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CRISPR-Cas systems: A revolution in genome editing and its diverse applications.
The clustered regularly interspaced short palindromic repeats (CRISPR) Cas (CRISPR6 associated protein) system is an advanced adaptive immune system found in prokaryotes. First discovered in1987, CRISPR Cas has revolutionized genetic research in the past two decades. CRISPR-Cas9 the most widespread system enables precise gene editing by creating double strand breaks. Its ease of use and cost-effectiveness has lowered the barrier to entry for genetic research. CRISPR holds immense potential in many fields from agriculture to medicine. In agriculture, CRISPR has accelerated crop improvement by enabling precise gene edits for desirable traits. In medicine, CRISPR holds promise in xenotransplant, cancers and infectious diseases (HIV) treatment. This review traces the historical development of CRISPR-Cas systems, explores their unique applications, and discusses future advancements aimed at enhancing CRISPR's precision and expanding its applications through technologies like prime and base editing.
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CRISPR-Cas9-mediated editing of starch branching enzymes results in altered starch structure in Brassica napus.
Starch branching enzymes (SBEs) are one of the major classes of enzymes that catalyze starch biosynthesis in plants. Here, we utilized the clustered regularly interspaced short palindromic repeats-CRISPR associated protein 9 (CRISPR-Cas9)-mediated gene editing system to investigate the effects of SBE mutation on starch structure and turnover in the oilseed crop Brassica napus. Multiple single-guide RNA (sgRNA) expression cassettes were assembled into a binary vector and two rounds of transformation were employed to edit all six BnaSBE genes. All mutations were heterozygous monoallelic or biallelic, and no chimeric mutations were detected from a total of 216 editing events. Previously unannotated gene duplication events associated with two BnaSBE genes were characterized through analysis of DNA sequencing chromatograms, reflecting the complexity of genetic information in B. napus. Five Cas9-free homozygous mutant lines carrying two to six mutations of BnaSBE were obtained, allowing us to compare the effect of editing different BnaSBE isoforms. We also found that in the sextuple sbe mutant, although indels were introduced at the genomic DNA level, an alternate transcript of one BnaSBE2.1 gene bypassed the indel-induced frame shift and was translated to a modified full-length protein. Subsequent analyses showed that the sextuple mutant possesses much lower SBE enzyme activity and starch branching frequency, higher starch-bound phosphate content, and altered pattern of amylopectin chain length distribution relative to wild-type (WT) plants. In the sextuple mutant, irregular starch granules and a slower rate of starch degradation during darkness were observed in rosette leaves. At the pod-filling stage, the sextuple mutant was distinguishable from WT plants by its thick main stem. This work demonstrates the applicability of the CRISPR-Cas9 system for the study of multi-gene families and for investigation of gene-dosage effects in the oil crop B. napus. It also highlights the need for rigorous analysis of CRISPR-Cas9-mutated plants, particularly with higher levels of ploidy, to ensure detection of gene duplications.
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Efficient correction of a deleterious point mutation in primary horse fibroblasts with CRISPR-Cas9.
Phenotypic selection during animal domestication has resulted in unwanted incorporation of deleterious mutations. In horses, the autosomal recessive condition known as Glycogen Branching Enzyme Deficiency (GBED) is the result of one of these deleterious mutations (102C > A), in the first exon of the GBE1 gene (GBE1102C>A). With recent advances in genome editing, this type of genetic mutation can be precisely repaired. In this study, we used the RNA-guided nuclease CRISPR-Cas9 (clustered regularly-interspaced short palindromic repeats/CRISPR-associated protein 9) to correct the GBE1102C>A mutation in a primary fibroblast cell line derived from a high genetic merit heterozygous stallion. To correct this mutation by homologous recombination (HR), we designed a series of single guide RNAs (sgRNAs) flanking the mutation and provided different single-stranded donor DNA templates. The distance between the Cas9-mediated double-stranded break (DSB) to the mutation site, rather than DSB efficiency, was the primary determinant for successful HR. This framework can be used for targeting other harmful diseases in animal populations.
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RNase L is a negative regulator of cell migration.
RNase L is a regulated endoribonuclease that functions in the interferon antiviral response. Activation of RNase L by 2', 5'-oligoadenylates has been linked to apoptosis, autophagy and inflammation. Genetic studies have also suggested the possible involvement of the RNase L gene (RNASEL) on chromosome 1q25.3 in several types of cancer. Here we report that ablation of RNase L in human prostate cancer PC3 cells by CRISPR/Cas9 gene editing technology enhanced cell migration as determined both by transwell assays and scratch wound healing assays. In addition, RNase L knockdown by means of RNAi increased migration of PC3 and DU145 cells in response to either fibronectin or serum stimulation, as did homozygous disruption of the RNase L gene in mouse embryonic fibroblasts. Serum or fibronectin stimulation of focal adhesion kinase (FAK) autophosphorylation on tyrosine-397 was increased by either knockdown or ablation of RNase L. In contrast, a missense mutant RNase L (R667A) lacking catalytic activity failed to suppress cell migration in PC3 cells. However, a nuclease-inactive mutant mouse RNase L (W630A) was able to partially inhibit migration of mouse fibroblasts. Consistent with a role for the catalytic activity of RNase L, transfection of PC3 cells with the RNase L activator, 2', 5'-oligoadenylate, suppressed cell migration. RNase L knockdown in PC3 cells enhanced tumor growth and metastasis following implantation in the mouse prostate. Our results suggest that naturally occurring mutations in the RNase L gene might promote enhanced cell migration and metastasis.
