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Roadmap and Considerations for Genome Editing in a Non-Model Organism: Genetic Variations and Off-Target Profiling.
The CRISPR/Cas genome editing approach in non-model organisms poses challenges that remain to be resolved. Here, we demonstrated a generalized roadmap for a de novo genome annotation approach applied to the non-model organism Macrobrachium rosenbergii. We also addressed the typical genome editing challenges arising from genetic variations, such as a high frequency of single nucleotide polymorphisms, differences in sex chromosomes, and repetitive sequences that can lead to off-target events. For the genome editing of M. rosenbergii, our laboratory recently adapted the CRISPR/Cas genome editing approach to embryos and the embryonic primary cell culture. In this continuation study, an annotation pipeline was trained to predict the gene models by leveraging the available genomic, transcriptomic, and proteomic data, and enabling accurate gene prediction and guide design for knock-outs. A next-generation sequencing analysis demonstrated a high frequency of genetic variations in genes on both autosomal and sex chromosomes, which have been shown to affect the accuracy of editing analyses. To enable future applications based on the CRISPR/Cas tool in non-model organisms, we also verified the reliability of editing efficiency and tracked off-target frequencies. Despite the lack of comprehensive information on non-model organisms, this study provides an example of the feasibility of selecting and editing specific genes with a high degree of certainty.
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CRISPR-Cas guide RNA indel analysis using CRISPResso2 with Nanopore sequencing data.
OBJECTIVE: Insertion and deletion (indel) analysis of CRISPR-Cas guide RNAs (gRNAs) is crucial in gene editing to assess gRNA efficiency and indel frequency. This study evaluates the utility of CRISPResso2 with Oxford Nanopore sequencing data (nCRISPResso2) for gRNA indel screening, compared to two common Sanger sequencing-based methods, TIDE and ICE. To achieve this, sheep and horse fibroblasts were transfected with Cas9 and a gRNA targeting the myostatin (MSTN) gene. DNA was subsequently extracted, and PCR products exceeding 600 bp were sequenced using both Sanger and Nanopore sequencing. Indel profiling was then conducted using TIDE, ICE, and nCRISPResso2. RESULTS: Comparison revealed close correspondence in indel formation among methods. For the sheep MSTN gRNA, indel percentages were 52%, 58%, and 64% for TIDE, ICE, and nCRISPResso2, respectively. Horse MSTN gRNA showed 81%, 87%, and 86% edited amplicons for TIDE, ICE, and nCRISPResso2. The frequency of each type of indel was also comparable among the three methods, with nCRISPResso2 and ICE aligning the closest. nCRISPResso2 offers a viable alternative for CRISPR-Cas gRNA indel screening, especially with large amplicons unsuitable for Illumina sequencing. CRISPResso2's compatibility with Nanopore data enables cost-effective and efficient indel profiling, yielding results comparable to common Sanger sequencing-based methods.
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TIGR on the loose: A dual-guide RNA system for DNA targeting.
A recent study1 unveils tandem interspaced guide RNAs (TIGRs) that simultaneously engage both strands of target DNA and direct Tas protein activity. It offers insights into the evolution of RNA-guided proteins and introduces a promising tool for genome editing.
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Making the Search for Genome Editing Tortured Phrases a Collective Effort.
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AcrIIA5 Inhibits a Broad Range of Cas9 Orthologs by Preventing DNA Target Cleavage.
CRISPR-Cas9 is an adaptive immune system for prokaryotes to defend against invasive genetic elements such as phages and has been used as a powerful tool for genome editing and modulation. To overcome CRISPR immunity, phages encode anti-CRISPR proteins (Acrs) to inhibit Cas9, providing an efficient "off-switch" tool for Cas9-based applications. Here, we characterized AcrIIA5, which is a Cas9 inhibitor discovered in a virulent phage of Streptococcus thermophilus. We found that AcrIIA5 is a potent and broad-spectrum inhibitor of CRISPR-Cas9, which can inhibit diverse Cas9 orthologs of type II-A, type II-B, and type II-C. AcrIIA5 inhibits Cas9 by preventing DNA target cleavage, but DNA target binding of Cas9 is unaffected. Importantly, it can affect the activity of the RuvC nuclease domain of Cas9 independent of the HNH nuclease domain. Our work expands the diversity of the inhibitory mechanisms used by Acrs and provides the guidance for developing controlling tools in Cas9-based applications.
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Recent Advances in In Vivo Somatic Cell Gene Modification in Newborn Pups.
