Expression of EGFP driven by BmNPV orf4 promoter, a novel immediate early promoter

Bombyx mori nucleopolyhedrovirus (BmNPV) orf4 has been shown to be expressed at very early stage of Bm-NPV infection cycle. In this study, using transient expression experiment, we demonstrated for the first time that orf4 promoter is an immediate early promoter, indicating that orf4 may play a role in the immediate-early stage of BmNPV infection. Moreover, with the recently developed Bac-to-Bac/BmNPV baculovirus expression system and a modified pFast-Bac1 whose polyhedrin promoter was replaced with orf4 promoter, a recombinant bacmid baculovirus expressing enhanced green fluorescent protein (EGFP) under the control of orf4 promoter in Bombyx mori (Bm) cells was successfully constructed. The result not only showed that the polyhedrin promoter can be replaced easily with other promoters to direct the expression of foreign genes by using this novel system but also laid the foundation for the rescue experiment of orf4 deletion mutant.     

Isolation of p10 gene fromBombyx mori nuclear polyhedrosis virus and study of its promoter activity in recombinant baculovirus vector system

A homologue ofAutographa californica NPV (AcNPV) p10 gene was identified and cloned fromBombyx mori NPV (BmNPV). BmNPV p10 gene encodes truncated protein of 70 amino acid residues that lacks carboxyl terminus comparing with the p10 protein encoded by AcNPV. The putative TATA box sequence and the ATAAG motif which is the consensus sequence of baculovirus very late promoter were conserved. A transfer vector, pBNT1, which includes the p10 promoter region of BmNPV for foreign gene expression was constructed. By using pBNT1, a recombinant BmNPV, Bmp10-Luc, in which the p10 gene was replaced by the firefly luciferase gene, was obtained. We also obtained another recombinant virus, BmPH-Luc, in which the polyhedrin gene was replaced by the luciferase gene. The luciferase activity detected in BoMo-15AIIc insect cells infected with Bmp10-Luc was approximately 50% of that infected with BmPH-Luc, suggesting that although both the p10 and polyhedrin promoters of BrnNPV are effective in high-level expression of foreign gene, the p10 promoter is not so strong as the polyhedrin promoter.     

Construction of the Bac-to-Bac system of <Emphasis Type="Italic">Bombyx mori</Emphasis> nucleopolyhedroviru

To construct the Bac-to-Bac expression system of Bombyx mori nucleopolyhedrovirus (BmNPV), a transfer vector was constructed which contained an Escherichia coli (E. coli) mini-F replicon and a lacZ: attTN7: lacZ cassette within the upstream and downstream regions of the BmNPV polyhedrin gene. B. mori larvae were cotransfected with wild-type BmNPV genomic DNA and the transfer vector through subcutaneous injection to generate recombinant viruses by homologous recombination in vivo. The genomic DNA of budded viruses extracted from the hemolymph of the transfected larvae was used to transform E. coli DH10B. Recombinant bacmids were screened by kanamycin resistance, PCR and restriction enzyme (REN) digestion. One of the bacmid colonies, BmBacJS13, which had similar REN profiles to that of wild-type BmNPV, was selected for further research. To investigate the infectivity of BmBacJS13, the polyhedrin gene was introduced into the bacmid and the resultant recombinant (BmBacJS13-ph) was transfected to BmN cells. The budded viruses were collected from the supernatant of the transfected cells and used for infecting BmN cells. Growth curve analysis indicated that BmBacJS13-ph had a similar growth curve to that of wild-type BmNPV. Bio-assays indicated that BmBacJS13-ph was also infectious to B. mori larvae. Foundation items: 973 (2003CB114202); Programme Strategic Scientific Alliances between China and the Netherlands (2004CB720404); National Natural Fundation of China project (30630002)     

