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Applications of the versatile CRISPR-Cas13 RNA targeting system.
CRISPR-Cas are adaptable natural prokaryotic defense systems that act against invading viruses and plasmids. Among the six currently known major CRISPR-Cas types, the type VI CRISPR-Cas13 is the only one known to exclusively bind and cleave foreign RNA. Within the last couple of years, this system has been adapted to serve numerous, and sometimes not obvious, applications, including some that might be developed as effective molecular therapies. Indeed, Cas13 has been adapted to kill antibiotic-resistant bacteria. In a cell-free environment, Cas13 has been used in the development of highly specific, sensitive, multiplexing-capable, and field-adaptable detection tools. Importantly, Cas13 can be reprogrammed and applied to eukaryotes to either combat pathogenic RNA viruses or in the regulation of gene expression, facilitating the knockdown of mRNA, circular RNA, and noncoding RNA. Furthermore, Cas13 has been harnessed for in vivo RNA modifications including programmable regulation of alternative splicing, A-to-I and C to U editing, and m6A modifications. Finally, approaches allowing for the detection and characterization of RNA-interacting proteins have also been demonstrated. Here, we provide a comprehensive overview of the applications utilizing CRISPR-Cas13 that illustrate its versatility. We also discuss the most important limitations of the CRISPR-Cas13-based technologies, and controversies regarding them. This article is categorized under: RNA Methods > RNA Analyses in Cells RNA Processing > RNA Editing and Modification RNA Interactions with Proteins and Other Molecules > Protein-RNA Interactions: Functional Implications.
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Gene editing prospects for treating inherited retinal diseases.
Retinal diseases (RD) include inherited retinal dystrophy (IRD), for example, retinitis pigmentosa and Leber's congenital amaurosis, or multifactorial forms, for example, age-related macular degeneration (AMD). IRDs are clinically and genetically heterogeneous in nature. To date, more than 200 genes are known to cause IRDs, which perturb the development, function and survival of rod and cone photoreceptors or retinal pigment epithelial cells. Conversely, AMD, the most common cause of blindness in the developed world, is an acquired disease of the macula characterised by progressive visual impairment. To date, available therapeutic approaches for RD include nutritional supplements, neurotrophic factors, antiangiogenic drugs for wet AMD and gene augmentation/interference strategy for IRDs. However, these therapies do not aim at correcting the genetic defect and result in inefficient and expensive treatments. The genome editing technology based on clustered regularly interspaced short palindromic repeat (CRISPR)-associated protein (Cas) and an RNA that guides the Cas protein to a predetermined region of the genome, represents an attractive strategy to tackle IRDs without available cure. Indeed, CRISPR/Cas system can permanently and precisely replace or remove genetic mutations causative of a disease, representing a molecular tool to cure a genetic disorder. In this review, we will introduce the mechanism of CRISPR/Cas system, presenting an updated panel of Cas variants and delivery systems, then we will focus on applications of CRISPR/Cas genome editing in the retina, and, as emerging treatment options, in patient-derived induced pluripotent stem cells followed by transplantation of retinal progenitor cells into the eye.
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Versatile genome editing.
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Synthetic threads through the web of life.
CRISPR-Cas gene editing tools have brought us to an era of synthetic biology that will change the world. Excitement over the breakthroughs these tools have enabled in biology and medicine is balanced, justifiably, by concern over how their applications might go wrong in open environments. We do not know how genomic processes (including regulatory and epigenetic processes), evolutionary change, ecosystem interactions, and other higher order processes will affect traits, fitness, and impacts of edited organisms in nature. However, anticipating the spread, change, and impacts of edited traits or organisms in heterogeneous, changing environments is particularly important with "gene drives on the horizon." To anticipate how "synthetic threads" will affect the web of life on Earth, scientists must confront complex system interactions across many levels of biological organization. Currently, we lack plans, infrastructure, and funding for field science and scientists to track new synthetic organisms, with or without gene drives, as they move through open environments.
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On RNA-programmable gene modulation as a versatile set of principles targeting muscular dystrophies.
