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Highly efficient CRISPR-Cas9 base editing in Bifidobacterium with bypass of restriction modification systems.
Intestinal microbiota members of the Bifidobacterium genus are increasingly explored as probiotics and therapeutics. However, the paucity of genetic tools and the widespread restriction modification (RM) systems in Bifidobacterium limit our ability to genetically manipulate these bacteria. Here we established a CRISPR-Cas9 cytosine base editor system (cBEST) for portable genome editing in bifidobacteria. Harboring different promoters characterized in this study, these cBEST plasmids showed a range of editing efficiencies in different strains and genomic contexts, highlighting the importance of fine-tuning base editor and sgRNA expression. Additionally, we showed that disruption or bypass of RM systems dramatically improved editing efficiencies in otherwise hard-to-edit genomic loci and Bifidobacterium strains. Notably, we demonstrated the use of RM-disrupted Bifidobacterium longum strains for simultaneous assembly, amplification, and methylation of the all-in-one editing plasmids, greatly streamlining the workflow for high-efficiency base editing. Last but not least, we showed the portability of cBESTs using the same editing construct to disrupt a conserved metabolic gene in multiple Bifidobacterium species. Looking ahead, the ability to efficiently edit and engineer bifidobacterial genomes will give rise to new opportunities for research and applications toward improving human health.IMPORTANCEThe ability to genetically manipulate specific genes and biological pathways in Bifidobacterium is essential to unlocking their probiotic and therapeutic potential in human health applications. The DNA double-strand break-free CRISPR-Cas9 cytosine base editor system established in this work allows portable and efficient base editing in Bifidobacterium spp. We further showed that bypass of restriction modification systems significantly improved base editing efficiency, especially for hard-to-edit genomic loci and strains. This expanded Bifidobacterium genome editing toolbox should facilitate mechanistic investigations into the roles of Bifidobacterium in host physiology and disease.
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Deconstructing cancer with precision genome editing.
Recent advances in genome editing technologies are allowing investigators to engineer and study cancer-associated mutations in their endogenous genetic contexts with high precision and efficiency. Of these, base editing and prime editing are quickly becoming gold-standards in the field due to their versatility and scalability. Here, we review the merits and limitations of these precision genome editing technologies, their application to modern cancer research, and speculate how these could be integrated to address future directions in the field.
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Enhancing Specificity, Precision, Accessibility, Flexibility, and Safety to Overcome Traditional CRISPR/Cas Editing Challenges and Shape Future Innovations.
Derived from the bacterial immune system, CRISPR/Cas9 induces DSBs at specific DNA sequences, which are repaired by the cell's endogenous mechanisms, leading to gene insertions, deletions, or substitutions. Despite its transformative potential, several challenges remain in optimizing of CRISPR/Cas systems, including off-target effects, delivery methods, PAM restrictions, and the limitations of traditional editing approaches. This review focuses on the interplay between these challenges and their contributions to gene editing precision, specificity, accessibility, flexibility, and safety. How reducing off-target effects enhances specificity and safety is explored, while discussing the role of HDR-based editing in achieving precise gene modifications, alongside alternative methods such as base editing and prime editing. Improved delivery mechanisms are examined for their impact on accessibility and efficiency, while the reduction of PAM restrictions is highlighted for its contributions to flexibility. Lastly, emerging cleavage-free editing technologies are evaluated as they relate to safety and accessibility. This focused review aims to clarify the connections among these aspects and outline future research directions for advancing CRISPR-based applications.
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A Highly Efficient CRISPR-Cas9-Based Genome Engineering Platform in Acinetobacter baumannii to Understand the H2O2-Sensing Mechanism of OxyR.
The rapid emergence of extensively drug-resistant A. baumannii has posed a major threat to global public health, emphasizing the desperate need for novel therapeutic strategies. We report the development of a highly efficient genome-engineering platform in A. baumannii by coupling a Cas9 nuclease-mediated genome cleavage system with the RecAb recombination system. We applied the CRISPR-Cas9/RecAb system to dissect the oxidative stress-sensing mechanism of OxyR by performing alanine scanning mutagenesis of 13 residues residing in the H2O2-sensing pocket, pinpointing new vital factors for H2O2 sensing. Moreover, we developed a cytidine base-editing system, enabling programmed C to T conversions. Exploiting this powerful technique, we systematically investigated the drug-resistant mechanisms in a clinically isolated multidrug-resistant A. baumannii strain by generating premature stop codons in the possible resistance genes, unveiling distinct roles of these genes in drug resistance. The development of these genome-engineering methods will facilitate new therapeutic-means development in A. baumannii and related organisms.
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Boosting plant genome editing with a versatile CRISPR-Combo system.
CRISPR-Cas9, its derived base editors and CRISPR activation systems have greatly aided genome engineering in plants. However, these systems are mostly used separately, leaving their combinational potential largely untapped. Here we develop a versatile CRISPR-Combo platform, based on a single Cas9 protein, for simultaneous genome editing (targeted mutagenesis or base editing) and gene activation in plants. We showcase the powerful applications of CRISPR-Combo for boosting plant genome editing. First, CRISPR-Combo is used to shorten the plant life cycle and reduce the efforts in screening transgene-free genome-edited plants by activation of a florigen gene in Arabidopsis. Next, we demonstrate accelerated regeneration and propagation of genome-edited plants by activation of morphogenic genes in poplar. Furthermore, we apply CRISPR-Combo to achieve rice regeneration without exogenous plant hormones, which is established as a new method to predominately enrich heritable targeted mutations. In conclusion, CRISPR-Combo is a versatile genome engineering tool with promising applications in crop breeding.
