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Highly efficient genome editing in Xanthomonas oryzae pv. oryzae through repurposing the endogenous type I-C CRISPR-Cas system.
Efficient and modular genome editing technologies that manipulate the genome of bacterial pathogens will facilitate the study of pathogenesis mechanisms. However, such methods are yet to be established for Xanthomonas oryzae pv. oryzae (Xoo), the causal agent of rice bacterial blight. We identified a single type I-C CRISPR-Cas system in the Xoo genome and leveraged this endogenous defence system for high-efficiency genome editing in Xoo. Specifically, we developed plasmid components carrying a mini-CRISPR array, donor DNA, and a phage-derived recombination system to enable the efficient and programmable genome editing of precise deletions, insertions, base substitutions, and gene replacements. Furthermore, the type I-C CRISPR-Cas system of Xoo cleaves target DNA unidirectionally, and this can be harnessed to generate large genomic deletions up to 212 kb efficiently. Therefore, the genome-editing strategy we have developed can serve as an excellent tool for functional genomics of Xoo, and should also be applicable to other CRISPR-harbouring bacterial plant pathogens.
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Interallelic gene conversion of leukemia-associated single nucleotide variants.
CRISPR-Cas9 is a useful tool for inserting precise genetic alterations through homology-directed repair (HDR), although current methods largely rely on provision of an exogenous repair template. Here, we tested the possibility of interchanging heterozygous single nucleotide variants (SNVs) using mutation-specific guide RNA, and the cell's own wild-type allele rather than an exogenous template. Using high-fidelity Cas9 to perform allele-specific CRISPR across multiple human leukemia cell lines as well as in primary hematopoietic cells from patients with leukemia, we find high levels of reversion to wild-type in the absence of exogenous template. Moreover, we demonstrate that bulk treatment to revert a truncating mutation in ASXL1 using CRISPR-mediated interallelic gene conversion (IGC) is sufficient to prolong survival in a human cell line-derived xenograft model (median survival 33 days vs 27.5 days; p = 0.0040). These results indicate that IGC is a useful laboratory tool which can be applied to numerous types of leukemia and can meaningfully alter cellular phenotypes at scale. Because our method targets single-base mutations, rather than larger variants targeted by IGC in prior studies, it greatly expands the pool of genetic lesions which could potentially be targeted by IGC. This technique may reduce cost and complexity for experiments modeling phenotypic consequences of SNVs. The principles of SNV-specific IGC demonstrated in this proof-of-concept study could be applied to investigate the phenotypic effects of targeted clonal reduction of leukemogenic SNV mutations.
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Enhancing genome editing in hPSCs through dual inhibition of DNA damage response and repair pathways.
Precise genome editing is crucial for establishing isogenic human disease models and ex vivo stem cell therapy from the patient-derived hPSCs. Unlike Cas9-mediated knock-in, cytosine base editor and prime editor achieve the desirable gene correction without inducing DNA double strand breaks. However, hPSCs possess highly active DNA repair pathways and are particularly susceptible to p53-dependent cell death. These unique characteristics impede the efficiency of gene editing in hPSCs. Here, we demonstrate that dual inhibition of p53-mediated cell death and distinct activation of the DNA damage repair system upon DNA damage by cytosine base editor or prime editor additively enhanced editing efficiency in hPSCs. The BE4stem system comprised of p53DD, a dominant negative p53, and three UNG inhibitor, engineered to specifically diminish base excision repair, improves cytosine base editor efficiency in hPSCs. Addition of dominant negative MLH1 to inhibit mismatch repair activity and p53DD in the conventional prime editor system also significantly enhances prime editor efficiency in hPSCs. Thus, combined inhibition of the distinct cellular cascades engaged in hPSCs upon gene editing could significantly enhance precise genome editing in these cells.
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CRISPR's unwanted anniversary.
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CRISPR-mediated editing of cis-regulatory elements in early mouse embryos: a tool for studying pluripotency gene regulation.
