A new design of a lentiviral shRNA vector with inducible co-expression of ARGONAUTE 2 for enhancing gene silencing efficiency

Background

RNA interference (RNAi) is a robust tool for inhibiting specific gene expression, but it is limited by the uncertain efficiency of siRNA or shRNA constructs. It has been shown that the overexpression of ARGONAUTE 2 (AGO2) protein increases silencing efficiency. However, the key elements required for AGO2-mediated enhancement of gene silencing in lentiviral vector has not been well studied.

Results

To explore the application of AGO2-based shRNA system in mammalian cells, we designed shRNA vectors targeting the EGFP reporter gene and evaluated the effects of various factors on silencing efficiency including stem length, loop sequence, antisense location as well as the ratio between AGO2 and shRNA. We found that 19 ~ 21-bp stem and 6- or 9-nt loop structure in the sense-loop-antisense (S-L-AS) orientation was an optimal design in the AGO2-shRNA system. Then, we constructed a single lentiviral vector co-expressing shRNA and AGO2 and demonstrated that the simultaneous expression of shRNA and AGO2 can achieve robust silencing of exogenous DsRed2 and endogenous ID1 and P65 genes. However, the titers of packaged lentivirus from constitutive expression of AGO2 vector were extremely low, severely limiting its broad application. For the first time, we demonstrated that the problem can be significantly improved by using the inducible expression of AGO2 lentiviral system.

Conclusions

We reported a novel lentiviral vector with an optimal design of shRNA and inducible AGO2 overexpression which provides a new tool for RNAi research.

     

下调人脐带间充质干细胞Mbd3基因shRNA慢病毒的构建及鉴定

研究构建靶向抑制人Mbd3表达的sh RNA慢病毒颗粒,感染人脐带间充质干细胞并用嘌呤霉素筛选获得Mbd3稳定下调的细胞系,为进一步探讨Mbd3在诱导型多潜能干细胞形成中的作用提供实验基础。研究根据Gene Bank中公布的Mbd3基因序列设计特异性si RNA干扰序列并合成可产生sh RNA的双链DNA,经双酶切后克隆至p LVsh RNA-EGFP(2A)Puro载体上构建慢病毒重组质粒,转化DH5α大肠杆菌PCR检测筛选阳性质粒,利用HEK293Ta包装产生含有Mbd3sh RNA的慢病毒颗粒。通过RT-PCR和Western blot检测慢病毒感染人脐带间充质干细胞(h UC-MSC)后Mbd3的转录和蛋白表达情况,进一步检测重组慢病毒对Mbd3的沉默效果并筛选出最佳抑制效果的sh RNA慢病毒载体。结果显示成功构建并筛选出下调Mbd3的最佳慢病毒干扰载体,慢病毒感染人脐带间充质干细胞48h后于荧光显微镜下可见绿色荧光,经嘌呤霉素筛选9 d后,RT-PCR检测Mbd3表达显著降低,Western blot检测Mbd3蛋白表达明显减少。说明构建的sh RNA重组慢病毒包装成功,具有较高的感染活性,可有效抑制人脐带间充质干细胞Mbd3的表达,为后续研究脐带间充质干细胞跨胚层分化打下前期研究基础。     

靶向WNT5A基因的shRNA逆转录病毒表达载体的构建与鉴定

目的:构建人WNT5A shRNA逆转录病毒表达载体.方法:根据人WNT5A基因mRNA序列设计并合成两条互补的DNA单链寡核苷酸,将退火后形成的双链连接于pSUPER Retro RNAi质粒,构建WNT5A shRNA逆转录病毒表达载体,经脂质体介导入GPG293细胞,包装成逆转录病毒.用该逆转录病毒感染人鼻咽癌细胞,Western blot法和RT-PCR检测细胞WNT5A的表达.结果:目的序列成功连接于载体并包装成逆转录病毒,免疫印迹检测和RT-PCR检测结果表明构建的WNT5A shRNA逆转录病毒表达载体能显著抑制鼻咽癌细胞WNT5A的表达.结论:成功构建人WNT5A shRNA逆转录病毒表达载体.     

Multiple shRNA expressions in a single plasmid vector improve RNAi against the XPA gene

To improve the efficiency of stable knockdown with short hairpin RNA (shRNA), we inserted multiple shRNA expression sequences into a single plasmid vector. In this study, the DNA repair factor XPA was selected as a target gene since it is not essential for cell viability and it is easy to check the functional knockdown of this gene. The efficiency of knockdown was compared among single and triple expression vectors. The single shRNA-expressing vector caused limited knockdown of the target protein in stable transfectants, however, the multiple expression vectors apparently increased the frequency of knockdown transfectants. There were correlations between the knockdown level and marker expression in multiple-expressing transfectants, whereas poorer correlations were observed in single vector transfectants. Multiple-transfectants exhibited reduced efficiency of repair of UV-induced DNA damage and an increased sensitivity to ultraviolet light-irradiation. We propose that multiple shRNA expression vectors might be a useful strategy for establishing knockdown cells.     

