It is confirmed that multi-targeting sgRNAs disproportionately impair cell fitness and that sgRNAs aligning to more than one location with a single mismatch can also reduce fitness, although to a lesser extent.
Abstract
Pooled genome-wide CRISPR-Cas9 knockout (CRISPR-KO) screening is a powerful approach for discovering new biology and identifying genetic vulnerabilities in cancers. This approach uses the Cas9 nuclease in combination with sgRNA libraries, typically consisting of 4-8 sgRNAs to induce mutations in each target gene. A critical assumption is that the effect of each sgRNA is solely due to Cas9 editing of the target gene. However, libraries can contain sgRNAs that direct Cas9 to multiple locations, thus potentially introducing bias into gene hit lists and leading to flawed biological hypotheses. Here we have developed GuideRefine, a pipeline to detect multi-targeting and off-targeting sgRNAs. GuideRefine outputs a virtual refined sub-library containing only on-target sgRNAs. Using GuideRefine with T2T-CHM13 as the reference genome, we surveyed the Brunello, TKOv3, Yusa, Avana, and Jacquere libraries, finding that ∼7.5% to ∼16% of sgRNAs are potentially problematic. We confirmed that multi-targeting sgRNAs disproportionately impair cell fitness and that sgRNAs aligning to more than one location with a single mismatch can also reduce fitness, although to a lesser extent. After flagging problematic sgRNAs and creating virtual “on-target only” sub-libraries, ∼10% to ∼16% of genes lose critical representation (< 3 sgRNAs per gene). Intriguingly, a set of 467 genes, characterised by short CDS length and lower PAM site density, have fewer than three sgRNAs in all sub-libraries, suggesting they cannot be well-targeted using current libraries. We anticipate that GuideRefine, together with caution in assessing the effects of problematic sgRNAs, will help prioritise biologically relevant hits.
CRISPR interference (CRISPRi) is a powerful technology for studying loss-of-function phenotypes, enabling transient and reversible control of gene expression without the introduction of double-stranded DNA breaks. The cost of conducting large-scale CRISPR screens necessitates the selection of effective and specific single-guide RNAs for the design of compact libraries. While several genome-wide CRISPRi-Cas9 libraries have been created, updates to transcript annotations, the generation of higher-resolution chromatin accessibility datasets, and the development of newer on-target prediction models motivate an updated CRISPRi library design approach. Here, we generate large CRISPRi datasets tiling essential and nonessential genes. We compare the performance of multiple KRAB domain systems, develop an updated CRISPRi-specific on-target scoring scheme, and quantitatively characterize off-target effects associated with seed-sequence patterns. We leverage these findings to design an optimized CRISPRi-Cas9 library, Katsano, and validate its performance with genome-wide viability screens.
Smriti Srikanth, Fengyi Zheng, Laura M Drepanos et al.· Cell Genomics· 0 citations
Two edgeR-based pipelines were constructed that would allow for direct comparison between two genome-wide CRISPR screening datasets of colorectal carcinoma, the Wellcome Sanger Institute’s (Sanger) and the Broad Institute's DepMap (Achilles) datasets, and Model-based Analysis of Genome-wide CRISPR/Cas9 Knockout (MAGeCK) for comparison and validation.
Khalif Hussein, Vasileios Theocharis, A. Lindlöf· 0 citations
Accurate identification of CRISPR-Cas9 off-target sites is essential for the safety assessment of genome-editing-based therapies. While numerous in silico prediction tools have been developed, their comparative performance and practical utility in preclinical workflows remain incompletely defined. We performed a systematic benchmarking of 14 in silico CRISPR-Cas9 off-target prediction tools, including both standard approaches and machine learning-based models. The analysis was based on a curated dataset derived from the CRISPRoffT database, comprising 3,827 deep-sequenced genomic sites across 26 guide RNA/Cas9 combinations in human cells. Sites with indel frequencies ≥0.1% were operationally defined as true off-targets. We evaluated tool performance using score distributions, correlation with indel frequencies, precision-recall characteristics, recall among top-ranked candidate sites, and the effect of combining tools. All tools assigned higher scores to true off-target sites compared with nontarget sites, although substantial overlap between classes was observed. Correlation between prediction scores and indel frequencies was weak to moderate, indicating limited ability to predict editing magnitude. Precision-recall performance was moderate across all tools, reflecting inherent trade-offs between sensitivity and specificity. Recall increased with the number of predicted sites considered, reaching approximately 77% among the top 500 and up to 83% among the top 1,250 sites, but leaving a substantial fraction of true off-targets undetected. Combining tools yielded only modest improvements. Current in silico tools enable prioritization of CRISPR-Cas9 off-target candidates but remain limited in their ability to comprehensively identify and quantitatively predict off-target activity. Our findings highlight the importance of considering both ranking performance and candidate site coverage and support the use of combined computational and experimental strategies for robust off-target assessment in preclinical gene editing workflows.
