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Cpf1-Database: web-based genome-wide guide RNA library design for gene knockout screens using CRISPR-Cpf1.
SUMMARY: Following the type II CRISPR-Cas9 system, type V CRISPR-Cpf1 endonucleases have been found to be applicable for genome editing in various organisms in vivo. However, there are as yet no web-based tools capable of optimally selecting guide RNAs (gRNAs) among all possible genome-wide target sites. Here, we present Cpf1-Database, a genome-wide gRNA library design tool for LbCpf1 and AsCpf1, which have DNA recognition sequences of 5'-TTTN-3' at the 5' ends of target sites. Cpf1-Database provides a sophisticated but simple way to design gRNAs for AsCpf1 nucleases on the genome scale. One can easily access the data using a straightforward web interface, and using the powerful collections feature one can easily design gRNAs for thousands of genes in short time. AVAILABILITY AND IMPLEMENTATION: Free access at http://www.rgenome.net/cpf1-database/. CONTACT: sangsubae@hanyang.ac.kr.
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Delivery approaches for CRISPR/Cas9 therapeutics in vivo: advances and challenges.
INTRODUCTION: Therapeutic gene editing is becoming a viable biomedical tool with the emergence of the CRISPR/Cas9 system. CRISPR-based technologies have promise as a therapeutic platform for many human genetic diseases previously considered untreatable, providing a flexible approach to high-fidelity gene editing. For many diseases, such as sickle-cell disease and beta thalassemia, curative therapy may already be on the horizon, with CRISPR-based clinical trials slated for the next few years. Translation of CRISPR-based therapy to in vivo application however, is no small feat, and major hurdles remain for efficacious use of the CRISPR/Cas9 system in clinical contexts. AREAS COVERED: In this topical review, we highlight recent advances to in vivo delivery of the CRISPR/Cas9 system using various packaging formats, including viral, mRNA, plasmid, and protein-based approaches. We also discuss some of the barriers which have yet to be overcome for successful translation of this technology. EXPERT OPINION: This review focuses on the challenges to efficacy for various delivery formats, with specific emphasis on overcoming these challenges through the development of carrier vehicles for transient approaches to CRISPR/Cas9 delivery in vivo.
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Live genome imaging by CRISPR engineering: progress and problems.
CRISPR-Cas-based genome imaging opened a new era of genome visualization in living cells. While genomic loci with repetitive sequences, such as centromeres and telomeres, can be reliably imaged, applying the technique to nonrepetitive genomic loci has remained challenging. Recent advancements in the design of CRISPR RNAs and Cas proteins, the development of novel fluorophores and the combination of CRISPR-Cas with other molecular machinery amplified target-specific signals and suppressed background signals, revolutionizing this unique genome imaging technique and enabling the tracking of genomic loci with a small number of CRISPR-Cas complexes, down to a single complex. Here we review the latest advancements in CRISPR-Cas-based genome imaging techniques and their application to imaging nonrepetitive genomic loci. The challenges that these techniques are currently facing are the cellular toxicity and genomic instability induced by the expression of CRISPR-Cas and its interference with DNA metabolism, which impacts DNA replication and genome maintenance. Recently reported adverse effects of CRISPR-Cas-based genome labeling are discussed here, along with perspectives on how to overcome the problem.
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Small molecule regulated sgRNAs enable control of genome editing in E. coli by Cas9.
CRISPR-Cas9 has led to great advances in gene editing for a broad spectrum of applications. To further the utility of Cas9 there have been efforts to achieve temporal control over its nuclease activity. While different approaches have focused on regulation of CRISPR interference or editing in mammalian cells, none of the reported methods enable control of the nuclease activity in bacteria. Here, we develop RNA linkers to combine theophylline- and 3-methylxanthine (3MX)-binding aptamers with the sgRNA, enabling small molecule-dependent editing in Escherichia coli. These activatable guide RNAs enable temporal and post-transcriptional control of in vivo gene editing. Further, they reduce the death of host cells caused by cuts in the genome, a major limitation of CRISPR-mediated bacterial recombineering.
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Progress and Application of CRISPR/Cas Technology in Biological and Biomedical Investigation.
Based on the tremendous progress of the understanding on the CRISPR-Cas systems, the application CRISPR/Cas technology has been extended into increasing scenarios in biological and biomedical investigation. The potency of gene editing has been greatly improved by the rapid development of engineered Cas9 variants and modified CRISPR platforms. As advanced sequencing technology identified vast causative genetic basis for human diseases, CRISPR toolkits are now able to mediate precise genetic disruption or correction in vitro and in vivo. In this review, we have discussed the recent development of the CRISPR/Cas gene-editing technology and the extensive applications of the CRISPR platforms in biological and biomedical investigation, including disease modeling in animal and human cell line, development of gene therapy, as well as high-throughput genetic screening. J. Cell. Biochem. 118: 3061-3071, 2017. © 2017 Wiley Periodicals, Inc.
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qEva-CRISPR: a method for quantitative evaluation of CRISPR/Cas-mediated genome editing in target and off-target sites.
