A modified glycosylase base editor without predictable DNA off-target effects.

Glycosylase base editor (GBE) can induce C-to-G transversion in mammalian cells, showing great promise for the treatment of human genetic disorders. However, the limited efficiency of transversion and the possibility of off-target effects caused by Cas9 restrict its potential clinical applications. In our recent study, we have successfully developed TaC9-CBE and TaC9-ABE by separating nCas9 and deaminase, which eliminates the Cas9-dependent DNA off-target effects without compromising editing efficiency. We developed a novel GBE called TaC9-GBEYE1, which utilizes the deaminase and UNG-nCas9 guided by TALE and sgRNA, respectively. TaC9-GBEYE1 showed comparable levels of on-target editing efficiency to traditional GBE at 19 target sites, without any off-target effects caused by Cas9 or TALE. The TaC9-GBEYE1 is a safe tool for gene therapy.

Improvement of TaC9-ABE mediated correction of human SMN2 gene.

Spinal muscular atrophy (SMA) is a devastating neuromuscular disease caused by mutations in the survival motor neuron 1 (SMN1) gene. Gene editing technology repairs the conversion of the 6th base T to C in exon 7 of the paralogous SMN2 gene, compensating for the SMN protein expression and promoting the survival and function of motor neurons. However, low editing efficiency and unintended off-target effects limit the application of this technology. Here, we optimized a TaC9-adenine base editor (ABE) system by combining Cas9 nickase with the transcription activator-like effector (TALE)-adenosine deaminase fusion protein to effectively and precisely edit SMN2 without detectable Cas9 dependent off-target effects in human cell lines. We also generated human SMA-induced pluripotent stem cells (SMA-iPSCs) through the mutation of the splice acceptor or deletion of the exon 7 of SMN1. TaC9-R10 induced 45% SMN2 T6 > C conversion in the SMA-iPSCs. The SMN2 T6 > C splice-corrected SMA-iPSCs were directionally differentiated into motor neurons, exhibiting SMN protein recovery and antiapoptosis ability. Therefore, the TaC9-ABE system with dual guides from the combination of Cas9 with TALE could be a potential therapeutic strategy for SMA with high efficacy and safety.

MiR-106a targets ATG7 to inhibit autophagy and angiogenesis after myocardial infarction.

BACKGROUND: Myocardial infarction (MI) is an acute condition in which the heart muscle dies due to the lack of blood supply. Previous research has suggested that autophagy and angiogenesis play vital roles in the prevention of heart failure after MI, and miR-106a is considered to be an important regulatory factor in MI. But the specific mechanism remains unknown. In this study, using cultured venous endothelial cells and a rat model of MI, we aimed to identify the potential target genes of miR-106a and discover the mechanisms of inhibiting autophagy and angiogenesis. METHODS: We first explored the biological functions of miR-106a on autophagy and angiogenesis on endothelial cells. Then we identified ATG7, which was the downstream target gene of miR-106a. The expression of miR-106a and ATG7 was investigated in the rat model of MI. RESULTS: We found that miR-106a inhibits the proliferation, cell cycle, autophagy and angiogenesis, but promoted the apoptosis of vein endothelial cells. Moreover, ATG7 was identified as the target of miR-106a, and ATG7 rescued the inhibition of autophagy and angiogenesis by miR-106a. The expression of miR-106a in the rat model of MI was decreased but the expression of ATG7 was increased in the infarction areas. CONCLUSION: Our results indicate that miR-106a may inhibit autophagy and angiogenesis by targeting ATG7. This mechanism may be a potential therapeutic treatment for MI.

Exonuclease editor promotes precision of gene editing in mammalian cells.

