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A review of virus host factor discovery using CRISPR screening.
The emergence of genome-scale forward genetic screening techniques, such as Haploid Genetic screen and clustered regularly interspaced short palindromic repeats (CRISPR) knockout screen has opened new horizons in our understanding of virus infection biology. CRISPR screening has become a popular tool for the discovery of novel host factors for several viruses due to its specificity and efficiency in genome editing. Here, we review how CRISPR screening has revolutionized our understanding of virus-host interactions from scientific and technological viewpoints. A summary of the published screens conducted thus far to uncover virus host factors is presented, highlighting their experimental design and significant findings. We will outline relevant methods for customizing the CRISPR screening process to answer more specific hypotheses and compile a glossary of conducted CRISPR screens to show their design aspects. Furthermore, using flaviviruses and severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) as examples, we hope to offer a broad-based perspective on the capabilities of CRISPR screening to serve as a reference point to guide future unbiased discovery of virus host factors.
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Design of a generic CRISPR-Cas9 approach using the same sgRNA to perform gene editing at distinct loci.
BACKGROUND: The CRISPR/Cas (clustered regularly interspaced short palindromic repeat and CRISPR-associated nucleases) based technologies have revolutionized genome engineering. While their use for prokaryotic genome editing is expanding, some limitations remain such as possible off-target effects and design constraints. These are compounded when performing systematic genome editing at distinct loci or when targeting repeated sequences (e.g. multicopy genes or mobile genetic elements). To overcome these limitations, we designed an approach using the same sgRNA and CRISPR-Cas9 system to independently perform gene editing at different loci. RESULTS: We developed a two-step procedure based on the introduction by homologous recombination of 'bait' DNA at the vicinity of a gene copy of interest before inducing CRISPR-Cas9 activity. The introduction of a genetic tool encoding a CRISPR-Cas9 complex targeting this 'bait' DNA induces a double strand break near the copy of interest. Its repair by homologous recombination can lead either to reversion or gene copy-specific editing. The relative frequencies of these events are linked to the impact of gene editing on cell fitness. In our study, we used this technology to successfully delete the native copies of two xenogeneic silencers lsr2 paralogs in Streptomyces ambofaciens. We observed that one of these paralogs is a candidate-essential gene since its native locus can be deleted only in the presence of an extra copy. CONCLUSION: By targeting 'bait' DNA, we designed a 'generic' CRISPR-Cas9 toolkit that can be used to edit different loci. The differential action of this CRISPR-Cas9 system is exclusively based on the specific recombination between regions surrounding the gene copy of interest. This approach is suitable to edit multicopy genes. One such particular example corresponds to the mutagenesis of candidate-essential genes that requires the presence of an extra copy of the gene before gene disruption. This opens new insights to explore gene essentiality in bacteria and to limit off-target effects during systematic CRISPR-Cas9 based approaches.
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Generation of transgene-free PDS mutants in potato by Agrobacterium-mediated transformation.
