Developing high-efficiency base editors by combining optimized synergistic core components with new types of nuclear localization signal peptide

The clustered regularly interspaced short palindromic repeats(CRISPR)–CRISPR-associated protein(Cas) system has been widely used for genome editing. In this system, the cytosine base editor(CBE) and adenine base editor(ABE) allow generating precise and irreversible base mutations in a programmable manner and have been used in many different types of cells and organisms. However, their applications are limited by low editing efficiency at certain genomic target sites or at specific target cytosine(C) or adenine(A) residues. Using a strategy of combining optimized synergistic core components, we developed a new multiplex super-assembled ABE(sABE) in rice that showed higher base-editing efficiency than previously developed ABEs. We also designed a new type of nuclear localization signal(NLS) comprising a FLAG epitope tag with four copies of a codon-optimized NLS(F4NLS^(r2)) to generate another ABE named F4NLS-sABE. This new NLS increased editing efficiency or edited additional A at several target sites. A new multiplex super-assembled CBE(sCBE) and F4NLS^(r2) involved F4NLS-sCBE were also created using the same strategy. F4NLS-sCBE was proven to be much more efficient than sCBE in rice. These optimized base editors will serve as powerful genome-editing tools for basic research or molecular breeding in rice and will provide a reference for the development of superior editing tools for other plants or animals.

Base editor-mediated large-scale screening of functional mutations in bacteria for industrial phenotypes

Base editing,the targeted introduction of point mutations into cellular DNA,holds promise for improving genome-scale functional genome screening to single-nucleotide resolution.Current efforts in prokaryotes,however,remain confined to loss-of-function screens using the premature stop codons-mediated gene inactivation library,which falls far short of fully releasing the potential of base editors.Here,we developed a base editor-mediated functional single nucleotide variant screening pipeline in Escherichia coli.We constructed a library with 31,123 sgRNAs targeting 462 stress response-related genes in E.coli,and screened for adaptive mutations under isobutanol and furfural selective conditions.Guided by the screening results,we successfully identified several known and novel functional mutations.Our pipeline might be expanded to the optimization of other phenotypes or the strain engineering in other microorganisms.

Correction of a CADASIL point mutation using adenine base editors in hiPsCsandbloodvessel organoids

Cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL) is a monogenic small vessel disease caused by mutations in the NOTCH3 gene. However, the pathogenesis of CADASIL remains unclear, and patients have limited treatment options. Here, we use human induced pluripotent stem cells (hiPSCs) generated from the peripheral blood mononuclear cells of a patient with CADASIL carrying a heterozygous NOTCH3 mutation (c.1261C>T, p.R421C) to develop a disease model. The correction efficiency of different adenine base editors (ABEs) is tested using the HEK293T-NOTCH3 reporter cell line. ABEmax is selected based on its higher efficiency and minimization of predicted off-target effects. Vascular smooth muscle cells (VSMCs) differentiated from CADASIL hiPSCs show NOTCH3 deposition and abnormal actin cytoskeleton structure, and the abnormalities are recovered in corrected hiPSC-derived VSMCs. Furthermore, CADASIL blood vessel organoids generated for in vivo modeling show altered expression of genes related to disease phenotypes, including the downregulation of cell adhesion, extracellular matrix organization, and vessel development. The dual adeno-associated virus (AAV) split-ABEmax system is applied to the genome editing of vascular organoids with an average editing efficiency of 8.82%. Collectively, we present potential genetic therapeutic strategies for patients with CADASIL using blood vessel organoids and the dual AAV split-ABEmax system.

Precise genome editing with base editors

Single-nucleotide variants account for about half of known pathogenic genetic variants in human.Genome editing strategies by reversing pathogenic point mutations with minimum side effects have great therapeutic potential and are now being actively pursued.The emerge of precise and effcient genome editing strategies such as base editing and prime editing provide powerful tools for nucleotide conversion without inducing double-stranded DNA breaks(DSBs),which have shown great potential for curing genetic disorders.A diverse toolkit of base editors has been devel-oped to improve the editing effciency and accuracy in different context of application.Here,we summarized the evolving of base editors(BEs),their limitations and future perspective of base editing-based therapeutic strategies.

