A Consensus Model of Homology-Directed Repair Initiated by CRISPR/Cas Activity.
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ABSTRACT:
SUBMITTER: Bloh K
PROVIDER: S-EPMC8067812 | biostudies-literature |
REPOSITORIES: biostudies-literature
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Project description:Gene correction is often referred to as the gold standard for precise gene editing and while CRISPR-Cas systems continue to expand the toolbox for clinically relevant genetic repair, mechanistic hurdles still hinder widespread implementation. One of the most prominent challenges to precise CRISPR-directed point mutation repair centers on the prevalence of on-site mutagenesis, wherein insertions and deletions appear at the targeted site following correction. Here, we introduce a pathway model for Homology Directed Correction, specifically point mutation repair, which enables a foundational analysis of genetic tools and factors influencing precise gene editing. To do this, we modified an in vitro gene editing system which utilizes a cell-free extract, CRISPR-Cas RNP and donor DNA template to catalyze point mutation repair. We successfully direct correction of four unique point mutations which include two unique nucleotide mutations at two separate targeted sites and visualize the repair profiles resulting from these reactions. This extension of the cell-free gene editing system to model point mutation repair may provide insight for understanding the factors influencing precise point mutation correction.
| S-EPMC9114366 | biostudies-literature
Project description:As CRISPR-Cas systems advance toward clinical application, it is essential to identify all the outcomes of gene-editing activity in human cells. Reports highlighting the remarkable success of homology-directed repair (HDR) in the treatment of inherited diseases may inadvertently underreport the collateral activity of this remarkable technology. We are utilizing an in vitro gene-editing system in which a CRISPR-Cas complex provides the double-stranded cleavage and a mammalian cell-free extract provides the enzymatic activity to promote non-homologous end joining, micro-homology mediated end joining, and homology-directed repair. Here, we detail the broad spectrum of gene-editing reaction outcomes utilizing Cas9 and Cas12a in combination with single-stranded donor templates of the sense and nonsense polarity. This system offers the opportunity to see the range of outcomes of gene-editing reactions in an unbiased fashion, detailing the distribution of DNA repair outcomes as a function of a set of genetic tools.
| S-EPMC6898364 | biostudies-literature
Project description:Eliminating or silencing a gene's level of activity is one of the classic approaches developmental biologists employ to determine a gene's function. A recently developed method of gene perturbation called CRISPR-Cas, which was derived from a prokaryotic adaptive immune system, has been adapted for use in eukaryotic cells. This technology has been established in several model organisms as a powerful and efficient tool for knocking out or knocking down the function of a gene of interest. It has been recently shown that CRISPR-Cas functions with fidelity and efficiency in Ciona robusta. Here, we show that in C. robusta CRISPR-Cas mediated genomic knock-ins can be efficiently generated. Electroporating a tissue-specific transgene driving Cas9 and a U6-driven gRNA transgene together with a fluorescent protein-containing homology directed repair (FP-HDR) template results in gene-specific patterns of fluorescence consistent with a targeted genomic insertion. Using the Tyrosinase locus to optimize reagents, we first characterize a new Pol III promoter for expressing gRNAs from the Ciona savignyi H1 gene, and then adapt technology that flanks gRNAs by ribozymes allowing cell-specific expression from Pol II promoters. Next, we examine homology arm-length efficiencies of FP-HDR templates. Reagents were then developed for targeting Brachyury and Pou4 that resulted in expected patterns of fluorescence, and sequenced PCR amplicons derived from single embryos validated predicted genomic insertions. Finally, using two differentially colored FP-HDR templates, we show that biallelic FP-HDR template insertion can be detected in live embryos of the F0 generation.
| S-EPMC6312475 | biostudies-literature
Project description:CRISPR and associated Cas nucleases are genetic engineering tools revolutionizing innovative approaches to cancer and inherited diseases. CRISPR-directed gene editing relies heavily on proper DNA sequence alignment between the guide RNA (gRNA)/CRISPR complex and its genomic target. Accurate hybridization of complementary DNA initiates gene editing in human cells, but inherent gRNA sequence variation that could influence the gene editing reaction has been clearly established among diverse genetic populations. As this technology advances toward clinical implementation, it will be essential to assess what degree of gRNA variation generates unwanted and erroneous CRISPR activity. With the use of a system in which a cell-free extract catalyzes nonhomologous end joining (NHEJ) and homology-directed repair (HDR), it is possible to observe a more representative population of all forms of gene editing outcomes. In this manuscript, we demonstrate CRISPR/Cas complexation at heterologous binding sites that facilitate precise and error-prone HDR. The tolerance of mispairing between the gRNA and target site of the DNA to enable HDR is surprisingly high and greatly influenced by polarity of the donor DNA strand in the reaction. These results suggest that some collateral genomic activity could occur at unintended sites in CRISPR-directed gene editing in human cells.
