Sustained high level transgene expression in mammalian cells mediated by the optimized piggyBac transposon system

Sustained,high level transgene expression in mammalian cells is desired in many cases for studying gene functions.Traditionally,stable transgene expression has been accomplished by using retroviral or lentiviral vectors.However,such viral vector-mediated transgene expression is often at low levels and can be reduced over time due to low copy numbers and/or chromatin remodeling repression.The piggyBac transposon has emerged as a promising nonviral vector system for efficient gene transfer into mammalian cells.Despite its inherent advantages over lentiviral and retroviral systems,piggyBac system has not been widely used,at least in part due to their limited manipulation flexibilities.Here,we seek to optimize piggyBac-mediated transgene expression and generate a more efficient,user-friendly piggyBac system.By engineering a panel of versatile piggyBac vectors and constructing recombinant adenoviruses expressing piggyBac transposase(PBase),we demonstrate that adenovirusmediated PBase expression significantly enhances the integration efficiency and expression level of transgenes in mesenchymal stem cells and osteosarcoma cells,compared to that obtained from co-transfection of the CMV-PBase plasmid.We further determine the drug selection timeline to achieve optimal stable transgene expression.Moreover,we demonstrate that the transgene copy number of piggyBac-mediated integration is approximately 10 times higher than that mediated by retroviral vectors.Using the engineered tandem expression vector,we show that three transgenes can be simultaneously expressed in a single vector with high efficiency.Thus,these results strongly suggest that the optimized piggyBac system is a valuable tool for making stable cell lines with sustained,high transgene expression.

PiggyBac Transposon Mediated Efficient eGFP Expression in Porcine Somatic Cells and Cloned Embryos

PiggyBac transposon has demonstrated its long-term and stable transposition on genomes of various species but lacking of the evidence on farm animal genomes. In this study, we constructed a piggyBac transposon marked with enhanced green fluorescent protein （eGFP） and showed efficient transposition in porcine somatic cells and cloned embryos. Our results demonstrated that piggyBac transposase could efficiently catalyze transposition in porcine fetal fibroblast cells, as well as in embryos. PiggyBac transposition generated 18-fold more eGFP-positive cell colonies compared to pEGFP-C1 random insertion mutagenesis, but excessive transposase might affect the transfection rate. Also piggyBac mediated 4-fold more eGFP expression than random insertion in cells and 17-fold in cloned embryos at mRNA level. When the mutagenized cells were used for somatic cell nuclear transfer （SCNT）, the cleavage rate and blastocyst rate of constructed embryos harboring piggyBac transposition had no difference with random insertion group. This study provides key information on the piggyBac transposon system as a tool for creating transgenic pigs.

人IL-12基因载体的构建及其在T细胞中的表达研究

目的:探究T细胞携载人IL-12基因对T细胞生长和功能的影响。方法:构建表达人IL-12基因的PiggyBac转座子载体,在电转下,将携载IL-12基因的转座子系统导入新鲜分离的淋巴细胞获得持续稳定表达。通过T细胞表型分析及体外功能实验研究初步探讨T细胞携载IL-12基因的可行性。结果:借助电转可将携载有IL-12基因的PiggyBac转座子系统高效导入新鲜分离的淋巴细胞并获得高效稳定表达;IL-12的分泌可促进T细胞增殖,增加CD4阳性细胞百分比;携载IL-12基因的T细胞在肿瘤细胞刺激下可进一步促进IL-12分泌,增强T细胞的杀瘤活性。结论:在电场作用下,Piggybac转座子系统可将人IL-12基因高效载入并整合至T细胞基因组获得持续稳定表达,分泌的功能性IL-12可促进T细胞增殖,增强杀瘤活性。

Impaired suppressive activities of human MUTYH variant proteins against oxidative mutagenesis

AIM:To investigate the suppressive activity of MUTYH variant proteins against mutations caused by oxidative lesion,8-hydroxyguanine(8OHG),in human cells.METHODS:p.R154H,p.M255V,p.L360P,and p.P377L MUTYH variants,which were previously found in patients with colorectal polyposis and cancer,were selected for use in this study.Human H1299 cancer cell lines inducibly expressing wild-type(WT) MUTYH(type 2) or one of the 4 above-mentioned MUTYH variants were established using the piggyBac transposon vector system,enabling the genomic integration of the transposon sequence for MUTYH expression.MUTYH expression was examined after cumate induction using Western blotting analysis and immunofluorescence analysis.The intracellular localization of MUTYH variants tagged with FLAG was also immunofluorescently examined.Next,the mutation frequency in the supF of the shuttle plasmid pMY189 containing a single 8OHG residue at position 159 of the supF was compared between empty vector cells and cells expressing WT MUTYH or one of the 4 MUTYH variants using a supF forward mutation assay.RESULTS:The successful establishment of human cell lines inducibly expressing WT MUTYH or one of the 4 MUTYH variants was concluded based on the detection of MUTYH expression in these cell lines after treatment with cumate.All of the MUTYH variants and WT MUTYH were localized in the nucleus,and nuclear localization was also observed for FLAG-tagged MUTYH.The mutation frequency of supF was 2.2 × 10-2 in the 8OHG-containing pMY189 plasmid and 2.5 × 10-4 in WT pMY189 in empty vector cells,which was an 86-fold increase with the introduction of 8OHG.The mutation frequency(4.7 × 10-3) of supF in the 8OHG-containing pMY189 plasmid in cells overexpressing WT MUTYH was significantly lower than in the empty vector cells(P < 0.01).However,the mutation frequencies of the supF in the 8OHG-containing pMY189 plasmid in cells overexpressing the p.R154H,p.M255V,p.L360P,or p.P377L MUTYH variant were 1.84 × 10-2,1.55 × 10-2,1.91 × 10-2,and 1.96 × 10-2,respectively,meaning that no significant difference was observed in the mutation frequency between the empty vector cells and cells overexpressing MUTYH mutants.CONCLUSION:The suppressive activities of p.R154H,p.M255V,p.L360P,and p.P377L MUTYH variants against mutations caused by 8OHG are thought to be severely impaired in human cells.

