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Modeling Dominant and Recessive Forms of Retinitis Pigmentosa by Editing Three Rhodopsin-Encoding Genes in Xenopus Laevis Using Crispr/Cas9.
The utility of Xenopus laevis, a common research subject for developmental biology, retinal physiology, cell biology, and other investigations, has been limited by lack of a robust gene knockout or knock-down technology. Here we describe manipulation of the X. laevis genome using CRISPR/Cas9 to model the human disorder retinitis pigmentosa, and to introduce point mutations or exogenous DNA sequences. We introduced and characterized in-frame and out-of-frame insertions and deletions in three genes encoding rhodopsin by co-injection of Cas9 mRNA, eGFP mRNA, and single guide RNAs into fertilized eggs. Deletions were characterized by direct sequencing and cloning; phenotypes were assessed by assays of rod opsin in retinal extracts, and confocal microscopy of cryosectioned and immunolabeled contralateral eyes. We obtained germline transmission of editing to F1 offspring. In-frame deletions frequently caused dominant retinal degeneration associated with rhodopsin biosynthesis defects, while frameshift phenotypes were consistent with knockout. We inserted eGFP or point mutations into rhodopsin genes by co-injection of repair fragments with homology to the Cas9 target sites. Our techniques can produce high frequency gene editing in X. laevis, permitting analysis in the F0 generation, and advancing the utility of X. laevis as a subject for biological research and disease modeling.
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Rapid Cell-Free Preparation of Circular Vector DNA for pegRNA Expression in Prime Editing.
The expression of prime editing guide RNA (pegRNA) is crucial for effective CRISPR-Cas9 prime genome editing, traditionally facilitated by DNA plasmids, which require a time-consuming process of bacterial cloning, validation, and purification. The Circular Vector (CV) protocol represents an efficient, fully synthetic, cell-free method that bypasses these traditional steps, allowing for the preparation of pegRNA expression vectors within 3 h. This approach involves circularizing and purifying linear double-stranded DNA (dsDNA) templates containing a promoter with pegRNA elements into compact, bacterial-backbone-free vectors. These CVs offer significant advantages: absence of a bacterial backbone, absence of endotoxins, and no contamination by bacterial nucleic acids, making them a superior choice for transfection in cell culture experiments, where they have shown performance equal to or better than that of traditional plasmids. The CV protocol not only speeds up the preparation process but also reduces costs and complexity, making it an ideal tool for rapid and efficient pegRNA expression in research settings.
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Nuclear-targeted CRISPR/Cas delivery by using aptamer-modified polymer lipid nanoparticles.
Efficient nuclear delivery of CRISPR/Cas ribonucleoproteins (RNP) remains a significant hurdle for non-viral systems. To address this, we developed a polymer-lipid hybrid nanoparticle functionalized with the AS1411 aptamer, targeting nucleolin to facilitate nucleus-directed delivery. Confocal imaging confirmed the accumulation of these aptamer-modified nanoparticles within the cell nuclei. For precise quantification, we utilized an AI-assisted segmentation approach based on deep convolutional neural networks (CNN) to analyse nanoparticle and DAPI colocalization. We further evaluated in vitro gene knockout efficiency of Cas9/sgRNA by using this nucleus-targeted system. Aptamer-functionalised nanoparticles reduced GFP-positive cells to 30.0%, compared with 40.8% for untargeted nanoparticles. Further evaluation targeting the Lcn2 gene demonstrated higher knockout efficacy and a more potent inhibition of breast cancer cell proliferation. These findings indicate that aptamer-mediated nuclear targeting enhances CRISPR/Cas9 editing efficacy and may offer the potential to advance the performance of non-viral gene therapies.
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hpCasMINI: An engineered hypercompact CRISPR-Cas12f system with boosted gene editing activity.
Compact CRISPR-Cas systems have demonstrated potential for effective packaging into adeno-associated viruses (AAVs) for use in gene therapy. However, their applications are currently limited due to modest gene-editing activity. Here we introduce an engineered compact CRISPR-Cas12f (hpCasMINI, 554 aa), with hyper editing efficiency in mammalian cells via adding an α-helix structure to the N-terminus of an Un1Cas12f1 variant CasMINI (529 aa). The hpCasMINI system boosts gene activation and DNA cleavage activity with about 1.4-3.0-fold and 1.1-19.5-fold, respectively, and maintains the high specificity when compared to CasMINI. In addition, the system can activate luciferase reporter gene and endogenous Fgf21 gene in adult mouse liver, as well as construct liver tumorigenesis model via disrupting Trp53 and Pten genes and inserting oncogenic KrasG12D into the Trp53 locus. When compared to SpCas9 and LbCas12a, hpCasMINI displays higher gene activation and exhibits higher DNA cleavage specificity, although with lower activity, at the tested sites. Moreover, with a similar strategy, we engineer compact versions of hpOsCas12f1 (458 aa) from enOsCas12f1 and hpAsCas12f1 (447 aa) from AsCas12f1-HKRA, both of which display increased DNA cleavage activity, with hpAsCas12f1 also showing improved gene activation capability. Therefore, we develop activity-increased miniature hpCasMINI, hpOsCas12f1 and hpAsCas12f1 nucleases, which hold great potential for gene therapy in the future.