BACKGROUND: Many efforts have been made to improve the precision of Cas9-mediated gene editing through increasing knock-in efficiency and decreasing byproducts, which proved to be challenging. RESULTS: Here, we have developed a human exonuclease 1-based genome-editing tool, referred to as exonuclease editor. When compared to Cas9, the exonuclease editor gave rise to increased HDR efficiency, reduced NHEJ repair frequency, and significantly elevated HDR/indel ratio. Robust gene editing precision of exonuclease editor was even superior to the fusion of Cas9 with E1B or DN1S, two previously reported precision-enhancing domains. Notably, exonuclease editor inhibited NHEJ at double strand breaks locally rather than globally, reducing indel frequency without compromising genome integrity. The replacement of Cas9 with single-strand DNA break-creating Cas9 nickase further increased the HDR/indel ratio by 453-fold than the original Cas9. In addition, exonuclease editor resulted in high microhomology-mediated end joining efficiency, allowing accurate and flexible deletion of targeted sequences with extended lengths with the aid of paired sgRNAs. Exonuclease editor was further used for correction of DMD patient-derived induced pluripotent stem cells, where 30.0% of colonies were repaired by HDR versus 11.1% in the control. CONCLUSIONS: Therefore, the exonuclease editor system provides a versatile and safe genome editing tool with high precision and holds promise for therapeutic gene correction.

Mild phototherapy mediated by IR780-Gd-OPN nanomicelles suppresses atherosclerotic plaque progression through the activation of the HSP27-regulated NF-κB pathway.

Reducing plaque lipid content and enhancing plaque stability without causing extensive apoptosis of foam cells are ideal requirements for developing a safe and effective treatment of atherosclerosis. In this study, we synthesized IR780-Gd-OPN nanomicelles by conjugating osteopontin (OPN) and loading a gadolinium-macrocyclic ligand (Gd-DOTA) onto near-infrared dye IR780-polyethylene glycol polymer. The nanomicelles were employed for mild phototherapy of atherosclerotic plaques and dual-mode imaging with near-infrared fluorescence and magnetic resonance. In vitro results reveal that the mild phototherapy mediated by IR780-Gd-OPN nanomicelles not only activates heat shock protein (HSP) 27 to protect foam cells against apoptosis but also inhibits the nuclear factor kappa-B (NF-κB) pathway to regulate lipid metabolism and macrophage polarization, thereby diminishing the inflammatory response. In vivo results further validate that mild phototherapy effectively reduces plaque lipid content and size while simultaneously enhancing plaque stability by regulating the ratio of M1 and M2-type macrophages. In summary, this study presents a promising approach for developing a safe and highly efficient method for the precise therapeutic visualization of atherosclerosis. STATEMENT OF SIGNIFICANCE: The rupture of unstable atherosclerotic plaques is a major cause of high mortality rates in cardiovascular diseases. Therefore, the ideal outcome of atherosclerosis treatment is to reduce plaque size while enhancing plaque stability. To address this challenge, we designed IR780-Gd-OPN nanomicelles for mild phototherapy of atherosclerosis. This treatment can effectively reduce plaque size while significantly improving plaque stability by increasing collagen fiber content and elevating the ratio of M2/M1 macrophages, which is mainly attributed to the inhibition of the NF-κB signaling pathway by mild phototherapy-activated HSP27. In summary, our proposed mild phototherapy strategy provides a promising approach for safe and effective treatment of atherosclerosis.

A spatiotemporal atlas of mouse liver homeostasis and regeneration.

The mechanism by which mammalian liver cell responses are coordinated during tissue homeostasis and perturbation is poorly understood, representing a major obstacle in our understanding of many diseases. This knowledge gap is caused by the difficulty involved with studying multiple cell types in different states and locations, particularly when these are transient. We have combined Stereo-seq (spatiotemporal enhanced resolution omics-sequencing) with single-cell transcriptomic profiling of 473,290 cells to generate a high-definition spatiotemporal atlas of mouse liver homeostasis and regeneration at the whole-lobe scale. Our integrative study dissects in detail the molecular gradients controlling liver cell function, systematically defining how gene networks are dynamically modulated through intercellular communication to promote regeneration. Among other important regulators, we identified the transcriptional cofactor TBL1XR1 as a rheostat linking inflammation to Wnt/ß-catenin signaling for facilitating hepatocyte proliferation. Our data and analytical pipelines lay the foundation for future high-definition tissue-scale atlases of organ physiology and malfunction.

