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Prime Editing: Game Changer for Modifying Plant Genomes.
Prime editing, developed by Anzalone et al., brings genome editing to a new level, because this approach allows introduction of all mutation types, including insertions, deletions, and all putative 12 types of base-to-base conversions. Previously tested in human cells, this technique has been adapted for use in plants by Lin et al.
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Engineered Cas12j-8 is a Versatile Platform for Multiplexed Genome Modulation in Mammalian Cells.
Cas12j-8 is a compact Cas nuclease discovered from the metagenome of giant bacteriophages, consisting of only 717 amino acids and recognizing the '5-TTN-3' protospacer adjacent motif (PAM) sequence. However, its low gene editing efficiency in mammalian cells limits its application in therapeutic gene editing. To address this limitation, structure-guided mutagenesis is employed to replace key negatively charged residues with arginine, strengthening DNA binding. The resulting quintuple mutant, engineered Cas12j-8 (enCas12j-8), demonstrates robust on-target editing efficiency comparable to LbCas12a while maintaining low off-target effects. Cytosine base editors (CBEs) and adenine base editors (ABEs) are developed using enCas12j-8, achieving up to 29.54-fold C-to-T and 36.57-fold A-to-G conversion efficiency compared with the wild-type at the dominated sites, respectively. Notably, enCas12j-8 enables multiplexed editing of three genomic loci simultaneously via a single crRNA array, achieving efficiencies comparable to single-guide approaches. Additionally, enCas12j-8-ABE facilitates the disruption of splice acceptor sites, effectively inducing exon skipping in the SOD1 gene. This strategy holds potential significance for therapeutic genome modulation. These findings establish enCas12j-8 as a versatile, high-precision tool for genome engineering, combining efficient delivery, multiplexing capability, and compatibility with diverse editing modalities.
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Efficient CRISPR/Cas9 genome editing with low off-target effects in zebrafish.
Gene modifications in animal models have been greatly facilitated through the application of targeted genome editing tools. The prokaryotic CRISPR/Cas9 type II genome editing system has recently been applied in cell lines and vertebrates. However, we still have very limited information about the efficiency of mutagenesis, germline transmission rates and off-target effects in genomes of model organisms. We now demonstrate that CRISPR/Cas9 mutagenesis in zebrafish is highly efficient, reaching up to 86.0%, and is heritable. The efficiency of the CRISPR/Cas9 system further facilitated the targeted knock-in of a protein tag provided by a donor oligonucleotide with knock-in efficiencies of 3.5-15.6%. Mutation rates at potential off-target sites are only 1.1-2.5%, demonstrating the specificity of the CRISPR/Cas9 system. The ease and efficiency of the CRISPR/Cas9 system with limited off-target effects make it a powerful genome engineering tool for in vivo studies.
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Evolution of CRISPR/Cas Systems for Precise Genome Editing.
The bacteria-derived CRISPR/Cas (an acronym for regularly interspaced short palindromic repeats/CRISPR-associated protein) system is currently the most widely used, versatile, and convenient tool for genome engineering. CRISPR/Cas-based technologies have been applied to disease modeling, gene therapies, transcriptional modulation, and diagnostics. Nevertheless, some challenges remain, such as the risk of immunological reactions or off-target effects. To overcome these problems, many new methods and CRISPR/Cas-based tools have been developed. In this review, we describe the current classification of CRISPR systems and new precise genome-editing technologies, summarize the latest applications of this technique in several fields of research, and, finally, discuss CRISPR/Cas system limitations, ethical issues, and challenges.
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Concurrent genome and epigenome editing by CRISPR-mediated sequence replacement.
BACKGROUND: Recent advances in genome editing have facilitated the direct manipulation of not only the genome, but also the epigenome. Genome editing is typically performed by introducing a single CRISPR/Cas9-mediated double-strand break (DSB), followed by non-homologous end joining (NHEJ)- or homology-directed repair-mediated repair. Epigenome editing, and in particular methylation of CpG dinucleotides, can be performed using catalytically inactive Cas9 (dCas9) fused to a methyltransferase domain. However, for investigations of the role of methylation in gene silencing, studies based on dCas9-methyltransferase have limited resolution and are potentially confounded by the effects of binding of the fusion protein. As an alternative strategy for epigenome editing, we tested CRISPR/Cas9 dual cutting of the genome in the presence of in vitro methylated exogenous DNA, with the aim of driving replacement of the DNA sequence intervening the dual cuts via NHEJ. RESULTS: In a proof of concept at the HPRT1 promoter, successful replacement events with heavily methylated alleles of a CpG island resulted in functional silencing of the HPRT1 gene. Although still limited in efficiency, our study demonstrates concurrent epigenome and genome editing in a single event. CONCLUSIONS: This study opens the door to investigations of the functional consequences of methylation patterns at single CpG dinucleotide resolution. Our results furthermore support the conclusion that promoter methylation is sufficient to functionally silence gene expression.