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Methods for Optimizing CRISPR-Cas9 Genome Editing Specificity.
Advances in the development of delivery, repair, and specificity strategies for the CRISPR-Cas9 genome engineering toolbox are helping researchers understand gene function with unprecedented precision and sensitivity. CRISPR-Cas9 also holds enormous therapeutic potential for the treatment of genetic disorders by directly correcting disease-causing mutations. Although the Cas9 protein has been shown to bind and cleave DNA at off-target sites, the field of Cas9 specificity is rapidly progressing, with marked improvements in guide RNA selection, protein and guide engineering, novel enzymes, and off-target detection methods. We review important challenges and breakthroughs in the field as a comprehensive practical guide to interested users of genome editing technologies, highlighting key tools and strategies for optimizing specificity. The genome editing community should now strive to standardize such methods for measuring and reporting off-target activity, while keeping in mind that the goal for specificity should be continued improvement and vigilance.
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Efficient CRISPR-Cas9-Mediated Genome Editing of the Cane Toad (Rhinella marina).
Invasive species inflict major ecological, economic, and cultural harm worldwide, highlighting the urgent need for innovative control strategies. Genome editing offers exciting possibilities for targeted control methods for invasive species. Here, we demonstrate CRISPR-Cas9 genome editing in the cane toad (Rhinella marina), one of Australia's most notorious invasive species, by targeting the tyrosinase gene to produce albino phenotypes as visual markers for assessing editing efficiency. Microinjection of Cas9 protein and guide RNAs into one-cell zygotes resulted in 87.6% of mosaic larvae displaying nearly complete albinism, with 2.3% exhibiting complete albinism. For completely albino individuals, genomic analysis confirmed predominantly frameshift mutations or large deletions at the target site, with no wild-type alleles detected. Germline transmission rates reflected the extent of albinism in the mosaic adult, with maternal transmission approaching 100%. This first application of CRISPR-Cas9 in the Bufonidae family opens possibilities for exploring basic research questions and population control strategies.
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High-efficiency genome editing using a dmc1 promoter-controlled CRISPR/Cas9 system in maize.
Previous studies revealed that the promoters for driving both Cas9 and sgRNAs are quite important for efficient genome editing by CRISPR/Cas9 in plants. Here, we report our results of targeted genome editing using the maize dmc1 gene promoter combined with the U3 promoter for Cas9 and sgRNA, respectively. Three loci in the maize genome were selected for targeting. The T0 plants regenerated were highly efficiently edited at the target sites with homozygous or bi-allelic mutants accounting for about 66%. The mutations in T0 plants could be stably transmitted to the T1 generation, and new mutations could be generated in gametes or zygotes. Whole-genome resequencing indicated that no off-target mutations could be detected in the predicted loci with sequence similarity to the targeted site. Our results show that the dmc1 promoter-controlled (DPC) CRISPR/Cas9 system is highly efficient in maize and provide further evidence that the optimization of the promoters used for the CRISPR/Cas9 system is important for enhancing the efficiency of targeted genome editing in plants. The evolutionary conservation of the dmc1 gene suggests its potential for use in other plant species.
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CRISPR-edited crops break new ground in Africa.
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Advances in Modeling Polyglutamine Diseases Using Genome Editing Tools.
Polyglutamine (polyQ) diseases, including Huntington's disease, are a group of late-onset progressive neurological disorders caused by CAG repeat expansions. Although recently, many studies have investigated the pathological features and development of polyQ diseases, many questions remain unanswered. The advancement of new gene-editing technologies, especially the CRISPR-Cas9 technique, has undeniable value for the generation of relevant polyQ models, which substantially support the research process. Here, we review how these tools have been used to correct disease-causing mutations or create isogenic cell lines with different numbers of CAG repeats. We characterize various cellular models such as HEK 293 cells, patient-derived fibroblasts, human embryonic stem cells (hESCs), induced pluripotent stem cells (iPSCs) and animal models generated with the use of genome-editing technology.
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Evaluation of CRISPR/Cas9 Constructs in Wheat Cell Suspension Cultures.
Despite intensive optimization efforts, developing an efficient sequence-specific CRISPR/Cas-mediated genome editing method remains a challenge, especially in polyploid cereal species such as wheat. Validating the efficacy of nuclease constructs prior to using them in planta is, thus, a major step of every editing experiment. Several construct evaluation strategies were proposed, with PEG-mediated plasmid transfection of seedling-derived protoplasts becoming the most popular. However, the usefulness of this approach is affected by associated construct copy number bias and chromatin relaxation, both influencing the outcome. Therefore, to achieve a reliable evaluation of CRISPR/Cas9 constructs, we proposed a system based on an Agrobacterium-mediated transformation of established wheat cell suspension cultures. This system was used for the evaluation of a CRISPR/Cas9 construct designed to target the ABA 8'-hydroxylase 1 gene. The efficiency of editing was verified by cost-effective means of Sanger sequencing and bioinformatic analysis. We discuss advantages and potential future developments of this method in contrast to other in vitro approaches.
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