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Guide RNA engineering enables efficient CRISPR editing with a miniature Syntrophomonas palmitatica Cas12f1 nuclease.
Gene therapy is limited by inefficient delivery of large clustered regularly interspaced short palindromic repeat (CRISPR) effectors, such as Cas9 and Cas12a nucleases. Cas12f nucleases are currently one of the most compact CRISPR genome editors. However, the available toolkit of efficient Cas12f editors is limited. Here, we report the characterization and engineering of a miniature CRISPR-Cas12f system from Syntrophomonas palmitatica (SpaCas12f1, 497 amino acids). We show that CRISPR-SpaCas12f1 cleaves double-stranded DNA (dsDNA) with 5' T-rich PAM specificity and is naturally active for genome editing in bacteria. We identify that CRISPR-SpaCas12f1 trans-activating CRISPR RNA (tracrRNA) harbors a unique head-to-toe hairpin structure, and the natural hairpin structure is a key factor in restricting genome editing by SpaCas12f1 in human cells. Systematical engineering of SpaCas12f1 guide RNA transforms CRISPR-SpaCas12f1 into an efficient genome editor comparable to Francisella novicida CRISPR-Cas12a. Our findings expand the mini CRISPR toolbox, paving the way for therapeutic applications of CRISPR-SpaCas12f1 and engineering compact genome manipulation technologies.
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Genetic engineering: Allele-specific genome editing of disease loci.
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A quantitative assay for the efficiency of RNA-guided genome editing in plants.
RNA-guided endonucleases originating from the bacterial CRISPR/Cas system are a versatile tool for targeted gene editing. To determine the functional relevance of a gene of interest, deletion of the entire open reading frame (ORF) by two independent double-strand breaks (DSBs) is particularly attractive. This strategy greatly benefits from high editing efficiency, which is strongly influenced by the Cas endonuclease version used. We developed two reporter switch-on assays, for quantitative comparison and optimization of Cas constructs. The assays are based on four components: (i) A reporter gene, the mRNA of which carries a hairpin (HP) loop targeted by (ii) the endoribonuclease Csy4. Cleavage of the mRNA at the HP loop by Csy4 abolishes the translation of the reporter. Csy4 was used as the target for full deletion. (iii) A Cas system targeting sites flanking the Csy4 ORF with a 20-bp spacer either side to preferentially detect full-deletion events. Loss of functional Csy4 would lead to reporter gene expression, allowing indirect quantification of Cas-mediated deletion events. (iv) A reference gene for normalization. We tested these assays on Nicotiana benthamiana leaves and Lotus japonicus calli induced on hypocotyl sections, using Firefly luciferase and mCitrine as reporter genes and Renilla luciferase and hygromycin phosphotransferase II as reference genes, respectively. We observed a >90% correlation between reporter expression and full Csy4 deletion events, demonstrating the validity of these assays. The principle of using the Csy4-HP module as Cas target should be applicable to other editing goals including single DSBs in all organisms.
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Gene drives gaining speed.
Gene drives are selfish genetic elements that are transmitted to progeny at super-Mendelian (>50%) frequencies. Recently developed CRISPR-Cas9-based gene-drive systems are highly efficient in laboratory settings, offering the potential to reduce the prevalence of vector-borne diseases, crop pests and non-native invasive species. However, concerns have been raised regarding the potential unintended impacts of gene-drive systems. This Review summarizes the phenomenal progress in this field, focusing on optimal design features for full-drive elements (drives with linked Cas9 and guide RNA components) that either suppress target mosquito populations or modify them to prevent pathogen transmission, allelic drives for updating genetic elements, mitigating strategies including trans-complementing split-drives and genetic neutralizing elements, and the adaptation of drive technology to other organisms. These scientific advances, combined with ethical and social considerations, will facilitate the transparent and responsible advancement of these technologies towards field implementation.
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Map of ethical conflicts of the CRISPR-Cas9 gene edition technique.
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Unlocking CRISPR-Cas9 editing for widely diverse Dictyostelid species.