Artificial evolution of OsEPSPS through an improved dual cytosine and adenine base editor generated a novel allele conferring rice glyphosate tolerance

Exploiting novel endogenous glyphosate-tolerant alleles is highly desirable and has promising potential for weed control in rice breeding. Here,through fusions of different effective cytosine and adenine deaminases with nCas9-NG, we engineered an effective surrogate two-component composite base editing system, STCBE-2, with improved C-to-T and A-to-G base editing efficiency and expanded the editing window. Furthermore,we targeted a rice endogenous OsEPSPS gene for artificial evolution through STCBE-2-mediated near-saturated mutagenesis. After hygromycin and glyphosate selection, we identified a novel OsEPSPS allele with an Asp-213-Asn(D213N)mutation(OsEPSPS-D213N) in the predicted glyphosate-binding domain, which conferred rice plants reliable glyphosate tolerance and had not been reported or applied in rice breeding. Collectively, we developed a novel dual base editor which will be valuable for artificial evolution of important genes in crops. And the novel glyphosate-tolerant rice germplasm generated in this study will benefit weeds management in rice paddy fields.

Human 8-cell embryos enable efficient induction of disease-preventive mutations without off-target effect by cytosine base editor

Approximately 140 million people worldwide are homozygous carriers of APOE4(ε4),a strong genetic risk factor for late onset familial and sporadic Alzheimer’s disease(AD),91%of whom will develop AD at earlier age than heterozygous carriers and noncarriers.Susceptibility to AD could be reduced by targeted editing of APOE4,but a technical basis for controlling the off-target effects of base editors is necessary to develop low-risk personalized gene therapies.Here,we first screened eight cytosine base editor variants at four injection stages(from 1-to 8-cell stage),and found that FNLS-YE1 variant in 8-cell embryos achieved the comparable base conversion rate(up to 100%)with the lowest bystander effects.In particular,80%of AD-susceptibleε4 allele copies were converted to the AD-neutralε3 allele in humanε4-carrying embryos.Stringent control measures combined with targeted deep sequencing,whole genome sequencing,and RNA sequencing showed no DNA or RNA off-target events in FNLS-YE1-treated human embryos or their derived stem cells.Furthermore,base editing with FNLS-YE1 showed no effects on embryo development to the blastocyst stage.Finally,we also demonstrated FNLS-YE1 could introduce known protective variants in human embryos to potentially reduce human susceptivity to systemic lupus erythematosus and familial hypercholesterolemia.Our study therefore suggests that base editing with FNLS-YE1 can efficiently and safely introduce known preventive variants in 8-cell human embryos,a potential approach for reducing human susceptibility to AD or other genetic diseases.

Effective gene editing by high-fidelity base editor 2 in mouse zygotes

Targeted point mutagenesis through homologous recombination has been widely used in genetic studies and holds considerable promise for repairing disease- causing mutations in patients. However, problems such as mosaicism and low mutagenesis efficiency continue to pose challenges to clinical applicaUon of such approaches. Recently, a base editor （BE） system built on cytidine （C） deaminase and CRISPR/Cas9 technology was developed as an alternative method for targeted point mutagenesis in plant, yeast, and human cells. Base editors convert C in the deamination window to thymidine （T） efficiently, however, it remains unclear whether targeted base editing in mouse embryos is feasible. In this report, we generated a modified high- fidelity version of base editor 2 （HF2-BE2）, and investigated its base editing efficacy in mouse embryos. We found that HF2-BE2 could convert C to T efficiently, with up to 100% biallelic mutation efficiency in mouse embryos. Unlike BE3, HF2-BE2 could convert C to T on both the target and non-target strand, expanding the editing scope of base editors. Surprisingly, we found HF2-BE2 could also deaminate C that was proximal to the gRNA-binding region. Taken together, our work demonstrates the feasibility of generating point mutations in mouse by base editing, and underscores the need to carefully optimize base editing systems in order to eliminate proximal-site deamination.