shRNA沉默卵巢癌细胞SKOV-3的IDO基因表达在体外对NK细胞杀伤作用敏感性的影响

目的通过shRNA沉默吲哚胺2,3-双加氧酶（indoleamine2,3-dioxygenase,IDO）基因表达,研究IDO表达在体外对NK细胞杀伤能力的作用。方法 shRNA沉默IDO基因表达质粒和空白质粒分别稳定转染至人卵巢癌细胞SKOV-3,应用Western blot检测IDO在SKOV-3、SKOV-3/Mock和SKOV-3/shIDO细胞中的表达情况,用MTT试剂盒检测3组肿瘤细胞体外生长速度和对NK细胞杀伤作用的敏感性。结果 IDO蛋白在SKOV-3/shIDO细胞中表达被抑制,在SKOV-3和SKOV-3/Mock细胞中有表达。3组肿瘤细胞体外生长曲线比较差异无统计学意义（P〉0.05）。SKOV-3/shIDO细胞存活的百分比明显低于其他2组对照（SKOV-3和SKOV-3/Mock）细胞,差异有统计学意义（P〈0.05）。结论本研究应用shRNA沉默IDO基因表达质粒稳定转染卵巢癌细胞SKOV-3,获得IDO无表达卵巢癌细胞SKOV-3/shIDO,结果显示抑制IDO表达对卵巢癌细胞体外生长速度无影响,但可增强卵巢癌细胞SKOV-3对NK细胞杀伤作用的敏感性。因此,IDO可以作为卵巢癌基因治疗的潜在新靶点,shRNA沉默IDO基因表达可以作为卵巢癌治疗的新方法。     

The piggyBac transposon is an integrating non-viral gene transfer vector that enhances the efficiency of GDEPT

Gene-directed enzyme prodrug therapy (GDEPT) is a strategy developed to selectively target cancer cells. However, the clinical benefit is limited due to its poor gene transfer efficiency. To overcome this obstacle, we took advantage of piggyBac (PB) transposon, a natural non-viral gene vector that can induce stable chromosomal integration and persistent gene expression in vertebrate cells, including human cells. To determine whether the vector can also mediate stable gene expression in ovarian cancer cells, we constructed a PB transposon system that simultaneously expresses the Herpes simplex virus thymidine kinase (HSV-tk) gene and the monomeric red fluorescent protein (mRFP1) reporter gene. The recombinant plasmid, pPB/TK, was transfected into ovarian adenocarcinoma cells SKOV3 with FuGENE HD reagent, and the efficiency was given by the percentage of mRFP1-positive cells detected by flow cytometry and confocal microscopy. The specific expression of HSV-tk in transfected cells was confirmed by RT-PCR and western blotting. The sensitivity of transfected cells to pro-drug ganciclovir (GCV) was determined by methylthiazoletetrazolium (MTT) assay. A total of 56.4 ± 8.4% cells transfected with pPB/TK were mRFP1 positive, compared to no measurable mRFP1 expression in pORF-HSVtk-transfected cells. The expression level of HSV-tk in pPB/TK-transfected cells was ∼10 times higher than in pORF-HSVtk-transfected cells. The results show that pPB/TK transfection increases the sensitivity of cells to GCV in a dose-dependent manner. Our data indicate that the PB transposon system could enhance the anti-tumor efficiency of GDEPT in ovarian cancer.     

Stable and heritable gene silencing in the malaria vector Anopheles stephensi

Heritable RNA interference (RNAi), triggered from stably expressed transgenes with an inverted repeat (IR) configuration, is an important tool for reverse genetic studies. Here we report on the development of stable RNAi in Anopheles stephensi mosquitoes, the major vector of human malaria in Asia. Trans genic mosquitoes stably expressing a RNAi transgene, designed to produce intron-spliced double-stranded RNA (dsRNA) targeting the green fluorescent protein EGFP gene, were crossed to an EGFP-expressing target line. EGFP expression was dramatically reduced at both the protein and RNA levels. The levels of gene silencing depended upon the RNAi gene copy number and its site of integration. These results demonstrate that specific RNAi-mediated knockdown of gene function can be achieved with high efficiency in Anopheles. This will be invaluable to systematically unravel the function of Anopheles genes determining the vectorial capacity of the malaria parasite.     

