Cas9蛋白变体VQR高效识别水稻NGAC前间区序列邻近基序

成簇的规律间隔短回文重复序列及CRISPR相关蛋白(clustered regularly interspaced short palindromic repeats/CRISPR-associated 9, CRISPR/Cas9)系统是近年来发展起来并被广泛应用的第三代基因组编辑工具。但是,该系统的酿脓链球菌Cas9(Streptococcus pyogenes, SpCas9)仅能识别NGG前间区序列邻近基序(protospacer adjacent motif, PAM),极大地限制了基因组编辑的范围。SpCas9变体VQR(D1135V/R1335Q/T1337R)在水稻中可识别NGAA、NGAG和NGAT PAM,但尚不清楚是否能识别NGAC PAM。本研究利用改进后的CRISPR/VQR系统对水稻中3个相对低效的VQR靶位点NAL1-Q1、NAL1-Q2和LPA1-Q进行了编辑,结果表明改进后的CRISPR/VQR系统可以高效编辑这3个靶位点,编辑效率分别为9.75%、43.90%和29.26%。为了明确改进后的CRISPR/VQR系统对NGAC PAM的识别情况,本研究选择水稻叶片宽度调控基因NARROW LEAF 1 (NAL1)中的NAL-C位点和蜡质合成基因GLOSSY1 (GL1)中的GL1-C位点进行基因编辑,并获得57株转基因水稻。靶位点PCR扩增及测序结果表明,NAL1-C和GL1-C靶标位点突变的植株分别为27株和44株,突变率分别为47.36%和77.19%;其中NAL1-C/GL1-C双突变植株为26株,双突变率为45.61%。进一步分析表明,CRISPR/VQR系统造成的突变有4种类型,分别为杂合突变、双等位突变、嵌合体突变和纯合突变,其中以杂合突变和双等位突变为主。这些结果表明,改进的CRISPR/VQR系统可以高效编辑水稻NGAC PAM位点,并产生丰富的突变类型。本研究为水稻及其他植物相关基因NGAC PAM位点的编辑提供了理论依据。     

Efficient genetic transformation and CRISPR/Cas9‐mediated genome editing in Lemna aequinoctialis

The fast growth, ease of metabolic labelling and potential for feedstock and biofuels production make duckweeds not only an attractive model system for understanding plant biology, but also a potential future crop. However, current duckweed research is constrained by the lack of efficient genetic manipulation tools. Here, we report a case study on genome editing in a duckweed species, Lemna aequinoctialis, using a fast and efficient transformation and CRISPR/Cas9 tool. By optimizing currently available transformation protocols, we reduced the duration time of Agrobacterium‐mediated transformation to 5–6 weeks with a success rate of over 94%. Based on the optimized transformation protocol, we generated 15 (14.3% success rate) biallelic LaPDS mutants that showed albino phenotype using a CRISPR/Cas9 system. Investigations on CRISPR/Cas9‐mediated mutation spectrum among mutated L. aequinoctialis showed that most of mutations were short insertions and deletions. This study presents the first example of CRISPR/Cas9‐mediated genome editing in duckweeds, which will open new research avenues in using duckweeds for both basic and applied research.     

Optimized paired‐sgRNA/Cas9 cloning and expression cassette triggers high‐efficiency multiplex genome editing in kiwifruit

Kiwifruit is an important fruit crop; however, technologies for its functional genomic and molecular improvement are limited. The clustered regulatory interspaced short palindromic repeats (CRISPR)/CRISPR‐associated protein (Cas) system has been successfully applied to genetic improvement in many crops, but its editing capability is variable depending on the different combinations of the synthetic guide RNA (sgRNA) and Cas9 protein expression devices. Optimizing conditions for its use within a particular species is therefore needed to achieve highly efficient genome editing. In this study, we developed a new cloning strategy for generating paired‐sgRNA/Cas9 vectors containing four sgRNAs targeting the kiwifruit phytoene desaturase gene (AcPDS). Comparing to the previous method of paired‐sgRNA cloning, our strategy only requires the synthesis of two gRNA‐containing primers which largely reduces the cost. We further compared efficiencies of paired‐sgRNA/Cas9 vectors containing different sgRNA expression devices, including both the polycistronic tRNA‐sgRNA cassette (PTG) and the traditional CRISPR expression cassette. We found the mutagenesis frequency of the PTG/Cas9 system was 10‐fold higher than that of the CRISPR/Cas9 system, coinciding with the relative expressions of sgRNAs in two different expression cassettes. In particular, we identified large chromosomal fragment deletions induced by the paired‐sgRNAs of the PTG/Cas9 system. Finally, as expected, we found both systems can successfully induce the albino phenotype of kiwifruit plantlets regenerated from the G418‐resistance callus lines. We conclude that the PTG/Cas9 system is a more powerful system than the traditional CRISPR/Cas9 system for kiwifruit genome editing, which provides valuable clues for optimizing CRISPR/Cas9 editing system in other plants.     