CRISPR-Cas nucleases and base editors for plant genome editing

Clustered regularly interspaced short palindromic repeats(CRISPR)—CRISPR-associated protein(Cas)and base editors are fundamental tools in plant genome editing.Cas9 from Streptococcus pyogenes(SpCas9),recognizing an NGG protospacer adjacent motif(PAM),is a widely used nuclease for genome editing in living cells.Cas12a nucleases,targeting T-rich PAMs,have also been recently demonstrated in several plant species.Furthermore,multiple Cas9 and Cas12a engineered variants and orthologs,with different PAM recognition sites,editing efficiencies and fidelity,have been explored in plants.These RNA-guided sequence-specific nucleases(SSN)generate double-stranded breaks(DSBs)in DNA,which trigger non-homologous end-joining(NHEJ)repair or homology-directed repair(HDR),resulting in insertion and deletion(indel)mutations or precise gene replacement,respectively.Alternatively,genome editing can be achieved by base editors without introducing DSBs.So far,several base editors have been applied in plants to introduce C-to-T or A-to-G transitions,but they are still undergoing improvement in editing window size,targeting scope,off-target effects in DNA and RNA,product purity and overall activity.Here,we summarize recent progress on the application of Cas nucleases,engineered Cas variants and base editors in plants.

Effective generation of maternal genome point mutated porcine embryos by injection of cytosine base editor into germinal vesicle oocytes

Cytosine and adenine base editors are promising new tools for introducing precise genetic modifications that are required to generate disease models and to improve traits in pigs. Base editors can catalyze the conversion of C→T(C>T) or A→G(A>G) in the target site through a single guide RNA. Injection of base editors into the zygote cytoplasm can result in the production of offspring with precise point mutations, but most F0 are mosaic, and breeding of F1 heterozygous pigs is time-intensive. Here, we developed a method called germinal vesicle oocyte base editing(GVBE) to produce point mutant F0 porcine embryos by editing the maternal alleles during the GV to MⅡ transition. Injection of cytosine base editor 3(BE3) mRNA and X-linked Dmdspecific guide RNAs into GVoocytes efficiently edited maternal Dmd during in vitro maturation and did not affect the maturation potential of the oocytes. The edited MⅡ oocytes developed into blastocysts after parthenogenetic activation(PA) or in vitro fertilization(IVF). However, BE3 may reduce the developmental potential of IVF blastocysts from 31.5%±0.8% to 20.4%±2.1%. There 40%–78.3% diploid PA blastocysts had no more than two different alleles, including up to 10% embryos that had only C>T mutation alleles. Genotyping of IVF blastocysts indicated that over 70% of the edited embryos had one allele or two different alleles of Dmd. Since the male embryos had only a copy of Dmd allele, all five(5/19) F0 male embryos are homozygous and three of them were Dmd precise C>T mutation. Nine(9/19) female IVF embryos had two different alleles including a WT and a C>T mutation. DNA sequencing showed that some of them might be heterozygous embryos. In conclusion, the GVBE method is a valuable method for generating F0 embryos with maternal point mutated alleles in a single step.

Single-nucleotide editing for zebra3 and wsl5 phenotypes in rice using CRISPR/Cas9-mediated adenine base editors

The CRISPR/Cas9-mediated base editing technology can efficiently generate point mutations in the genome without introducing a double-strand break(DSB)or supplying a DNA donor template for homology-directed repair(HDR).In this study,adenine base editors(ABEs)were used for rapid generation of precise point mutations in two distinct genes,OsWSL5,and OsZEBRA3(Z3),in both rice protoplasts and regenerated plants.The precisely engineered point mutations were stably inherited to subsequent generations.These single nucleotide alterations resulted in single amino acid changes and associated wsl5 and z3 phenotypes as evidenced by white stripe leaf and light green/dark green leaf pattern,respectively.Through selfing and genetic segregation,transgene-free,base edited wsl5 and z3 mutants were obtained in a short period of time.We noticed a novel mutation(V540A)in Z3 locus could also mimic the phenotype of Z3 mutation(S542P).Furthermore,we observed unexpected non-A/G or T/C mutations in the ABE editing window in a few of the edited plants.The ABE vectors and the method from this study could be used to simultaneously generate point mutations in multiple target genes in a single transformation and serve as a useful base editing tool for crop improvement as well as basic studies in plant biology.