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Function Analysis of the PR55/B Gene Related to Self-Incompatibility in Chinese Cabbage Using CRISPR/Cas9.
Chinese cabbage, a major crop in Korea, shows self-incompatibility (SI). SI is controlled by the type 2A serine/threonine protein phosphatases (PP2As). The PP2A gene is controlled by regulatory subunits that comprise a 36 kDa catalyst C subunit, a 65 kDa regulatory A subunit, and a variety of regulatory B subunits (50-70 kDa). Among them, the PP2A 55 kDa B regulatory subunit (PR55/B) gene located in the A05 chromosome has 13 exons spanning 2.9 kb, and two homologous genes, Bra018924 and Bra014296, were found to be present on the A06 and A08 chromosome, respectively. In this study, we performed a functional analysis of the PR55/B gene using clustered regularly interspaced short palindromic repeats/CRISPR-associated system 9 (CRISPR/Cas9)-mediated gene mutagenesis. CRISPR/Cas9 technology can be used to easily introduce mutations in the target gene. Tentative gene-edited lines were generated by the Agrobacterium-mediated transfer and were selected by PCR and Southern hybridization analysis. Furthermore, pods were confirmed to be formed in flower pollination (FP) as well as bud pollination (BP) in some gene-edited lines. Seed fertility of gene-edited lines indicated that the PR55/B gene plays a key role in SI. Finally, self-compatible T-DNA-free T2 gene-edited plants and edited sequences of target genes were secured. The self-compatible Chinese cabbage developed in this study is expected to contribute to Chinese cabbage breeding.
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Focused ultrasound-mediated APOE4 knockdown in mouse brain.
INTRODUCTION: The apolipoprotein E (APOE) ε4 allele is widely recognized as the strongest genetic risk factor for late-onset Alzheimer's disease. Therapeutic strategies to reduce apoE4 expression in APOE ε4 carriers hold promise to mitigate neuroinflammatory and neurodegenerative processes driving disease progression. METHODS: Focused ultrasound (FUS) was employed to transiently open the blood-brain barrier (BBB) for efficient knockdown of humanized APOE ε4 in the mouse brain via gene editing. The all-in-one clustered regularly interspaced short palindromic repeats (CRISPR)-based adeno-associated virus (AAV) vectors were administered intravenously at a dose of 1.5×1012 vg per mouse to determine the gene-editing efficacy within the hippocampus. RESULTS: FUS-enhanced delivery of AAV resulted in a 12.6% knockdown of APOE ε4 gene expression in the targeted hippocampus, accompanied by an over 20% decrease in apoE4 protein levels and significant reductions in astrocyte and microglia levels. DISCUSSION: Our findings demonstrate a noninvasive, targeted approach for APOE ε4 knockdown, highlighting FUS-mediated brain-directed interventions as a promising therapeutic strategy for Alzheimer's disease. HIGHLIGHTS: Focused ultrasound (FUS) enables noninvasive, transient blood-brain barrier (BBB) opening for enhanced adeno-associated virus (AAV) delivery. FUS-mediated gene editing achieves a 12.6% knockdown in APOE ε4 expression within the hippocampus of mouse brain. APOE ε4 knockdown significantly reduces apoE4 protein levels and astrocyte and microglia levels. No detectable gross toxicity was observed following the FUS-mediated gene editing.
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CRISPR Gene Editing of Murine Blood Stem and Progenitor Cells Induces MLL-AF9 Chromosomal Translocation and MLL-AF9 Leukaemogenesis.
Chromosomal rearrangements of the mixed lineage leukaemia (MLL, also known as KMT2A) gene on chromosome 11q23 are amongst the most common genetic abnormalities observed in human acute leukaemias. MLL rearrangements (MLLr) are the most common cytogenetic abnormalities in infant and childhood acute myeloid leukaemia (AML) and acute lymphocytic leukaemia (ALL) and do not normally acquire secondary mutations compared to other leukaemias. To model these leukaemias, we have used clustered regularly interspaced short palindromic repeats (CRISPR)/Cas9 gene editing to induce MLL-AF9 (MA9) chromosomal rearrangements in murine hematopoietic stem and progenitor cell lines and primary cells. By utilizing a dual-single guide RNA (sgRNA) approach targeting the breakpoint cluster region of murine Mll and Af9 equivalent to that in human MA9 rearrangements, we show efficient de novo generation of MA9 fusion product at the DNA and RNA levels in the bulk population. The leukaemic features of MA9-induced disease were observed including increased clonogenicity, enrichment of c-Kit-positive leukaemic stem cells and increased MA9 target gene expression. This approach provided a rapid and reliable means of de novo generation of Mll-Af9 genetic rearrangements in murine haematopoietic stem and progenitor cells (HSPCs), using CRISPR/Cas9 technology to produce a cellular model of MA9 leukaemias which faithfully reproduces many features of the human disease in vitro.
