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Riboregulated toehold-gated gRNA for programmable CRISPR-Cas9 function.
Predictable control over gene expression is essential to elicit desired synthetic cellular phenotypes. Although CRISPR-Cas9 offers a simple RNA-guided method for targeted transcriptional control, it lacks the ability to integrate endogenous cellular information for efficient signal processing. Here, we present a new class of riboregulators termed toehold-gated gRNA (thgRNA) by integrating toehold riboswitches into sgRNA scaffolds, and demonstrate their programmability for multiplexed regulation in Escherichia coli with minimal cross-talks.
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Endogenous Fluorescence Tagging by CRISPR.
Fluorescent proteins have revolutionized biomedical research as they are easy to use for protein tagging, cope without fixation or permeabilization, and thus, enable live cell imaging in various models. Current methods allow easy and quick integration of fluorescent markers to endogenous genes of interest. In this review, we introduce the three central methods, zinc finger nucleases (ZFNs), transcription activator-like effectors (TALENs), and CRISPR, that have been widely used to manipulate cells or organisms. Focusing on CRISPR technology, we give an overview on homology-directed repair (HDR)-, microhomology-mediated end joining (MMEJ)-, and nonhomologous end joining (NHEJ)-based strategies for the knock-in of markers, figure out recent developments of the technique for highly efficient knock-in, and demonstrate pros and cons. We highlight the unique aspects of fluorescent protein knock-ins and pinpoint specific improvements and perspectives, like the combination of editing with stem cell derived organoid development.
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Heritable genome editing with CRISPR/Cas9 induces anosmia in a crop pest moth.
Lepidoptera suffer critical lack of genetic tools and heritable genome edition has been achieved only in a few model species. Here we demonstrate that the CRISPR/Cas9 system is highly efficient for genome editing in a non-model crop pest Lepidoptera, the noctuid moth Spodoptera littoralis. We knocked-out the olfactory receptor co-receptor Orco gene to investigate its function in Lepidoptera olfaction. We find that 89.6% of the injected individuals carried Orco mutations, 70% of which transmitted them to the next generation. CRISPR/Cas9-mediated Orco knockout caused defects in plant odor and sex pheromone olfactory detection in homozygous individuals. Our work genetically defines Orco as an essential OR partner for both host and mate detection in Lepidoptera, and demonstrates that CRISPR/Cas9 is a simple and highly efficient genome editing technique in noctuid pests opening new routes for gene function analysis and the development of novel pest control strategies.
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CRISPR-Cas9-Mediated Genome Editing and Transcriptional Control in Yarrowia lipolytica.
The discovery and adaptation of RNA-guided nucleases has resulted in the rapid development of efficient, scalable, and easily accessible synthetic biology tools for targeted genome editing and transcriptional control. In these systems, for example CRISPR-Cas9 from Streptococcus pyogenes, a protein with nuclease activity is targeted to a specific nucleotide sequence by a short RNA molecule, whereupon binding it cleaves the targeted nucleotide strand. To extend this genome-editing ability to the industrially important oleaginous yeast Yarrowia lipolytica, we developed a set of easily usable and effective CRISPR-Cas9 episomal vectors. In this protocols chapter, we first present a method by which arbitrary protein-coding genes can be disrupted via indel formation after CRISPR-Cas9 targeting. A second method demonstrates how the same CRISPR-Cas9 system can be used to induce markerless gene cassette integration into the genome by inducing homologous recombination after DNA cleavage by Cas9. Finally, we describe how a catalytically inactive form of Cas9 fused to a transcriptional repressor can be used to control transcription of native genes in Y. lipolytica. The CRISPR-Cas9 tools and strategies described here greatly increase the types of genome editing and transcriptional control that can be achieved in Y. lipolytica, and promise to facilitate more advanced engineering of this important oleaginous host.
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Leveraging CRISPR activation for rapid assessment of gene editing products in human pluripotent stem cells.
Verification of genome editing in human pluripotent stem cells (hPSCs), particularly at silent loci, is desirable but challenging, as it often requires complex and time-intensive differentiation to induce their expression. Here, we establish a rapid and effective workflow for verifying genome-edited hPSC lines targeting unexpressed genes using CRISPR-mediated transcriptional activation (CRISPRa). We systematically compared the efficiency of various CRISPRa systems and identified the synergistic activation mediator (SAM) system as the most potent for activating silent genes in hPSCs. Furthermore, combining SAM with TET1, a demethylation module, enhanced the activation of methylated genes. By inducing targeted gene activation in undifferentiated hPSCs using CRISPRa, we successfully verified single- and dual-reporter lines, functionally tested degradation tag (dTAG) knockins, and validated silent gene knockouts within 48 h. This approach bypasses the need to induce target gene expression through differentiation, providing a rapid and effective assay for verifying silent gene editing at the hPSC stage.
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Detection of unintended on-target effects in CRISPR genome editing by DNA donors carrying diagnostic substitutions.