The repurposing of RNA-programmable CRISPR systems from genome editing into epigenome editing tools is gaining pace, including in research and development efforts directed at tackling human disorders. This momentum stems from the increasing knowledge regarding the epigenetic factors and networks underlying cell physiology and disease etiology and from the growing realization that genome editing principles involving chromosomal breaks generated by programmable nucleases are prone to unpredictable genetic changes and outcomes. Hence, engineered CRISPR systems are serving as versatile DNA-targeting scaffolds for heterologous and synthetic effector domains that, via locally recruiting transcription factors and chromatin remodeling complexes, seek interfering with loss-of-function and gain-of-function processes underlying recessive and dominant disorders, respectively. Here, after providing an overview about epigenetic drugs and CRISPR-Cas-based activation and interference platforms, we cover the testing of these platforms in the context of molecular therapies for muscular dystrophies. Finally, we examine attributes, obstacles, and deployment opportunities for CRISPR-based epigenetic modulating technologies.
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Evaluation of a d-octaarginine-linked polymer for CRISPR-Cas9 ribonucleoprotein (RNP) delivery and genome editing in murine dendritic cells.
We previously reported that poly (N-vinylacetamide-co-acrylic acid) coupled with d-octaarginine (VP-R8) efficiently introduces proteins and nucleic acids into cells. Based on these results, we hypothesized that VP-R8 can introduce a complex composed of guide RNA and Cas9 (RNP complex) into cells and induce genome editing mediated by the CRISPR-Cas9 system. We tested this hypothesis using a mouse dendritic cell line and mouse primary dendritic cells. The RNP complexes formed by guide RNA consisting of CRISPR RNA (crRNA), fluorescently labeled trans-activating crRNA (tracrRNA), and GFP-fused Cas9 were introduced into a mouse dendritic cell line using VP-R8 or control transfection reagents. Cells transfected using VP-R8 exhibited higher fluorescence than those transfected with other transfection reagents, indicating that VP-R8 efficiently introduced the RNP complex into the mouse dendritic cell line. Genome editing of the target DNA was detected in cells transfected with the RNP complex using VP-R8 and dominant relative to other transfection reagents. We also observed that VP-R8 effectively delivered RNP complexes consisting of single-guide RNA and Cas9 and induced genome editing in the dendritic cell line. Additionally, VP-R8 efficiently delivered RNP complexes into mouse primary dendritic cells and induced genome editing of the functional gene without producing early inflammatory cytokines. Thus, VP-R8 shows potential as a transfection tool to generate dendritic cells with specific gene regions deleted by genome editing via the CRISPR-Cas9 system. This approach aims to elucidate the detailed molecular mechanisms of dendritic cell function for its application to vaccines.
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Benchmarking the PAM compatibility of Cas12a variants for high-throughput yeast genetic variant engineering.
Saccharomyces cerevisiae is an important organism for basic research and applied biotechnology. Genome editing techniques, particularly CRISPR/Cas9 from Streptococcus pyogenes, have greatly facilitated saturation genome editing in yeast to understand mutant functions on a large scale. However, Cas9 is restricted by its targeting preference for G-rich protospacer-adjacent motif (PAM) sequences. To broaden the targeting scope, we established an efficient homology-integrated CRISPR/Cas12a system to install genetic variants through homologous recombination by targeting T-rich PAMs. We benchmarked the PAM compatibility of PAM-relaxed Cas12a variants and identified the improved LbCas12a (impLbCas12a) as the most efficient and PAM-relaxed variant in S. cerevisiae, showing high editing purity and an editing window centering the double-strand break. We show that our system can be used to perform targeted saturation mutagenesis to reveal functional variants not captured previously. By using a homology-integrated CRISPR RNA array, we utilized the multiplexing capability of CRISPR/Cas12a to realize multiplex genetic variant installation. Our system enriches the yeast genetic variant engineering toolbox, complementing the commonly used CRISPR/Cas9 system.IMPORTANCECRISPR/Cas9 has facilitated yeast functional genomics by generating a large number of precise genetic variants in a very short period of time. This enabled the interrogation of reconstituted natural genetic variants across different genetic backgrounds or entirely synthetic mutations to discover novel or improved functions. However, Cas9 only targets a limited genomic sequence space due to its preference for G-rich PAM sequences. In this study, we close this gap by developing a CRISPR/Cas12a-based system to engineer user-defined genetic variants targeting T-rich PAM sequences. Our system adopts a homology-integrated design and the most PAM-relaxed Cas12a characterized in yeast to date. These features collectively enabled the creation of genetic variant libraries and multiplex edited strains. This genome editing tool can be used together with Cas9-based tools to interrogate a greater genomic sequence space.