Enhancing prime editor flexibility with coiled-coil heterodimers.

BACKGROUND: Prime editing enables precise base substitutions, insertions, and deletions at targeted sites without the involvement of double-strand DNA breaks or exogenous donor DNA templates. However, the large size of prime editors (PEs) hampers their delivery in vivo via adeno-associated virus (AAV) due to the viral packaging limit. Previously reported split PE versions provide a size reduction, but they require intricate engineering and potentially compromise editing efficiency. RESULTS: Herein, we present a simplified split PE named as CC-PE, created through non-covalent recruitment of reverse transcriptase to the Cas9 nickase via coiled-coil heterodimers, which are widely used in protein design due to their modularity and well-understood sequence-structure relationship. We demonstrate that the CC-PE maintains or even surpasses the efficiency of unsplit PE in installing intended edits, with no increase in the levels of undesired byproducts within tested loci amongst a variety of cell types (HEK293T, A549, HCT116, and U2OS). Furthermore, coiled-coil heterodimers are used to engineer SpCas9-NG-PE and SpRY-PE, two Cas9 variants with more flexible editing scope. Similarly, the resulting NG-CC-PE and SpRY-CC-PE also achieve equivalent or enhanced efficiency of precise editing compared to the intact PE. When the dual AAV vectors carrying CC-PE are delivered into mice to target the Pcsk9 gene in the liver, CC-PE enables highly efficient precise editing, resulting in a significant reduction of plasma low-density lipoprotein cholesterol and total cholesterol. CONCLUSIONS: Our innovative, modular system enhances flexibility, thus potentially facilitating the in vivo applicability of prime editing.

Precise large-fragment deletions in mammalian cells and mice generated by dCas9-controlled CRISPR/Cas3.

Currently, the Cas9 and Cas12a systems are widely used for genome editing, but their ability to precisely generate large chromosome fragment deletions is limited. Type I-E CRISPR mediates broad and unidirectional DNA degradation, but controlling the size of Cas3-mediated DNA deletions has proven elusive thus far. Here, we demonstrate that the endonuclease deactivation of Cas9 (dCas9) can precisely control Cas3-mediated large-fragment deletions in mammalian cells. In addition, we report the elimination of the Y chromosome and precise retention of the Sry gene in mice using CRISPR/Cas3 and dCas9-controlled CRISPR/Cas3, respectively. In conclusion, dCas9-controlled CRISPR/Cas3-mediated precise large-fragment deletion provides an approach for establishing animal models by chromosome elimination. This method also holds promise as a potential therapeutic strategy for treating fragment mutations or human aneuploidy diseases that involve additional chromosomes.

An optimized culture system for efficient derivation of porcine expanded potential stem cells from preimplantation embryos and by reprogramming somatic cells.

Pigs share anatomical and physiological traits with humans and can serve as a large-animal model for translational medicine. Bona fide porcine pluripotent stem cells (PSCs) could facilitate testing cell and drug therapies. Agriculture and biotechnology may benefit from the ability to produce immune cells for studying animal infectious diseases and to readily edit the porcine genome in stem cells. Isolating porcine PSCs from preimplantation embryos has been intensively attempted over the past decades. We previously reported the derivation of expanded potential stem cells (EPSCs) from preimplantation embryos and by reprogramming somatic cells of multiple mammalian species, including pigs. Porcine EPSCs (pEPSCs) self-renew indefinitely, differentiate into embryonic and extra-embryonic lineages, and permit precision genome editing. Here we present a highly reproducible experimental procedure and data of an optimized and robust porcine EPSC culture system and its use in deriving new pEPSC lines from preimplantation embryos and reprogrammed somatic cells. No particular expertise is required for the protocols, which take ~4-6 weeks to complete. Importantly, we successfully established pEPSC lines from both in vitro fertilized and somatic cell nuclear transfer-derived embryos. These new pEPSC lines proliferated robustly over long-term passaging and were amenable to both simple indels and precision genome editing, with up to 100% targeting efficiency. The pEPSCs differentiated into embryonic cell lineages in vitro and teratomas in vivo, and into porcine trophoblast stem cells in human trophoblast stem cell medium. We show here that pEPSCs have unique epigenetic features, particularly H3K27me3 levels substantially lower than fibroblasts.