杆状病毒凋亡抑制基因IAP1促进家蚕CyclinB的核内积累

[目的]家蚕核型多角体病毒(Bombyx mori nucleopolyhedrovirus,BmNPV)是生产上危害最严重的病原之一。BmNPV感染BmN-SWU1细胞将细胞周期阻滞于G2/M期。CyclinB是调控细胞周期G2期向M期转换的重要细胞周期蛋白。因此,研究BmNPV感染后CyclinB变化对解析病毒调控细胞周期的机制具有重要意义,同时探究这个过程中与CyclinB互作的病毒蛋白,可为构建家蚕转基因品系提供分子靶标。[方法]qRT-PCR检测BmNPV感染后BmCyclinB的表达变化;免疫荧光观察病毒感染前后BmCyclinB的定位变化,通过细胞质细胞核蛋白分离实验验证。免疫共沉淀钓取与BmCyclinB互作的病毒蛋白。BmNPV感染期间敲除BmNPV IAP1观察BmCyclinB的入核比例。[结果]BmNPV感染后BmCyclinB转录水平下调。BmNPV感染前BmCyclinB主要定位于细胞质,而感染后主要定位于细胞核。BmNPV感染BmN-SWU1细胞后促进BmCyclinB在核内积累。共钓取了7个与BmCyclinB互作的病毒蛋白,免疫共沉淀和细胞共定位证明BmNPV IAP1与BmCyclinB之间存在相互作用。敲除BmNPV IAP1后BmCyclinB进入细胞核的数量显著减少。[结论]BmNPV IAP1可通过与BmCyclinB互作,促进BmCyclinB在核内积累。     

家蚕ADP/ATP转运酶(BmANT)抑制BmNPV增殖作用机制研究

【目的】家蚕核型多角体病毒(Bombyx mori nucleopolyhedrovirus,BmNPV)隶属于杆状病毒,需要借助宿主细胞能量代谢进行自身增殖复制。家蚕ADP/ATP转运酶(Bombyx mori ADP/ATP translocase,BmANT)是线粒体转运蛋白,在BmNPV感染条件下和家蚕热休克蛋白60(heatshockprotein60,BmHSP60)具有直接的相互作用。因此,鉴定Bmant基因在BmNPV感染过程中的功能特征,有助于解析杆状病毒劫持宿主细胞因子促进自身增殖复制机制,完善杆状病毒和宿主相互作用网络。【方法】通过结构域预测BmANT蛋白的结构特征,荧光定量PCR分析Bmant基因在BmNPV感染后的变化特征;并过表达BmANT检测其对病毒DNA复制和病毒蛋白表达变化影响;进一步在转录水平分析Bmant和Bmhsp60基因的调控关系;最后通过流式细胞术等技术鉴定Bmant和Bmhsp60基因共同调控BmNPV增殖复制的机制。【结果】SMART软件预测显示BmANT包含3个线粒体载体结构域,BmNPV感染24 h后Bmant基因持续下调表达。过表达Bmant基因能够显著抑制BmNPV DNA的复制和VP39蛋白表达。荧光定量PCR分析显示Bmant和Bmhsp60基因具有相互拮抗作用,能够相互抑制转录。Bmant和Bmhsp60共同过表达分析显示,BmANT和BmHSP60共同作用BmNPV能够抑制病毒的增殖复制。【结论】结果表明,BmANT是一个线粒体载体蛋白,具有显著的抗病毒作用,能够下调Bmhsp60基因表达,并抑制BmNPV增殖复制。     

The effects of BmNPV on biochemical changes in primary cultures of Bombyx mori embryonic tissue

The effect of Bombyx mori nuclear polyhedrosis virus (BmNPV) on biochemical changes of TC-100 medium containing 10% fetal bovine serum (FBS) in embryonic primary cultures of silkworm was investigated. The primary cultures that reached 60% confluence were infected by 0.5, 1, and 2-ml viral inoculums (diluted with TC-100 medium representing multiplicity of infection (MOI) of 0.25, 0.5, and 1). Glucose, uric acid, urea, total protein, cholesterol, and alkaline phosphatase were measured in the medium of BmNPV-infected primary cultures. All biochemical compounds showed significant changes. Glucose decreased considerably by about 55 mg/ml, while different concentrations of the virus inoculums did not demonstrate significant differences among them. Total protein had only increased in 2 ml concentration and there were no changes in other concentrations. Uric acid as a by-product accumulated dramatically in all concentrations, while the amount of urea reduced in all treatments and this reduction was more evident in lower concentrations. Cholesterol consumption was high in cultures postinfection, while alkaline phosphatase (ALP) activity decreased in infected cells.     

Efficient Protein Expression in <Emphasis Type="Italic">Bombyx mori</Emphasis> Larvae of the Strain d17 Highly Sensitive to <Emphasis Type="Italic">B. mori</Emphasis> Nucleopolyhedrovirus

The recombinant protein expression by Bombyx mori nucleopolyhedrovirus (BmNPV) infecting silkworm larvae or pupae may endow us with a potent system for the production of large eukaryotic proteins. However, the screening of silkworm strains ideally suited to this method has scarcely been conducted. In the present study, we injected recombinant BmNPV containing a reporter gene, luciferase or DsRed, into hemocoel of fifth instar larvae of selected 12 silkworm strains. Among them, the strain d17 is found to be the highest in reporter expression from the intrinsic polyhedrin promoter of Autographa californica NPV or the silkworm actin A3 promoter. These results suggest that the d17 strain is highly permissive for BmNPV replication and is the most likely candidate of a “factory” for large-scale expression using the BmNPV bacmid system.     

