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A New-Generation Base Editor with an Expanded Editing Window for Microbial Cell Evolution In Vivo Based on CRISPR‒Cas12b Engineering.
Base editors (BEs) are widely used as revolutionary genome manipulation tools for cell evolution. To screen the targeted individuals, it is often necessary to expand the editing window to ensure highly diverse variant library. However, current BEs suffer from a limited editing window of 5-6 bases, corresponding to only 2-3 amino acids. Here, by engineering the CRISPR‒Cas12b, the study develops dCas12b-based CRISPRi system, which can efficiently repress gene expression by blocking the initiation and elongation of gene transcription. Further, based on dCas12b, a new-generation of BEs with an expanded editing window is established, covering the entire protospacer or more. The expanded editing window results from the smaller steric hindrance compared with other Cas proteins. The universality of the new BE is successfully validated in Bacillus subtilis and Escherichia coli. As a proof of concept, a spectinomycin-resistant E. coli strain (BL21) and a 6.49-fold increased protein secretion efficiency in E. coli JM109 are successfully obtained by using the new BE. The study, by tremendously expanding the editing window of BEs, increased the capacity of the variant library exponentially, greatly increasing the screening efficiency for microbial cell evolution.
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Harnessing the endogenous Type I-C CRISPR-Cas system for genome editing in Bifidobacterium breve.
Bifidobacterium breve, one of the main bifidobacterial species colonizing the human gastrointestinal tract in early life, has received extensive attention for its purported beneficial effects on human health. However, exploration of the mode of action of such beneficial effects exerted by B. breve is cumbersome due to the lack of effective genetic tools, which limits its synthetic biology application. The widespread presence of CRISPR-Cas systems in the B. breve genome makes endogenous CRISPR-based gene editing toolkits a promising tool. This study revealed that Type I-C CRISPR-Cas systems in B. breve can be divided into two groups based on the amino acid sequences encoded by cas gene clusters. Deletion of the gene coding uracil phosphoribosyl-transferase (upp) was achieved in five B. breve strains from both groups using this system. In addition, translational termination of uracil phosphoribosyl-transferase was successfully achieved in B. breve FJSWX38M7 by single-base substitution of the upp gene and insertion of three stop codons. The gene encoding linoleic acid isomerase (bbi) in B. breve, being a characteristic trait, was deleted after plasmid curing, which rendered it unable to convert linoleic acid into conjugated linoleic acid, demonstrating the feasibility of successive editing. This study expands the toolkit for gene manipulation in B. breve and provides a new approach toward functional genome editing and analysis of B. breve strains.IMPORTANCEThe lack of effective genetic tools for Bifidobacterium breve is an obstacle to studying the molecular mechanisms of its health-promoting effects, hindering the development of next-generation probiotics. Here, we introduce a gene editing method based on the endogenous CRISPR-Cas system, which can achieve gene deletion, single-base substitution, gene insertion, and successive gene editing in B. breve. This study will facilitate discovery of functional genes and elucidation of molecular mechanisms of B. breve pertaining to health-associated benefits.
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Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR)-Cas Unleashed: Transforming Gene Editing With Breakthroughs, Applications, and Ethical Dilemmas.
The most significant breakthrough in gene editing is the advent of the clustered regularly interspaced short palindromic repeats (CRISPR)-Cas system. This innovative technology enables scientists to insert or delete genes using specific enzymes, facilitating modifications to genomes that can influence an organism's phenotype. The Cas9 enzyme is the most widely used within the CRISPR framework and has already received approval for treating sickle cell disease, with many other applications likely to follow. As this rapidly evolving field continues to advance, it holds great promise for addressing genetic disorders and diseases. This article will explore the various enzymes available in the CRISPR system, the range of diseases and conditions that could be treated using this technology, alternative gene therapy methods, and the ethical considerations surrounding its use.
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CRISPR/Cas9 system and its applications in nervous system diseases.
The clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR-associated protein 9 (Cas9) system is an acquired immune system of many bacteria and archaea, comprising CRISPR loci, Cas genes, and its associated proteins. This system can recognize exogenous DNA and utilize the Cas9 protein's nuclease activity to break DNA double-strand and to achieve base insertion or deletion by subsequent DNA repair. In recent years, multiple laboratory and clinical studies have revealed the therapeutic role of the CRISPR/Cas9 system in neurological diseases. This article reviews the CRISPR/Cas9-mediated gene editing technology and its potential for clinical application against neurological diseases.
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The big bang of genome editing technology: development and application of the CRISPR/Cas9 system in disease animal models.
Targeted genome editing technology has been widely used in biomedical studies. The CRISPR-associated RNA-guided endonuclease Cas9 has become a versatile genome editing tool. The CRISPR/Cas9 system is useful for studying gene function through efficient knock-out, knock-in or chromatin modification of the targeted gene loci in various cell types and organisms. It can be applied in a number of fields, such as genetic breeding, disease treatment and gene functional investigation. In this review, we introduce the most recent developments and applications, the challenges, and future directions of Cas9 in generating disease animal model. Derived from the CRISPR adaptive immune system of bacteria, the development trend of Cas9 will inevitably fuel the vital applications from basic research to biotechnology and bio-medicine.
