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Search-and-remove genome editing allows selection of cells by DNA sequence.
The selection of cells that have acquired a desired gene edit is often done by the introduction of additional genes that confer drug resistance or encode fluorophores. However, such marker genes can have unintended physiological effects and are not compatible with editing of single nucleotides. Here, we present SNIPE, a method that allows the marker-free selection of edited cells based on single nucleotide differences to unedited cells. SNIPE drastically enriches for cells, which have been precisely edited (median 7-fold). We validate the approach for 42 different edits using Cas9 or Cas12a in different cell types and species. We use it to enrich for combinations of substitutions that change missense mutations carried by all people today back to the ancestral state seen in Neandertals and Denisovans. We also show that it can be used to kill cultured tumor cells with aberrant genotypes and to repair heterozygous tumorigenic mutations.
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An innovative approach using CRISPR-ribonucleoprotein packaged in virus-like particles to generate genetically engineered mouse models.
Genetically engineered mouse models (GEMMs) are crucial for investigating disease mechanisms, developing therapeutic strategies, and advancing fundamental biological research. While CRISPR gene editing has greatly facilitated the creation of these models, existing techniques still present technical challenges and efficiency limitations. Here, we establish a CRISPR-VLP-induced targeted mutagenesis (CRISPR-VIM) strategy, enabling precise genome editing by co-culturing zygotes with virus-like particle (VLP)-delivered gene editing ribonucleoproteins (RNPs) without requiring physical manipulation or causing cellular damage. We generate Plin1- and Tyr-knockout mice through VLP-based SpCas9 or adenine base editor (ABE)/sgRNA RNPs and characterize their phenotype and germline transmission. Additionally, we demonstrate cytosine base editor (CBE)/sgRNA-based C-to-T substitution or SpCas9/sgRNA-based knock-in using VLPs. This method further simplifies and accelerates GEMM generation without specialized techniques or equipment. Consequently, the CRISPR-VIM method can facilitate mouse modeling and be applied in various research fields.
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Novel miR-29b target regulation patterns are revealed in two different cell lines.
MicroRNAs (miRNAs) are a class of small non-coding RNAs that regulate gene or protein expression by targeting mRNAs and triggering either translational repression or mRNA degradation. Distinct expression levels of miRNAs, including miR-29b, have been detected in various biological fluids and tissues from a large variety of disease models. However, how miRNAs "react" and function in different cellular environments is still largely unknown. In this study, the regulation patterns of miR-29b between human and mouse cell lines were compared for the first time. CRISPR/Cas9 gene editing was used to stably knockdown miR-29b in human cancer HeLa cells and mouse fibroblast NIH/3T3 cells with minimum off-targets. Genome editing revealed mir-29b-1, other than mir-29b-2, to be the main source of generating mature miR-29b. The editing of miR-29b decreased expression levels of its family members miR-29a/c via changing the tertiary structures of surrounding nucleotides. Comparing transcriptome profiles of human and mouse cell lines, miR-29b displayed common regulation pathways involving distinct downstream targets in macromolecular complex assembly, cell cycle regulation, and Wnt and PI3K-Akt signalling pathways; miR-29b also demonstrated specific functions reflecting cell characteristics, including fibrosis and neuronal regulations in NIH/3T3 cells and tumorigenesis and cellular senescence in HeLa cells.
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The Complete Genome of Emcibacter congregatus ZYLT, a Marine Bacterium Encoding a CRISPR-Cas 9 Immune System.
Emcibacter congregatus ZYLT was isolated from a sediment sample cultured in situ in a coast located in the East China Sea. The genome of E. congregatus ZYLT was sequenced and assembled into one single circular chromosome with the size of 4,189,011 bp and G+C content of 52.6%. Genomic annotation showed that E. congregatus ZYLT had an intact Type II-C CRISPR-Cas system consists of three cas genes (cas 9, cas 1, and cas 2), 34 direct repeat sequences with the length of 36 bp, and 33 spacers. The predicted Cas 9 protein was smaller than most of existing genome editing tools. This structure might have potential in developing new gene editing system and uncovering the regulatory mechanisms of CRISPR-Cas system. Besides, the comparison between E. congregatus ZYLT and its relative species living in neritic environments unraveled some common traits of the defective strategies of these bacteria to face inshore challenges including the motility, multidrug resistance, and universal efflux pumps.
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Structure-based functional mechanisms and biotechnology applications of anti-CRISPR proteins.
CRISPR loci and Cas proteins provide adaptive immunity in prokaryotes against invading bacteriophages and plasmids. In response, bacteriophages have evolved a broad spectrum of anti-CRISPR proteins (anti-CRISPRs) to counteract and overcome this immunity pathway. Numerous anti-CRISPRs have been identified to date, which suppress single-subunit Cas effectors (in CRISPR class 2, type II, V and VI systems) and multisubunit Cascade effectors (in CRISPR class 1, type I and III systems). Crystallography and cryo-electron microscopy structural studies of anti-CRISPRs bound to effector complexes, complemented by functional experiments in vitro and in vivo, have identified four major CRISPR-Cas suppression mechanisms: inhibition of CRISPR-Cas complex assembly, blocking of target binding, prevention of target cleavage, and degradation of cyclic oligonucleotide signalling molecules. In this Review, we discuss novel mechanistic insights into anti-CRISPR function that have emerged from X-ray crystallography and cryo-electron microscopy studies, and how these structures in combination with function studies provide valuable tools for the ever-growing CRISPR-Cas biotechnology toolbox, to be used for precise and robust genome editing and other applications.
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[Experimental Selection of Effective sgRNAs for MmCas12m Targeting the Region of the Start Codon of the HIV-1 gag Gene].