Selective gene dosage by CRISPR‐Cas9 genome editing in hexaploid Camelina sativa

In many plant species, gene dosage is an important cause of phenotype variation. Engineering gene dosage, particularly in polyploid genomes, would provide an efficient tool for plant breeding. The hexaploid oilseed crop Camelina sativa, which has three closely related expressed subgenomes, is an ideal species for investigation of the possibility of creating a large collection of combinatorial mutants. Selective, targeted mutagenesis of the three delta‐12‐desaturase (FAD2) genes was achieved by CRISPR‐Cas9 gene editing, leading to reduced levels of polyunsaturated fatty acids and increased accumulation of oleic acid in the oil. Analysis of mutations over four generations demonstrated the presence of a large variety of heritable mutations in the three isologous CsFAD2 genes. The different combinations of single, double and triple mutants in the T3 generation were isolated, and the complete loss‐of‐function mutants revealed the importance of delta‐12‐desaturation for Camelina development. Combinatorial association of different alleles for the three FAD2 loci provided a large diversity of Camelina lines with various lipid profiles, ranging from 10% to 62% oleic acid accumulation in the oil. The different allelic combinations allowed an unbiased analysis of gene dosage and function in this hexaploid species, but also provided a unique source of genetic variability for plant breeding.     

CRISPR/Cas9基因组编辑技术在农业动物中的应用

CRISPR(Clustered regularly interspaced short palindromic repeats)/Cas(CRISPR associated proteins)是在细菌和古细菌中发现的一种用来抵御病毒或质粒入侵的获得性免疫系统.目前已发现的CRISPR/Cas系统包括Ⅰ,Ⅱ和Ⅲ型,其中Ⅱ型系统的组成较简单,由其改造成的CRISPR/Cas9技术已成为一种高效的基因组编辑工具.自2013年CRISPR/Cas9技术成功用于哺乳动物基因组定点编辑以来,应用该技术进行基因组编辑的报道呈现出爆发式的增长.农业动物不仅是重要的经济动物,也是人类疾病和生物医药研究的重要模式动物.本文综述了CRISPR/Cas9技术在农业动物中的研究和应用进展,简述了该技术的脱靶效应及减少脱靶的主要方法,并展望了该技术的应用前景.     

CRISPR/Cas9在丝状真菌基因组编辑中的应用

丝状真菌(filamentous fungi)通常指那些菌丝体较发达且不产生大型肉质子实体结构的真核微生物。丝状真菌不仅在自然界物质循环中发挥着重要作用,还与人类健康和工农业生产有着紧密的联系。然而,对丝状真菌进行遗传操作相对困难,极大地妨碍了丝状真菌的遗传学研究。成簇的规律间隔的短回文重复序列及其相关系统(clustered regulatory interspaced short palindromic repeats/CRISPR-associated protein 9, CRISPR/Cas9)是近年来发现的一种存在于细菌和古菌中保守的获得性免疫防御机制。最近,CRISPR/Cas9被开发成为了一种方便灵活的基因组编辑技术。目前,该技术已经广泛应用在不同物种的基因组编辑中。本文概述了CRISPR/Cas9在丝状真菌基因组编辑中的应用进展,旨在为开展该领域的研究工作提供参考。     

CRISPR/Cas9-mediated genome editing assists protein dynamics studies in live cells

Spatial and temporal regulation of molecular reactions dictates cell fate. Thus, studying molecular dynamics is essential to understand how cells decide what to do and the fundamental perturbations causing disease. Classically, molecular dynamics has been studied by protocols based in the overexpression of fluorescent fusion proteins. However, overexpression is associated to altered stoichiometry, molecular dynamics and subcellular distribution. We here discuss the necessity to study molecular dynamics of fluorescent fusion proteins expressed under physiological mechanisms in the cell, pointing to CRISPR/Cas9-mediated genome editing as the ideal means to do so. Current genome editing protocols enable us to study molecular dynamics while avoiding drawbacks associated to overexpression.     

Genome editing with the CRISPR‐Cas system: an art,ethics and global regulatory perspective

Over the last three decades, the development of new genome editing techniques, such as ODM, TALENs, ZFNs and the CRISPR‐Cas system, has led to significant progress in the field of plant and animal breeding. The CRISPR‐Cas system is the most versatile genome editing tool discovered in the history of molecular biology because it can be used to alter diverse genomes (e.g. genomes from both plants and animals) including human genomes with unprecedented ease, accuracy and high efficiency. The recent development and scope of CRISPR‐Cas system have raised new regulatory challenges around the world due to moral, ethical, safety and technical concerns associated with its applications in pre‐clinical and clinical research, biomedicine and agriculture. Here, we review the art, applications and potential risks of CRISPR‐Cas system in genome editing. We also highlight the patent and ethical issues of this technology along with regulatory frameworks established by various nations to regulate CRISPR‐Cas‐modified organisms/products.     

