抑制性消减杂交技术在细菌活的非可培养状态研究中的应用

在基因分离与克隆中,构建各种cDNA文库是近些年发现新基因及研究基因功能常用的基础工具之一。其中,抑制性消减杂交技术(SSH)是一种高效分离差异表达基因的方法,在分离筛选细菌活的非可培养状态(VBNC)与正常菌株差异基因中,应用这种研究方法是研究细菌VBNC状态菌株毒力、致病性和耐药性及菌株遗传分化关系的重要途径。文章旨在介绍SSH构建消减cDNA文库在原核生物中的应用及对其在细菌VBNC状态新基因筛选中的应用前景,并提出了展望。     

猪蛔虫感染期幼虫抑制消减cDNA文库的构建

为筛选与线虫感染性相关的基因,本研究以猪蛔虫为对象,构建猪蛔虫感染期幼虫差异表达消减cDNA文库,为研究线虫期特异性发育的分子机制奠定基础。分别提取感染期幼虫和其它各期幼虫及成虫的总RNA,纯化mRNA后,采用Clontech公司PCR-selectTM试剂盒进行反转录合成cDNA并进行抑制消减杂交(SSH),构建猪蛔虫感染期幼虫差异表达的消减cDNA文库,并采用Southern斑点杂交进行消减效率的检测。随机从文库中抽取45个克隆进行测序及在线BLAST分析。试验结果表明,感染期幼虫差异表达的消减cDNA文库具有较强的特异性;在得到的41个表达序列标签(ESTs)中,有40个ESTs与已报道的基因有较高的相似性,主要代表猪蛔虫第三期幼虫基因和成虫头部基因,有1个cDNA片段可能代表新基因。猪蛔虫感染期幼虫差异表达消减cDNA文库的成功构建,为进一步研究幼虫发育差异表达基因的功能奠定了基础。     

cDNA-RDA方法筛选与分析VBNC状态沙门菌差异基因的研究

为了研究VBNC状态沙门菌特异性基因,探讨细菌VBNC状态发生机制,试验应用cDNA代表性差异分析技术(cDNA-RDA)对VBNC状态沙门菌特异性基因进行筛选及分析。结果表明:经过3轮差减杂交后,获得8条差异基因片段;分析差异基因功能,推测其中5条差异基因可能与沙门菌VBNC状态发生机制以及合成蛋白相关。     

牦牛外周血单个核细胞抑制消减cDNA文库的构建及部分差异表达分子的克隆分析

为筛选牦牛外周血单核细胞(PBMC)差异性基因,以刀豆素A(ConA)和脂多糖(LPS)联合刺激的PBMC cDNA为实验组,未经诱导刺激的PBMC cDNA为驱动组,利用抑制性消减杂交技术(SSH)构建了丝裂原诱导刺激PBMC的消减文库并对其部分阳性克隆进行了EST序列分析.从消减文库中随机挑取16个阳性克隆,进行PCR鉴定,显示克隆的重组率大于93%,插入片段大小大部分集中在200 bp～1 000 bp之间.随机挑取100个克隆进行测序及同源性分析,初步获得27条差异表达基因片段,其中24个为已知基因,3个为新ESTs序列;随机选择非重复的6个差异表达的序列设计引物,以半定量PCR方法验证其消减效率.结果显示,均从构建的消减文库中扩增到目的片段,其中5个为诱导性差异表达分子,1个为诱导特异性表达分子,说明该文库有较高的质量.本研究应用抑制消减杂交技术构建了牦牛PBMC的差异表达cDNA文库,并高通量克隆鉴定了相关功能基因片段,表明该技术手段有助于快速发现牦牛新功能基因.     

鸡白痢沙门氏菌活的非可培养状态相关基因ybbB和rh1B的鉴定

为鉴定细菌活的非可培养状态(VBNC)下的转录基因,本研究采用液体LB培养基在4℃条件下诱导鸡白痢沙门氏菌(S.pullorum) CVCC578株进入VBNC状态,并利用mRNA差异显示RT-PCR技术(DDRT-PCR)分析S.pullorum VBNC状态与正常状态所表达的差异基因.结果表明,在S.pullorum的VBNC状态下克隆得到两个转录基因片段,分别为422 bp和573 bp.序列分析表明:422bp的cDNA片段与不同沙门氏菌株的tRNA硒尿核苷合成酶(tRNA 2-selenouridine synthase)的ybbB基因的核苷酸和氨基酸同源性均为99％;573bp的cDNA片段则与不同菌株S.pullorum的ATP依赖性的RNA解旋酶基因(rh1B)的核苷酸同源性为95％～100％,氨基酸同源性为98％以上.在VBNC状态下这两个转录基因的发现,将为S.pullorum的VBNC机理研究奠定基础.     

