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Polyvalent Guide RNAs Enhance the CRISPR-Mediated Suppression of a Human Coronavirus.
While CRISPR enzymes have become important tools for targeted gene editing in mammalian cells, they can also be used to specifically target and deplete viral nucleic acids to treat infections; this can be accomplished by delivering an RNA-targeting CRISPR effector like Cas13 along with a guide RNA (gRNA) that recognizes sequences from the genomes of single-stranded RNA (ssRNA) viruses. Previously, we hypothesized that by designing individual gRNAs able to target multiple, similar-but-not-identical viral sequences simultaneously ("polyvalent" guide RNAs or pgRNAs), gRNA's polyvalency would overcome any deficits caused by mispairing between the gRNA and the viral targets and, hence, still increase Cas13's antiviral potency and prevent mutagenic escape. We subsequently demonstrated this was the case using a model of viral infection in plants; however, it was not determined whether this strategy would also work against a human virus. Here, pgRNAs were designed to target multiple RNA sequences within human coronavirus 229E (hCoV-229E) and delivered along with Cas13 into a human lung epithelial cell line infected by hCoV-229E. CRISPR antiviral treatments using pgRNAs exhibited significant viral suppression in a CRISPR-dependent manner─more so than their single-target gRNA counterparts, even when multiple single-target gRNAs were used simultaneously. This improvement was also observed even as Cas13 with those same pgRNAs exhibited less "collateral" or nonspecific RNase activity relative to their single-target counterparts, which could imply that they may have greater specificity and safety profiles as therapeutic agents. Our findings demonstrate a computational and experimental pipeline by which pgRNAs, created using an unconventional gRNA design strategy, can be generated and validated to target human viruses using CRISPR antiviral biotechnologies more effectively.
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An improved strategy for CRISPR/Cas9 gene knockout and subsequent wildtype and mutant gene rescue.
A fluorescence marker mOrange was inserted to the popular pLentiCrispr-V2 to create pLentiCrispr-V2-mOrange (V2mO) that contained both a puromycin selection and a fluorescent marker, making viral production and target transduction visible. Lentiviruses packaged with this plasmid and appropriate guide RNAs (gRNAs) successfully knocked out the genes RhoA, Gli1, and Gal3 in human gastric cancer cell lines. Cas9-gRNA editing efficiency could be estimated directly from Sanger electropherograms of short polymerase chain reaction products around the gRNA regions in Cas9-gRNA transduced cells. Single cloning of transduced target cell pools must be performed to establish stable knockout clones. Rescue of wildtype (RhoA and Gal3) and mutant (RhoA.Y42C) genes into knockout cells was successful only when cDNAs, where gRNAs bind, were modified by three nucleotides while the amino acid sequences remained unchanged. Stringent on-target CRISPR/Cas9 editing was observed in Gal3 gene, but not in RhoA gene since RhoA.Y42C already presented a nucleotide change in gRNA5 binding site. In summary, our improved strategy added these advantages: adding visual marker to the popular lentiviral system, monitoring lentiviral production and transduction efficiencies, cell-sorting Cas9+ cells in target cells by fluorescence-activated cell sorting, direct estimation of gene editing efficiency of target cell pools by short PCR electropherograms around gRNA binding sites, and successful rescue of wildtype and mutant genes in knockout cells, overcoming Cas9 editing by modifying cDNAs.
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Efficient genome editing by CRISPR-Mb3Cas12a in mice.
As an alternative and complementary approach to Cas9-based genome editing, Cas12a has not been widely used in mammalian cells largely due to its strict requirement for the TTTV protospacer adjacent motif (PAM) sequence. Here, we report that Mb3Cas12a (Moraxella bovoculi AAX11_00205) can efficiently edit the mouse genome based on the TTV PAM sequence with minimal numbers of large on-target deletions or insertions. When TTTV PAM sequence-targeting CRISPR (cr)RNAs of 23 nt spacers are used, >70% of the founders obtained are edited. Moreover, the use of Mb3Cas12a tagged to monomeric streptavidin (mSA) in conjunction with biotinylated DNA donor template leads to high knock-in efficiency in two-cell mouse embryos, with 40% of founders obtained containing the desired knock-in sequences.
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Computer logic meets cell biology: how cell science is getting an upgrade.
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Response to "Unexpected mutations after CRISPR-Cas9 editing in vivo".
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Self-Cutting and Integrating CRISPR Plasmids Enable Targeted Genomic Integration of Genetic Payloads for Rapid Cell Engineering.
Since observations that CRISPR nucleases function in mammalian cells, many strategies have been devised to adapt them for genetic engineering. Here, we investigated self-cutting and integrating CRISPR-Cas9 plasmids (SCIPs) as easy-to-use gene editing tools that insert themselves at CRISPR-guided locations. SCIPs demonstrated similar expression kinetics and gene disruption efficiency in mouse (EL4) and human (Jurkat) cells, with stable integration in 3-6% of transfected cells. Clonal sequencing analysis indicated that integrants showed bi- or mono-allelic integration of entire CRISPR plasmids in predictable orientations and with limited insertion or deletion formation. Interestingly, including longer homology arms (HAs; 500 bp) in varying orientations only modestly increased knock-in efficiency (by around twofold). Using a SCIP-payload design (SCIPpay) that liberates a promoter-less sequence flanked by HAs thereby requiring perfect homology-directed repair for transgene expression, longer HAs resulted in higher integration efficiency and precision of the payload but did not affect integration of the remaining plasmid sequence. As proofs of concept, we used SCIPpay to insert (1) a gene fragment encoding tdTomato into the CD69 locus of Jurkat cells, thereby creating a cell line that reports T-cell activation, and (2) a chimeric antigen receptor gene into the TRAC locus. Here, we demonstrate that SCIPs function as simple, efficient, and programmable tools useful for generating gene knock-out/knock-in cell lines, and we suggest future utility in knock-in site screening/optimization, unbiased off-target site identification, and multiplexed, iterative, and/or library-scale automated genome engineering.