Dictyostelids are a species-rich clade of cellular slime molds that are widely found in soils and have been studied for over a century. Due to a lack of genome editing methods, most molecular research in Dictyostelids has focused on only a single species, Dictyostelium discoideum, which has severely limited broad-scale comparative analyses. Here, we introduce the first CRISPR-Cas9 editing approach that is cloning-free, selection-free, highly efficient, and effective across Dictyostelid species that diverged millions of years ago. Depending on the CRISPR-Cas9 target site, our editing approach generates knock-out efficiencies of up to 90% and knock-in efficiencies of up to 50% without a selective marker. We show that mutants can be isolated as soon as one day post-transfection, vastly outpacing existing methods for generating knock-outs, fusion proteins, and expression reporters. Leveraging single-cell sorting and fluorescent microscopy, we could readily apply our CRISPR-Cas9 editing approach to phylogenetically distant Dictyostelid species, including those that have never been genome edited before. Our methods therefore open the door to performing broad-scale genetic interrogations across the Dictyostelids.
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Preclinical Anticipation of On- and Off-Target Resistance Mechanisms to Anti-Cancer Drugs: A Systematic Review.
The advent of targeted therapies has led to tremendous improvements in treatment options and their outcomes in the field of oncology. Yet, many cancers outsmart precision drugs by developing on-target or off-target resistance mechanisms. Gaining the ability to resist treatment is the rule rather than the exception in tumors, and it remains a major healthcare challenge to achieve long-lasting remission in most cancer patients. Here, we discuss emerging strategies that take advantage of innovative high-throughput screening technologies to anticipate on- and off-target resistance mechanisms before they occur in treated cancer patients. We divide the methods into non-systematic approaches, such as random mutagenesis or long-term drug treatment, and systematic approaches, relying on the clustered regularly interspaced short palindromic repeats (CRISPR) system, saturated mutagenesis, or computational methods. All these new developments, especially genome-wide CRISPR-based screening platforms, have significantly accelerated the processes for identification of the mechanisms responsible for cancer drug resistance and opened up new avenues for future treatments.
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Genome Editing Using Cas9-gRNA Ribonucleoprotein in Human Pluripotent Stem Cells for Disease Modeling.
The discovery that the CRISPR/Cas9 system could be used for genome editing purposes represented a major breakthrough in the field. This advancement has notably facilitated the introduction or correction of disease-specific mutations in healthy or disease stem cell lines respectively; therefore, easing disease modeling studies in combination with differentiation protocols. For many years, variability in the genetic background of different stem cell lines has been a major burden to specifically identify phenotypes arising uniquely from the presence of the mutation and not from differences in other genomic regions.Here, we provide a complete protocol to introduce random indels in human wild type pluripotent stem cells using CRISPR/Cas9 in order to generate clonal lines with potential pathogenic alterations in any gene of interest. In this protocol, we use transfection of a ribonucleoprotein complex to diminish the risk of off-target effects, and select clonal lines with promising indels to obtain disease induced pluripotent stem cell lines.
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Disabling iron uptake and pilus assembly in uropathogenic Escherichia coli using CRISPR-Cas9: a step towards antivirulence therapy.
Uropathogenic Escherichia coli (UPEC) is the leading cause of urinary tract infections (UTIs), driven by virulence factors such as iron acquisition systems and adhesive pili. In this study, we employed CRISPR-Cas9-mediated genome editing to functionally inactivate two critical virulence genes-iucD, involved in aerobactin-mediated iron uptake, and papC, encoding the outer membrane usher protein essential for P pilus assembly. Using a clinical UPEC isolate, we introduced premature stop codons via homologous repair templates guided by gene-specific single-guide RNAs. Colony PCR and Sanger sequencing confirmed precise site-specific editing, leading to truncated protein variants. In silico analyses using InterPro and Swiss-Model revealed a complete loss of essential domains in both proteins. Molecular docking studies demonstrated a marked reduction in binding affinities of truncated iucD for NAD(P)H and impaired protein-protein interaction between truncated PapC and PapG. This study highlights the utility of CRISPR-Cas9 as a powerful tool for dissecting bacterial pathogenesis and supports the potential of targeting virulence determinants like iucD and papC as part of an antivirulence strategy for managing UPEC infections.
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VERVE-101: a promising CRISPR-based gene editing therapy that reduces LDL-C and PCSK9 levels in HeFH patients.
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