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Guarding the genome: strategies for off-target detection and minimization in CRISPR/Cas9 system.
INTRODUCTION: CRISPR-based genome editing has revolutionized molecular diagnostics and therapeutic applications, offering precise genetic modifications. However, off-target effects remain a significant challenge, potentially leading to unintended mutations and genomic instability. Addressing these concerns is crucial for ensuring the clinical safety and efficacy of CRISPR technologies. AREAS COVERED: This review provides a comprehensive analysis of strategies for detecting and mitigating off-target effects in CRISPR genome editing. We discuss in silico, in vitro, and in vivo detection methods, highlighting their strengths and limitations. Additionally, we examine advancements in guide RNA (gRNA) engineering, improved Cas variants, optimized delivery systems, base and prime editing technologies, and anti-CRISPR proteins as key approaches to enhance genome-editing precision. EXPERT OPINION: While significant progress has been made in off-target detection and mitigation, challenges remain in accurately assessing unintended genomic modifications in vivo and ensuring long-term safety in clinical applications. Future research should focus on developing high-fidelity CRISPR variants, refining computational prediction models, and integrating multi-modal detection systems. Advancing delivery mechanisms and regulatory strategies will be essential for translating CRISPR into safe and effective therapeutic interventions.
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Comparative analysis of lipid-mediated CRISPR-Cas9 genome editing techniques.
CRISPR-Cas technology has revolutionized genome engineering. While Cas9 was not the first programmable endonuclease identified, its simplicity of use has driven widespread adoption in a short period of time. While CRISPR-Cas genome editing holds enormous potential for clinical applications, its use in laboratory settings for genotype-phenotype studies and genome-wide screens has led to breakthroughs in the understanding of many molecular pathways. Numerous protocols have been described for introducing CRISPR-Cas components into cells, and here we sought to simplify and optimize a protocol for genome editing using readily available and inexpensive tools. We compared plasmid, ribonucleoprotein (RNP), and RNA transfection to determine which was method was most optimal for editing cells in a laboratory setting. We limited our comparison to lipofection-mediated introduction because the reagents are widely available. To facilitate optimization, we developed a novel reporter assay to measure gene disruption and the introduction of a variety of exogenous DNA tags. Each method efficiently disrupted endogenous genes and was able to stimulate the introduction of foreign DNA at specific sites, albeit to varying efficiencies. RNP transfection produced the highest level of gene disruption and was the most rapid and efficient method overall. Finally, we show that very short homology arms of 30 base pairs can mediate site-specific editing. The methods described here should broaden the accessibility of RNP-mediated lipofection for laboratory genome-editing experiments.
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T4 DNA polymerase prevents deleterious on-target DNA damage and enhances precise CRISPR editing.
Unintended on-target chromosomal alterations induced by CRISPR/Cas9 in mammalian cells are common, particularly large deletions and chromosomal translocations, and present a safety challenge for genome editing. Thus, there is still an unmet need to develop safer and more efficient editing tools. We screened diverse DNA polymerases of distinct origins and identified a T4 DNA polymerase derived from phage T4 that strongly prevents undesired on-target damage while increasing the proportion of precise 1- to 2-base-pair insertions generated during CRISPR/Cas9 editing (termed CasPlus). CasPlus induced substantially fewer on-target large deletions while increasing the efficiency of correcting common frameshift mutations in DMD and restored higher level of dystrophin expression than Cas9-alone in human cardiomyocytes. Moreover, CasPlus greatly reduced the frequency of on-target large deletions during mouse germline editing. In multiplexed guide RNAs mediating gene editing, CasPlus repressed chromosomal translocations while maintaining gene disruption efficiency that was higher or comparable to Cas9 in primary human T cells. Therefore, CasPlus offers a safer and more efficient gene editing strategy to treat pathogenic variants or to introduce genetic modifications in human applications.
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Bringing gene therapy to where it's needed.
Gene editing allows the precise modification of cells to correct genetic defects or enhance immunotherapies. A limitation is the delivery of this technology to specific cells or organs. Recently, Banskota et al. reported the use of virus-like particles (VLPs) loaded with gene-editing agents for gene therapy delivery directly inside the body.
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Better base editors.
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