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Enhanced mammalian genome editing by new Cas12a orthologs with optimized crRNA scaffolds.
CRISPR-Cas12a/Cpf1, a single RNA-guided endonuclease system, provides a promising tool for genome engineering. However, only three Cas12a orthologs have been employed for mammalian genome editing, and the editing efficiency as well as targeting coverage still requires improvements. Here, we harness six novel Cas12a orthologs for genome editing in human and mouse cells, some of which utilize simple protospacer adjacent motifs (PAMs) that remarkably increase the targeting range in the genomes. Moreover, we identify optimized CRISPR RNA (crRNA) scaffolds that can increase the genome editing efficiency of Cas12a.
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Gene Editing, Enhancing and Women's Role.
A recent article on the front page of The Independent (September 18, 2015) reported that the genetic 'manipulation' of IVF embryos is to start in Britain, using a new revolutionary gene-editing technique, called Crispr/Cas9. About three weeks later (Saturday 10, October 2015), on the front page of the same newspaper, it was reported that the National Health Service (NHS) faces a one billion pound deficit only 3 months into the new year. The hidden connection between these reports is that gene editing could be used to solve issues related to health care allocation. Improving the health of future generations might coincide with public health goals; it might improve the health of individuals and communities, and, if successful, might be seen as a public good. However, enhancing future generations will require In Vitro Fertilisation and Pre-implantation Genetic Diagnosis. Remarkably, the necessary involvement of women in an enhancing scenario has not been discussed by its proponents. The present discourse on moral obligations of future generations, although not referring to women, seems to imply that women might be required, morally, if not legally, to reproduce with IVF. Enhancing future generations will be gendered, unless the artificial womb is developed. These are challenging issues that require a wider perspective, of both women and men. Despite the lack of a unified feminist conclusion in the discussions about the merits and risks of human genome modification, there is an urgent need to clarify the role of women in this scenario.
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EpiCRISPR: Improving CRISPR/Cas9 On- and Off-Target Prediction by Flanking Sequences, Epigenetic Marks, and High-Throughput Datasets.
CRISPR/Cas9 technology has revolutionized gene-editing technologies. However, the endogenous gene-editing efficiency at the target site, unintended off-target sites (OTSs), and the DNA repair outcomes are affected by various factors, among them are the sequence of the site, its flanking sequences, and the epigenetic marks harboring it. Researchers have developed computational methods to predict endogenous efficiency, OTSs, and repair outcomes. However, previous studies have failed to successfully incorporate the factors that affect on- and off-target activity, and repair outcomes, and the methods were trained and evaluated on small datasets. A recent dataset of endogenous on-target efficiencies and repair outcomes of nearly 1,600 measurements in T cells, and a recently preprocessed dataset of 78 OTS experiments in T cells provide a unique opportunity to develop a method to predict endogenous on-target efficiency, OTSs, and repair outcomes. Here, we developed EpiCRISPROn and EpiCRISPROff to improve on-target efficiency and OTSs prediction, respectively, by combining various inputs: the site and its flanking sequences, multiple epigenetic marks, and a high-throughput-based prediction. In EpiCRISPROn and EpiCRISPROff, the additional non-sequence features improved prediction performance from an average Spearman correlation of 0.31 to 0.51 in 5-fold cross-validation and from an average AUPRC of 0.436 to 0.441 on a held-out test set, respectively. Moreover, EpiCRISPROn and EpiCRISPROff were trained on one cell type and successfully generalized to other cell types. In contrast, the inclusion of flanking sequences and epigenetic features did not improve repair-outcome prediction. Furthermore, by interrogating EpiCRISPROn and EpiCRISPROff trained models we shed light on on-target and OTS editing preferences. We expect EpiCRISPROn and EpiCRISPROff to advance the field of gene editing by providing improved cell-type-aware prediction of endogenous CRISPR/Cas9 on- and off-target activity.
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Heterogeneity in establishment of polyethylene glycol-mediated plasmid transformations for five forest pathogenic Phytophthora species.
Plasmid-mediated DNA transformation is a foundational molecular technique and the basis for most CRISPR-Cas9 gene editing systems. While plasmid transformations are well established for many agricultural Phytophthora pathogens, development of this technique in forest Phytophthoras is lacking. Given our long-term research objective to develop CRISPR-Cas9 gene editing in a forest pathogenic Phytophthora species, we sought to establish the functionality of polyethylene glycol (PEG)-mediated plasmid transformation in five species: P. cactorum, P. cinnamomi, P. cryptogea, P. ramorum, and P. syringae. We used the agricultural pathogen P. sojae, a species for which PEG-mediated transformations are well-established, as a transformation control. Using a protocol previously optimized for P. sojae, we tested transformations in the five forest Phytophthoras with three different plasmids: two developed for CRISPR-Cas9 gene editing and one developed for fluorescent protein tagging. Out of the five species tested, successful transformation, as indicated by stable growth of transformants on a high concentration of antibiotic selective growth medium and diagnostic PCR, was achieved only with P. cactorum and P. ramorum. However, while transformations in P. cactorum were consistent and stable, transformations in P. ramorum were highly variable and yielded transformants with very weak mycelial growth and abnormal morphology. Our results indicate that P. cactorum is the best candidate to move forward with CRISPR-Cas9 protocol development and provide insight for future optimization of plasmid transformations in forest Phytophthoras.