BACKGROUND: Gene editing using the CRISPR/Cas9 system has become a routinely applied method in several plant species. The most convenient gene delivery system is Agrobacterium-mediated gene transfer with antibiotic selection and stable genomic integration of transgenes, including Cas9. For elimination of transgenes in the segregating progeny, selfing is applied in many plant species. This approach, however, cannot be widely employed in potato because most of the commercial potato cultivars are self-incompatible. RESULTS: In this study, the efficiency of a transient Cas9 expression system with positive/negative selection based on codA-nptII fusion was tested. The PHYTOENE DESATURASE (PDS) gene involved in carotenoid biosynthesis was targeted. A new vector designated PROGED::gPDS carrying only the right border of T-DNA was constructed. Using only the positive selection function of PROGED::gPDS and the restriction enzyme site loss method in PCR of genomic DNA after digestion with the appropriate restriction enzyme, it was demonstrated that the new vector is as efficient in gene editing as a traditional binary vector with right- and left-border sequences. Nevertheless, 2 weeks of positive selection followed by negative selection did not result in the isolation of PDS mutants. In contrast, we found that with 3-day positive selection, PDS mutants appear in the regenerating population with a minimum frequency of 2-10%. Interestingly, while large deletions (> 100 bp) were generated by continuous positive selection, the 3-day selection resulted in deletions and substitutions of only a few bp. Two albinos and three chimaeras with white and green leaf areas were found among the PDS mutants, while all the other PDS mutant plants were green. Based on DNA sequence analysis some of the green plants were also chimaeras. Upon vegetative propagation from stem segments in vitro, the phenotype of the plants obtained even by positive selection did not change, suggesting that the expression of Cas9 and gPDS is silenced or that the DNA repair system is highly active during the vegetative growth phase in potato. CONCLUSIONS: Gene-edited plants can be obtained from potatoes by Agrobacterium-mediated transformation with 3-day antibiotic selection with a frequency high enough to identify the mutants in the regenerating plant population using PCR.
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Treating Genetic Disorders Using State-Of-The-Art Technology.
CRISPR-Cas9 (clustered regularly interspaced short palindromic repeats-CRISPR associated Protein 9), basically a bacterial immune system is now widely applicable to engineer genomes of a number of cells and organisms because of its simplicity and robustness. In research avenue the system has been optimized to regulate gene expression, modify epigenome and edit target locus. These applications make CRISPR/Cas9, a technology of choice to edit disease causing mutations as well as the epigenome more efficiently than ever before. Meanwhile its application in in vivo and ex vivo cells is encouraging the scientific community for more vigorous gene therapy and in clinical setups for therapeutic genome editing. Here we review the recent advances that CRISPR-Cas9 mediated genome editing has achieved and is reported in previous studies and address the challenges associated with it.
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Harnessing CRISPR technology for the diagnosis of Bordetella pertussis: advances and implications.
Following the discovery of the prokaryotic adaptive immune system known as clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR-associated (Cas) proteins, this technology has revolutionized biotechnology as a multifaceted genome-editing tool with a wide range of applications. CRISPR technology has not only provided novel treatment options, especially for genetic diseases, but also transformed molecular diagnostic platforms. The specific, sensitive, and adaptable nature of the CRISPR-Cas systems has led to the development of innovative solutions for the detection of diseases, including viral and bacterial infections. This review provides an overview of the CRISPR-Cas systems and mainly focuses on the application of CRISPR-based assays for the detection of Bordetella pertussis, which is the main causative agent of a highly infectious disease, whooping cough. The review emphasizes the need for novel diagnostic tools for B. pertussis, along with highlighting some future perspectives, since its diagnosis can be challenging due to nonspecific early symptoms and interference from closely related Bordetella species. In this regard, CRISPR-based diagnostic platforms can offer a promising avenue for rapid and accurate detection of B. pertussis, helping the management of whooping cough.
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CRISPR-Cas9/CRISPRi tools for cell factory construction in E. coli.
The innovative CRISPR-Cas based genome editing technology provides some functionality and advantages such as the high efficiency and specificity as well as ease of handling. Both aspects of the CRISPR-Cas9 system including genetic engineering and gene regulation are advantageously applicable to the construction of microbial cell factories. As one of the most extensively used cell factories, E. coli has been engineered to produce various high value-added chemical compounds such as pharmaceuticals, biochemicals, and biofuels. Therefore, to improve the production of valuable metabolites, many investigations have been performed by focusing on CRISPR-Cas- based metabolic engineering of this host. In the current review, the biology underlying CRISPR-Cas9 system was briefly explained and then the applications of CRISPR-Cas9/CRISPRi tools were considered for cell factory construction in E. coli.
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Procreative Non-Maleficence: A South African Human Rights Perspective on Heritable Human Genome Editing.