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The Ethics of Gene Editing from an Islamic Perspective: A Focus on the Recent Gene Editing of the Chinese Twins.
In light of the development of "CRISPR" technology, new promising advances in therapeutic and preventive approaches have become a reality. However, with it came many ethical challenges. The most recent worldwide condemnation of the first use of CRISPR to genetically modify a human embryo is the latest example of ethically questionable use of this new and emerging field. Monotheistic religions are very conservative about such changes to the human genome and can be considered an interference with God's creation. Moreover, these changes could cause perpetual changes to future generations. The Muslim scholars establish their decisions by addressing five foundations of Islamic law i.e. "maqāṣid al sharı̄`a"; the purposes of the law. These are dın̄ (religion), nafs (life), nasl (progeny), `aql (intellect) and māl (wealth). To achieve this, the five principles should all be met before approval of an experiment like the Chinese embryo modifications; Qaṣd (intention) which is achieved in this case as it aims to protect the embryo from HIV. Yaqın̄ (certainty) and Ḍarar (injury) were not satisfied as they require strong scientific certainty of the procedures, and evidence of safety. Ḍarūra (necessity) by which the alternatives being compared; in this case more established and proven safe alternatives to protect the HIV transmission from the father are available, so this principle is not met. The final principle is `Urf (custom), by which the social context of using any contemporary technology should be taken in consideration, and clearly this was not achieved. Collectively, germline changes are rejected from an Islamic perspective until the five principles are fulfilled. In the Chinese Twins gene editing case, there was clearly no justification or support for it according to the Muslim Jurisprudence laws. These laws and approaches can serve as an ethical checklist for such controversial research, especially in early stages of the research.
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Integration of CRISPR-engineering and hiPSC-based models of psychiatric genomics.
Neuropsychiatric disorders are highly heritable polygenic disorders arising from the complex interplay of highly penetrant rare variants and common variants of small effect. There is a large index of comorbidity and shared genetic risk between disorders, reflecting the pleiotropy of individual variants as well as predicted downstream pathway-level convergence. Importantly, the mechanism(s) through which psychiatric disease-associated variants interact to contribute to disease risk remains unknown. Human induced pluripotent stem cell (hiPSC)-based models are increasingly useful for the systematic study of the complex genetics associated with brain diseases, particularly when combined with CRISPR-mediated genomic engineering, which together facilitate isogenic comparisons of defined neuronal cell types. In this review, we discuss the latest CRISPR technologies and consider how they can be successfully applied to the functional characterization of the growing list genetic variants linked to psychiatric disease.
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Rapid and marker-free gene replacement in citric acid-producing Aspergillus tubingensis (A. niger) WU-2223L by the CRISPR/Cas9 system-based genome editing technique using DNA fragments encoding sgRNAs.
Strains belonging to Aspergillus section Nigri, including Aspergillus niger, are used for industrial production of citric acid from carbohydrates such as molasses and starch. The objective of this study was to construct the genome editing system that could enable rapid and efficient gene replacement in citric acid-producing fungi for genetic breeding. Using the citric acid-hyperproducer A. tubingensis (formerly A. niger) WU-2223L as a model strain, we developed a CRISPR/Cas9 system-based genome editing technique involving co-transformation of Cas9 and the DNA fragment encoding single guide RNA (sgRNA). Using this system, ATP-sulfurylase gene (sC) knock-out strain derived from WU-2223L was generated; the knock-out efficiency was 29 transformants when 5 μg Cas9 was added to 5 × 105 protoplasts. In the gene replacement method based on this system, a DNA fragment encoding sgRNAs that target both the gene of interest and marker gene was used, and replacement of nitrate reductase gene (niaD) using sC gene as a marker gene was attempted. More than 90% of the sC-knock-out transformants exhibited replaced niaD, indicating efficient gene replacement. Moreover, one-step marker rescue of the sC marker gene was accomplished by excising the knock-in donor via intramolecular homologous recombination, enabling marker-free genome editing and drastically shortening the gene replacement period by circumventing the transformation procedure to recover the sC gene. Thus, we succeeded in constructing a CRISPR/Cas9 system-based rapid and marker-free gene replacement system for the citric acid-hyperproducer strain WU-2223L.
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Selective targeting of KRAS oncogenic alleles by CRISPR/Cas9 inhibits proliferation of cancer cells.
Mutations within the KRAS oncogene are associated with the proliferation of various cancers. Therapeutic approaches for treating cancers with such mutations have focused on targeting the downstream protein effectors of KRAS. However, to date, no approved treatment has targeted the mutated KRAS oncogene directly. Presently, we used the selectivity of the CRISPR/Cas9 system to directly target mutated KRAS alleles. We designed single-guide RNAs (sgRNAs) to target two specific single-nucleotide missense mutations on KRAS codon-12 located in the seed region adjacent to a protospacer adjacent motif (PAM). Lentiviral transduction of Cas9 and the sgRNAs into cancer cells with respective KRAS mutations resulted in high frequency of indels in the seed region. Indel-associated disruption of the mutant KRAS alleles correlated with reduced viability of the cancer cells. The results indicate that CRISPR-Cas9-mediated genome editing can potentially be used for the treatment of cancer patients, specifically those with oncogenic KRAS mutations.
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