Genome editing technology based on engineered nucleases has been increasingly applied for targeted modification of genes in a variety of cell types and organisms. However, the methods currently used for evaluating the editing efficiency still suffer from many limitations, including preferential detection of some mutation types, sensitivity to polymorphisms that hamper mismatch detection, lack of multiplex capability, or sensitivity to assay conditions. Here, we describe qEva-CRISPR, a new quantitative method that overcomes these limitations and allows simultaneous (multiplex) analysis of CRISPR/Cas9-induced modifications in a target and the corresponding off-targets or in several different targets. We demonstrate all of the advantages of the qEva-CRISPR method using a number of sgRNAs targeting the TP53, VEGFA, CCR5, EMX1 and HTT genes in different cell lines and under different experimental conditions. Unlike other methods, qEva-CRISPR detects all types of mutations, including point mutations and large deletions, and its sensitivity does not depend on the mutation type. Moreover, this approach allows for successful analysis of targets located in 'difficult' genomic regions. In conclusion, qEva-CRISPR may become a method of choice for unbiased sgRNA screening to evaluate experimental conditions that affect genome editing or to distinguish homology-directed repair from non-homologous end joining.
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Research Techniques Made Simple: CRISPR Genetic Screens.
CRISPR and Cas proteins, often referred to as CRISPR/Cas, are the components of a bacterial genome editing system that can be used to perturb genes in cells and tissues. A classic application is to use CRISPR/Cas to generate genetic loss-of-function. When performed at large scale and combined with deep sequencing techniques, CRISPR-based perturbations can be performed in a high throughput setting to screen many candidate genomic elements for their roles in a phenotype of interest. Here, we discuss major considerations in the design, execution, and analysis of CRISPR screens. We focus on CRISPR knockout screens but also review adaptations to the CRISPR/Cas system that highlight the versatility of the system to make other types of experimental genetic changes as well. We also discuss examples of CRISPR genetic screens in investigative dermatology and how they may be used to answer key scientific questions in the field.
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Simplified CRISPR tools for efficient genome editing and streamlined protocols for their delivery into mammalian cells and mouse zygotes.
Genome editing using the CRISPR/Cas9 system requires the presence of guide RNAs bound to the Cas9 endonuclease as a ribonucleoprotein (RNP) complex in cells, which cleaves the host cell genome at sites specified by the guide RNAs. New genetic material may be introduced during repair of the double-stranded break via homology dependent repair (HDR) if suitable DNA templates are delivered with the CRISPR components. Early methods used plasmid or viral vectors to make these components in the host cell, however newer approaches using recombinant Cas9 protein with synthetic guide RNAs introduced directly as an RNP complex into cells shows faster onset of action with fewer off-target effects. This approach also enables use of chemically modified synthetic guide RNAs that have improved nuclease stability and reduces the risk of triggering an innate immune response in the host cell. This article provides detailed methods for genome editing using the RNP approach with synthetic guide RNAs using lipofection or electroporation in mammalian cells or using microinjection in murine zygotes, with or without addition of a single-stranded HDR template DNA.
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"Split-and-Click" sgRNA.
CRISPR-Cas9 gene editing is dependent on a programmable single guide RNA (sgRNA) that directs Cas9 endonuclease activity. This RNA is often generated by enzymatic reactions, however the process becomes time-consuming as the number of sgRNAs increases and does not allow the incorporation of chemical modifications that can improve or expand the functionality of CRISPR. Solid-phase RNA synthesis can overcome these issues, but highly pure full-length sgRNA remains at the limits of current synthetic methods. Here, we demonstrate a "split-and-click" approach that separates the sgRNA into its two smaller components - a DNA-targeting ~20-mer RNA and a constant Cas9-binding 79-mer RNA - and chemically ligates them together to generate a biologically active sgRNA. The benefits of our approach lie in the stringent purification of the DNA-targeting 20-mer, the reduced synthesis of the constant 79-mer each time a new sgRNA is required, and the rapid access it provides to custom libraries of sgRNAs.
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CRISPR-Cas13 Inhibitors Block RNA Editing in Bacteria and Mammalian Cells.
Cas13 has demonstrated unique and broad utility in RNA editing, nucleic acid detection, and disease diagnosis; however, a constantly active Cas enzyme may induce unwanted effects. Bacteriophage- or prophage-region-encoded anti-CRISPR (acr) gene molecules provide the potential to control targeting specificity and potency to allow for optimal RNA editing and nucleic acid detection by spatiotemporally modulating endonuclease activities. Using integrated approaches to screen acrVI candidates and evaluate their effects on Cas13 function, we discovered a series of acrVIA1-7 genes that block the activities of Cas13a. These VI-A CRISPR inhibitors substantially attenuate RNA targeting and editing by Cas13a in human cells. Strikingly, type VI-A anti-CRISPRs (AcrVIAs) also significantly muffle the single-nucleic-acid editing ability of the dCas13a RNA-editing system. Mechanistically, AcrVIA1, -4, -5, and -6 bind LwaCas13a, while AcrVIA2 and -3 can only bind the LwaCas13-crRNA (CRISPR RNA) complex. These identified acr molecules may enable precise RNA editing in Cas13-based application and study of phage-bacterium interaction.
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