家蚕核型多角体病毒lef-11基因RNA干扰策略的优化

【目的】家蚕核型多角体病毒(Bombyx mori nucleopolyhedrovirus,BmNPV)lef-11基因作为杆状病毒高度保守的晚期表达因子之一,对病毒晚期基因的表达极其重要。因此对lef-11基因进行有效RNA干扰将提高宿主细胞对BmNPV的抗性。【方法】本文基于经典的sh-RNA-loop骨架及家蚕内源性的miRNA骨架,构建以BmNPV lef-11基因为靶标的干扰载体pIZ-shRNA1、pIZ-shRNA2和pIZ-Ds RedamiR279;分别构建基于A4、IE1、IE1-295、IE2、IE2-339、hr3A4和hsp70启动子驱动的干扰载体,用以评价不同启动子驱动的干扰载体的抗病毒效果,并对干扰载体进行优化。【结果】首先,本文通过比较miRNA-based和shRNA-based RNAi载体对同一靶基因同一位点的干扰效率,发现pIZ-Ds Red-amiR279对BmNPV lef11基因的干扰效率超过90%,远优于shRNA-based RNAi载体的干扰效果;其次,通过对干扰载体进行优化,发现IE1启动子的效果最优,由其驱动的pIZ-Ds Red-milef11干扰载体也是本研究中的最优干扰载体,对病毒的增殖抑制效果最为明显。【结论】对目的基因的干扰效果并非启动子的活性越高、miRNA积累得越多就越好,只有综合考虑干扰片段的选择、启动子的活性以及靶基因自身的功能等多方面的因素,才能提高干扰效率,达到干扰目的。     

家蚕CVDAR品系对BmNPV的抗性特征分析

【目的】家蚕核型多角体病毒(Bombyx mori nucleopolyhedrovirus,BmNPV)促使的血液型脓病是一种产业上非常严重的家蚕疾病,目前有效的防控方法较少。本研究以大造和CVDAR家蚕品系(对BmNPV有较强抗性的品系)为试验材料,通过分析CVDAR对BmNPV抗性特征,以期确定CVDAR对BmNPV的抗性机制。【方法】本研究通过半致死剂量分析,发现CVDAR品系比大造品系对BmNPV感染的半致死剂量提高10倍以上;进一步HE染色分析大造与CVDAR品系病毒感染前后的中肠组织的变化,具体解析抗性品系CVDAR的抗BmNPV机制。【结果】感染BmNPV 72 h后,大造中肠细胞细胞核明显膨大,着色变浅,到96h后,细胞核持续增大有脱落趋势;而CVDAR抗性品系只在感染96 h后有中肠部分细胞核膨大,但排列整齐;同时通过荧光定量分析大造与CVDAR品系病毒感染后的增殖情况,结合各个时期代表病毒基因的转录水平分析比较发现,感染BmNPV后0–12h也没有发现抗性品系CVDAR和大造之间的病毒拷贝数以及病毒基因转录水平的不同,但感染24h后发现抗性品系CVDAR无论是病毒拷贝数还是病毒基因的转录表达水平都明显低于对照大造。【结论】证明CVDAR口服添毒后中肠中病毒基因的转录在第一轮复制期间不受影响,之后转录水平降低。鉴定CVDAR品系抑制BmNPV增殖的关键时期是在感染BmNPV后的24 h,为解析抗性机制奠定基础。     

pH对红褐斑腿蝗中肠主要蛋白酶活性的影响

为评价pH对红褐斑腿蝗Catantops pinguis (Stål)中肠蛋白酶活性的影响, 本文用3种专性底物测定了不同pH环境下蝗虫中肠类胰蛋白酶和类胰凝乳蛋白酶的活性。结果表明: 雄性红褐斑腿蝗中肠肠液的pH值为6.92±0.043, 雌性为7.03±0.054, 两性间差异不显著（P>0.05）。并且发现3种蛋白酶的最适pH值各不相同, 其中雌雄虫的强碱性类胰蛋白酶（以BAPNA为底物）最适pH分别为8.5和10.5; 雌雄虫的弱碱性类胰蛋白酶（以TAME为底物）最适pH分别为9.0和9.5; 而雌雄虫的类胰凝乳蛋白酶（以BTEE为底物）最适pH雌性为8.5, 雄性为8.0。统计结果显示, pH对红褐斑腿蝗中肠蛋白酶活性影响显著（P<0.01）, 两性间蛋白酶活性差异显著（P<0.01）。在最适pH情况下, 雌性的类胰蛋白酶活性高于雄性, 而类胰凝乳蛋白酶活性则是雄性高于雌性。在中肠pH范围内雌性比雄性具有更高的消化蛋白酶活性, 显示雌性具有较强的食物处理能力以摄取更多的营养物质为繁殖活动（孕卵）作准备, 而该种蝗虫最适pH范围较宽, 可能与其取食植物范围较宽有关。     