Robust genome and RNA editing via CRISPR nucleases in PiggyBac systems

CRISPR/Cas-mediated genome editing in human pluripotent stem cells(hPSCs)offers unprecedented opportunities for developing in vitro disease modeling,drug screening and cell-based therapies.To efficiently deliver the CRISPR components,here we developed two all-in-one vectors containing Cas9/gRNA and inducible Cas13d/gRNA cassettes for robust genome editing and RNA interference respectively.These vectors utilized the PiggyBac transposon system,which allows stable expression of CRISPR components in hPSCs.The Cas9 vector PB-CRISPR exhibited high efficiency(up to 99%)of inducing gene knockout in both protein-coding genes and long non-coding RNAs.The other inducible Cas13d vector achieved extremely high efficiency in RNA knockdown(98%knockdown for CD90)with optimized gRNA designs.Taken together,our PiggyBac CRISPR vectors can serve as powerful toolkits for studying gene functions in hPSCs.

CD38基因敲除的淋巴瘤细胞株构建

目的:构建Luc^(+)CD38^(-)的Raji细胞株,并进行功能的初步验证,为后期探索淋巴瘤细胞CD38位点免疫逃逸现象奠定基础。方法:通过CRISPR-cas9技术和Piggy Bac(PB)转座子系统,对Luc^(+)Raji细胞的CD38基因位点进行敲除,构建Luc^(+)CD38^(-)Raji细胞株,使用流式细胞术检测与Luc^(+)CD38^(-)Raji细胞株以1:1的比例共孵育CD19 CAR-T和CD38 CAR-T以及未转导的原始T细胞表面活化因子CD69的表达水平,荧光素酶检测法检测上述几组效应细胞对Luc^(+)CD38^(-)Raji细胞株的杀伤效率。结果:成功构建Luc^(+)CD38^(-)Raji细胞,激活实验结果显示,CD19 CAR-T与CD38 CAR-T均可以被Luc^(+)Raji细胞激活。而Luc^(+)CD38^(-)Raji19号单克隆细胞由于缺失CD38的表达,仅能够激活CD19 CAR-T。杀伤实验结果显示,两种CAR-T细胞均能够对Luc^(+)Raji细胞进行杀伤,而CD38 CAR-T对Luc^(+)CD38^(-)Raji19号单克隆细胞的杀伤效率与原始的T细胞相似。结论:成功构建了Luc^(+)CD38^(-)Raji细胞株,为后期探索淋巴瘤CD38位点免疫逃逸现象奠定基础。

稳定表达猪IRF7基因的PK-15细胞系建立及其抗病毒效果评价

为探讨猪IRF7基因对某些猪源病毒在PK-15细胞系中增值的影响,利用Piggy Bac真核转座子系统将猪源IRF7基因转染入PK-15细胞中,通过嘌呤霉素和绿色荧光进行双重筛选获得阳性转化细胞,再经克隆纯化得到单个阳性细胞克隆株。通过观察细胞荧光和荧光定量PCR鉴定,最终获得了稳定表达IRF7基因的PK-15细胞系。在Poly I:C诱导下,该细胞系能够显著上调IFN-β的表达。初步研究了该细胞系对病毒复制的影响,结果表明过表达IRF-7基因能够显著抑制猪伪狂犬病病毒(PRV)和猪水泡性口炎病毒(VSV)的复制。本研究为进一步探索猪IRF7基因的功能与作用机制提供有效工具。

Genome Editing:From Drosophila to Non-Model Insects and Beyond

Insect is the largest group of animals on land.Many insect species inflict economical and health losses to humans.Yet many more benefit us by helping to maintain balances in our ecosystem.The benefits that insects offer remain largely untapped,justifying our continuing efforts to develop tools to better understand their biology and to better manage their activities.Here we focus on reviewing the progresses made in the development of genome engineering tools for model insects.Instead of detailed descriptions of the molecular mechanisms underlying each technical advance,we focus our discussion on the logistics for implementing similar tools in non-model insects.Since none of the tools were developed specific for insects,similar approaches can be applied to other non-model organisms.

Tissue-specific genome editing of laminA/C in the posterior silk glands of Bombyx mori

The RNA-guided CRISPR/Cas9 system has been shown to be a powerful tool for genome editing in various organisms. A comprehensive toolbox for multiplex genome editing has been developed for the silkworm,Bombyx mori, a lepidopteran model insect of economic importance. However, as previous methods mainly relied on delivery of transient Cas9/guide RNA（gRNA）, they could not be used in loss-of-function studies of essential genes. Here, we report a simple and versatile tissue-specific genome editing strategy.We perform a proof-of-principle demonstration by establishing and crossing two transgenic B. mori lines,one expressing Cas9 protein in the posterior silk glands（PSGs） and the other constitutively expressing BmlaminA/C（BmLMN） gRNA. All BmLMN alleles in the PSG cells were edited precisely at the target genome region, resulting in diverse mutations. mRNA expression of BmLMN was reduced by up to 75%,and only very low levels of BmLaminA/C protein were detected. Knockout of BmLMN produced obvious defects in gland cell development and cocoon production. In this study, we developed an efficient strategy for spatially controlled genome editing, providing unprecedented opportunities for investigating the function of essential/lethal genes in B. mori, with potential application for other insects.