基因编辑技术在猪育种中的研究进展

以CRISPR/Cas9为代表的基因编辑技术为猪育种提供了前所未有的新工具和新方法,不仅能突破现有遗传变异资源的限制,还可以缩短育种周期,提高育种效率。该文对基因编辑技术的研究进展及其在猪遗传育种方面的应用情况进行综合介绍,以期为相关科研人员、育种工作者以及政策制定者提供参考,进一步推动基因编辑技术在猪育种方面的应用。

信息质量视角下算法分发与编辑分发的对比研究

【目的】了解用户当前对算法分发与编辑分发的信息质量感知及差异,为相关理论研究和实践活动提供借鉴。【方法】参考已有文献,设计包含算法分发的信息质量和编辑分发的信息质量两个潜在变量的测量量表。采用问卷调查法,获取273份有效样本,利用描述性统计和配对样本t-检验方法进行数据分析。【结果】相比于编辑分发,用户当前整体上更认可算法分发具备的信息质量。具体而言,用户认为在全面性、准确性、新颖性和符合需求等信息质量维度上,算法分发均优于编辑分发;算法分发在准确性维度的优势不显著,在其他3个维度的优势均显著。【结论】算法分发用户应注重提升算法素养,编辑分发亟须提升显示度和影响力。

益生菌遗传育种方法研究进展

益生菌的多样化益生作用使其在人类健康领域发挥着重要作用,基于益生菌生产的药品、食品和膳食补充剂也受到越来越多的关注。目前,研究人员致力于为药品和食品行业选育新型益生菌,以期为食品药品行业的发展提供新的思路。遗传育种为选育具有有益特性的益生菌菌株提供了一个很好的平台,这对提升益生菌的市场价值和人类健康具有重要意义。为了今后更好的开展益生菌育种工作,该文综述了原生质体融合、基因组重排、常压室温等离子体诱变及基因编辑技术[成簇规律间隔的短回文重复序列相关蛋白(clustered regularly interspaced short palindromic repeats-associated,CRISPR-Cas)技术和碱基编辑技术]等遗传育种技术的研究现状及在益生菌中的应用,并讨论了遗传育种的安全性,旨在为优良益生菌的选育提供参考,促进益生菌资源的开发和利用。

线粒体DNA编辑技术及其在生物医学中的应用

线粒体拥有一套独立的基因组,参与维持线粒体功能。对线粒体DNA(mitochondrial DNA,mtDNA)进行编辑,可以为其基因功能、相关疾病机理和治疗研究提供重要线索。但由于mtDNA所处环境和损伤修复机制的特殊性,可用于mtDNA编辑的工具较为有限。近年来,随着核酸酶技术和碱基编辑技术的快速发展,可靶向线粒体的核酸酶工具和碱基编辑器相继问世,为mtDNA编辑提供了有力工具。本文总结了近年来针对动物mtDNA而开发的一系列靶向基因编辑工具的主要进展及其在生物医学领域的应用,重点围绕mtDNA碱基编辑器DdCBE,并对mtDNA编辑目前存在的问题与应用前景做了初步展望,以期为线粒体基因编辑新工具的开发,及其在基础研究、疾病模拟和临床治疗等场景中更广泛的应用提供有益参考。

碱基编辑技术及其在微生物合成生物学中的应用

CRISPR/Cas系统的发现与发展对生命科学领域产生了革命性的影响,借助CRISPR/Cas系统研发出的一系列工具为相关领域的研究带来了极大的便利。碱基编辑器便是其中一类基于CRISPR/Cas系统开发的可实现碱基转换和颠换的基因编辑工具,其通过将胞苷或腺苷脱氨酶以及其他功能元件与失去双链切割活性的Cas蛋白相融合,由sgRNA引导,实现对基因组上目标位置胞嘧啶或腺嘌呤的碱基转换。碱基编辑器一经开发便在生物学、医学等领域展现出巨大的应用潜力,虽然经过不断优化,但目前在使用时仍然存在着许多制约因素。本文简述了几种主要碱基编辑器的发展,并介绍了碱基编辑器存在的靶向范围受限和脱靶编辑的问题以及现有的优化措施。同时列举了我国部分科研工作者将碱基编辑技术运用于微生物合成生物学领域的进展,并展望了碱基编辑技术的发展及其在微生物合成生物学领域的应用前景。