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A CRISPR/Cas9 toolkit for efficient targeted base editing to induce genetic variations in rice.
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In the business of base editors: Evolution from bench to bedside.
With the advent of recombinant DNA technology in the 1970s, the idea of using gene therapies to treat human genetic diseases captured the interest and imagination of scientists around the world. Years later, enabled largely by the development of CRISPR-based genome editing tools, the field has exploded, with academic labs, startup biotechnology companies, and large pharmaceutical corporations working in concert to develop life-changing therapeutics. In this Essay, we highlight base editing technologies and their development from bench to bedside. Base editing, first reported in 2016, is capable of installing C•G to T•A and A•T to G•C point mutations, while largely circumventing some of the pitfalls of traditional CRISPR/Cas9 gene editing. Despite their youth, these technologies have been widely used by both academic labs and therapeutics-based companies. Here, we provide an overview of the mechanics of base editing and its use in clinical trials.
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Coupling of both a transactivation module and a double-stranded DNA-binding domain boosts Cas12i3 variant-based cytosine and adenine editing in plants.
CRISPR/Cas12i3 belongs to the type V-I Cas system, characterized by its smaller protein size and less restricted canonical "TTN" protospacer adjacent motif. Developments of Cas12i3-mediated base editing systems for either C-to-T or A-to-G transitions will expand the editing scope and enrich the plant base editing toolkits for crop improvement. However, while the Cas12i3-based cytosine base editor (CBE) only shows very low editing efficiency in plants, its adenine base editor (ABE) has not been documented as yet. Here, we engineered a series of Cas12i3 (5M)-based CBEs (V0-V5) and ABEs (V0-V5) by fusing a deactivated dCas12i3 (5M) with a transactivation module VP64, a single-stranded DNA-binding domain Rad51, or a double-stranded DNA-binding domain HMG-D, or in combinations, and systemically evaluated their performance in rice protoplasts. Our results demonstrated that synergistic combinations of both VP64 and HMG-D outperformed other architectures and significantly boosted the efficiencies of Cas12i3 (5M)-based CBE and ABE for C-to-T and A-to-G base editing and expanded the editing window. In stable lines, in comparison to the non-fusion control, the optimized Cas12i3 (5M)-based CBE-V5 and ABE-V5 enabled up to 4.78- and 3.35-fold higher editing efficiencies, with the maximum C-to-T and A-to-G efficiencies reaching 32.35% and 38.24%, respectively, and a higher proportion of homozygous mutants in the T0 generation. Furthermore, we generated herbicide-resistant rice germplasm by using CBE-V5 and ABE-V5, demonstrating their potential for precision breeding in crops. Together, here, we report novel Cas12i3 (5M)-based CBE and ABE that substantially enrich base editing toolkits for improvement of rice and potentially other crops.
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RNA editing as a therapeutic approach for retinal gene therapy requiring long coding sequences.
RNA editing aims to treat genetic disease through altering gene expression at the transcript level. Pairing site-directed RNA-targeting mechanisms with engineered deaminase enzymes allows for the programmable correction of G>A and T>C mutations in RNA. This offers a promising therapeutic approach for a range of genetic diseases. For inherited retinal degenerations caused by point mutations in large genes not amenable to single-adeno-associated viral (AAV) gene therapy such as USH2A and ABCA4, correcting RNA offers an alternative to gene replacement. Genome editing of RNA rather than DNA may offer an improved safety profile, due to the transient and potentially reversible nature of edits made to RNA. This review considers the current site-directing RNA editing systems, and the potential to translate these to the clinic for the treatment of inherited retinal degeneration.
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A bibliometric mapping of advancements and trends in genome editing in pigs.
Researchers have widely undertaken targeted genome editing in pigs to optimize pig productivity, disease tolerance and for biomedical research. The present study aimed to investigate research advancements, focus areas, gaps, and challenges in genome editing in pigs using bibliometric analysis. The bibliographic information of publications on genome editing in pigs from 2010 to 2023 was retrieved from the Scopus database. Bibliometric parameters, such as coauthorship, keyword co-occurrence, citation, bibliographic coupling, and cocitation, was analyzed using VOSviewer. Literature mining was conducted to evaluate the emerging areas and challenges in the development of genome-edited pigs. We found 725 documents on genome editing in pigs, 407 of which were research articles authored by 2826 researchers from 1359 research organizations across 40 countries. The two countries, China and the United States, account for more than 50% of the research publications on genome editing in pigs. Investigations on the optimization of the procedure, delivery methods, editing efficiency, and reducing off-target effects dominated the early phase of research, which has shifted to its application for generating knockout (KO) or knockin (KI) pigs in recent years. Areas such as xenotransplantation, disease resistance, higher muscling, and disease models have dominated the research horizon for genome editing in pigs. Emerging areas in gene editing include base editing, CRISPR-based screens, diagnostics, and therapeutics. However, investigations on reducing heat stress and environmental footprint through genetic alterations need more attention from scientists. Challenges such as off-target effects and regulatory, ethical and societal issues related to channelizing gene-edited pigs from lab to land and then from farm to fork continue to restrain this field.
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