In brief Cis-regulatory elements and transcription factor binding motifs play crucial roles in regulating the spatial and temporal patterns of gene expression during development. This study tested the utility of CRISPR/Cas9 as a tool to interrogate the function of transcription factor AP2 gamma motifs in pluripotency gene expression during mouse preimplantation embryo development. Abstract Clustered regularly interspaced short palindromic repeat/CRISPR-associated nuclease 9 (CRISPR/Cas9) is a highly efficient tool that enables the generation of gene knockouts, knock-ins, and single base substitutions in a variety of organisms. Recently, we used CRISPR to examine the activity of cis-regulatory elements (CREs) in mouse preimplantation embryos. However, there is limited information on the feasibility of using CRISPR in preimplantation embryos to interrogate the function of select transcription factor (TF) binding motifs located within critical CREs in pluripotency genes. In the current study we employed CRISPR to disrupt TF AP2 gamma (TFAP2C) binding motifs located within key CREs involved in the regulation of Pou5f1 and Sox2 expression in early embryos. Microinjection of ribonucleoprotein complexes containing Cas9 and single guide RNAs (sgRNAs) targeting TFAP2C motifs located within a distal enhancer and proximal promoter substantially impaired Pou5f1 and Sox2 expression, respectively. Quantification of the editing efficiencies at each targeted CRE revealed that the targeting sgRNA sequences and the number of sgRNAs injected influenced the overall editing rates. Lastly, we investigated whether TFAP2C-induced activation of Sox2 expression in 2-cell embryos required TFAP2C motifs located within the Sox2 proximal promoter. CRISPR-mediated editing of these motifs diminished the activation of Sox2 expression. In summary, these findings indicate that CRISPR/Cas9 is a feasible approach for editing TF motifs in preimplantation embryos and provide evidence that TFAP2C directly contributes to Pou5f1 and Sox2 expression in preimplantation embryos.
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Development of a simple and locus-restricted DNA methylation editing system using direct fusion of a nickase-type SpCas9 and DNA methylation-related enzymes in Arabidopsis thaliana.
DNA methylation is an important epigenetic modification that regulates gene expression and supports genome stability. DNA methylation editing technology differs from conventional genome editing technology, which introduces mutations into genes, in that it enables changing gene expression without altering the base sequence. In this study, we attempted simple and locus-restricted DNA methylation editing in Arabidopsis thaliana using fusion proteins directly linking a nickase-type SpCas9 protein with DNA methylation-related enzymes. First, fusion of the human Ten-eleven translocation methyl cytosine dioxygenase 1 (TET1) catalytic domain (TET1cd) to nSpCas9 led to removing 5-methylcytosine in the FLOWERING LOCUS WA (FWA) promoter region of the wild-type plant, resulting in increased expression of the FWA gene and consequently, a late-flowering phenotype. Conversely, fusion of a mutant form of the bacterial DNA methyltransferase MQ1 (MQ1v) to nSpCas9 induced de novo DNA methylation in the fwa101-D mutant, in which the FWA promoter region is hypomethylated, and suppressed FWA gene expression, resulting in an early-flowering phenotype compared with the fwa101-D mutant. Of particular importance, our nSpCas9 system achieves targeted DNA methylation editing within a genomic window of ~10-20 kb. The nSpCas9 system features a compact and simplified vector structure due to the DNA methylation-related enzyme directly fusing to nSpCas9. Furthermore, sgRNA can be easily replaced, making it highly flexible. We propose a new method for targeted epigenome editing technology in plants, paving the way for innovative strategies in both basic research on epigenetics and crop development through epigenome editing.
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Site-specific genome editing for correction of induced pluripotent stem cells derived from dominant dystrophic epidermolysis bullosa.