BE-dot:为单碱基编辑设计sgRNA及预测脱靶图谱的工具

目的 单碱基编辑器作为修复基因组点突变的有力工具,在生物技术开发和临床应用中具有极大潜力。对于目标改造的单核苷酸变异(SNV),首先要选择可用于编辑的单碱基编辑器(base editors,BEs)和单向导RNA (single guide RNA,sgRNA)。目前,尽管有较多工具实现了设计sgRNA,但缺少将设计sgRNA与评估单碱基编辑器特异性完整结合起来的工具。方法 纳入主流的27种胞嘧啶碱基编辑器(CBEs)和12种腺嘌呤碱基编辑器(ABEs)对SNV设计编辑方案,并通过调用第三方工具BE-Hive对编辑方案进行效率预测。综合使用多个脱靶预测工具对编辑方案的脱靶图谱进行评估。最后结合BEs类型和脱靶位点,分析得到所有可能的脱靶编辑产物,再调用ANNOVAR这一变异注释工具进行脱靶产物的功能分析。结果 本文提出了一个综合性工具BE-dot,它可以实现对目标编辑的SNV从设计sgRNA到预测脱靶图谱的完整过程,并对脱靶产物进行功能注释。利用密码子的简并性,BE-dot除了提供DNA水平上的精确校正方案,还可以在蛋白质水平进行同义校正。在对单碱基编辑系统做脱靶图谱的预测时,BE-dot综合了Cas-OFFinder、CALITAS、CFD、u CRISPR、BEdeepoff等多个工具,可以更全面地评估单碱基编辑系统的特异性,为用户选择BEs和sgRNA提供参考。此外,BE-dot可以自动分析得到脱靶位点处所有可能的编辑产物,并转换为avinput格式供ANNOVAR进行功能注释,避免了以往手工注释的繁琐。结论 BE-dot能为单碱基编辑技术应用于纠正或引入SNV设计编辑方案,并且能够从编辑效率、脱靶图谱、脱靶带来的功能影响等方面对编辑方案进行全面的评估。

BEguider:一个单碱基编辑器sgRNA设计与编辑效率预测工具

单碱基编辑器是实用且高效的基因编辑工具,其编辑效率与单向导RNA(single guide RNA,sgRNA)序列的设计密切相关。目前单碱基编辑器sgRNA序列的设计缺少特定的法则,主要依靠经验和大量尝试完成。本研究基于卷积神经网络,开发了一个单碱基编辑器sgRNA序列设计工具BEguider。BEguider利用TensorFlow 2深度学习框架建立编辑效率预测模型,能够在人基因组范围内针对NGG PAM序列依赖的单碱基编辑器ABE7.10-NGG和BE4-NGG批量设计sgRNA序列,预测编辑效率。此外,通过整合Cas-OFFinder,BEguider能够提供对sgRNA脱靶情况的评估。利用BEguider设计sgRNA序列,有助于研究人员提高实验效率,节约实验成本。

医学期刊编辑的学科专业素质及其培养

从作者自身工作体会出发,阐述作为医学期刊编辑应具备宽厚扎实的医学专业知识,以提高策划、审稿、编稿能力;掌握一定的循证医学知识,以提高论文结果的说服力;提高英语应用能力,以提高英文内容的编校水平。并提出培养提高学科专业素质的若干措施。

提升医学编辑素质,提高临床研究质量——循证医学与医学杂志编辑高级研修班小结

分析并总结循证医学与医学杂志编辑高级研修班的师资、授课内容与方式、学员来源分布及此次培训所取得的近期成效,为提高医学期刊编辑业务素质,促进临床研究质量提高探索一条新思路。

焊接专家系统知识库的管理

介绍了一种知识库的系统管理方法。它利用知识编辑器来对知识进行管理,利用机器学习对知识更新,使用校验规则来对用户输入的数据进行合理性检验,利用追踪解释法对得出的结论做出解释。这样整个操作过程变得非常简单,系统易于维护。