Project description:Rats are reference laboratory animal models for understanding human diseases. Engineered point mutation rat model is a powerful tool for understanding the relationship between single nucleotide polymorphisms (SNPs) and human diseases. The newly developed adenine base editor (ABE), fused a modified tRNA adenosine deaminase with a catalytically impaired Cas9 mutant, showed a powerful tool for base editing in target genome sequence. Together with cytosine base editor (CBE), ABE enable the introduction of all four nucleotides transitions (C to T, A to G, T to C, and G to A) in target genomic sequence. Here, we report this new developed base editing tool for application in rat genome base editing with high efficiency even in a multiple method.
Project description:Rats are reference laboratory animal models for understanding human diseases. Engineered point mutation rat model is a powerful tool for understanding the relationship between single nucleotide polymorphisms (SNPs) and human diseases. The newly developed adenine base editor (ABE), fused a modified tRNA adenosine deaminase with a catalytically impaired Cas9 mutant, showed a powerful tool for base editing in target genome sequence. Together with cytosine base editor (CBE), ABE enable the introduction of all four nucleotides transitions (C to T, A to G, T to C, and G to A) in target genomic sequence. Here, we report this new developed base editing tool for application in rat genome base editing with high efficiency even in a multiple method.
Project description:Novel therapeutic means against Staphylococcus aureus infections are urgently needed due to the emergence of drug-resistant S. aureus. We report the development of a CRISPR RNA-guided cytidine deaminase (pnCasSA-BEC), enabling highly efficient gene inactivation and point mutations in S. aureus. We engineered a fusion of a Cas9 nickase (Cas9D10A) and a cytidine deaminase (APOBEC1) that can be guided to a target genomic locus for gene inactivation via generating a premature stop codon. The pnCasSA-BEC system nicks the non-edited strand of the genomic DNA, directly catalyzes the conversion of cytidine (C) to uridine (U), and relies on DNA replication to achieve C ? T (G ? A) conversion without using donor repair templates. The development of the base-editing system will dramatically accelerate drug-target exploration in S. aureus and provides critical insights into the development of base-editing tools in other microbes.
Project description:Recent advances in base editing have created an exciting opportunity to precisely correct disease-causing mutations. However, the large size of base editors and their inherited off-target activities pose challenges for in vivo base editing. Moreover, the requirement of a protospacer adjacent motif (PAM) nearby the mutation site further limits the targeting feasibility. Here we modify the NG-targeting adenine base editor (iABE-NGA) to overcome these challenges and demonstrate the high efficiency to precisely edit a Duchenne muscular dystrophy (DMD) mutation in adult mice. Systemic delivery of AAV9-iABE-NGA results in dystrophin restoration and functional improvement. At 10 months after AAV9-iABE-NGA treatment, a near complete rescue of dystrophin is measured in mdx4cv mouse hearts with up to 15% rescue in skeletal muscle fibers. The off-target activities remains low and no obvious toxicity is detected. This study highlights the promise of permanent base editing using iABE-NGA for the treatment of monogenic diseases.
Project description:Nucleotide base editors in plants have been limited to conversion of cytosine to thymine. Here, we describe a new plant adenine base editor based on an evolved tRNA adenosine deaminase fused to the nickase CRISPR/Cas9, enabling A•T to G•C conversion at frequencies up to 7.5% in protoplasts and 59.1% in regenerated rice and wheat plants. An endogenous gene is also successfully modified through introducing a gain-of-function point mutation to directly produce an herbicide-tolerant rice plant. With this new adenine base editing system, it is now possible to precisely edit all base pairs, thus expanding the toolset for precise editing in plants.
Project description:The ability to precisely edit individual bases of bacterial genomes would accelerate the investigation of the function of genes. Here we utilized a nickase Cas9-cytidine deaminase fusion protein to direct the conversion of cytosine to thymine within prokaryotic cells, resulting in high mutagenesis frequencies in Escherichia coli and Brucella melitensis. Our study suggests that CRISPR/Cas9-guided base-editing is a viable alternative approach to generate mutant bacterial strains.
Project description:BACKGROUND:Cytidine base editors (CBEs), composed of a cytidine deaminase fused to Cas9 nickase (nCas9), enable efficient C-to-T conversion in various organisms. However, current base editors can induce unwanted bystander C-to-T conversions when multiple Cs are present in the ~?5-nucleotide activity window of cytidine deaminase, which negatively affects their precision. Here, we develop a new base editor which significantly reduces unwanted bystander activities. RESULTS:We used an engineered human APOBEC3G (eA3G) C-terminal catalytic domain with preferential cytidine-deaminase activity in motifs with a hierarchy CCC>CCC>CC (where the preferentially deaminated C is underlined), to develop an eA3G-BE with distinctive CC context-specificity and reduced generation of bystander mutations. Targeted editing efficiencies of 18.3-58.0% and 54.5-92.2% with excellent CC context-specificity were generated in human cells and rabbit embryos, respectively. In addition, a base editor that can further recognize relaxed NG PAMs is achieved by combining hA3G with an engineered SpCas9-NG variant. The A3G-BEs were used to induce accurate single-base substitutions which led to nonsense mutation with an efficiency of 83-100% and few bystander mutations in Founder (F0) rabbits at Tyr loci. CONCLUSIONS:These novel base editors with improved precision and CC context-specificity will expand the toolset for precise gene modification in organisms.