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Innovative Strategies of Reprogramming Immune System Cells by Targeting CRISPR/Cas9-Based Genome-Editing Tools: A New Era of Cancer Management.
The recent developments in the study of clustered regularly interspaced short palindromic repeats/associated protein 9 (CRISPR/Cas9) system have revolutionized the art of genome-editing and its applications for cellular differentiation and immune response behavior. This technology has further helped in understanding the mysteries of cancer progression and possible designing of novel antitumor immunotherapies. CRISPR/Cas9-based genome-editing is now often used to engineer universal T-cells, equipped with recombinant T-cell receptor (TCR) or chimeric antigen receptor (CAR). In addition, this technology is used in cytokine stimulation, antibody designing, natural killer (NK) cell transfer, and to overcome immune checkpoints. The innovative potential of CRISPR/Cas9 in preparing the building blocks of adoptive cell transfer (ACT) immunotherapy has opened a new window of antitumor immunotherapy and some of them have gained FDA approval. The manipulation of immunogenetic regulators has opened a new interface for designing, implementation and interpretation of CRISPR/Cas9-based screening in immuno-oncology. Several cancers like lymphoma, melanoma, lung, and liver malignancies have been treated with this strategy, once thought to be impossible. The safe and efficient delivery of CRISPR/Cas9 system within the immune cells for the genome-editing strategy is a challenging task which needs to be sorted out for efficient immunotherapy. Several targeting approaches like virus-mediated, electroporation, microinjection and nanoformulation-based methods have been used, but each procedure offers some limitations. Here, we elaborate the recent updates of cancer management through immunotherapy in partnership with CRISPR/Cas9 technology. Further, some innovative methods of targeting this genome-editing system within the immune system cells for reprogramming them, as a novel strategy of anticancer immunotherapy is elaborated. In addition, future prospects and clinical trials are also discussed.
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Efficient selection of a biallelic and nonchimeric gene-edited tree using Oxford Nanopore Technologies sequencing.
The clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR-associated protein 9 nuclease system is a versatile and essential biotechnological tool in the life sciences that allows efficient genome editing. When generating gene-edited trees, T0-generation plants are often used for subsequent analysis because of the time that is required to obtain the desired mutants via crossing. However, T0-generation plants exhibit various unexpected mutations, which emphasizes the need to identify mutants with expected mutation patterns. The two critical checkpoints in this process are to confirm the expected mutation patterns in both alleles and to exclude somatic chimeric plants. In this study, we generated gene-edited Cryptomeria japonica plants and established a method to determine chimerism and mutation patterns using fragment analysis and Oxford Nanopore Technologies (ONT)-based amplicon sequencing. In the first screening, fragment analysis, i.e., indel detection via amplicon analysis, was used to predict indel mutation patterns in both alleles and to discriminate somatic chimeric plants in 188 candidate mutants. In the second screening, we precisely determined the mutation patterns and chimerism in the mutants using ONT-based amplicon sequencing, where confirmation of both alleles can be achieved using allele-specific markers flanking the single guide RNA target site. In the present study, a bioinformatic analysis procedure was developed and provided for the rapid and accurate determination of DNA mutation patterns using ONT-based amplicon sequencing. As ONT amplicon sequencing has a low running cost compared with other long-read analysis methods, such as PacBio, it is a powerful tool in plant genetics and biotechnology to select gene-edited plants with expected indel patterns in the T0-generation.
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Gene editing as applied to prevention of reproductive porcine reproductive and respiratory syndrome.
Porcine Reproductive and Respiratory Syndrome (PRRS) causes severe reproductive failure in sows as well as transplacental transfer of PRRS virus (PRRSV) to late-gestation fetuses, resulting in abortions, early farrowing, increased number of stillborn piglets, and weak neonatal piglets. PRRSV-infected boars present with anorexia and lethargy, and have decreased sperm quality. The gene for the cellular receptor that the PRRSV uses, Cluster of differentiation 163 (CD163), was edited using Clustered regularly interspaced short palindromic repeats (CRISPR)/Cas9 gene-editing technology to create biallelic DNA edits to the CD163 gene in 100% of the offspring. CD163-null pigs challenged with virus were completely resistant to both Type 1 and Type 2 PRRSV isolates, as measured by clinical signs, viremia, antibody response, and lung histopathology. In vitro studies showed that CD163-null alveolar macrophages were also not permissive to infection by a panel of six Type 1 and nine Type 2 viral isolates. Thus, DNA editing of the CD163 gene prevented PRRSV infection and reproductive losses associated with infection.
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