resided at the predicted off-target site in the myelodysplasia-associated EZH2 gene that were subject to ZFPM2 gRNA targeting in Donors 2 and 3 at day 4 and day 10 timepoints. While Donor 1 displayed on-target cleavage at ZFPM2, we found no off-target activity at EZH2. Sanger sequencing revealed a homozygous single nucleotide polymorphism (SNP) at position 14bp distal from the Cas9 protospacer adjacent motif in EZH2 that eliminated any detectable off-target activity. We found no evidence of exonic off-target INDELs with either of the AAVS1 or HBB gRNAs. These findings indicate that clinically relevant delivery of high-fidelity Cas9 to primary HSPCs and ex vivo culture up to 10 days does not introduce or enrich for tumorigenic variants and that even a single SNP outside the seed region of the gRNA protospacer is sufficient to eliminate Cas9 off-target activity with this method of delivery into primary, repair competent human HSPCs.

scholarly journals Optimized sgRNA design by deep learning to balance the off-target effects and on-target activity of CRISPR/Cas9

2020 ◽  
Author(s):  
Jie Lan ◽  
Yang Cui ◽  
Xiaowen Wang ◽  
Guangtao Song ◽  
Jizhong Lou
Keyword(s):  
Dna Sequences ◽  
Large Scale ◽  
Prediction Models ◽  
Design Tool ◽  
Biological Study ◽  
Support Vector ◽  
Neuron Network ◽  
Sgrna Design ◽  
Target Activity ◽  
Target Effects

ABSTRACTThe CRISPR/Cas9 system derived from bacteria especially Streptococcus pyogenes (SpyCas9) is currently considered as the most advanced tool used for numerous areas of biological study in which it is useful to target or modify specific DNA sequences. However, low on-target cleavage efficiency and off-target effects impede its wide application. Several different sgRNA design tools for SpyCas9 by using various algorithms have been developed, including linear regression model, support vector machine (SVM) model and convolutional neuron network model. While the deep insight into the sgRNA features contributing for both on-target activity and off-target still remains to be determined. Here, with public large-scale CRISPR screen data, we evaluated contribution of different features influence sgRNA activity and off-target effects, and developed models for sgRNA off-target evaluation and on-target activity prediction. In addition, we combined both activity and off-target prediction models and packaged them as an online sgRNA design tool, OPT-sgRNA.

scholarly journals Blackjack mutations improve the on-target activities of increased fidelity variants of SpCas9 with 5′G-extended sgRNAs

2020 ◽  
Vol 11 (1) ◽  
Author(s):  
Péter István Kulcsár ◽  
András Tálas ◽  
Eszter Tóth ◽  
Antal Nyeste ◽  
Zoltán Ligeti ◽  
...  
Keyword(s):  
Target Space ◽  
Target Activity ◽  
Target Effects

AbstractIncreased fidelity mutants of the SpCas9 nuclease constitute the most promising approach to mitigating its off-target effects. However, these variants are effective only in a restricted target space, and many of them are reported to work less efficiently when applied in clinically relevant, pre-assembled, ribonucleoprotein forms. The low tolerance to 5′-extended, 21G-sgRNAs contributes, to a great extent, to their decreased performance. Here, we report the generation of Blackjack SpCas9 variant that shows increased fidelity yet remain effective with 21G-sgRNAs. Introducing Blackjack mutations into previously reported increased fidelity variants make them effective with 21G-sgRNAs and increases their fidelity. Two “Blackjack” nucleases, eSpCas9-plus and SpCas9-HF1-plus are superior variants of eSpCas9 and SpCas9-HF1, respectively, possessing matching on-target activity and fidelity but retaining activity with 21G-sgRNAs. They facilitate the use of existing pooled sgRNA libraries with higher specificity and show similar activities whether delivered as plasmids or as pre-assembled ribonucleoproteins.

scholarly journals MSCV-based retroviral plasmids expressing 3xFLAG-Sp-dCas9 for enChIP analysis

