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Improved CRISPR/Cas9 Tools for the Rapid Metabolic Engineering of Clostridium acetobutylicum.
Clustered regularly interspaced short palindromic repeats (CRISPR)/Cas (CRISPR-associated proteins)9 tools have revolutionized biology-several highly efficient tools have been constructed that have resulted in the ability to quickly engineer model bacteria, for example, Escherichia coli. However, the use of CRISPR/Cas9 tools has lagged behind in non-model bacteria, hampering engineering efforts. Here, we developed improved CRISPR/Cas9 tools to enable efficient rapid metabolic engineering of the industrially relevant bacterium Clostridium acetobutylicum. Previous efforts to implement a CRISPR/Cas9 system in C. acetobutylicum have been hampered by the lack of tightly controlled inducible systems along with large plasmids resulting in low transformation efficiencies. We successfully integrated the cas9 gene from Streptococcuspyogenes into the genome under control of the xylose inducible system from Clostridium difficile, which we then showed resulted in a tightly controlled system. We then optimized the length of the editing cassette, resulting in a small editing plasmid, which also contained the upp gene in order to rapidly lose the plasmid using the upp/5-fluorouracil counter-selection system. We used this system to perform individual and sequential deletions of ldhA and the ptb-buk operon.
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On-line Sequencing of CRISPR Guide RNAs and Their Impurities via the Use of Immobilized Ribonuclease Cartridges Attached to a 2D/3D-LC-MS System.
In this study, for the first time, the automated digestion and sequencing of an RNA molecule via the use of immobilized RNase cartridges attached to a multidimensional liquid chromatography (LC)-mass spectrometry (MS) system are presented. We first developed an on-line digestion-HILIC two-dimensional (2D)-LC-MS method in order to sequence CRISPR guide RNAs for gene editing. Three RNases (T1, A, and U2) were immobilized on polyetheretherketone cartridges, and their performance was evaluated. Ultrafast digestions were performed within 2.3 min with the on-line approach versus 30 min via the conventional off-line approach. The higher sequence coverage was achieved by the RNase T1 (71%), which is the same as the off-line mode. A 20-fold reduction in the gRNA sample amount was achieved with the on-line digestion approach (6.5 μg) in comparison to that with the off-line approach (130 μg). In the second step, a three-dimensional (3D)-LC-MS method was developed for the sequencing of fractions collected on-line across the main peak and the partially separated tail by the reference ion-pairing RPLC method. Additional insights were gained in order to better understand the cause of the main peak tailing.
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Modeling Disease In Vivo With CRISPR/Cas9.
The recent advent of CRISPR/Cas9-mediated genome editing has created a wave of excitement across the scientific research community, carrying the promise of simple and effective genomic manipulation of nearly any cell type. CRISPR has quickly become the preferred tool for genetic manipulation, and shows incredible promise as a platform for studying gene function in vivo. I discuss the current application of CRISPR technology to create new in vivo disease models, with a particular focus on how these tools, derived from an adaptive bacterial immune system, are helping us to better model the complexity of human cancer.
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An efficient and cost-effective method for disrupting genes in RAW264.7 macrophages using CRISPR-Cas9.
The clustered regularly interspaced short palindromic repeats (CRISPR) and CRISPR-associated protein 9 (Cas9) are widely used for genome editing in cultured cell lines. However, the implementation of genome editing is still challenging due to the complex and often costly multi-step process associated with this technique. Moreover, the efficiency of genome editing varies across cell types, often limiting utility. Herein, we describe pCRISPR-EASY, a vector for simplified cloning of single guide RNAs (sgRNAs) and its simultaneous introduction with CRISPR-Cas9 into cultured cells using a non-viral delivery system. We outline a comprehensive, step-by-step protocol for genome editing in RAW264.7 macrophages, a mouse macrophage cell line widely used in biomedical research for which genome editing using CRISPR-Cas9 has been restricted to lentiviral or expensive commercial reagents. This provides an economical, highly efficient and reliable method for genome editing that can easily be adapted for use in other systems.
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CRISPR-Cas9-mediated Large Cluster Deletion and Multiplex Genome Editing in Paenibacillus polymyxa.
The use of molecular tools based on the clustered regularly interspaced short palindromic repeats-Cas (CRISPR-Cas) systems has rapidly advanced genetic engineering. These molecular biological tools have been applied for different genetic engineering purposes in multiple organisms, including the quite rarely explored Paenibacillus polymyxa. However, only limited studies on large cluster deletion and multiplex genome editing have been described for this highly interesting and versatile bacterium. Here, we demonstrate the utilization of a Cas9-based system to realize targeted deletions of four biosynthetic gene clusters in the range of 12-41 kb by the use of a single targeting sgRNA. Furthermore, we also harnessed the system for multiplex editing of genes and large genomic regions. Multiplex deletion was achieved with more than 80% efficiency, while simultaneous integration at two distantly located sites was obtained with 58% efficiency. The findings reported in this study are anticipated to accelerate future research in P. polymyxa and related species.
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An Undergraduate Laboratory on Recombineering and CRISPR/Cas9-Assisted Gene Editing in Escherichia coli.