If the safety and efficacy issues relating to heritable genome editing can be resolved, how should liberal democratic societies regulate the use of this technology by prospective parents who wish to effect edits to the genomes of their prospective children? We suggest that recent developments in South African law can be useful in this regard. The country's apex court recently recognized as a legal principle that the scope of possible reproductive decisions that parents may make when using new reproductive technologies excludes decisions that will cause harm to the prospective child-the principle of procreative non-maleficence. We suggest that the principle of procreative non-maleficence provides a mechanism for striking an equitable balance between two competing interests that are given legal recognition in most liberal democracies: the reproductive rights of prospective parents and the state's duty to protect child welfare.
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CRISPR-based genetic screens advance cancer immunology.
CRISPR technologies have revolutionized research areas ranging from fundamental science to translational medicine. CRISPR-based genetic screens offer a powerful platform for unbiased screening in various fields, such as cancer immunology. Immune checkpoint blockade (ICB) therapy has been shown to strongly affect cancer treatment. However, the currently available ICBs are limited and do not work in all cancer patients. Pooled CRISPR screens enable the identification of previously unknown immune regulators that can regulate T-cell activation, cytotoxicity, persistence, infiltration into tumors, cytokine secretion, memory formation, T-cell metabolism, and CD4+ T-cell differentiation. These novel targets can be developed as new immunotherapies or used with the current ICBs as new combination therapies that may yield synergistic efficacy. Here, we review the progress made in the development of CRISPR technologies, particularly technological advances in CRISPR screens and their application in novel target identification for immunotherapy.
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Lessons from Enzyme Kinetics Reveal Specificity Principles for RNA-Guided Nucleases in RNA Interference and CRISPR-Based Genome Editing.
RNA-guided nucleases (RGNs) provide sequence-specific gene regulation through base-pairing interactions between a small RNA guide and target RNA or DNA. RGN systems, which include CRISPR-Cas9 and RNA interference (RNAi), hold tremendous promise as programmable tools for engineering and therapeutic purposes. However, pervasive targeting of sequences that closely resemble the intended target has remained a major challenge, limiting the reliability and interpretation of RGN activity and the range of possible applications. Efforts to reduce off-target activity and enhance RGN specificity have led to a collection of empirically derived rules, which often paradoxically include decreased binding affinity of the RNA-guided nuclease to its target. We consider the kinetics of these reactions and show that basic kinetic properties can explain the specificities observed in the literature and the changes in these specificities in engineered systems. The kinetic models described provide a foundation for understanding RGN targeting and a necessary conceptual framework for their rational engineering.
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CRISPR and Myelin regeneration: a systematic review of applications in demyelinating CNS Disorders, with a focus on MS.
AIMS: Current treatments for demyelinating disorders focus on slowing progression but fail to repair damaged myelin. Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR) -based technology has the potential to address key challenges in myelin repair by targeting genetic dysfunctions, modulating immune responses, and promoting oligodendrocyte differentiation. This systematic review aimed to evaluate CRISPR applications for myelin regeneration. METHODS: A comprehensive search of PubMed, Scopus, and other databases identified 48 studies. The included studies employed CRISPR in diverse experimental models, targeting genes associated with immune regulation and astrocyte activity, as well as correcting RNA splicing dysfunctions linked to neurodegeneration. RESULTS: CRISPR-edited stem cells showed significant potential in promoting myelin regeneration, with enhanced functional recovery in animal models of multiple sclerosis (MS). While most research focused on MS, promising applications were also observed in neuromyelitis optica spectrum disorder (NMOSD), such as reducing astrocytic damage via AQP4 targeting, and in progressive multifocal leukoencephalopathy (PML), where CRISPR disrupted JC polyomavirus replication. CONCLUSIONS: Despite its promise, challenges remain. Future research should prioritize optimizing CRISPR delivery systems, expanding applications to underexplored disorders, and conducting long-term safety assessments. Early results are encouraging, but further studies are essential to translate preclinical success into clinical therapies.
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