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PAM-flexible Engineered FnCas9 variants for robust and ultra-precise genome editing and diagnostics.
The clinical success of CRISPR therapies hinges on the safety and efficacy of Cas proteins. The Cas9 from Francisella novicida (FnCas9) is highly precise, with a negligible affinity for mismatched substrates, but its low cellular targeting efficiency limits therapeutic use. Here, we rationally engineer the protein to develop enhanced FnCas9 (enFnCas9) variants and broaden their accessibility across human genomic sites by ~3.5-fold. The enFnCas9 proteins with single mismatch specificity expanded the target range of FnCas9-based CRISPR diagnostics to detect the pathogenic DNA signatures. They outperform Streptococcus pyogenes Cas9 (SpCas9) and its engineered derivatives in on-target editing efficiency, knock-in rates, and off-target specificity. enFnCas9 can be combined with extended gRNAs for robust base editing at sites which are inaccessible to PAM-constrained canonical base editors. Finally, we demonstrate an RPE65 mutation correction in a Leber congenital amaurosis 2 (LCA2) patient-specific iPSC line using enFnCas9 adenine base editor, highlighting its therapeutic utility.
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Large chromosomal segment deletions by CRISPR/LbCpf1-mediated multiplex gene editing in soybean.
The creation of new soybean varieties has been limited by genomic duplication and redundancy. Efficient multiplex gene editing and large chromosomal segment deletion through clustered regularly interspaced palindromic repeats (CRISPR)/CRISPR-associated protein (Cas) systems are promising strategies for overcoming these obstacles. CRISPR/Cpf1 is a robust tool for multiplex gene editing. However, large chromosomal excision mediated by CRISPR/Cpf1 has been reported in only a few non-plant species. Here, we report on CRISPR/LbCpf1-induced large chromosomal segment deletions in soybean using multiplex gene targeting. The CRISPR/LbCpf1 system was optimized for direct repeat and guide RNA lengths in crispr RNA (crRNA) array. The editing efficiency was evaluated using LbCpf1 driven by the CaMV35S and soybean ubiquitin promoter. The optimized system exhibited editing efficiencies of up to 91.7%. Our results showed eight gene targets could be edited simultaneously in one step when a single eight-gRNA-target crRNA array was employed, with an efficiency of up to 17.1%. We successfully employed CRISPR/LbCpf1 to produce small fragments (<1 Kb) and large chromosomal segment deletions (10 Kb-1 Mb) involving four different gene clusters in soybean. Together, these data demonstrate the power of the CRISPR/LbCpf1 platform for multiplex gene editing and chromosomal segment deletion in soybean, supporting the use of this technology in both basic research and agricultural applications.
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Evolution of an adenine base editor into a small, efficient cytosine base editor with low off-target activity.
Cytosine base editors (CBEs) are larger and can suffer from higher off-target activity or lower on-target editing efficiency than current adenine base editors (ABEs). To develop a CBE that retains the small size, low off-target activity and high on-target activity of current ABEs, we evolved the highly active deoxyadenosine deaminase TadA-8e to perform cytidine deamination using phage-assisted continuous evolution. Evolved TadA cytidine deaminases contain mutations at DNA-binding residues that alter enzyme selectivity to strongly favor deoxycytidine over deoxyadenosine deamination. Compared to commonly used CBEs, TadA-derived cytosine base editors (TadCBEs) offer similar or higher on-target activity, smaller size and substantially lower Cas-independent DNA and RNA off-target editing activity. We also identified a TadA dual base editor (TadDE) that performs equally efficient cytosine and adenine base editing. TadCBEs support single or multiplexed base editing at therapeutically relevant genomic loci in primary human T cells and primary human hematopoietic stem and progenitor cells. TadCBEs expand the utility of CBEs for precision gene editing.
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Compact zinc finger base editors that edit mitochondrial or nuclear DNA in vitro and in vivo.