猪杂种一代与亲本肌肉组织间正反向消减cDNA文库的构建

应用抑制消减杂交技术成功构建了杂种一代梅大猪、亲代大白猪的背最长肌正反向消减cDNA文库。以β-actin为指标检测2个文库的消减效率分别为2^15和2^10倍。从相应的质粒文库中分别获取了700个和623个有效阳性克隆，PCR检测插入片段主要分布在150～600bp之间。亲本与子代肌肉组织间消减cDNA文库的构建为进一步分离、鉴定与杂种优势相关的基因奠定了基础。     

大梅与大白猪背最长肌正反消减文库的构建

杂种与亲本间的基因差异表达与杂种优势有关.为从基因差异表达的角度来研究杂种优势的机理,构建了大梅与大白猪背最长肌正反消减文库,以G3PDH为指标检测的2个文库的消减效率均达到了25倍;并从相应文库中分别挑选了550,535个有效阳性克隆,PCR检测插入片段主要分布在200～1 000 bp之间.亲本与子代肌肉组织间消减cDNA文库的构建为进一步分离、鉴定与杂种优势相关的基因,研究杂种优势的分子机理奠定了基础.     

抑制性消减杂交技术在对虾基因克隆中的应用

抑制性消减杂交技术是一项筛选、分离未知差异表达基因的试验方法,该技术具有快速、简便、灵敏、特异、高效,所需起始样本量较少等优点。利用该技术构建对虾组织消减cDNA文库,鉴定差异表达相关基因及其表达特性。通过对对虾差异性表达的免疫相关基因、抗病基因及其他性状基因的了解,旨在为进一步研究对虾抗病机理奠定基础,为利用抗病基因进行抗病育种提供一个有效途径,为提高对虾的经济效益提供前景。     

鸡大肠杆菌活的非可培养状态发生相关基因克隆与分析

本研究旨在从分子水平探究细菌活的非可培养状态(VBNC)的发生机制。应用冰乙酸和4℃联合诱导条件,使鸡大肠杆菌进入VBNC状态,并利用mRNA差异显示技术(DDRT-PCR)获得VBNC相关基因。结果表明,从VBNC大肠杆菌中筛选得到的3个差异片段与大肠杆菌23S核糖体RNA基因序列具有较高的核苷酸同源性,分别为98%、98%和99%,而氨基酸的同源性也均在97%以上,表明这3个序列是大肠杆菌23S核糖体rRNA基因的部分序列,同时也是与大肠杆菌VBNC状态发生密切相关的基因。由此推知,当正常大肠杆菌在未暴露任何压力下时,其转录水平较低,特别是23S rRNA的某一(些)基因不显示或受到强烈抑制。当进入VBNC状态后,面临生存压力时,这一(些)基因转录水平明显强于正常状态,而核糖体作为蛋白质合成的主要结构与场所,其某些基因也将积极参与新蛋白质的生物合成。     

SSH法构建奶牛乳房炎抗性相关基因的cDNA文库

以经产荷斯坦奶牛的乳腺组织为材料,抽提总的RNA,分离提纯Poly(A)+RNA,反转录并合成单链和双链的cDNA,经酶切形成200～800 bp的片段.将患乳房炎奶牛的cDNA分成2组,分别与不同的接头连接,再与正常奶牛的cDNA进行2次消减杂交和2次抑制性的PCR扩增;第2次PCR产物与pGEM-T载体连接,转化大肠杆菌TOP10感受态细胞进行文库扩增,构建了具有高消减效率的奶牛乳房炎抗性相关cDNA文库.文库扩增后得到361个白色阳性克隆,随机挑选克隆进行PCR签定,插入片段主要分布在200～800 bp.文库的成功构建为进一步筛选、克隆与奶牛乳房炎抗性相关基因奠定了基础,对研究奶牛乳房炎抗性的分子机制以及乳房炎的综合防制具有重要意义.     

Phase I evaluation of CCNU (lomustine) in tumor-bearing cats

1-(2-Chloroethyl)3-cyclohexyl-1-nitrosourea (CCNU) is an alkylating agent in the nitrosourea subclass. A prospective evaluation of CCNU was done to determine the maximally tolerated dosage of CCNU in tumor-bearing cats. Response data were obtained when available. Twenty-five cats were treated with CCNU at a dosage of 50-60 mg/m3 body surface area. Complete hematologic data were available for 13 cats. Neutropenia was the acute dose-limiting toxicity. The median neutrophil count at the nadir was 1,000 cells/microL (mean, 2,433 cells/microL; range, 0-9,694 cells/microL). The time of neutrophil nadir was variable, occurring 7-28 days after treatment, and counts sometimes did not return to normal for up to 14 days after the nadir. Based on these findings, a 6-week dosing interval and weekly hematologic monitoring after the 1st treatment with CCNU are recommended. The nadir of the platelet count may occur 14-21 days after treatment. The median platelet count at the nadir was 43,500 cells/microL. No gastrointestinal, renal, or hepatic toxicities were observed after a single CCNU treatment, and additional studies to evaluate the potential for cumulative toxicity should be performed. Five cats with lymphoma and 1 cat with mast cell tumor had measurable responses to CCNU. Phase II studies to evaluate antitumor activity should be completed with a dosing regimen of 50-60 mg/m3 every 6 weeks.     

