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Best practice for CRISPR design using current tools and resources.
Users facing the task of designing gRNAs for a CRISPR-mutagenesis experiment are typically confronted with a large variety of possible tools and existing libraries. Here we examine the design principles for such resources, and suggest a best practice which allows a user to evaluate and effectively use any of the existing CRISPR design tools or genome-wide libraries.
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Recovering a Targeted Mutation in Mice from Embryonic Stem Cell Chimeras or CRISPR-Cas Founders.
Following the production of chimeras from targeted embryonic stem (ES) cells or obtaining founders from CRISPR-Cas gene editing in preimplantation embryos, the desired targeted mutation must be recovered and established in the heterozygous state in a strain or stock of mice for further study. The breeding schemes for ES chimeras and CRISPR-Cas founders differ. For ES cell chimeras, we discuss the relative benefits of breeding from male or female chimeras. We discuss the importance of genetic background and provide practical advice for putting the mutation on inbred or outbred backgrounds or producing a coisogenic strain. For CRISPR-Cas founders, which will most likely be mosaic for different mutations, initial breeding strategies are discussed to maintain a desired genetic background at the same time as producing progeny to segregate different alleles. Strategies for testing the progeny to recognize indels, missense mutations, and knock-in mutations are discussed. In the event that ES cell chimeras or CRISPR-Cas founders produce no offspring or fail to transmit the mutant allele(s), there is a troubleshooting guide to pinpoint the problem. If heterozygous offspring from the chimeras or founders are normal, fertile, and of both sexes, the analysis of homozygous effects of the mutation can now begin; if not, possible dominant effects are considered.
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Multiplex genome engineering in Clostridium beijerinckii NCIMB 8052 using CRISPR-Cas12a.
Clostridium species are re-emerging as biotechnological workhorses for industrial acetone-butanol-ethanol production. This re-emergence is largely due to advances in fermentation technologies but also due to advances in genome engineering and re-programming of the native metabolism. Several genome engineering techniques have been developed including the development of numerous CRISPR-Cas tools. Here, we expanded the CRISPR-Cas toolbox and developed a CRISPR-Cas12a genome engineering tool in Clostridium beijerinckii NCIMB 8052. By controlling the expression of FnCas12a with the xylose-inducible promoter, we achieved efficient (25-100%) single-gene knockout of five C. beijerinckii NCIMB 8052 genes (spo0A, upp, Cbei_1291, Cbei_3238, Cbei_3832). Moreover, we achieved multiplex genome engineering by simultaneously knocking out the spo0A and upp genes in a single step with an efficiency of 18%. Finally, we showed that the spacer sequence and position in the CRISPR array can affect the editing efficiency outcome.
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Mannosylated neutrophil vesicles targeting macrophages alleviate liver inflammation by delivering CRISPR/Cas9 RNPs.
Background: Inflammation is a key driver of various liver diseases. NLRP3 inflammasome in hepatic macrophages is a key mediator of inflammation and has emerged as a promising target. Genome editing presents a powerful approach to modulate inflammation by directly disrupting genes such as NLRP3 directly. However, efficient and cell-specific delivery of CRISPR/Cas9 ribonucleoproteins (RNPs) remains challenging. Methods: We developed a novel delivery system by encapsulating CRISPR/Cas9 RNPs within mannosylated neutrophil membranes vesicles (Cas9/gNLRP3@M-N) to enhance targeting hepatic macrophages. Results: Cas9/gNLRP3@M-N selectively accumulated in hepatic macrophages, effectively disrupted the NLRP3 gene, attenuated inflammation in acute fulminant hepatitis, and improved disease outcomes in chronic steatohepatitis model. Conclusions: Cas9/gNLRP3@M-N represents a promising targeted gene-editing approach for the treatment of inflammatory liver diseases.
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CRISPR/Cas9 and Genome Editing for Viral Disease-Is Resistance Futile?
Chronic viral infections remain a major public health issue affecting millions of people worldwide. Highly active antiviral treatments have significantly improved prognosis and infection-related morbidity and mortality but have failed to eliminate persistent viral forms. Therefore, new strategies to either eradicate or control these viral reservoirs are paramount to allow patients to stop antiretroviral therapy and realize a cure. Viral genome disruption based on gene editing by programmable endonucleases is one promising curative gene therapy approach. Recent findings on RNA-guided human immunodeficiency virus 1 (HIV-1) genome cleavage by Cas9 and other gene-editing enzymes in latently infected cells have shown high levels of site-specific genome disruption and potent inhibition of virus replication. However, HIV-1 can readily develop resistance to genome editing at a single antiviral target site. Current data suggest that cellular repair associated with DNA double-strand breaks can accelerate the emergence of resistance. On the other hand, a combination antiviral target strategy can exploit the same repair mechanism to functionally cure HIV-1 infection in vitro while avoiding the development of resistance. This perspective summarizes recent findings on the biology of resistance to genome editing and discusses the significance of viral genetic diversity on the application of gene editing strategies toward cure.
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Genome editing across Dictyostelia species enables comparative functional genetics of social amoebas.