Laboratory experience is vital to undergraduate science education. It allows students to observe and conduct engaging experiments to enhance their skills and literacy, helps them retain knowledge, and deepens their understanding of related content covered in lectures. This paper reports a 4-week undergraduate laboratory exercise on Escherichia coli gene editing by recombineering, recombination-mediated genetic engineering, with or without clustered regularly interspaced short palindromic repeats and their associated protein 9 (CRISPR/Cas9). Gene editing makes precise modifications to the DNA of living organisms that influence their development and functions. As technology evolves, recombineering and CRISPR/Cas9 have replaced methods that use restriction enzymes and DNA ligase and are applied to a wide variety of research and applications. It is necessary to introduce undergraduates to these two rapidly growing technologies. Student results obtained from the lab indicate that antisense single-stranded oligodeoxynucleotide (ssODN) has a 15-20 times higher recombineering efficiency than the sense strand. Treatment with a plasmid containing the crRNA target of CRISPR/Cas9 increased recombineering efficiency. Instructional assessments, based on student feedback, revealed that the lab had clear objectives, instructions, and explicit protocols, with sufficient time to complete them, and was found to be interesting and worthwhile. Student learning outcomes, assessed by comparing pre-lab questions and post-lab tests, suggested that they learned the underlying principles and detailed molecular mechanisms. Besides learning the technologies and acquiring basic laboratory skills, students practiced key components of scientific research, such as data collection, analysis, and scientific communication.
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Spatiotemporal control of CRISPR/Cas9 gene editing.
The clustered regularly interspaced short palindromic repeats (CRISPR)/associated protein 9 (CRISPR/Cas9) gene editing technology, as a revolutionary breakthrough in genetic engineering, offers a promising platform to improve the treatment of various genetic and infectious diseases because of its simple design and powerful ability to edit different loci simultaneously. However, failure to conduct precise gene editing in specific tissues or cells within a certain time may result in undesirable consequences, such as serious off-target effects, representing a critical challenge for the clinical translation of the technology. Recently, some emerging strategies using genetic regulation, chemical and physical strategies to regulate the activity of CRISPR/Cas9 have shown promising results in the improvement of spatiotemporal controllability. Herein, in this review, we first summarize the latest progress of these advanced strategies involving cell-specific promoters, small-molecule activation and inhibition, bioresponsive delivery carriers, and optical/thermal/ultrasonic/magnetic activation. Next, we highlight the advantages and disadvantages of various strategies and discuss their obstacles and limitations in clinical translation. Finally, we propose viewpoints on directions that can be explored to further improve the spatiotemporal operability of CRISPR/Cas9.
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Large scale control and programming of gene expression using CRISPR.
The control of gene expression in cells and organisms allows to unveil gene to function relationships and to reprogram biological responses. Several systems, such as Zinc fingers, TALE (Transcription activator-like effectors), and siRNAs (small-interfering RNAs), have been exploited to achieve this. However, recent advances in Clustered Regularly Interspaced Short Palindromic Repeats and Cas9 (CRISPR-Cas9) have overshadowed them due to high specificity, compatibility with many different organisms, and design flexibility. In this review we summarize state-of-the art for CRISPR-Cas9 technology for large scale gene perturbation studies, including single gene and multiple genes knock-out, knock-down, knock-up libraries, and their associated screening assays. We feature in particular the combination of these methods with single-cell transcriptomics approaches. Finally, we highlight the application of CRISPR-Cas9 systems in building synthetic circuits that can be interfaced with gene networks to control cellular states.
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Unexpected gene activation following CRISPR-Cas9-mediated genome editing.
The discovery of the Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR) and its development as a genome editing tool has revolutionized the field of molecular biology. In the DNA damage field, CRISPR has brought an alternative to induce endogenous double-strand breaks (DSBs) at desired genomic locations and study the DNA damage response and its consequences. Many systems for sgRNA delivery have been reported in order to efficiently generate this DSB, including lentiviral vectors. However, some of the consequences of these systems are not yet well understood. Here, we report that lentiviral-based sgRNA vectors can integrate into the endogenous genomic target location, leading to undesired activation of the target gene. By generating a DSB in the regulatory region of the ABCB1 gene using a lentiviral sgRNA vector, we can induce the formation of Taxol-resistant colonies. We show that these colonies upregulate ABCB1 via integration of the EEF1A1 and the U6 promoters from the sgRNA vector. We believe that this is an unreported CRISPR/Cas9 on-target effect that researchers need to be aware of when using lentiviral vectors for genome editing.
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Binding and Ligand Activation Driven Enrichment-Directed Evolution of SaCas9 gRNAs Improves Gene Editing Efficiency.
Clustered regularly interspaced short palindromic repeats-based editing is inefficient at over two-thirds of genetic targets. A primary cause is ribonucleic acid (RNA) misfolding that can occur between the spacer and scaffold regions of the gRNA, which hinders the formation of functional Cas9 ribonucleoprotein (RNP) complexes. Here, we uncover hundreds of highly efficient gRNA variant scaffolds for Staphylococcus aureus (Sa)Cas9 utilizing an innovative binding and ligand activation driven enrichment (BLADE) methodology, which leverages asymmetrical product dissociation over rounds of evolution. SaBLADE-derived gRNA scaffolds contain 7%-42% of nucleotide variation relative to wild type. gRNA variants are able to improve gene editing efficiency at all targets tested, and they achieve their highest levels of editing improvement (>400%) at the most challenging DNA target sites for the wild-type SaCas9 gRNA. This arsenal of SaBLADE-derived gRNA variants showcases the power and flexibility of combinatorial chemistry and directed evolution to enable efficient gene editing at challenging, or previously intractable, genomic sites.
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