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Stimuli-responsive peptide nanocarriers for tumor-specific CRISPR/Cas9 delivery and precision genome editing.
CRISPR/Cas9 ribonucleoprotein (RNP) delivery remains a critical challenge due to its large size, instability, and off-target effects. Here, we report a stimuli-responsive cationic amphiphilic peptide, (CR3)3C, designed for cancer-targeted delivery of CRISPR/Cas9 RNP. The peptide integrates three functional domains: (1) a naphthyl-diphenylalanine (Nap-FF) motif enabling self-assembly into stable nanoparticles via aromatic interactions, (2) a matrix metalloproteinase-7 (MMP7)-cleavable linker (GPLGLA) for tumor microenvironment-specific activation, and (3) a redox-responsive cationic domain ((CRRR)3-C) for electrostatic RNP binding and glutathione (GSH)-triggered intracellular release. The (CR3)3C/RNP nanocomplexes (108.8 nm diameter, ζ = +10.89 mV) demonstrate exceptional stability and cellular uptake efficiency. Mechanistic studies reveal caveolae-mediated endocytosis and lipid raft-associated pathways, proton sponge effect-driven endosomal escape, and nuclear localization facilitated by Cas9's nuclear localization signal. In HeLa-EGFP cells, (CR3)3C/RNP shows 33.8 % gene editing efficiency at 100 nM RNP with >90 % cell viability. This work establishes a programmable, non-viral platform that synergizes enzymatic and redox responsiveness for tumor-targeted genome editing, addressing critical barriers in CRISPR therapeutics.
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Genomic and Transcriptomic Analyses of Prime Editing Guide RNA-Independent Off-Target Effects by Prime Editors.
Prime editors (PEs) were developed to induce versatile edits at a guide-specified genomic locus. With all RNA-guided genome editors, guide-dependent off-target (OT) mutations can occur at other sites bearing similarity to the intended target. However, whether PEs carry the additional risk of guide-independent mutations elicited by their unique enzymatic moiety (i.e., reverse transcriptase) has not been examined systematically in mammalian cells. Here, we developed a cost-effective sensitive platform to profile guide-independent OT effects in human cells. We did not observe guide-independent OT mutations in the DNA or RNA of prime editor 3 (PE3)-edited cells, or alterations to their telomeres, endogenous retroelements, alternative splicing events, or gene expression. Together, our results showed undetectable prime editing guide RNA-independent OT effects of PE3 in human cells, suggesting the high editing specificity of its reverse-transcriptase moiety.
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Gene editing in the context of an increasingly complex genome.
The reporting of the first draft of the human genome in 2000 brought with it much hope for the future in what was felt as a paradigm shift toward improved health outcomes. Indeed, we have now mapped the majority of variation across human populations with landmark projects such as 1000 Genomes; in cancer, we have catalogued mutations across the primary carcinomas; whilst, for other diseases, we have identified the genetic variants with strongest association. Despite this, we are still awaiting the genetic revolution in healthcare to materialise and translate itself into the health benefits for which we had hoped. A major problem we face relates to our underestimation of the complexity of the genome, and that of biological mechanisms, generally. Fixation on DNA sequence alone and a 'rigid' mode of thinking about the genome has meant that the folding and structure of the DNA molecule -and how these relate to regulation- have been underappreciated. Projects like ENCODE have additionally taught us that regulation at the level of RNA is just as important as that at the spatiotemporal level of chromatin.In this review, we chart the course of the major advances in the biomedical sciences in the era pre- and post the release of the first draft sequence of the human genome, taking a focus on technology and how its development has influenced these. We additionally focus on gene editing via CRISPR/Cas9 as a key technique, in particular its use in the context of complex biological mechanisms. Our aim is to shift the mode of thinking about the genome to that which encompasses a greater appreciation of the folding of the DNA molecule, DNA- RNA/protein interactions, and how these regulate expression and elaborate disease mechanisms.Through the composition of our work, we recognise that technological improvement is conducive to a greater understanding of biological processes and life within the cell. We believe we now have the technology at our disposal that permits a better understanding of disease mechanisms, achievable through integrative data analyses. Finally, only with greater understanding of disease mechanisms can techniques such as gene editing be faithfully conducted.