家蚕hsp20.4启动子克隆及其驱动表达产物EGT对家蚕蛹体发育的影响

为验证家蚕Bombyx mori热休克蛋白基因hsp20.4启动子的活性以及家蚕核多角体病毒egt的表达产物对家蚕发育的影响, 本实验通过PCR扩增分别得到hsp20.4启动子片段和egt片段。利用hsp20.4的启动子和红色荧光蛋白报告基因DsRed构建重组载体, 在家蚕BmN细胞以及家蚕组织中得到了瞬时表达, 表明所克隆的hsp20.4启动子序列具有热休克蛋白基因的启动子活性。又利用hsp20.4启动子和家蚕核多角体病毒的egt构建重组载体, 通过注射到蚕蛹中进行瞬时表达, 以检测egt表达产物对家蚕发育的影响, 经42℃ 1 h热诱导后, hsp20.4启动子控制的egt表达产物可以延迟家蚕发育。     

Establishment of a Bombyx mori nucleopolyhedrovirus (BmNPV) hyper-sensitive cell line from the silkworm e21 strain

Baculoviral expression systems, including those of Autographa californica multiple nucleopolyhedrovirus Bombyx mori nucleopolyhedrovirus (BmNPV), are used for recombinant protein production. Four B. mori-derived (BmN4, Bm5, Bmc140, and Bme21) cell lines were infected with recombinant BmNPV viruses expressing firefly luciferase or EGFP as reporters under the control of a viral polyhedrin promoter. Bme21 exhibited significantly higher (100-fold) luciferase activity than BmN4 and Bm5. With the EGFP reporter protein, Bme21 cells showed a marked increase in the ratio of EGFP-positive cells, reaching 90?% on day 4 post-infection, while Bm5 and BmN4 cells had a slow increase in the ratio of their EGFP-positive population. The viral titer in a supernatant of Bme21 cell culture increased faster than those of Bm5 and BmN4 cells. This susceptibility indicates that the Bme21 cell line is useful for large-scale protein expression using BmNPV.     

斜纹夜蛾核多角体病毒gp37及其邻近序列的克隆及分析

从斜纹夜蛾核多角体病毒(Spodoptera litura nucleopolyhedrovirus, SpltMNPV)基因组中克隆了gp37基因.分子生物学软件分析表明,在gp37基因内部存在糖基化位点.含有晚期表达基因的启动子序列(ATAAG),推测为晚期表达的病毒膜糖蛋白基因.通过GP37蛋白的同源性比较,绘制了以gp37基因为基础的杆状病毒进化树, 发现与以多角体蛋白基因（polyhedrin）为基础所绘制的杆状病毒分子进化树有较大差异.以polyhedrin基因为基础绘制的杆状病毒分子进化树将家蚕核多角体病毒（Bombyx mori nucleopolyhedrovirus, BmNPV）与杆状病毒代表种——苜蓿丫纹夜蛾核多角体病毒（Autographa californica multinucleocapsid nucleopolyhedrovirus, AcMNPV）分开,根据gp37基因分析则将二者归到同一分枝,这与以egt基因为基础绘制的杆状病毒分子进化树结果一致.     

Production of a Cellulase in Silkworm Larvae using a Recombinant Bombyx mori nucleopolyhedrovirus lacking the Virus-encoded Chitinase and Cathepsin Genes

The expression efficiency of an insect-derived cellulase was assayed in silkworm larvae infected with recombinant Bombyx mori nucleopolyhedrovirus (BmNPV) mutants lacking the virus-encoded chitinase (chiA) and/or cathepsin (v-cath) genes. Expression was increased by approx. 10% in mutants lacking chiA or v-cath and 17% in a mutant lacking both chiA and v-cath compared with that of the unmodified recombinant BmNPV. The recombinant BmNPV lacking both chiA and v-cath can therefore be used for a large-scale production of foreign proteins in silkworms. Revisions requested 27 September 2005 and 16 December 2005; Revisions received 6 December 2005 and 3 February 2006