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Systematic high-throughput evaluation reveals FrCas9's superior specificity and efficiency for therapeutic genome editing.
CRISPR-Cas9 systems have revolutionized genome editing, but the off-target effects of Cas9 limit its use in clinical applications. Here, we systematically evaluate FrCas9, a variant from Faecalibaculum rodentium, for cell and gene therapy (CGT) applications and compare its performance to SpCas9 and OpenCRISPR-1. OpenCRISPR-1 is a CRISPR system synthesized de novo using large language models (LLMs) but has not yet undergone systematic characterization. Using AID-seq, Amplicon sequencing, and GUIDE-seq, we assessed the on-target activity and off-target profiles of these systems across multiple genomic loci. FrCas9 demonstrated higher on-target efficiency and substantially fewer off-target effects than SpCas9 and OpenCRISPR-1. Furthermore, TREX2 fusion with FrCas9 reduced large deletions and translocations, enhancing genomic stability. Through screening of 1903 sgRNAs targeting 21 CGT-relevant genes using sequential AID-seq, Amplicon sequencing, and GUIDE-seq analysis, we identified optimal sgRNAs for each gene. Our high-throughput screening platform highlights FrCas9, particularly in its TREX2-fused form, as a highly specific and efficient tool for precise therapeutic genome editing.
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CRISPR/Cas9 corrects retinal dystrophy in rats.
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Assessment the Efficacy of the CRISPR System for Inducing Mutations in the AIMP2 Gene to Create a Cell Line Model of HLD17 Disease.
Hypomyelinating leukodystrophy-17 is a neurodevelopmental disorder caused by autosomal recessive mutations in the AIMP2 gene, resulting in a lack of myelin deposition during brain development, leading to variable neurological symptoms. Research on brain function in these disorders is challenging due to the lack of access to brain tissue. To overcome this problem, researchers have utilized different cell and animal models. The CRISPR-Cas9 system is considered the most optimal and effective method for genetic modification and developing cell models. We studied the efficacy of the CRISPR-Cas9 technology in inducing mutations in the AIMP2 gene in HEK293 cell lines. The study involved transfecting HEK293 cells with recombinant PX458 plasmids targeting spCas-9 and AIMP2 sgRNA. The cells were evaluated using fluorescent microscopy and enriched using serial dilution. The CRISPR/Cas9 plasmids were validated through PCR and Sanger sequencing. After serial dilution, AS-PCR, Sanger sequencing, and TIDE program analysis showed the construct successfully induces an indel mutation in HEK cells. Our findings demonstrated the great efficacy of the CRISPR system and produced a construct for inducing mutations in the AIMP2 gene, which can be utilized to edit the AIMP2 gene in nerve cells and create a cellular model of the HLD17 disease.
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Expanding the range of editable targets in the wheat genome using the variants of the Cas12a and Cas9 nucleases.
The development of CRISPR-based editors recognizing distinct protospacer-adjacent motifs (PAMs), or having different spacer length/structure requirements broadens the range of possible genomic applications. We evaluated the natural and engineered variants of Cas12a (FnCas12a and LbCas12a) and Cas9 for their ability to induce mutations in endogenous genes controlling important agronomic traits in wheat. Unlike FnCas12a, LbCas12a-induced mutations in the wheat genome, even though with a lower rate than that reported for SpCas9. The eight-fold improvement in the gene editing efficiency was achieved for LbCas12a by using the guides flanked by ribozymes and driven by the RNA polymerase II promoter from switchgrass. The efficiency of multiplexed genome editing (MGE) using LbCas12a was mostly similar to that obtained using the simplex RNA guides and showed substantial increase after subjecting transgenic plants to high-temperature treatment. We successfully applied LbCas12a-MGE for generating heritable mutations in a gene controlling grain size and weight in wheat. We showed that the range of editable loci in the wheat genome could be further expanded by using the engineered variants of Cas12a (LbCas12a-RVR) and Cas9 (Cas9-NG and xCas9) that recognize the TATV and NG PAMs, respectively, with the Cas9-NG showing higher editing efficiency on the targets with atypical PAMs compared to xCas9. In conclusion, our study reports a set of validated natural and engineered variants of Cas12a and Cas9 editors for targeting loci in the wheat genome not amenable to modification using the original SpCas9 nuclease.
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Lateral Root Initiation and the Analysis of Gene Function Using Genome Editing with CRISPR in Arabidopsis.