HIV-1 remains a threat to global health. There is no effective vaccine or drug for a complete cure of HIV infection. Work continues on the development of gene therapy drugs against HIV-1. The use of DNA base editors delivered to the editing site by CRISPR-Cas systems has shown some success in the field of HIV-1 gene therapy. The MmCas12m isoform obtained from Mycolicibacterium mucogenicum can become a promising platform for this task. MmCas12m has a compact size, the ability to bind strongly to the target DNA sequence, and an absence of nuclease activity. Thus, MmCas12m can act not only as a platform for the delivery of DNA base editors, but also as an inhibitor of transcription from HIV-1 proviral DNA. We experimentally selected in vitro the most effective sgRNAs for MmCas12m to target the start codon of the gag HIV-1, the product of which is important in virion assembly. Of the nine sgRNAs we selected, four showed statistically significant effectiveness in targeting the desired region of the HIV-1 genome. To test the effectiveness of each sgRNA, we have developed a system suitable for evaluating the binding of any Cas protein to the target site of HIV-1 genome editing.
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T cell-specific inactivation of mouse CD2 by CRISPR/Cas9.
The CRISPR/Cas9 system can be used to mutate target sequences by introduction of double-strand breaks followed by imprecise repair. To test its use for conditional gene editing we generated mice transgenic for CD4 promoter-driven Cas9 combined with guide RNA targeting CD2. We found that within CD4(+) and CD8(+) lymphocytes from lymph nodes and spleen 1% and 0.6% were not expressing CD2, respectively. T cells lacking CD2 carryied mutations, which confirmed that Cas9 driven by cell-type specific promoters can edit genes in the mouse and may thus allow targeted studies of gene function in vivo.
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Double-stranded DNA deaminase DddAE1347A can increase the efficiency and targeting range of cytidine base editors.
BACKGROUND: Cytidine base editors (CBEs) consist of a single-strand specific cytidine deaminase fused to Cas9 nickase, enabling efficient C-to-T conversion across diverse organisms. Enhancing editing range and efficiency of these tools is essential for expanding their applications. RESULTS: In this study, we report that fusing a double-stranded DNA-specific cytosine deaminase DddAE1347A to CBEs significantly improves editing activity and broadens the editing window in cell lines, embryos, tobacco, and cotton. Compared to BE4max, the optimized DddAE1347A-BE4max exhibits up to a 93- fold increase in editing efficiency, achieving up to 52% efficiency at C14 and C15 in cell lines. Further investigation reveals that DddAE1347A is compatible with various Cas9 variants (SpCas9, SpaCas9, and Nme2Cas9) and deaminase variants (rA1, A3G, and A3A). Additionally, we demonstrate that cytosine deaminases with single-stranded DNA activity fail to enhance the CBE system. In contrast, various DddA variants can improve CBE editing activity at PAM-proximal cytosine positions, highlighting the modularity of fusion between DddAs and CBEs. CONCLUSIONS: These findings suggest that the double-stranded DNA-specific cytosine deaminase protein can act as an engineered fusion module in the CBE system, altering the performance (window/efficiency) of CBEs.
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Streamlined CRISPR genome engineering in wild-type bacteria using SIBR-Cas.
CRISPR-Cas is a powerful tool for genome editing in bacteria. However, its efficacy is dependent on host factors (such as DNA repair pathways) and/or exogenous expression of recombinases. In this study, we mitigated these constraints by developing a simple and widely applicable genome engineering tool for bacteria which we termed SIBR-Cas (Self-splicing Intron-Based Riboswitch-Cas). SIBR-Cas was generated from a mutant library of the theophylline-dependent self-splicing T4 td intron that allows for tight and inducible control over CRISPR-Cas counter-selection. This control delays CRISPR-Cas counter-selection, granting more time for the editing event (e.g. by homologous recombination) to occur. Without the use of exogenous recombinases, SIBR-Cas was successfully applied to knock-out several genes in three wild-type bacteria species (Escherichia coli MG1655, Pseudomonas putida KT2440 and Flavobacterium IR1) with poor homologous recombination systems. Compared to other genome engineering tools, SIBR-Cas is simple, tightly regulated and widely applicable for most (non-model) bacteria. Furthermore, we propose that SIBR can have a wider application as a simple gene expression and gene regulation control mechanism for any gene or RNA of interest in bacteria.
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CRISPR/Cas9 mediated targeting of multiple genes in Dictyostelium.
CRISPR/Cas9 has emerged in various organisms as a powerful technology for targeted gene knockout; however, no reports of editing the Dictyostelium genome efficiently using this system are available. We describe here the application of CRISPR/Cas9-mediated gene modification in Dictyostelium. The endogenous tRNA-processing system for expressing sgRNA was approximately 10 times more effective than the commonly used U6 promoter. The resulting sgRNA affected the sub-nuclear localisation of Cas9, indicating that the expression level of sgRNA was sufficiently high to form Cas9 and sgRNA complexes within the nucleus. The all-in-one vector containing Cas9 and sgRNA was transiently expressed to generate mutants in five PI3K genes. Mutation detective PCR revealed the mutagenesis frequency of the individual genes to be between 72.9% and 100%. We confirmed that all five targeting loci in the four independent clones had insertion/deletion mutations in their target sites. Thus, we show that the CRISPR/Cas9 system can be used in Dictyostelium cells to enable efficient genome editing of multiple genes. Since this system utilises transient expression of the all-in-one vector, it has the advantage that the drug resistance cassette is not integrated into the genome and simple vector construction, involving annealing two oligo-DNAs.
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