M. M. Kaufmann, Maren Hackenberg, William Jobson Pargeter et al.· Human Gene Therapy· 0 citations
Clustered regularly interspaced short palindromic repeats (CRISPR) and CRISPR-associated (Cas) proteins constitute adaptive immune systems in prokaryotes and have transformed life sciences, precision medicine, and synthetic biology as programmable genome-editing tools. Despite their broad utility, naturally occurring DNA-targeting Cas effectors remain constrained by several intrinsic limitations, including large protein size that complicates delivery, stringent protospacer adjacent motif (PAM) requirements that restrict targetable genomic space, and mismatch tolerance that can lead to off-target activity and potential genotoxicity. These challenges have made Cas protein engineering and the discovery of novel CRISPR and CRISPR-like systems from metagenomic resources central to the development of next-generation genome-editing platforms. This Review places recent advances within an integrated synthetic biology engineering continuum that links natural effector discovery, structure-guided hypothesis generation, high-throughput functional screening, machine learning-enabled model construction, and iterative redesign. This Review summarizes progress in the screening, optimization, and functional engineering of DNA-targeting CRISPR and CRISPR-like effectors, with emphasis on structure-guided rational design, directed evolution coupled with high-throughput screening, bioinformatics- and evolution-guided mining of novel systems from large-scale sequence databases, and artificial intelligence-assisted development. By integrating these strategies, we highlight how CRISPR effector engineering is moving toward design-build-test-learn (DBTL)-inspired workflows that expand the functional landscape of genome-editing technologies and advance genome editing toward improved efficiency, safety, and programmability.
Lingwei She, Zeyu Liang, Qin Zou et al.· ACS Synthetic Biology· 1 citation
Five previously uncharacterized MG102-like Cas9d orthologs are identified that share the hallmark genomic, sequence, and structural features of type II-D Cas9 and establish compact MG102-like Cas9d orthologs as robust and specific genome editors and provide promising, single-AAV– compatible scaffolds for in vivo therapeutic genome editing.
Qiaochu Wang, Ahmed Saleh, G. S. Rao et al.· bioRxiv· 0 citations
Human induced pluripotent stem cells (hiPSCs) represent a powerful platform for disease modeling, especially in monogenic diseases as they preserve the donor’s genetic background while enabling directed differentiation into disease-relevant cell types. This makes them highly suitable for studying disease mechanisms in a patient-specific and physiologically relevant context. Although CRISPR/Cas9 is widely applied for genome editing, precise correction of pathogenic variants in hiPSCs remains challenging due to the lack of standardized CRISPR component selection and experimental design. Here, we describe an optimized CRISPR-based strategy for correcting a heterozygous HNF1A frameshift mutation (c.235_236insG; p.Glu79Glyfs*16) in HNF1A-MODY patient-derived hiPSCs. Using electroporation, we efficiently delivered CRISPR components, including a ribonucleoprotein complex of Cas9 and single-guide RNA, along with a single-stranded oligodeoxynucleotide repair template. Corrected hiPSC lines were validated for pluripotency, absence of exogenous reprogramming factors, and off-target effects. Additionally, we discuss key technical challenges encountered during the editing process and provide practical recommendations that may improve the generation of mutation-corrected hiPSC lines. These guidelines could serve as a useful reference for researchers employing CRISPR-based strategies for generation of reliable disease modelling tools.
D. Skoczek, Jerzy Hohendorff, Maciej T. Małecki et al.· Human Genetics· 0 citations