Unraveling the role of Xist in X chromosome inactivation: insights from rabbit model and deletion analysis of exons and repeat A.

X chromosome inactivation (XCI) is a process that equalizes the expression of X-linked genes between males and females. It relies on Xist, continuously expressed in somatic cells during XCI maintenance. However, how Xist impacts XCI maintenance and its functional motifs remain unclear. In this study, we conducted a comprehensive analysis of Xist, using rabbits as an ideal non-primate model. Homozygous knockout of exon 1, exon 6, and repeat A in female rabbits resulted in embryonic lethality. However, X∆ReAX females, with intact X chromosome expressing Xist, showed no abnormalities. Interestingly, there were no significant differences between females with homozygous knockout of exons 2-5 and wild-type rabbits, suggesting that exons 2, 3, 4, and 5 are less important for XCI. These findings provide evolutionary insights into Xist function.

Programmable RNA 5-methylcytosine (m5C) modification of cellular RNAs by dCasRx conjugated methyltransferase and demethylase.

5-Methylcytosine (m5C), an abundant RNA modification, plays a crucial role in regulating RNA fate and gene expression. While recent progress has been made in understanding the biological roles of m5C, the inability to introduce m5C at specific sites within transcripts has hindered efforts to elucidate direct links between specific m5C and phenotypic outcomes. Here, we developed a CRISPR-Cas13d-based tool, named reengineered m5C modification system (termed 'RCMS'), for targeted m5C methylation and demethylation in specific transcripts. The RCMS editors consist of a nuclear-localized dCasRx conjugated to either a methyltransferase, NSUN2/NSUN6, or a demethylase, the catalytic domain of mouse Tet2 (ten-eleven translocation 2), enabling the manipulation of methylation events at precise m5C sites. We demonstrate that the RCMS editors can direct site-specific m5C incorporation and demethylation. Furthermore, we confirm their effectiveness in modulating m5C levels within transfer RNAs and their ability to induce changes in transcript abundance and cell proliferation through m5C-mediated mechanisms. These findings collectively establish RCMS editors as a focused epitranscriptome engineering tool, facilitating the identification of individual m5C alterations and their consequential effects.

Genome-edited rabbits: Unleashing the potential of a promising experimental animal model across diverse diseases.

Animal models are extensively used in all aspects of biomedical research, with substantial contributions to our understanding of diseases, the development of pharmaceuticals, and the exploration of gene functions. The field of genome modification in rabbits has progressed slowly. However, recent advancements, particularly in CRISPR/Cas9-related technologies, have catalyzed the successful development of various genome-edited rabbit models to mimic diverse diseases, including cardiovascular disorders, immunodeficiencies, aging-related ailments, neurological diseases, and ophthalmic pathologies. These models hold great promise in advancing biomedical research due to their closer physiological and biochemical resemblance to humans compared to mice. This review aims to summarize the novel gene-editing approaches currently available for rabbits and present the applications and prospects of such models in biomedicine, underscoring their impact and future potential in translational medicine.

Targeted mutagenesis in mice via an engineered AsCas12f1 system.

SpCas9 and AsCas12a are widely utilized as genome editing tools in human cells, but their applications are largely limited by their bulky size. Recently, AsCas12f1 protein, with a small size (422 amino acids), has been demonstrated to be capable of cleaving double-stranded DNA protospacer adjacent motif (PAM). However, low editing efficiency and large differences in activity against different genomic loci have been a limitation in its application. Here, we show that engineered AsCas12f1 sgRNA has significantly improved the editing efficiency in human cells and mouse embryos. Moreover, we successfully generated three stable mouse mutant disease models using the engineered CRISPR-AsCas12f1 system in this study. Collectively, our work uncovers the engineered AsCas12f1 system expands mini CRISPR toolbox, providing a remarkable promise for therapeutic applications.