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HIV-1 mRNA knockdown with CRISPR/CAS9 enhances neurocognitive function.
Mixed glia are infiltrated with HIV-1 virus early in the course of infection leading to the development of a persistent viral reservoir in the central nervous system. Modification of the HIV-1 genome using gene editing techniques, including CRISPR/Cas9, has shown great promise towards eliminating HIV-1 viral reservoirs; whether these techniques are capable of removing HIV-1 viral proteins from mixed glia, however, has not been systematically evaluated. Herein, the efficacy of adeno-associated virus 9 (AAV9)-CRISPR/Cas9 gene editing for eliminating HIV-1 messenger RNA (mRNA) from cortical mixed glia was evaluated in vitro and in vivo. In vitro, a within-subjects experimental design was utilized to treat mixed glia isolated from neonatal HIV-1 transgenic (Tg) rats with varying doses (0, 0.9, 1.8, 2.7, 3.6, 4.5, or 5.4 µL corresponding to a physical titer of 0, 4.23 × 109, 8.46 × 109, 1.269 × 1010, 1.692 × 1010, 2.115 × 1010, and 2.538 × 1010 gc/µL) of CRISPR/Cas9 for 72 h. Dose-dependent decreases in the number of HIV-1 mRNA, quantified using an innovative in situ hybridization technique, were observed in a subset (i.e., n = 5 out of 8) of primary mixed glia. In vivo, HIV-1 Tg rats were retro-orbitally inoculated with CRISPR/Cas9 for two weeks, whereby treatment resulted in profound excision (i.e., approximately 53.2%) of HIV-1 mRNA from the medial prefrontal cortex. Given incomplete excision of the HIV-1 viral genome, the clinical relevance of HIV-1 mRNA knockdown for eliminating neurocognitive impairments was evaluated via examination of temporal processing, a putative neurobehavioral mechanism underlying HIV-1-associated neurocognitive disorders (HAND). Indeed, treatment with CRISPR/Cas9 protractedly, albeit not permanently, restored the developmental trajectory of temporal processing. Proof-of-concept studies, therefore, support the susceptibility of mixed glia to gene editing and the potential of CRISPR/Cas9 to serve as a novel therapeutic strategy for HAND, even in the absence of full viral eradication.
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CRISPR/Cas9-mediated editing of carotenoid biosynthesis genes alters carotenoid concentrations in kiwifruit.
BACKGROUND: CRISPR/Cas9 technology has garnered increasing attention for its simplicity and precision in genome editing, making it an indispensable tool for gene function research and crop genetic improvement. However, the inefficiency and time-consuming nature of genetic transformation continue to pose substantial challenges to its widespread application in woody plants. RESULTS: In this study, we developed a rapid and efficient Agrobacterium-mediated transformation system using petioles as explants for kiwifruit. Positive resistant seedlings were obtained within three months by inoculating on MS medium supplemented with 2.0 mg·L-1 6-benzylaminopurine (6-BA), 0.2 mg·L-1 naphthaleneacetic acid (NAA), and 10 mg·L-1 hygromycin, which was faster than using leaves as explants. Using this system, CRISPR/Cas9-mediated editing of phytoene desaturase (AcPDS) and ζ-carotene desaturase (AcZDS) achieved an editing efficiency of 20%. Transgenic kiwifruit lines with edited AcZDS exhibited a significant reduction in carotenoid content. CONCLUSIONS: Overall, we established an efficient Agrobacterium-mediated transformation system using petioles as explants, which is applicable for CRISPR/Cas9-mediated gene editing in kiwifruit, thereby facilitating functional gene studies and genetic improvement.
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Graphene oxide-mediated Cas9/sgRNA delivery for efficient genome editing.
Direct cellular delivery of CRISPR/Cas9 complexes is of great significance for genome editing and other recently developed applications, such as gene expression regulation and RNA/DNA imaging. Here, we first constructed a graphene oxide (GO)-polyethylene glycol (PEG)-polyethylenimine (PEI) nanocarrier for the delivery of high-molecular-weight Cas9/single-guide RNA (sgRNA) complexes for endocytosis, endosomal escape, nuclear entry, and gene editing. The results demonstrate that the nanocarrier can be used successfully for efficient gene editing in human AGS cells with an efficiency of ∼39%. The results also show that this nanocarrier can protect sgRNA from enzymatic degradation, thus exhibiting extremely high stability, which is critical for future in vivo applications. Thus, this GO-mediated Cas9/sgRNA delivery system has potential as a new approach for biomedical research and targeted gene engineering applications.
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