DddA-derived cytosine base editors (DdCBEs) use programmable DNA-binding TALE repeat arrays, rather than CRISPR proteins, a split double-stranded DNA cytidine deaminase (DddA), and a uracil glycosylase inhibitor to mediate C•G-to-T•A editing in nuclear and organelle DNA. Here we report the development of zinc finger DdCBEs (ZF-DdCBEs) and the improvement of their editing performance through engineering their architectures, defining improved ZF scaffolds, and installing DddA activity-enhancing mutations. We engineer variants with improved DNA specificity by integrating four strategies to reduce off-target editing. We use optimized ZF-DdCBEs to install or correct disease-associated mutations in mitochondria and in the nucleus. Leveraging their small size, we use a single AAV9 to deliver into heart, liver, and skeletal muscle in post-natal mice ZF-DdCBEs that efficiently install disease-associated mutations. While off-target editing of ZF-DdCBEs is likely too high for therapeutic applications, these findings demonstrate a compact, all-protein base editing research tool for precise editing of organelle or nuclear DNA without double-strand DNA breaks.
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Adenine base editing in an adult mouse model of tyrosinaemia.
In contrast to traditional CRISPR-Cas9 homology-directed repair, base editing can correct point mutations without supplying a DNA-repair template. Here we show in a mouse model of tyrosinaemia that hydrodynamic tail-vein injection of plasmid DNA encoding the adenine base editor (ABE) and a single-guide RNA (sgRNA) can correct an A>G splice-site mutation. ABE treatment partially restored splicing, generated fumarylacetoacetate hydrolase (FAH)-positive hepatocytes in the liver, and rescued weight loss in mice. We also generated FAH+ hepatocytes in the liver via lipid-nanoparticle-mediated delivery of a chemically modified sgRNA and an mRNA of a codon-optimized base editor that displayed higher base-editing efficiency than the standard ABEs. Our findings suggest that adenine base editing can be used for the correction of genetic diseases in adult animals.
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Beyond CRISPR/Cas9: emerging genome editing technologies for next-generation crop improvement.
Genome editing has changed plant biology and accelerated crop improvement. CRISPR/Cas9 allows precise and efficient genetic changes in many species. Still, Cas9 has limits like PAM restrictions, off-target effects, and varying editing success. This led to new systems. Editors like Cas12a, CasΦ, CasMINI, and CasX offer more targeting options, can edit RNA, and work better with hard to edit plant genomes. Precision tools such as base editors and prime editors make precise changes by swapping nucleotides or adding small pieces without cutting both DNA strands. This improves accuracy. Beyond single tools, combined and step by step editing methods can be used for handling complex traits controlled by many genes. Using several methods like CRISPR knockouts, base and prime editing, epigenome editing and recombinase systems-breeders can improve traits while reducing unwanted side effects. Stepwise editing helps to test changes, confirm their effects, and improve entire biological pathways. Combining these approaches with AI-driven analysis, target prediction, and design optimization makes it easier to pick the best genes and edits for desired traits. These advanced editing methods are used to boost stress tolerance, fight diseases, improve nutrition, increase yields, and enhance quality after harvest. Despite progress, problems remain with how efficient edits can be made, delivering tools into plants, reliance on specific genotypes, unclear regulations, and acceptance by society. Looking ahead, joying genome editing with AI, fast breeding techniques help develop stronger, high yielding crops and support global food security.
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CRISPR/Cas9-mediated base-editing enables a chain reaction through sequential repair of sgRNA scaffold mutations.
Cell behavior is controlled by complex gene regulatory networks. Although studies have uncovered diverse roles of individual genes, it has been challenging to record or control sequential genetic events in living cells. In this study, we designed two cellular chain reaction systems that enable sequential sgRNA activation in mammalian cells using a nickase Cas9 tethering of a cytosine nucleotide deaminase (nCas9-CDA). In these systems, thymidine (T)-to-cytosine (C) substitutions in the scaffold region of the sgRNA or the TATA box-containing loxP sequence (TATAloxP) are corrected by the nCas9-CDA, leading to activation of the next sgRNA. These reactions can occur multiple times, resulting in cellular chain reactions. As a proof of concept, we established a chain reaction by repairing sgRNA scaffold mutations in 293 T cells. Importantly, the results obtained in yeast or in vitro did not match those obtained in mammalian cells, suggesting that in vivo chain reactions need to be optimized in appropriate cellular contexts. Our system may lay the foundation for building cellular chain reaction systems that have a broad utility in the future biomedical research.