2021 ◽  
Author(s):  
Miyuki Yuno ◽  
Toshitsugu Fujita ◽  
Hodaka Fujii
Keyword(s):  
Dna Binding ◽  
Streptococcus Pyogenes ◽  
Chromatin Immunoprecipitation ◽  
Genomic Region ◽  
Target Cells ◽  
Drug Selection ◽  
Guide Rna ◽  
Inactive Form ◽  
Genomic Regions ◽  
Selection Of

Abstract Engineered DNA-binding molecule–mediated chromatin immunoprecipitation (enChIP) is a technology for purifying specific genomic regions to facilitate identification of their associated molecules, including proteins, RNAs, and other genomic regions. In enChIP, the target genomic region is tagged with engineered DNA-binding molecules, e.g., a variant of the clustered regularly interspaced short palindromic repeats (CRISPR) system consisting of a guide RNA (gRNA) and a catalytically inactive form of Cas9 (dCas9). In this study, to increase the flexibility of enChIP and expand the range of target cells, we generated murine stem cell virus (MSCV)-based retroviral plasmids for expressing dCas9. We constructed MSCV-based retroviral plasmids expressing Streptococcus pyogenes dCas9 fused to a 3xFLAG-tag (3xFLAG-Sp-dCas9) and various drug resistance genes. We showed that by using these plasmids, it is feasible to purify target genomic regions with yields comparable to those reported using other systems. These systems might give enChIP users greater flexibility in choosing optimal systems for drug selection of transduced cells.

scholarly journals CRISPR/Cas “non-target” sites inhibit on-target cutting rates

2020 ◽  
Author(s):  
Eirik A. Moreb ◽  
Mitchell Hutmacher ◽  
Michael D. Lynch
Keyword(s):  
Genome Editing ◽  
Target Site ◽  
High Fidelity ◽  
List Type ◽  
Dependent Manner ◽  
Guide Rna ◽  
Protospacer Adjacent Motif ◽  
Target Sites ◽  
Dose Dependent ◽  
Target Activity

AbstractCRISPR/Cas systems have become ubiquitous for genome editing in eukaryotic as well as bacterial systems. Cas9 associated with a guide RNA (gRNA) searches DNA for a matching sequence (target site) next to a protospacer adjacent motif (PAM) and once found, cuts the DNA. The number of PAM sites in the genome are effectively a non-target pool of inhibitory substrates, competing with the target site for the Cas9/gRNA complex. We demonstrate that increasing the number of non-target sites for a given gRNA reduces on-target activity in a dose dependent manner. Furthermore, we show that the use of Cas9 mutants with increased PAM specificity towards a smaller subset of PAMs (or smaller pool of competitive substrates) improves cutting rates. Decreasing the non-target pool by increasing PAM specificity provides a path towards improving on-target activity for slower high fidelity Cas9 variants. These results demonstrate the importance of competitive non-target sites on Cas9 activity and, in part, may help to explain sequence and context dependent activities of gRNAs. Engineering improved PAM specificity to reduce the competitive non-target pool offers an alternative strategy to engineer Cas9 variants with increased specificity and maintained on-target activity.HighlightsThe pool of non-target PAM sites inhibit Cas9/gRNA on-target activitynon-target PAM inhibition is dose dependentnon-target PAM inhibition is a function of gRNA sequencenon-target PAM inhibition is a function of Cas9 levels

scholarly journals Massively parallel CRISPRi assays reveal concealed thermodynamic determinants of dCas12a binding

2019 ◽  
Author(s):  
David A. Specht ◽  
Yasu Xu ◽  
Guillaume Lambert
Keyword(s):  
Dna Binding ◽  
Dna Sequences ◽  
Transcriptional Control ◽  
Target Recognition ◽  
Specific Binding ◽  
Massively Parallel ◽  
Nucleic Acid Detection ◽  
Factors Affecting ◽  
The Impact ◽  
Target Effects