| S-EPMC7177190 | biostudies-literature
Project description:Background:Microalgae are considered as a sustainable feedstock for the production of biofuels and other value-added compounds. In particular, Nannochloropsis spp. stand out from other microalgal species due to their capabilities to accumulate both triacylglycerol (TAG) and polyunsaturated fatty acids (PUFAs). However, the commercialization of microalgae-derived products is primarily hindered by the high production costs compared to less sustainable alternatives. Efficient genome editing techniques leading to effective metabolic engineering could result in strains with enhanced productivities of interesting metabolites and thereby reduce the production costs. Competent CRISPR-based genome editing techniques have been reported in several microalgal species, and only very recently in Nannochloropsis spp. (2017). All the reported CRISPR-Cas-based systems in Nannochloropsis spp. rely on plasmid-borne constitutive expression of Cas9 and a specific guide, combined with repair of double-stranded breaks (DSB) by non-homologous end joining (NHEJ) for the target gene knockout. Results:In this study, we report for the first time an alternative approach for CRISPR-Cas-mediated genome editing in Nannochloropsis sp.; the Cas ribonucleoproteins (RNP) and an editing template were directly delivered into microalgal cells via electroporation, making Cas expression dispensable and homology-directed repair (HDR) possible with high efficiency. Apart from widely used SpCas9, Cas12a variants from three different bacterium were used for this approach. We observed that FnCas12a from Francisella novicida generated HDR-based targeted mutants with highest efficiency (up to 93% mutants among transformants) while AsCas12a from Acidaminococcus sp. resulted in the lowest efficiency. We initially show that the native homologous recombination (HR) system in N. oceanica IMET1 is not efficient for easy isolation of targeted mutants by HR. Cas9/sgRNA RNP delivery greatly enhanced HR at the target site, generating around 70% of positive mutant lines. Conclusion:We show that the delivery of Cas RNP by electroporation can be an alternative approach to the presently reported plasmid-based Cas9 method for generating mutants of N. oceanica. The co-delivery of Cas-RNPs along with a dsDNA repair template efficiently enhanced HR at the target site, resulting in a remarkable higher percentage of positive mutant lines. Therefore, this approach can be used for efficient generation of targeted mutants in Nannochloropsis sp. In addition, we here report the activity of several Cas12a homologs in N. oceanica IMET1, identifying FnCas12a as the best performer for high efficiency targeted genome editing.
| S-EPMC6432748 | biostudies-literature
Project description:Based on the hypothesis that, enhancing the local concentration of donor oligos could increase the correction rates, we generated and tested novel CRISPR-Cas9 systems, in which the DNA repair template is covalently conjugated to Cas9 (RNPD system). To validate our results from the HEK293T reporter cells, we here tested our approach at different endogenous genomic loci and in different cell types. We first targeted the human beta globin (HBB) locus in the K562 cell line, and analyzed correction- and editing frequencies using next generation sequencing (NGS). Next we targeted the Rosa26 and proprotein convertase subtilisin/kexin type 9 (Pcsk9) locus in mouse embryonic stem cells (mESCs). Here, RNPD system was always compared to Cas9 SNAP-tag fusion proteins with uncoupled donor oligos. To also directly compare the engineered RNPD system to the classical CRISPR-Cas9 system, we performed experiments where we used wild-type Cas9 with the uncoupled donor oligos as a control. We therefore targeted the fluorescent reporter locus as well as the endogenous loci HBB, empty spiracles homeobox 1 (EMX1), and C-X-C chemokine receptor type 4 (CXCR4) in HEK293T cells. Finally, we performed the analysis of three computationally predicted off-target sites of the reporter locus.