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An adenine base editor with expanded targeting scope using SpCas9-NGv1 in rice.
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A novel cloning strategy for one-step assembly of multiplex CRISPR vectors.
One key advantage of the CRISPR/Cas9 system in comparison with other gene editing approaches lies in its potential for multiplexing. Here, we describe an elaborate procedure that allows the assembly of multiple gRNA expression cassettes into a vector of choice within a single step, termed ASAP(Adaptable System for Assembly of multiplexed Plasmids)-cloning. We demonstrate the utility of ASAP-cloning for multiple CRISPR-mediated applications, including efficient multiplex gene editing, robust transcription activation and convenient analysis of Cas9 activity in the presence of multiple gRNAs.
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Current understanding of mitochondrial DNA genetic diseases and gene therapy.
Mitochondria, as crucial organelles within eukaryotic cells, have their proteins and RNAs encoded by both the nuclear genome and the mitochondrial genome. They play vital roles in energy regulation, cellular metabolism, signal transduction, and various other physiological activities. Additionally, mitochondria interact with multiple organelles to collectively maintain cellular homeostasis. Mitochondria can also be transferred between cells and tissues through mechanisms such as migrasomes. Mitochondrial DNA (mtDNA) mutations often cause severe inherited rare diseases, characterized by tissue specificity, heterogeneity, multiple mutation sites, and challenges in achieving a complete cure. Gene editing of mtDNA holds promise for fundamentally curing such diseases. Traditional gene-editing nucleases, such as zinc-finger nucleases (ZFNs) and transcription activator-like effector nuclease (TALENs), as well as novel gene editors like DddA-derived cytosine base editors (DdCBEs), have been demonstrated to correct certain mtDNA mutations. However, CRISPR-based technologies-despite their superior programmability and efficiency-are currently limited due to the technical bottleneck of inefficient sgRNA delivery into mitochondria. This article systematically reviews the structure and function of mitochondria, related diseases, and the current state of mtDNA gene-editing therapies. Furthermore, it explores future directions for optimizing therapeutic tools to overcome the challenge of sgRNA delivery, thereby addressing the treatment barriers posed by pathogenic mtDNA mutations in inherited rare diseases.
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Guanidyl-rich highly branched poly(β-amino ester)s for the delivery of dual CRISPR ribonucleoprotein for efficient large DNA fragment deletion.
Gene editing technologies, particularly clustered regularly interspersed short palindromic repeats (CRISPR) and CRISPR-associated (Cas) proteins, have revolutionized the ability to modify gene sequences in living cells for therapeutic purposes. Delivery of CRISPR/Cas ribonucleoprotein (RNP) is preferred over its DNA and RNA formats in terms of gene editing effectiveness and low risk of off-target events. However, the intracellular delivery of RNP poses significant challenges and necessitates the development of non-viral vectors. Our previous study has demonstrated that phenyl guanidine (PG) group modified linear poly(β-amino ester)s (PAEs) can facilitate CRISPR/Cas9 RNP mediated gene knockout in HeLa cells. Here, we further investigated the utilization of highly branched PAEs (HPAEs) with PG groups (HPAE-PG) for efficient delivery of cytosolic protein and CRISPR/Cas9 RNP complexes, while also examining the influence of branching units and branching ratios on the delivery process. The efficiency of HPAE-PG/RNP transfection for large DNA fragment deletion was assessed using a dual sgRNA-guided approach to delete exon 80 of the human COL7A1 gene, which harbors mutations associated with dystrophic epidermolysis bullosa (DEB). Our findings demonstrate that HPAE-PG/RNP successfully induced a deletion of 56 base pairs (exon 80) within COL7A1 in both HEK cells and keratinocytes derived from recessive DEB patients. This study highlights the potential of HPAE-PG as a non-viral vector for large DNA fragment deletion, emphasizing the importance of branching factors of HPAEs in optimizing CRISPR RNP delivery for therapeutic applications in genetic disorders.
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Successful In Vitro Modification of the Dmd Gene Using Prime Editing.
Duchenne muscular dystrophy (DMD) is a fatal X-linked neuromuscular disorder caused by mutations in the dystrophin gene. Prime editing is a versatile genome editing technology capable of introducing precise nucleotide changes without generating double-strand DNA breaks, making it a promising approach for correcting pathogenic point mutations. In this study, we applied prime editing to modify mdx-4cv and mdx-5cv mutation-equivalent sites in mouse C2C12 myoblasts in vitro. Initial editing efficiencies were unexpectedly low and were associated with the presence of a 5'-TTCT-3' motif within engineered prime editing guide RNAs (epegRNAs). epegRNA designs containing this motif exhibited reduced prime editing efficiency, whereas silent substitution eliminating the motif significantly improved editing outcomes, indicating that specific sequence features within epegRNAs can influence editing performance. Rational redesign of epegRNAs to remove this motif substantially enhanced editing efficiency, achieving up to 20% modification at the 4cv target site using an NGG PAM and 21% editing at the 5cv locus using an NGAG PAM. These findings highlight an important sequence-dependent constraint in epegRNA design and provide practical guidance for optimizing prime editing strategies targeting Dmd mutations in vitro.
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