CRISPR/Cas9基因组编辑技术在HIV-1感染治疗中的应用进展

基因治疗是将外源正常基因通过一定方式导入人体靶细胞以纠正或补偿因基因缺陷和异常引起的疾病,从而达到治疗目的。因此,基因治疗的技术方法在研究持续感染HIV-1或潜伏感染HIV-1原病毒患者的治疗中具有重大的现实意义。目前,现有的基因治疗方法存在识别靶向位点有限及脱靶几率大等主要问题。最新研究表明来源于细菌和古菌的规律间隔成簇短回文重复序列及其相关核酸酶9系统[Clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR-associated nuclease 9 (Cas9), CRISPR/Cas9]已被成功改造成基因组定点编辑工具。因此,如何利用CRISPR/Cas9系统实现对HIV-1病毒基因组进行高效靶向修饰,从而达到治疗HIV-1感染病患的目的已经成为当前研究的热点。本文参考最新国内外研究成果,重点介绍了 CRISPR/Cas9基因组编辑技术在HIV-1感染疾病治疗中的应用,主要包括CCR5基因编辑、清除HIV-1原病毒以及活化HIV-1原病毒,以期为HIV-1感染疾病的预防与治疗提供重要研究参考。     

Development of an Agrobacterium‐delivered CRISPR/Cas9 system for wheat genome editing

CRISPR/Cas9 has been widely used for genome editing in many organisms, including important crops like wheat. Despite the tractability in designing CRISPR/Cas9, efficacy in the application of this powerful genome editing tool also depends on DNA delivery methods. In wheat, the biolistics based transformation is the most used method for delivery of the CRISPR/Cas9 complex. Due to the high frequency of gene silencing associated with co‐transferred plasmid backbone and low edit rate in wheat, a large T₀ transgenic plant population are required for recovery of desired mutations, which poses a bottleneck for many genome editing projects. Here, we report an Agrobacterium‐delivered CRISPR/Cas9 system in wheat, which includes a wheat codon optimized Cas9 driven by a maize ubiquitin gene promoter and a guide RNA cassette driven by wheat U6 promoters in a single binary vector. Using this CRISPR/Cas9 system, we have developed 68 edit mutants for four grain‐regulatory genes, TaCKX2‐1, TaGLW7, TaGW2, and TaGW8, in T₀, T₁, and T₂ generation plants at an average edit rate of 10% without detecting off‐target mutations in the most Cas9‐active plants. Homozygous mutations can be recovered from a large population in a single generation. Different from most plant species, deletions over 10 bp are the dominant mutation types in wheat. Plants homozygous of 1160‐bp deletion in TaCKX2‐D1 significantly increased grain number per spikelet. In conclusion, our Agrobacterium‐delivered CRISPR/Cas9 system provides an alternative option for wheat genome editing, which requires a small number of transformation events because CRISPR/Cas9 remains active for novel mutations through generations.     

CRISPR/Cas9介导的基因组定点编辑技术在丝状真菌中的研究进展

CRISPR/Cas9技术是在特定的RNA引导下,利用特异的核酸酶实现对基因组进行编辑的新技术。自2013年该技术体系建立起来已成功应用于动物、植物及真菌中。本文简述了3种基于核酸酶的基因编辑技术及其应用,概述了CRISPR/Cas9系统的组成及其作用机理,总结了CRISPR/Cas9在模式真菌酿酒酵母及丝状真菌中的应用,并就在丝状真菌中应用该技术时sg RNA表达盒的设计、Cas9表达盒的优化、抗性标记的筛选、受体的选择等方面提出具体的研究方法。另外,针对该技术应用过程中出现的脱靶效应、Cas9核定位信号的添加、启动子的选择及多个靶基因的编辑等问题提出了建议与展望,希望能够为初次涉足该领域的科研人员提供理论参考和技术支持。     