Gene manipulation is essential for understanding biological mechanisms, yet genetic modification in the social amoebas (Dictyostelia) has been largely limited to Dictyostelium discoideum. Here, we aimed to establish a CRISPR/Cas9-based genome-editing system applicable across the phylogenetic breadth of Dictyostelia, spanning Groups 1-4. Using an extrachromosomal CRISPR/Cas9 vector from D. discoideum, we disrupted stlA and pkaC in Polysphondylium violaceum and pkaC in two early-branching species, Heterostelium pallidum and Cavenderia fasciculata. In D. discoideum, co-introduction of donor oligos with the CRISPR vector enabled selection-free knockout generation of pkaC with 28.6% efficiency. In H. pallidum, where genome editing is typically inefficient, co-electroporation of donor oligos with the CRISPR/Cas9 vector followed by 4 days of drug selection increased the frequency of pkaC disruption from 0.9% to 8.3%. These results demonstrated that the D. discoideum CRISPR/Cas9 system can be extended across Dictyostelia, providing a versatile platform for comparative genetic and evolutionary developmental studies.
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Development of Plant Prime-Editing Systems for Precise Genome Editing.
Prime-editing systems have the capability to perform efficient and precise genome editing in human cells. In this study, we first developed a plant prime editor 2 (pPE2) system and test its activity by generating a targeted mutation on an HPT-ATG reporter in rice. Our results showed that the pPE2 system could induce programmable editing at different genome sites. In transgenic T0 plants, pPE2-generated mutants occurred with 0%-31.3% frequency, suggesting that the efficiency of pPE2 varied greatly at different genomic sites and with prime-editing guide RNAs of diverse structures. To optimize editing efficiency, guide RNAs were introduced into the pPE2 system following the PE3 and PE3b strategy in human cells. However, at the genomic sites tested in this study, pPE3 systems generated only comparable or even lower editing frequencies. Furthemore, we developed a surrogate pPE2 system by incorporating the HPT-ATG reporter to enrich the prime-edited cells. The nucleotide editing was easily detected in the resistant calli transformed with the surrogate pPE2 system, presumably due to the enhanced screening efficiency of edited cells. Taken together, our results indicate that plant prime-editing systems we developed could provide versatile and flexible editing in rice genome.
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3D Genome Engineering Using CRISPR/dCas Systems.
The spatial organization of the genome has emerged as a central regulator of gene expression and cellular function. Chromatin architecture is organized hierarchically across multiple spatial scales and involves chromatin loops, topologically associating domains (TADs), chromatin compartments, and specialized nuclear environments that collectively shape regulatory interactions within the nucleus. Disruption of these structures contributes to a wide range of diseases, including developmental disorders, cancer, and laminopathies, stimulating growing interest in technologies capable of programmable manipulation of genome topology. The emergence of CRISPR/dCas-based technologies has transformed the field from descriptive 3D genomics to programmable genome engineering. Catalytically inactive Cas proteins fused to architectural or epigenetic effectors enable targeted manipulation of chromatin loops, loop extrusion, subnuclear positioning, and local chromatin states without altering the underlying DNA sequence. In this review, we summarize current CRISPR/dCas-based approaches for engineering three-dimensional genome architecture, discuss their mechanistic basis and applications, and highlight emerging therapeutic opportunities and major technical challenges in the field.
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Toward an all-in-one recombinant adeno-associated virus vector for functionally ablating the prion gene using CRISPR-Cas technology.
Any strategy that can selectively and persistently lower the brain levels of the cellular prion protein (PrPC) is expected to extend survival in prion diseases. Recent advances in the virus-mediated delivery of gene therapies prompted us to explore if a recombinant adeno-associated virus (rAAV) vector delivering a CRISPR-Cas-based gene editor can be devised that induces a functional knockout of the prion gene. Whereas the eventual objective is to assess the therapeutic potency of an optimized vector in prion-infected mice, in this proof-of-concept study, we evaluated tools and methods that are suited to achieve this goal. The result of these efforts is a first-generation all-in-one rAAV vector that codes for a prion gene-specific guide RNA and a small Cas9 endonuclease, whose expression is controlled by a truncated neural cell adhesion molecule 1 (NCAM1) promoter that is active in PrPC expressing cells. We also constructed a second rAAV vector coding for a prion gene-specific 'traffic light reporter' (TLR). The TLR can be used to monitor prion gene-editing efficacy by coding for red and green fluorescent proteins separated by a segment of the prion gene that is targeted by the gene editor. For the purification of AAVs, we adopted a robust and scalable rAAV vector assembly pipeline and undertook proof-of-concept prion gene editing experiments in human cells and mice, which to date yielded prion gene editing rates of approximately 20% and 5%, respectively. Finally, we compared brain distributions of rAAV vectors following intrathalamic versus retro-orbital injection, and selected the 9P31 capsid for future studies based on a 7.5-fold higher heterologous gene expression level as compared to the PHP.eB capsid.
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CRISPRtools: a flexible computational platform for performing CRISPR/Cas9 experiments in the mouse.
Genome editing using the CRISPR/Cas9 RNA-guided endonuclease system has rapidly become a driving force for discovery in modern biomedical research. This simple yet elegant system has been widely used to generate both loss-of-function alleles and precision knock-in mutations using single-stranded donor oligonucleotides. Our CRISPRtools platform supports both of these applications in order to facilitate the use of CRISPR/Cas9. While there are several tools that facilitate CRISPR/Cas9 design and screen for potential off-target sites, the process is typically performed sequentially on single genes, limiting scalability for large-scale programs. Here, the design principle underlying gene ablation is based upon using paired guides flanking a critical region/exon of interest to create deletions. Guide pairs are rank ordered based upon published efficiency scores and off-target analyses, and reported in a concise format for downstream implementation. The exon deletion strategy simplifies characterization of founder animals and is the strategy employed for the majority of knockouts in the mouse. In proof-of-principle experiments, the effectiveness of this approach is demonstrated using microinjection and electroporation to introduce CRISPR/Cas9 components into mouse zygotes to delete critical exons.
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