Germline manipulation at the zygote stage using the CRISPR/Cas9 system has been extensively employed for creating genetically modified animals and maintaining established lines. However, this approach requires a long and laborious task. Recently, many researchers have attempted to overcome these limitations by generating somatic mutations in the adult stage through tail vein injection or local administration of CRISPR reagents, as a new strategy called "in vivo somatic cell genome editing". This approach does not require manipulation of early embryos or strain maintenance, and it can test the results of genome editing in a short period. The newborn is an ideal stage to perform in vivo somatic cell genome editing because it is immune-privileged, easily accessible, and only a small amount of CRISPR reagents is required to achieve somatic cell genome editing throughout the entire body, owing to its small size. In this review, we summarize in vivo genome engineering strategies that have been successfully demonstrated in newborns. We also report successful in vivo genome editing through the neonatal introduction of genome editing reagents into various sites in newborns (as exemplified by intravenous injection via the facial vein), which will be helpful for creating models for genetic diseases or treating many genetic diseases.
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Fine-Tuning Next-Generation Genome Editing Tools.
The availability of genome sequences of numerous organisms and the revolution brought about by genome editing tools (e.g., ZFNs, TALENs, and CRISPR/Cas9 or RGENs) has provided a breakthrough in introducing targeted genetic changes both to explore emergent phenotypes and to introduce new functionalities. However, the wider application of these tools in biology, agriculture, medicine, and biotechnology is limited by off-target mutation effects. In this review, we compare available methods for detecting, measuring, and analyzing off-target mutations. Furthermore, we particularly focus on CRISPR/Cas9 regarding various methods, tweaks, and software tools available to nullify off-target effects.
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Somatostatin receptor-targeted polymeric nanoplatform for efficient CRISPR/Cas9 gene editing to enhance synergistic hepatocellular carcinoma therapy.
The CRISPR/Cas9 system-based gene therapy can fundamentally address the issues of cancer occurrence, development, progression, and metastasis. However, the lack of targeting and effectiveness hinders gene therapy from entering clinical application. Herein, a somatostatin receptor-targeted polymeric nanoplatform is developed for the delivery of a PD-L1-targeted CRISPR/Cas9 system and synergistic treatment of hepatocellular carcinoma. This nanoplatform can effectively incorporate the CRISPR/Cas9 system and the chemotherapeutic drug paclitaxel to simultaneously address the biological safety and packaging capacity issues of viral vectors. After the octreotide-modified polymer (LNA-PEG-OCT) guided the nanoparticle into hepatoma carcinoma cells, the nanoparticle protected the CRISPR/Cas9 ribonucleoprotein complex (RNP) and achieved lysosomal escape. Then, the RNP reached the target gene (PD-L1) under the guidance of the single guide RNA (sgRNA) in the RNP. The PD-L1 gene editing efficiency reached up to 55.8% for HepG2 cells in vitro and 46.0% for tumor tissues in vivo, leading to effective suppression of PD-L1 protein expression. Substantial inhibition of hepatocellular carcinoma cell proliferation and further 79.45% growth repression against subcutaneous xenograft tumors were achieved. Overall, this somatostatin receptor-targeted polymeric nanoplatform system not only provides a promising nanocarrier for CRISPR/Cas9 system delivery, but also expands the potential of combining gene editing and chemotherapy.
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SuperFi-Cas9: High Fidelity Meets High Activity.
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RiboCas: A Universal CRISPR-Based Editing Tool for Clostridium.
Members of the genus Clostridium represent a diverse assemblage of species exhibiting both medical and industrial importance. Deriving both a greater understanding of their biology, while at the same time enhancing their exploitable properties, requires effective genome editing tools. Here, we demonstrate the first implementation in the genus of theophylline-dependent, synthetic riboswitches exhibiting a full set of dynamic ranges, also suitable for applications where tight control of gene expression is required. Their utility was highlighted by generating a novel riboswitch-based editing tool-RiboCas-that overcomes the main obstacles associated with CRISPR/Cas9 systems, including low transformation efficiencies and excessive Cas9 toxicity. The universal nature of the tool was established by obtaining chromosomal modifications in C. pasteurianum, C. difficile, and C. sporogenes, as well as by carrying out the first reported example of CRISPR-targeted gene disruption in C. botulinum. The high efficiency (100% mutant generation) and ease of application of RiboCas make it suitable for use in a diverse range of microorganisms.
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