Furosemide continuous rate infusion in the horse: evaluation of enhanced efficacy and reduced side effects

Continuous rate infusion (CRI) of furosemide in humans is considered superior to intermittent administration (IA). This study examined whether furosemide CRI, compared with IA, would increase diuretic efficacy with decreased fluid and electrolyte fluctuations and activation of the renin-angiotensin-aldosterone system (RAAS) in the horse. Five mares were used in a crossover-design study. During a 24-hour period, each horse received a total of 3 mg/kg furosemide by either CRI (0.12 mg/kg/h preceded by a loading dose of 0.12 mg/kg IV) or IA (1 mg/kg IV q8h). There was not a statistically significant difference in urine volume over 24 hours between methods; however, urine volume was significantly greater after CRI compared with IA during the first 8 hours ([median 25th percentile, 75th percentile]: 9.6 L [8.9, 14.4] for CRI versus 5.9 L [5.3, 6.0] for IA). CRI produced a more uniform urine flow, decreased fluctuations in plasma volume, and suppressed renal concentrating ability throughout the infusion period. Potassium, Ca, and Cl excretion was greater during CRI than IA (1,133 mmol [1.110, 1,229] versus 764 mmol [709, 904], 102.7 mmol [96.0, 117.2] versus 73.3 mmol [65.0, 73.5], and 1,776 mmol [1,657, 2.378] versus 1,596 mmol [1,457, 1,767], respectively). Elimination half-lives of furosemide were 1.35 and 0.47 hours for CRI and IA, respectively. The area under the excretion rate curve was 1,285.7 and 184.2 mL x mg/mL for CRI and IA, respectively. Furosemide CRI (0.12 mg/kg/h) for 8 hours, preceded by a loading dose (0.12 mg/kg), is recommended when profound diuresis is needed acutely in horses.     

Prevalence of gastric lesions in racing Alaskan sled dogs

Human and equine athletes are reported to have a high prevalence of gastric disease, and anecdotal evidence suggests a similar phenomenon applies to racing sled dogs. To investigate the prevalence of gastric disease in racing sled dogs, we conducted 2 gastroscopy studies on dogs competing in the annual Iditarod Sled Dog Race. A pilot study of dogs that were either dropped from the 2000 Iditarod Sled Dog Race because of illness or that finished the race indicated that, approximately 5 days after competing, 10 of 28 dogs (35%) had endoscopic evidence of gastric ulceration, erosion, or hemorrhage. The next year, an endoscopic study of 73 dogs participating in the 2001 Iditarod race was performed in order to evaluate a larger population of dogs. Data from 70 of these dogs could be used; 34 (48.5%) had ulceration, erosion, gastric hemorrhage, or some combination of these findings. When this group of 70 dogs was compared retrospectively to a control group of 87 dogs presented to the Texas A&M University (TAMU) Veterinary Medical Teaching Hospital, the Iditarod sled dogs had a significantly higher prevalence (P = .049) of gastric lesions. These findings suggest that, similar to athletes of other species, elite canine athletes have an increased prevalence of gastric disease compared to the canine population at large.     

Internal Parasites and Haematological Values in Cattle Slaughtered in Buea Subdivision of Cameroon