Engineered domain-inlaid Nme2Cas9 adenine base editors with increased on-target DNA editing and targeting scope.

BACKGROUND: Nme2ABE8e has been constructed and characterized as a compact, accurate adenine base editor with a less restrictive dinucleotide protospacer-adjacent motif (PAM: N4CC) but low editing efficiency at challenging loci in human cells. Here, we engineered a subset of domain-inlaid Nme2Cas9 base editors to bring the deaminase domain closer to the nontarget strand to improve editing efficiency. RESULTS: Our results demonstrated that Nme2ABE8e-797 with adenine deaminase inserted between amino acids 797 and 798 has a significantly increased editing efficiency with a wide editing window ranging from 4 to 18 bases in mammalian cells, especially at the sites that were difficult to edit by Nme2ABE8e. In addition, by swapping the PAM-interacting domain of Nme2ABE8e-797 with that of SmuCas9 or introducing point mutations of eNme2-C in Nme2ABE8e-797, we created Nme2ABE8e-797Smu and Nme2ABE8e-797-C, respectively, which exhibited robust activities at a wide range of sites with N4CN PAMs in human cells. Moreover, the modified domain-inlaid Nme2ABE8e can efficiently restore or install disease-related loci in Neuro-2a cells and mice. CONCLUSIONS: These novel Nme2ABE8es with increased on-target DNA editing and expanded PAM compatibility will expand the base editing toolset for efficient gene modification and therapeutic applications.

Development of a highly efficient prime editor system in mice and rabbits.

The recently developed prime-editing (PE) technique is more precise than previously available techniques and permits base-to-base conversion, replacement, and insertions and deletions in the genome. However, previous reports show that the efficiency of prime editing is insufficient to produce genome-edited animals. In fact, prime-guide RNA (pegRNA) designs have posed a challenge in achieving favorable editing efficiency. Here, we designed prime binding sites (PBS) with a melting temperature (Tm) of 42 °C, leading to optimal performance in cells, and we found that the optimal Tm was affected by the culture temperature. In addition, the ePE3max system was developed by updating the PE architecture to PEmax and expressing engineered pegRNA (epegRNA) based on the original PE3 system. The updated ePE3max system can efficiently induce gene editing in mouse and rabbit embryos. Furthermore, we successfully generated a Hoxd13 (c. 671 G > T) mutation in mice and a Tyr (c. 572 del) mutation in rabbits by ePE3max. Overall, the editing efficiency of modified ePE3max systems is superior to that of the original PE3 system in producing genome-edited animals, which can serve as an effective and versatile genome-editing tool for precise genome modification in animal models.

Modeling SHANK3-associated autism spectrum disorder in Beagle dogs via CRISPR/Cas9 gene editing.

Despite intensive studies in modeling neuropsychiatric disorders especially autism spectrum disorder (ASD) in animals, many challenges remain. Genetic mutant mice have contributed substantially to the current understanding of the molecular and neural circuit mechanisms underlying ASD. However, the translational value of ASD mouse models in preclinical studies is limited to certain aspects of the disease due to the apparent differences in brain and behavior between rodents and humans. Non-human primates have been used to model ASD in recent years. However, a low reproduction rate due to a long reproductive cycle and a single birth per pregnancy, and an extremely high cost prohibit a wide use of them in preclinical studies. Canine model is an appealing alternative because of its complex and effective dog-human social interactions. In contrast to non-human primates, dog has comparable drug metabolism as humans and a high reproduction rate. In this study, we aimed to model ASD in experimental dogs by manipulating the Shank3 gene as SHANK3 mutations are one of most replicated genetic defects identified from ASD patients. Using CRISPR/Cas9 gene editing, we successfully generated and characterized multiple lines of Beagle Shank3 (bShank3) mutants that have been propagated for a few generations. We developed and validated a battery of behavioral assays that can be used in controlled experimental setting for mutant dogs. bShank3 mutants exhibited distinct and robust social behavior deficits including social withdrawal and reduced social interactions with humans, and heightened anxiety in different experimental settings (n = 27 for wild-type controls and n = 44 for mutants). We demonstrate the feasibility of producing a large number of mutant animals in a reasonable time frame. The robust and unique behavioral findings support the validity and value of a canine model to investigate the pathophysiology and develop treatments for ASD and potentially other psychiatric disorders.