2018-06-04 | E-MTAB-6808 | biostudies-arrayexpress
Project description:Mutations in transforming growth factor-beta-induced (TGFBI) gene cause clinically distinct types of corneal dystrophies. To delineate the mechanisms driving these dystrophies, we focused on the R124C mutation in TGFBI that causes lattice corneal dystrophy type1 (LCD1) and generated novel transgenic mice harbouring a single amino acid substitution of arginine 124 with cysteine in TGFBI via ssODN-mediated base-pair substitution using CRISPR/Cas9 technology. Eighty percent of homozygous and 9.1% of heterozygous TGFBI-R124C mice developed a corneal opacity at 40 weeks of age. Hematoxylin and eosin and Masson trichrome staining showed eosinophilic deposits in subepithelial corneal stroma that stained negative for Congo-red. Although amyloid deposition was not observed in TGFBI-R124C mice, irregular amorphous deposits were clearly observed via transmission electron microscopy near the basement membrane. Interestingly, we found that the corneal deposition of TGFBI protein (TGFBIp) was significantly increased in homozygous TGFBI-R124C mice, suggesting a pathogenic role for the mutant protein accumulation. Furthermore, as observed in the LCD1 patients, corneal epithelial wound healing was significantly delayed in TGFBI-R124C mice. In conclusion, our novel mouse model of TGFBI-R124C corneal dystrophy reproduces features of the human disease. This mouse model will help delineate the pathogenic mechanisms of human corneal dystrophy.
| S-EPMC7005300 | biostudies-literature
Project description:CRISPR/Cas9 has become a powerful tool for genome editing in zebrafish that permits the rapid generation of loss of function mutations and the knock-in of specific alleles using DNA templates and homology directed repair (HDR). We examined the efficiency of synthetic, chemically modified gRNAs and demonstrate induction of indels and large genomic deletions in combination with recombinant Cas9 protein. We developed an in vivo genetic assay to measure HDR efficiency and we utilized this assay to test the effect of altering template design on HDR. Utilizing synthetic gRNAs and linear dsDNA templates, we successfully performed knock-in of fluorophores at multiple genomic loci and demonstrate transmission through the germline at high efficiency. We demonstrate that synthetic HDR templates can be used to knock-in bacterial nitroreductase (ntr) to facilitate lineage ablation of specific cell types. Collectively, our data demonstrate the utility of combining synthetic gRNAs and dsDNA templates to perform homology directed repair and genome editing in vivo.
| S-EPMC7144937 | biostudies-literature
Project description:CRISPR-Cas proteins are RNA-guided nucleases used to introduce double-stranded breaks (DSBs) at targeted genomic loci. DSBs are repaired by endogenous cellular pathways such as non-homologous end joining (NHEJ) and homology-directed repair (HDR). Providing an exogenous DNA template during repair allows for the intentional, precise incorporation of a desired mutation via the HDR pathway. However, rates of repair by HDR are often slow compared to the more rapid but less accurate NHEJ-mediated repair. Here, we describe comprehensive design considerations and optimized methods for highly efficient HDR using single-stranded oligodeoxynucleotide (ssODN) donor templates for several CRISPR-Cas systems including S.p. Cas9, S.p. Cas9 D10A nickase, and A.s. Cas12a delivered as ribonucleoprotein (RNP) complexes. Features relating to guide RNA selection, donor strand preference, and incorporation of blocking mutations in the donor template to prevent re-cleavage were investigated and were implemented in a novel online tool for HDR donor template design. These findings allow for high frequencies of precise repair utilizing HDR in multiple mammalian cell lines. Tool availability: https://www.idtdna.com/HDR.
| S-EPMC8484621 | biostudies-literature
Project description:BackgroundGene knock-in (KI) in animal cells via homology-directed repair (HDR) is an inefficient process, requiring a laborious work for screening from few modified cells. HDR tends to occur in the S and G2/M phases of cell cycle; therefore, strategies that enhance the proportion of cells in these specific phases could improve HDR efficiency.ResultsWe used various types of cell cycle inhibitors to synchronize the cell cycle in S and G2/M phases in order to investigate their effect on regulating CRISPR/Cas9-mediated HDR. Our results indicated that the four small molecules-docetaxel, irinotecan, nocodazole and mitomycin C-promoted CRISPR/Cas9-mediated KI with different homologous donor types in various animal cells. Moreover, the small molecule inhibitors enhanced KI in animal embryos. Molecular analysis identified common signal pathways activated during crosstalk between cell cycle and DNA repair. Synchronization of the cell cycle in the S and G2/M phases results in CDK1/CCNB1 protein accumulation, which can initiate the HDR process by activating HDR factors to facilitate effective end resection of CRISPR-cleaved double-strand breaks. We have demonstrated that augmenting protein levels of factors associated with the cell cycle via overexpression can facilitate KI in animal cells, consistent with the effect of small molecules.ConclusionSmall molecules that induce cell cycle synchronization in S and G2/M phases promote CRISPR/Cas9-mediated HDR efficiency in animal cells and embryos. Our research reveals the common molecular mechanisms that bridge cell cycle progression and HDR activity, which will inform further work to use HDR as an effective tool for preparing genetically modified animals or for gene therapy.
| S-EPMC10676593 | biostudies-literature