Tropical Animal Health and Production -     

The Epidemiology of Gastrointestinal Nematodes of Dairy Cattle in Central Kenya

The epidemiology of H. placei and of other gastrointestinal nematodes in yearling dairy cattle was examined on two farms in Kiambu District, central Kenya during each of 13 one-month periods from April 1993 to April 1994. On each farm, 32 newly weaned dairy calves were given a single dose of albendazole and then placed on experimental pastures. Twelve of the animals were designated for bi-monthly slaughter (n = 2) and analysis of worm population characteristics and 20 were designated for blood and faecal collection and for weighing. Two parasite-free tracer calves were grazed alongside the weaner calves each month throughout the study period and were also slaughtered for analysis of worm populations. Faecal egg counts, haematological and serum pepsinogen determinations, herbage larval counts, and animal live weight changes were recorded monthly. The study revealed that Haemonchus placei, Trichostrongylus axei, Cooperia spp. and Oesophagostomum radiatum were responsible for parasitic gastroenteritis and that H. placei was the predominant nematode present in the young cattle on both farms. Faecal egg counts from resident cattle and necropsy worm counts revealed that pasture larval levels were directly related to the amount of rainfall. The total worm burdens in the animals were highest during the rainy season (March–June and October–December) and lowest during the dry seasons (July–September and January–February). The very low recovery of immature larvae of H. placei from the tracer calves indicated that arrested development is not a feature of the life cycle of this parasite in central Kenya. The maintenance of the parasite population depended on continuous cycling of infection between the host and the pasture. The agroclimatic conditions of the study area were such that, in general, favourable weather conditions for the development and survival of the free-living stages of gastrointestinal nematodes existed all year round.     

Diversity of Ectoparasites in Sheep Flocks in Sa~o Paulo,Brazil

The occurrence of ectoparasites in sheep flocks is frequently reported but seldom quantified. Sheep production used to be a predominantly family activity in the state of Sa~o Paulo (Brazil), but it began to become a commercial activity in the past decade. Thus, information about the ectoparasites existing in sheep flocks has become necessary. The present data were obtained by means of questionnaires sent to all sheep breeders belonging to the `Associaça~o Paulista de Criadores de Ovinos' (ASPACO; Sa~o Paulo State Association of Sheep Breeders). Response reliability was tested by means of random visits paid to 10.6% of the respondents. Most of the properties (89.5%) reported the presence of one or more ectoparasites. Screw-worm (Cochliomyia hominivorax) was the most frequent ectoparasite (72.5%), followed by bot fly larvae (Dermatobia hominis, 45.0%), ticks (Amblyomma cajennense) and Boophilus microplus, 31.3%) and finally lice (Damalinia ovis, 13.8%). Combined infestations also occurred, the most common one being screw-worm with bot fly larvae (36.0%) followed by bot fly larvae with ticks (13.9%), screw-worm with ticks (9.3%), bot fly larvae with lice (6.9%), and ticks with lice (5.0%). The most common triple combination was screw-worm, bot fly larvae and ticks (12.8%). Breeds raised for meat or wool were attacked by bot fly larvae and ticks more often than other breeds. Lice were only absent from animals of indigenous breeds. The relationships among these ectoparasites are discussed in terms of sheep breeds, flock size, seasonality and the ectoparasitic combinations on the host.     

Chemotaxis of macrophage in inflammation

Our particular attention in this article was given to natural mediators for macrophages isolated from the sites of tissue injury. A number of chemotactic factors, which may satisfy many criteria making them acceptable as inflammatory leucocyte chemotactic factors, has been separated. Among them, our laboratory has isolated three macrophage (monocyte) chemotactic factors (MCF-a, -b and -c). Their purification, characterization and functional specificity are discussed.     

Evaluation of biohydrogenation rate of canola vs. soya bean seeds as unsaturated fatty acids sources for ruminants in situ

An experiment was conducted to study disappearance of C14 to C18 fatty acids, lag times and biohydrogenation (BH) rates of C18 fatty acids of ground soya bean and canola seeds in situ. Three ruminally fistulated Dallagh sheep were used to determine ruminal BH of unsaturated fatty acids (UFAs). Differences in the disappearance of fatty acids through the bags and lag times were observed between the oilseeds. We saw that the longer the incubation time of the oilseeds in the rumen, the lower the content of C18:2 and C18:3. Significantly higher lag times for both C18:2 and C18:3 were observed in ground canola compared to ground soya bean. BH rates of C18:2 and C18:3 fatty acids in soya bean were three times higher than those of canola. These results suggest that the fatty acid profile of fat source can affect the BH of UFAs by rumen micro‐organisms. So that UFAs of canola had higher ability to escape from ruminal BH. It seems that fatty acid profile of ruminant products is more affected by canola seed compared to soya bean seed.     

Serum biochemical values and mineral element contents of tissues in yaks

Serum biochemical values and the wet weight to dry weight ratios of tissues were determined in yaks in Shandan county of Gansu province. The liver, kidney, heart and muscle contents of seven elements in yaks were also analysed. Most serum biochemical values were similar to those of cattle, camels and sheep, but the calcium concentration was considerably above the normal range for other ruminants. The liver contained the highest concentrations of copper, manganese and cobalt and the kidney of selenium, iron and calcium.Abbreviations Alb albumin - ALT alanine aminotransferase - AST aspartate aminotransferase - BUN blood urea nitrogen - Chol cholesterol - Glob globulin - -GT -glutamyl transpeptidase - IP inorganic phosphorus - TP total protein