Evaluation of guide-free Cas9-induced genomic damage and transcriptome changes in pig embryos.

Cas9 protein without sgRNAs can induce genomic damage at the cellular level in vitro. However, whether the detrimental effects occur in embryos after Cas9 treatment remains unknown. Here, using pig embryos as subjects, we observed that Cas9 protein transcribed from injected Cas9 mRNA can persist until at least the blastocyst stage. Cas9 protein alone can induce genome damage in preimplantation embryos, represented by the increased number of phosphorylated histone H2AX foci on the chromatin fiber, which led to apoptosis and decreased cell number of blastocysts. In addition, single-blastocyst RNA sequencing confirmed that Cas9 protein without sgRNAs can cause changes in the blastocyst transcriptome, depressing embryo development signal pathways, such as cell cycle, metabolism, and cellular communication-related signal pathways, while activating apoptosis and necroptosis signal pathways, which together resulted in impaired preimplantation embryonic development. These results indicated that attention should be given to the detrimental effects caused by the Cas9 protein when using CRISPR-Cas9 for germline genome editing, especially for the targeted correction of human pathological mutations using germline gene therapy.

A strategy for Cas13 miniaturization based on the structure and AlphaFold.

The small size of the Cas nuclease fused with various effector domains enables a broad range of function. Although there are several ways of reducing the size of the Cas nuclease complex, no efficient or generalizable method has been demonstrated to achieve protein miniaturization. In this study, we establish an Interaction, Dynamics and Conservation (IDC) strategy for protein miniaturization and generate five compact variants of Cas13 with full RNA binding and cleavage activity comparable the wild-type enzymes based on a combination of IDC strategy and AlphaFold2. In addition, we construct an RNA base editor, mini-Vx, and a single AAV (adeno-associated virus) carrying a mini-RfxCas13d and crRNA expression cassette, which individually shows efficient conversion rate and RNA-knockdown activity. In summary, these findings highlight a feasible strategy for generating downsized CRISPR/Cas13 systems based on structure predicted by AlphaFold2, enabling targeted degradation of RNAs and RNA editing for basic research and therapeutic applications.

VCFshiny: an R/Shiny application for interactively analyzing and visualizing genetic variants.

Summary: Next-generation sequencing generates variants that are typically documented in variant call format (VCF) files. However, comprehensively examining variant information from VCF files can pose a significant challenge for researchers lacking bioinformatics and programming expertise. To address this issue, we introduce VCFshiny, an R package that features a user-friendly web interface enabling interactive annotation, interpretation, and visualization of variant information stored in VCF files. VCFshiny offers two annotation methods, Annovar and VariantAnnotation, to add annotations such as genes or functional impact. Annotated VCF files are deemed acceptable inputs for the purpose of summarizing and visualizing variant information. This includes the total number of variants, overlaps across sample replicates, base alterations of single nucleotides, length distributions of insertions and deletions (indels), high-frequency mutated genes, variant distribution in the genome and of genome features, variants in cancer driver genes, and cancer mutational signatures. VCFshiny serves to enhance the intelligibility of VCF files by offering an interactive web interface for analysis and visualization. Availability and implementation: The source code is available under an MIT open source license at https://github.com/123xiaochen/VCFshiny with documentation at https://123xiaochen.github.io/VCFshiny.