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Efficient Gene Transfer and Gene Editing in Sterlet (Acipenser ruthenus).
The sturgeon (Acipenseriformes) is an important farmed species because of its economical value. However, neither gene transfer nor gene editing techniques have been established in sturgeon for molecular breeding and gene functional study until now. In this study, we accomplished gene transfer and gene editing in sterlet (Acipenser ruthenus), which has the shortest sexual maturation period of sturgeons. The plasmid encoding enhanced green fluorescent protein (EGFP) was transferred into the embryos of sterlet at injection concentration of 100 ng/μL, under which condition high survival rate and gene transfer rate could be achieved. Subsequently, exogenous EGFP was efficiently disrupted by transcription activator-like effector nucleases (TALENs) or clustered regularly interspaced short palindromic repeats (CRISPR)/Cas9 nuclease/guide RNA (gRNA), with injection concentrations of 300 ng/μL TALENs, or 100 ng/μL Cas9 nuclease and 30 ng/μL gRNA, respectively, under which condition high survival rate and gene mutation rate could be achieved. Finally, the endogenous gene no tail in sterlet was successfully mutated by Cas9 nuclease/gRNA. We observed the CRISPR-induced no tail mutation, at a high efficiency with the mutant P0 embryos displaying the expected phenotype of bent spine and twisted tail.
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Editing streptomycete genomes in the CRISPR/Cas9 age.
Covering: up to December 2018 This article aims to highlight advantages, drawbacks and issues that users should consider when implementing the use of CRISPR/Cas9-tools for genome editing in streptomycetes, the most prolific source of antimicrobial natural products to date. Here, we examine four toolkits that have so far been made available for streptomycete in vivo-engineering and one for in vitro-editing, and review how they have been applied over the last three years. Our critical evaluation of these toolkits intends to support potential users in determining what they could achieve, what they should consider and what system they should select/optimise for their application.
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Efficient SNP editing in haploid human pluripotent stem cells.
PURPOSE: To correct a potentially damaging mutation in haploid human embryonic stem cells. METHODS: Exome sequencing was performed on DNA extracted from parthenogenetically derived embryonic stem cell line (pES12). An SLC10A2 gene mutation, which affects bile acid transport, was chosen as mutation of interest in this proof of concept study to attempt correction in human pluripotent haploid cells. Confirmation of the mutation was verified, and guide RNA and a correction template was designed in preparation of performing CRISPR. Haploid cells underwent serial fluorescence activated cell sorting (FACS) with Hoechst 33342 to create an increasingly haploid (1n) enriched culture. Nucleofection was performed on p. 37 and then cells were sorted for 1n DNA content with +GFP to identify the haploid cells that expressed Cas9 tagged with GFP. RESULTS: 104,686 haploid GFP + cells were collected. Cells were cultured, individual colonies picked, and 48 clones were sent for Sanger sequencing. CRIPSR efficiency was 77.1%, with 7/48 (14.6%) clones resulting in a corrected SLC10A2 mutation. Confirmation of persistence of haploid cells was achieved with repeated FACS sorting and centromere quantification. Given the large number of passages and exposure to CRISPR, we also performed analysis of karyotypes and of off-target effects. Cells evaluated were karyotypically normal and there was no evident off target effects. CONCLUSIONS: CRISPR/Cas9 can be effectively utilized to edit mutations in haploid human embryonic stem cells. Establishment and maintenance of a haploid cell culture provides a novel way to utilize CRISPR/Cas9 in gene editing, particularly in the study of recessive alleles.
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