Genome editing with engineered site-specific endonucleases involves nonhomologous end-joining, leading to reading frame disruption. The approach is applicable to dominant negative disorders, which can be treated simply by knocking out the mutant allele, while leaving the normal allele intact. We applied this strategy to dominant dystrophic epidermolysis bullosa (DDEB), which is caused by a dominant negative mutation in the COL7A1 gene encoding type VII collagen (COL7). We performed genome editing with TALENs and CRISPR/Cas9 targeting the mutation, c.8068_8084delinsGA. We then cotransfected Cas9 and guide RNA expression vectors expressed with GFP and DsRed, respectively, into induced pluripotent stem cells (iPSCs) generated from DDEB fibroblasts. After sorting, 90% of the iPSCs were edited, and we selected four gene-edited iPSC lines for further study. These iPSCs were differentiated into keratinocytes and fibroblasts secreting COL7. RT-PCR and Western blot analyses revealed gene-edited COL7 with frameshift mutations degraded at the protein level. In addition, we confirmed that the gene-edited truncated COL7 could neither associate with normal COL7 nor undergo triple helix formation. Our data establish the feasibility of mutation site-specific genome editing in dominant negative disorders.
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CasY7: An optimized Cas12i system for enhanced genome editing in monocot crops.
The CRISPR-Cas12 family nucleases, particularly the Cas12i subtypes, are considered promising alternatives to Cas9 for genome editing in plants. We previously developed a new Cas12i variant, CasY7, which has been successfully applied in clinical trials; its performance in plants remains to be investigated. Initial testing in stable transgenic maize and rice showed that the codon-optimized CasY7 (pCasY7e1) achieved average editing efficiencies of 58.7% and 62.3% across five target sites, respectively, outperforming the typical Cpf1 (pCpf1) control that targets the same sites. To further enhance activity, we fused T5 exonuclease to CasY7 (pCasY7e2), which shifted mutation profiles toward larger deletions, and subsequently integrated an MS2 aptamer into the crRNA scaffold (pCasY7e3). The optimized pCasY7e3 system increased editing efficiencies to 87.7% in maize and 82.9% in rice-approximately 2.7-fold higher than pCpf1. We further demonstrated multiplexed editing in maize, generating biallelic dwarf mutants, and validated functionality in hexaploid wheat with editing efficiencies up to 58.8%. Overall, our comprehensive validation across 942 transgenic plants confirmed robust editing in maize, rice, and wheat, establishing CasY7 as a high-efficiency addition to the CRISPR toolkit.
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Host-Informed Expression of CRISPR Guide RNA for Genomic Engineering in Komagataella phaffii.
There is growing interest in the use of nonmodel microorganisms as hosts for biopharmaceutical manufacturing. These hosts require genomic engineering to meet clinically relevant product qualities and titers, but the adaptation of tools for editing genomes, such as CRISPR-Cas9, has been slow for poorly characterized hosts. Specifically, a lack of biochemical characterization of RNA polymerase III transcription has hindered reliable expression of guide RNAs in new hosts. Here, we present a sequencing-based strategy for the design of host-specific cassettes for modular, reliable, expression of guide RNAs. Using this strategy, we achieved up to 95% gene editing efficiency in the methylotrophic yeast Komagataella phaffii. We applied this approach for the rapid, multiplexed engineering of a complex phenotype, achieving humanized product glycosylation in two sequential steps of engineering. Reliable extension of simple gene editing tools to nonmodel manufacturing hosts will enable rapid engineering of manufacturing strains tuned for specific product profiles and potentially decrease the costs and timelines for process development.
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Extension of the crRNA enhances Cpf1 gene editing in vitro and in vivo.
Engineering of the Cpf1 crRNA has the potential to enhance its gene editing efficiency and non-viral delivery to cells. Here, we demonstrate that extending the length of its crRNA at the 5' end can enhance the gene editing efficiency of Cpf1 both in cells and in vivo. Extending the 5' end of the crRNA enhances the gene editing efficiency of the Cpf1 RNP to induce non-homologous end-joining and homology-directed repair using electroporation in cells. Additionally, chemical modifications on the extended 5' end of the crRNA result in enhanced serum stability. Also, extending the 5' end of the crRNA by 59 nucleotides increases the delivery efficiency of Cpf1 RNP in cells and in vivo cationic delivery vehicles including polymer nanoparticle. Thus, 5' extension and chemical modification of the Cpf1 crRNA is an effective method for enhancing the gene editing efficiency of Cpf1 and its delivery in vivo.
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