Assessment of Cas12a‐mediated gene editing efficiency in plants

The CRISPR/Cas12a editing system opens new possibilities for plant genome engineering. To obtain a comparative assessment of RNA‐guided endonuclease (RGEN) types in plants, we adapted the CRISPR/Cas12a system to the GoldenBraid (GB) modular cloning platform and compared the efficiency of Acidaminococcus (As) and Lachnospiraceae (Lb) Cas12a variants with the previously described GB‐assembled Streptococcus pyogenes Cas9 (SpCas9) constructs in eight Nicotiana benthamiana loci using transient expression. All three nucleases showed drastic target‐dependent differences in efficiency, with LbCas12 producing higher mutagenesis rates in five of the eight loci assayed, as estimated with the T7E1 endonuclease assay. Attempts to engineer crRNA direct repeat (DR) had little effect improving on‐target efficiency for AsCas12a and resulted deleterious in the case of LbCas12a. To complete the assessment of Cas12a activity, we carried out genome editing experiments in three different model plants, namely N. benthamiana, Solanum lycopersicum and Arabidopsis thaliana. For the latter, we also resequenced Cas12a‐free segregating T2 lines to assess possible off‐target effects. Our results showed that the mutagenesis footprint of Cas12a is enriched in deletions of ?10 to ?2 nucleotides and included in some instances complex rearrangements in the surroundings of the target sites. We found no evidence of off‐target mutations neither in related sequences nor somewhere else in the genome. Collectively, this study shows that LbCas12a is a viable alternative to SpCas9 for plant genome engineering.     

The CRISPR/Cas9 system produces specific and homozygous targeted gene editing in rice in one generation

The CRISPR/Cas9 system has been demonstrated to efficiently induce targeted gene editing in a variety of organisms including plants. Recent work showed that CRISPR/Cas9‐induced gene mutations in Arabidopsis were mostly somatic mutations in the early generation, although some mutations could be stably inherited in later generations. However, it remains unclear whether this system will work similarly in crops such as rice. In this study, we tested in two rice subspecies 11 target genes for their amenability to CRISPR/Cas9‐induced editing and determined the patterns, specificity and heritability of the gene modifications. Analysis of the genotypes and frequency of edited genes in the first generation of transformed plants (T0) showed that the CRISPR/Cas9 system was highly efficient in rice, with target genes edited in nearly half of the transformed embryogenic cells before their first cell division. Homozygotes of edited target genes were readily found in T0 plants. The gene mutations were passed to the next generation (T1) following classic Mendelian law, without any detectable new mutation or reversion. Even with extensive searches including whole genome resequencing, we could not find any evidence of large‐scale off‐targeting in rice for any of the many targets tested in this study. By specifically sequencing the putative off‐target sites of a large number of T0 plants, low‐frequency mutations were found in only one off‐target site where the sequence had 1‐bp difference from the intended target. Overall, the data in this study point to the CRISPR/Cas9 system being a powerful tool in crop genome engineering.     

CRISPR/Cas9基因组编辑技术在癌症研究中的应用

CRISPR/cas9基因组编辑技术因其设计简单以及操作容易,使其在基因编辑的研究中越来越受到欢迎。利用该技术,科研人员可以实现在碱基的水平对基因组进行定点修饰。CRISPR系统现已经被广泛地应用到多个物种的基因组编辑以及癌症的相关研究中。本文在最新研究进展的基础上,结合对癌症研究及基因组编辑技术的理解,对CRISPR/Cas9技术在癌症研究中的应用进行了综述。     

Accelerating genome editing in CHO cells using CRISPR Cas9 and CRISPy,a web‐based target finding tool

Chinese hamster ovary (CHO) cells are widely used in the biopharmaceutical industry as a host for the production of complex pharmaceutical proteins. Thus genome engineering of CHO cells for improved product quality and yield is of great interest. Here, we demonstrate for the first time the efficacy of the CRISPR Cas9 technology in CHO cells by generating site‐specific gene disruptions in COSMC and FUT8, both of which encode proteins involved in glycosylation. The tested single guide RNAs (sgRNAs) created an indel frequency up to 47.3% in COSMC, while an indel frequency up to 99.7% in FUT8 was achieved by applying lectin selection. All eight sgRNAs examined in this study resulted in relatively high indel frequencies, demonstrating that the Cas9 system is a robust and efficient genome‐editing methodology in CHO cells. Deep sequencing revealed that 85% of the indels created by Cas9 resulted in frameshift mutations at the target sites, with a strong preference for single base indels. Finally, we have developed a user‐friendly bioinformatics tool, named “CRISPy” for rapid identification of sgRNA target sequences in the CHO‐K1 genome. The CRISPy tool identified 1,970,449 CRISPR targets divided into 27,553 genes and lists the number of off‐target sites in the genome. In conclusion, the proven functionality of Cas9 to edit CHO genomes combined with our CRISPy database have the potential to accelerate genome editing and synthetic biology efforts in CHO cells. Biotechnol. Bioeng. 2014; 111: 1604–1616. © 2014 The Authors. Biotechnology and Bioengineering Published by Wiley Periodicals, Inc.