CRISPR nucleases can introduce double-stranded DNA breaks in genomes at positions specified by guide RNAs. When repaired by the cell, this may result in the introduction of insertions and deletions or nucleotide substitutions provided by exogenous DNA donors. However, cellular repair can also result in unintended on-target effects, primarily larger deletions and loss of heterozygosity due to gene conversion. Here we present a strategy that allows easy and reliable detection of unintended on-target effects as well as the generation of control cells that carry wild-type alleles but have demonstratively undergone genome editing at the target site. Our 'sequence-ascertained favorable editing' (SAFE) donor approach relies on the use of DNA donor mixtures containing the desired nucleotide substitutions or the wild-type alleles together with combinations of additional 'diagnostic' substitutions unlikely to have any effects. Sequencing of the target sites then results in that two different sequences are seen when both chromosomes are edited with 'SAFE' donors containing different sets of substitutions, while a single sequence indicates unintended effects such as deletions or gene conversion. We analyzed more than 850 human embryonic stem cell clones edited with 'SAFE' donors and detect all copy number changes and almost all clones with gene conversion.
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Barriers to genome editing with CRISPR in bacteria.
Genome editing is essential for probing genotype-phenotype relationships and for enhancing chemical production and phenotypic robustness in industrial bacteria. Currently, the most popular tools for genome editing couple recombineering with DNA cleavage by the CRISPR nuclease Cas9 from Streptococcus pyogenes. Although successful in some model strains, CRISPR-based genome editing has been slow to extend to the multitude of industrially relevant bacteria. In this review, we analyze existing barriers to implementing CRISPR-based editing across diverse bacterial species. We first compare the efficacy of current CRISPR-based editing strategies. Next, we discuss alternatives when the S. pyogenes Cas9 does not yield colonies. Finally, we describe different ways bacteria can evade editing and how elucidating these failure modes can improve CRISPR-based genome editing across strains. Together, this review highlights existing obstacles to CRISPR-based editing in bacteria and offers guidelines to help achieve and enhance editing in a wider range of bacterial species, including non-model strains.
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Causal effect estimation from trans-regulatory single-cell CRISPR screens.
Recent advances in single-cell transcriptomics and CRISPR-based genome editing have enabled large-scale perturbation experiments with genome-wide expression readouts. Single-cell CRISPR screens offer the opportunity to move beyond correlation and estimate causal effects of genetic perturbations on gene expression at scale. These approaches promise to substantially deepen insights into cellular functions and disease mechanisms. However, interpreting statistical associations as causal effects requires additional assumptions beyond those needed for standard statistical analyses. In this minireview, we introduce key concepts and principles for causal effect estimation in trans-regulatory single-cell CRISPR studies. We describe a set of assumptions under which estimates from existing statistical methods admit a causal interpretation and provide a concise overview of these approaches. Finally, through an illustrative example, we demonstrate how violations of these assumptions can bias estimated effects.
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RNA and CRISPR Interferences: Past, Present, and Future Perspectives.
RNA interference (RNAi), a natural gene silencing process, is a widely used technique in basic research, preclinical studies, and drug development strategies. Although the technique has great potential to generate new human therapies and treat undruggable diseases, the clinical application of RNAi is still challenging primarily because of the delivery problem and potential off-target effects. Over the past two decades, great efforts have been undertaken to develop delivery agents and chemical modifications to overcome these challenges. Such advances in RNA delivery and chemical modifications have benefited researchers who are developing gene-editing therapies based on CRISPR-Cas9, an RNA-guided endonuclease, which is already having a major impact on biology and medicine. Here, I review the discovery of these two interference tools, identify the technical challenges yet to be overcome and provide some perspectives on how these two RNA-based technologies can be harnessed to treat human diseases.
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Ethical issues of CRISPR technology and gene editing through the lens of solidarity.
BACKGROUND: The avalanche of commentaries on CRISPR-Cas9 technology, a bacterial immune system modified to recognize any short DNA sequence, cut it out, and insert a new one, has rekindled hopes for gene therapy and other applications and raised criticisms of engineering genes in future generations. SOURCES OF DATA: This discussion draws on articles that emphasize ethics, identified partly through PubMed and Google, 2014-2016. AREAS OF AGREEMENT: CRISPR-Cas9 has taken the pace and prospects for genetic discovery and applications to a high level, stoking anticipation for somatic gene engineering to help patients. We support a moratorium on germ line manipulation. AREAS OF CONTROVERSY: We place increased emphasis on the principle of solidarity and the public good. The genetic bases of some diseases are not thoroughly addressable with CRISPR-Cas9. We see no new ethical issues, compared with gene therapy and genetic engineering in general, apart from the explosive rate of findings. Other controversies include eugenics, patentability and unrealistic expectations of professionals and the public. GROWING POINTS: Biggest issues are the void of research on human germ cell biology, the appropriate routes for oversight and transparency, and the scientific and ethical areas of reproductive medicine. AREAS TIMELY FOR DEVELOPING RESEARCH: The principle of genomic solidarity and priority on public good should be a lens for bringing clarity to CRISPR debates. The valid claim of genetic exceptionalism supports restraint on experimentation in human germ cells, given the trans-generational dangers and the knowledge gap in germ cell biology.
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