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Targeting mtDNA to Modulate Mitochondrial Dysfunction in Neurodegenerative Diseases.
Mitochondrial dysfunction is a common pathological feature of neurodegenerative diseases namely Alzheimer's disease, Parkinson's disease, amyotrophic lateral sclerosis, and Huntington's disease. Although these disorders are primarily driven by disease-specific genetic and proteopathic mechanisms, increasing evidence suggests that secondary mitochondrial DNA (mtDNA) damage and heteroplasmy shifts may exacerbate bioenergetic failure and neuronal vulnerability. Distinguishing primary disease mechanisms from downstream mtDNA alterations is critical to accurately evaluate emerging therapeutic strategies. Recent advances in mtDNA-targeted genome editing have enabled the direct manipulation of mitochondrial genomes. Mitochondrially targeted zinc finger nucleases and TALENs can selectively alter mutant mtDNA to induce heteroplasmy shifts, whereas DddA-derived cytosine base editors allow precise base editing without double-strand breaks. However, each platform has distinct limitations related to the target scope, off-target risk, design complexity, and delivery efficiency. The application of CRISPR/Cas-based systems to mammalian mtDNA remains constrained by the unresolved challenges in guiding RNA import. This review critically examines mitochondrial dysfunction and mutant mtDNA accumulation in neurodegenerative diseases. It also evaluates current and emerging mtDNA-editing techniques, and highlights key translational barriers. We highlighted that mtDNA-targeted interventions can be a promising approach for disease-modifying or adjunctive strategies, rather than curative approaches.
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Enhancing drought resilience in crops: mechanistic approaches in the face of climate challenge.
Enhancing drought resilience in crops has become a critical challenge in the face of global climate change, which is exacerbating the frequency and severity of drought events. This review explores mechanistic approaches aimed to improve crop drought tolerance, focusing on physiological, biochemical, and molecular mechanisms. We examine the key molecular pathways involved in drought stress responses, including the Mitogen-Activated Protein Kinase (MAPKs) signaling pathway, hormonal regulation, transcriptional control, and post-translational modifications such as ubiquitination-mediated protein degradation, and plant-microbe interaction. The review also delves into the mechanisms of drought stress tolerance, including drought escape, avoidance, and tolerance. It highlights significant traits contributing to drought resilience, such as stomatal regulation and root architecture. Furthermore, we discuss genomics and breeding approaches, including quantitative trait loci (QTL) mapping, marker-assisted selection (MAS), and cutting-edge CRISPR-Cas-based genome editing technologies. These advanced techniques, such as base editing, prime editing, and multiplexing, transform crop improvement strategies by facilitating precise and efficient modifications for enhanced drought resilience, with the success stories in crops such as rice, maize, wheat, and others. Integrating these mechanistic and technological approaches offers promising avenues for developing drought-resilient crops, ensuring food security under increasingly unpredictable climate conditions.
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A combinatorial synthetic strategy for developing genome-editing protein-delivery agents targeting mouse retina.
CRISPR/Cas9-based gene-editing technologies offer promise for treating inherited retinal diseases (IRDs), however safe and efficient ocular delivery of precision editors remains challenging. To address this challenge, we report a class of Coomassie brilliant blue (CBB)-derived lipidoids that bind and deliver proteins. Subretinal injection of Cre complexed with these lipidoids into mT/mG mice leads to robust recombination in the retinal pigment epithelium and photoreceptors. We employ the CBB-lipidoid platform to deliver adenine base editor (ABE) ribonucleoproteins (RNP). Incorporating CBB lipidoids into liposomes improves delivery efficiency. CBB11 stands out for facilitating precise in vivo ABE-mediated gene editing. Delivery of liposome-CBB11-RNP complexes results in a 120-fold increase in base editing compared to RNP alone and restores the scotopic ERG b-wave response in the rd12 mouse model. These results demonstrate the potential of CBB-augmented, liposome-RNP systems for therapeutic gene editing in the eye, paving the way for single-dose precision medicines to treat IRDs.
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