The versatility of CRISPR-Cas endonucleases as a tool for biomedical research has lead to diverse applications in gene editing, programmable transcriptional control, and nucleic acid detection. Most CRISPR-Cas systems, however, suffer from off-target effects and unpredictable non-specific binding that negatively impact their reliability and broader applicability. To better evaluate the impact of mismatches on DNA target recognition and binding, we develop a massively parallel CRISPR interference (CRISPRi) assay to measure the binding energy between tens of thousands of CRISPR RNA (crRNA) and target DNA sequences. By developing a general thermodynamic model of CRISPR-Cas binding dynamics, our results unravel a comprehensive map of the energetic landscape of Francisella novicida Cas12a (FnCas12a) as it searches for its DNA target. Our results reveal concealed thermodynamic factors affecting FnCas12a DNA binding which should guide the design and optimization of crRNA that limit off-target effects, including the crucial role of an extended PAM sequence and the impact of the specific base composition of crRNA-DNA mismatches. Our generalizable approach should also provide a mechanistic understanding of target recognition and DNA binding when applied to other CRISPR-Cas systems.

scholarly journals A positive, growth-based PAM screen identifies noncanonical motifs recognized by the S. pyogenes Cas9

2020 ◽  
Vol 6 (29) ◽  
pp. eabb4054 ◽  
Author(s):  
D. Collias ◽  
R. T. Leenay ◽  
R. A. Slotkowski ◽  
Z. Zuo ◽  
S. P. Collins ◽  
...  
Keyword(s):  
Escherichia Coli ◽  
Molecular Dynamics ◽  
Dna Binding ◽  
Molecular Dynamics Simulations ◽  
Streptococcus Pyogenes ◽  
Human Cells ◽  
Induced Fit ◽  
Positive Growth ◽  
Dynamics Simulations

CRISPR technologies have overwhelmingly relied on the Streptococcus pyogenes Cas9 (SpyCas9), with its consensus NGG and less preferred NAG and NGA protospacer-adjacent motifs (PAMs). Here, we report that SpyCas9 also recognizes sequences within an N(A/C/T)GG motif. These sequences were identified on the basis of preferential enrichment in a growth-based screen in Escherichia coli. DNA binding, cleavage, and editing assays in bacteria and human cells validated recognition, with activities paralleling those for NAG(A/C/T) PAMs and dependent on the first two PAM positions. Molecular-dynamics simulations and plasmid-clearance assays with mismatch-intolerant variants supported induced-fit recognition of an extended PAM by SpyCas9 rather than recognition of NGG with a bulged R-loop. Last, the editing location for SpyCas9-derived base editors could be shifted by one nucleotide by selecting between (C/T)GG and adjacent N(C/T)GG PAMs. SpyCas9 and its enhanced variants thus recognize a larger repertoire of PAMs, with implications for precise editing, off-target predictions, and CRISPR-based immunity.

scholarly journals On-target activity predictions enable improved CRISPR–dCas9 screens in bacteria

2020 ◽  
Vol 48 (11) ◽  
pp. e64-e64 ◽  
Author(s):  
Alicia Calvo-Villamañán ◽  
Jérome Wong Ng ◽  
Rémi Planel ◽  
Hervé Ménager ◽  
Arthur Chen ◽  
...  
Keyword(s):  
High Throughput ◽  
High Throughput Screening ◽  
Cost Effective ◽  
Target Sequence ◽  
Guide Rna ◽  
E Coli ◽  
Genome Wide ◽  
High Throughput Screens ◽  
Target Activity ◽  
Target Effects

Abstract The ability to block gene expression in bacteria with the catalytically inactive mutant of Cas9, known as dCas9, is quickly becoming a standard methodology to probe gene function, perform high-throughput screens, and engineer cells for desired purposes. Yet, we still lack a good understanding of the design rules that determine on-target activity for dCas9. Taking advantage of high-throughput screening data, we fit a model to predict the ability of dCas9 to block the RNA polymerase based on the target sequence, and validate its performance on independently generated datasets. We further design a novel genome wide guide RNA library for E. coli MG1655, EcoWG1, using our model to choose guides with high activity while avoiding guides which might be toxic or have off-target effects. A screen performed using the EcoWG1 library during growth in rich medium improved upon previously published screens, demonstrating that very good performances can be attained using only a small number of well designed guides. Being able to design effective, smaller libraries will help make CRISPRi screens even easier to perform and more cost-effective. Our model and materials are available to the community through crispr.pasteur.fr and Addgene.

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