Project description:Adenosine-to-inosine RNA base editing is a strategy developed to safely manipulate genetic information at the RNA level. Particularly promising for clinical implementation is the use of the ubiquitously expressed endogenous editing enzyme ADAR (adenosine deaminase acting on RNA) with tailored guide RNAs. However, the precision of editing could be compromised by global off-target events that can potentially occur throughout the transcriptome. In this study, we introduce a novel circular CLUSTER guide RNA design that recruits endogenous ADAR in vivo. The goals of the whole transcriptome sequencing experiment were to evaluate the A-to-G RNA editing index and the global editing precision of this novel design. To achieve this, Rett syndrome mice harboring a Mecp2 W104Amber mutation were treated either with a circular CLUSTER guide RNA targeting the mutant Mecp2 transcript or a scrambled and thus non-targeting control guide RNA. Both the targeting and the non-targeting guide RNA were encoded as AAV and delivered via retro-orbital injection of 4x10^12 viral genomes per mouse. The used AAV serotype PHP.eB allows cargo delivery to the mouse brain after systemic administration. Four weeks after injection the thalamus was isolated for NGS analysis. Whole transcriptome sequencing showed that the A-to-G RNA editing index was unaffected by treatment with the targeting guide RNA compared to the scrambled non-targeting control. We were unable to identify any global off-target events, excluding mouse to mouse variability, which suggests a very high precision of our approach on the transcriptome-wide level. Harnessing endogenous ADAR with permanent, AAV-driven CLUSTER guide RNAs in the CNS is an important next step towards the development of novel drug modalities that fight neurological diseases.
Project description:Klebsiella pneumoniae is a promising industrial microorganism as well as a major human pathogen. The recent emergence of carbapenem-resistant K. pneumoniae has posed a serious threat to public health worldwide, emphasizing a dire need for novel therapeutic means against drug-resistant K. pneumoniae Despite the critical importance of genetics in bioengineering, physiology studies, and therapeutic-means development, genome editing, in particular, the highly desirable scarless genetic manipulation in K. pneumoniae, is often time-consuming and laborious. Here, we report a two-plasmid system, pCasKP-pSGKP, used for precise and iterative genome editing in K. pneumoniae By harnessing the clustered regularly interspaced short palindromic repeat (CRISPR)-Cas9 genome cleavage system and the lambda Red recombination system, pCasKP-pSGKP enabled highly efficient genome editing in K. pneumoniae using a short repair template. Moreover, we developed a cytidine base-editing system, pBECKP, for precise C?T conversion in both the chromosomal and plasmid-borne genes by engineering the fusion of the cytidine deaminase APOBEC1 and a Cas9 nickase. By using both the pCasKP-pSGKP and the pBECKP tools, the bla KPC-2 gene was confirmed to be the major factor that contributed to the carbapenem resistance of a hypermucoviscous carbapenem-resistant K. pneumoniae strain. The development of the two editing tools will significantly facilitate the genetic engineering of K. pneumoniae IMPORTANCE Genetics is a key means to study bacterial physiology. However, the highly desirable scarless genetic manipulation is often time-consuming and laborious for the major human pathogen K. pneumoniae We developed a CRISPR-Cas9-mediated genome-editing method and a cytidine base-editing system, enabling rapid, highly efficient, and iterative genome editing in both industrial and clinically isolated K. pneumoniae strains. We applied both tools in dissecting the drug resistance mechanism of a hypermucoviscous carbapenem-resistant K. pneumoniae strain, elucidating that the bla KPC-2 gene was the major factor that contributed to the carbapenem resistance of the hypermucoviscous carbapenem-resistant K. pneumoniae strain. Utilization of the two tools will dramatically accelerate a wide variety of investigations in diverse K. pneumoniae strains and relevant Enterobacteriaceae species, such as gene characterization, drug discovery, and metabolic engineering.
Project description:Multidrug-resistant Mycobacterium tuberculosis (Mtb) infection seriously endangers global human health, creating an urgent need for new treatment strategies. Efficient genome editing tools can facilitate identification of key genes and pathways involved in bacterial physiology, pathogenesis, and drug resistance mechanisms, and thus contribute to the development of novel treatments for drug-resistant tuberculosis. Here, we report a two-plasmid system, MtbCBE, used to inactivate genes and introduce point mutations in Mtb. In this system, the assistant plasmid pRecX-NucSE107A expresses RecX and NucSE107A to repress RecA-dependent and NucS-dependent DNA repair systems, and the base editor plasmid pCBE expresses a fusion protein combining cytidine deaminase APOBEC1, Cas9 nickase (nCas9), and uracil DNA glycosylase inhibitor (UGI). Together, the two plasmids enabled efficient G:C to A:T base pair conversion at desired sites in the Mtb genome. The successful development of a base editing system will facilitate elucidation of the molecular mechanisms underlying Mtb pathogenesis and drug resistance and provide critical inspiration for the development of base editing tools in other microbes.