Lateral root initiation is a post-embryonic process that requires the specification of a subset of pericycle cells adjacent to the xylem pole in the primary root into lateral root founder cells. The first visible event of lateral root initiation in Arabidopsis is the simultaneous migration of nuclei in neighbouring founder cells. Coinciding cell cycle activation is essential for founder cells in the pericycle to undergo formative divisions, resulting in the development of a lateral root primordium (LRP). The plant signalling molecule, auxin, is a major regulator of lateral root development; the understanding of the molecular mechanisms controlling lateral root initiation has progressed tremendously by the use of the Arabidopsis model and a continual improvement of molecular methodologies. Here, we provide an overview of the visible events, cell cycle regulators, and auxin signalling cascades related to the initiation of a new LRP. Furthermore, we highlight the potential of genome editing technology to analyse gene function in lateral root initiation, which provides an excellent model to answer fundamental developmental questions such as coordinated cell division, growth axis establishment as well as the specification of cell fate and cell polarity.
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Optimized protocols for the characterization of Cas12a activities.
The CRISPR-associated (Cas) Cas12a is the effector protein for type V-A CRISPR systems. Cas12a is a sequence-specific endonuclease that targets and cleaves DNA containing a cognate short signature motif, called the protospacer adjacent motif (PAM), flanked by a 20 nucleotide (nt) segment that is complementary to the "guide" region of its CRISPR RNA (crRNA). The guide sequence of the crRNA can be programmed to target any DNA with a cognate PAM and is the basis for Cas12a's current use for gene editing in numerous organisms and for medical diagnostics. While Cas9 (type II effector protein) is widely used for gene editing, Cas12a possesses favorable features such as its smaller size and creation of staggered double-stranded DNA ends after cleavage that enhances cellular recombination events. Collected here are protocols for the recombinant purification of Cas12a and the transcription of its corresponding programmable crRNA that are used in a variety of Cas12a-specific in vitro activity assays such as the cis, the trans and the guide-RNA independent DNA cleavage activities with multiple substrates. Correspondingly, protocols are included for the quantification of the activity assay data using ImageJ and the use of MATLAB for rate constant calculations. These procedures can be used for further structural and mechanistic studies of Cas12a orthologs and other Cas proteins.
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Cas9-assisted recombineering in C. elegans: genome editing using in vivo assembly of linear DNAs.
Recombineering, the use of endogenous homologous recombination systems to recombine DNA in vivo, is a commonly used technique for genome editing in microbes. Recombineering has not yet been developed for animals, where non-homology-based mechanisms have been thought to dominate DNA repair. Here, we demonstrate, using Caenorhabditis elegans, that linear DNAs with short homologies (∼35 bases) engage in a highly efficient gene conversion mechanism. Linear DNA repair templates with homology to only one side of a double-strand break (DSB) initiate repair efficiently, and short overlaps between templates support template switching. We demonstrate the use of single-stranded, bridging oligonucleotides (ssODNs) to target PCR fragments for repair of DSBs induced by CRISPR/Cas9 on chromosomes. Based on these findings, we develop recombineering strategies for precise genome editing that expand the utility of ssODNs and eliminate in vitro cloning steps for template construction. We apply these methods to the generation of GFP knock-in alleles and gene replacements without co-integrated markers. We conclude that, like microbes, metazoans possess robust homology-dependent repair mechanisms that can be harnessed for recombineering and genome editing.
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Single and combinatorial gene inactivation in Aspergillus niger using selected as well as genome-wide gRNA library pools.
Aspergillus niger is a saprotroph, a pathogen, an endophyte, a food spoiler and an important cell factory. Only a minor fraction of its genes has been experimentally characterized. We here set up a CRISPR/Cas9 mutagenesis screen for functional gene analysis using co-transformation of a pool of gene editing plasmids that are maintained under selection pressure and that each contain a gRNA. First, a pool of gRNA vectors was introduced in A. niger targeting five genes with easy selectable phenotypes. Transformants were obtained with all possible single, double, triple, quadruple and quintuple gene inactivation phenotypes. Their genotypes were confirmed using the gRNA sequences in the transforming vector as barcodes. Next, a gRNA library was introduced in A. niger targeting > 9600 genes. Gene nsdC was identified as a sporulation gene using co-transformation conditions that favored uptake of one or two gRNA construct(s) from the genome-wide vector pool. Together, CRISPR/Cas9 vectors with a (genome-wide) pool of gRNAs can be used for functional analysis of genes in A. niger with phenotypes that are the result of the inactivation of a single or multiple genes.
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Treatments that made headlines in 2018.
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The way to true plant genome editing.
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