Production of transgenic calves expressing an shRNA targeting myostatin

Myostatin (MSTN) is a well-known negative regulator of muscle growth. Animals that possess mutations within this gene display an enhanced muscling phenotype, a desirable agricultural trait. Increased neonatal morbidity is common, however, resulting from complications arising from the birth of offspring with increased fetal muscle mass. The objective of the current research was to generate an attenuated MSTN-null phenotype in a large-animal model using RNA interference to enhance muscle development without the detrimental consequences of an inactivating mutation. To this end, we identified a series of short interfering RNAs that demonstrated effective suppression of MSTN mRNA and protein levels. To produce transgenic offspring capable of stable MSTN suppression in vivo, a recombinant lentiviral vector expressing a short hairpin RNA (shRNA) targeting MSTN for silencing was introduced into bovine fetal fibroblasts. These cells were used as nucleus donors for somatic cell nuclear transfer (SCNT). Twenty blastocysts were transferred into seven recipient cows resulting in five pregnancies. One transgenic calf developed to term, but died following delivery by Caesarean-section. As an alternative strategy, microinjection of recombinant lentiviral particles into the perivitelline space of in vitro-produced bovine zygotes was utilized to produce 40 transgenic blastocysts that were transferred into 14 recipient cows, resulting in 7 pregnancies. Five transgenic calves were produced, of which three expressed the transgene. This is the first report of transgenic livestock produced by direct injection of a recombinant lentivirus, and expressing transgenes encoding shRNAs targeting an endogenous gene (myostatin) for silencing.     

The effects of nanofiber topography on astrocyte behavior and gene silencing efficiency

Astrocyte-nanofiber interactions are studied by culturing primary rat cortical astrocytes on poly[caprolactone-co-(ethyl ethylene phosphate)] electrospun nanofibers and solvent-cast films (two-dimensional control). The results indicate that nanofiber topography significantly suppresses astrocyte proliferation and enhances apoptosis, without altering cellular activation as compared to films. Moreover, nanofiber topography enhances gene-silencing efficiency in astrocytes. The results suggest that nanofibers may serve as potential substrates for nerve regeneration by suppressing astrocyte growth and may further facilitate the use of gene-silencing to enhance CNS regeneration.     

重组马铃薯X病毒载体介导的烟草γ-微管蛋白基因沉默

用重组马铃薯X病毒(potato virus X,PVX)载体将γ-微管蛋白反义基因导入烟草(Nicotiana tabacum var.Samsun NN),得到了γ-微管蛋白基因沉默的烟草植株。它与侵染PVX空载体的正对照相比有明显的差异:不同形态的叶片分层交替生长;到生殖期所有的花苞都提前脱落;小孢子不能发育到四分体阶段。沉默的形态反应主要起始于顶端幼嫩组织。在沉默过程中除存在基因沉默及恢复现象外还出现靶基因水平的陡然升高,甚至有时会明显反超过正常对照水平。     

萤火虫荧光素酶基因cDNA真核表达载体在细菌中的高效表达

将荧火虫荧光素酶基因cDNA真核表达载体pGL2导入大肠杆菌HB101、鼠伤寒杆菌LB5000和X4064中,它在这些原核细胞中均有较好的表达效果。它在大肠杆菌HB101的表达量是该基因cDNA原核表达载体pUHF12-1的表达量的30倍。采用计算机PC／GENE程序包分析,pGL2的SV40早期启动子序列中含有SV40基因组HindⅢB片断中一段长为49bp的DNA序列,这一序列可能就是SV40基因组HindⅢB片断的原核增强子功能的决定序列,正是该序列使pGL2在细菌中获得了高效表达。     

Inclusion of a matrix-attached region in a 7SK pol III vector increases the efficiency of shRNA-mediated gene silencing in embryonic carcinoma cells

RNA interference is a widely used tool for analysis of gene function in mammalian cells. Stable knockdown of specific target genes can be maintained in cell lines and live organisms using vector-based delivery of short hairpins (shRNAs) driven by RNA polymerase III promoters. Here we describe a vector incorporating the human 7SK promoter for shRNA-mediated gene silencing in the P19 embryonic carcinoma stem cell line. Our preliminary experiments with the 7SK shRNA expression vector indicated that its activity could be hindered by random genomic integration. In order to counter this inhibitory mechanism, we inserted a matrix-attached region sequence to generate an episomal vector system. We compared the effects of insertion versus exclusion of the MAR sequence on the shRNA-mediated gene-specific silencing of the beta-tubulin III and Cyclophilin A genes. While the MAR sequence is not strongly correlated with the episomal status of the expression vector, our studies indicate that inclusion of the MAR element significantly enhances the stability of shRNA-mediated gene silencing in the P19 stem cells.     

Development of a virus induced gene silencing vector from a legumes infecting tobamovirus

Medicago truncatula, the model plant of legumes, is well characterized, but there is only a little knowledge about it as a viral host. Viral vectors can be used for expressing foreign genes or for virus-induced gene silencing (VIGS), what is a fast and powerful tool to determine gene functions in plants. Viral vectors effective on Nicotiana benthamiana have been constructed from a number of viruses, however, only few of them were effective in other plants. A Tobamovirus, Sunnhemp mosaic virus (SHMV) systemically infects Medicago truncatula without causing severe symptoms. To set up a viral vector for Medicago truncatula, we prepared an infectious cDNA clone of SHMV. We constructed two VIGS vectors differing in the promoter element to drive foreign gene expression. The vectors were effective both in the expression and in the silencing of a transgene Green Fluorescent Protein (GFP) and in silencing of an endogenous gene Phytoene desaturase (PDS) on N. benthamiana. Still only one of the vectors was able to successfully silence the endogenous Chlorata 42 gene in M. truncatula.