电化学发光-聚合酶链式反应方法检测胰腺癌中K-ras基因点突变

发展了一种可用于快速检测胰腺癌中K-ras癌基因点突变的电化学发光-聚合酶链式反应(ECL-PCR)分析方法。该法采用三联吡啶钌标记的上游引物和生物素标记的下游引物对目的片段进行PCR扩增;再采用限制性内切酶MvaI对扩增产物进行酶切。由于野生型样品和突变型样品间存在酶切位点的变化,其中只有野生型样品能被切断;通过生物素与链霉亲和素包被的磁珠连接,将生物素标记的DNA片段收集到检测池中,进行电化学发光检测。采用该法对13例胰腺癌组织中的K-ras癌基因第12位密码子进行点突变分析,只需要10μL样品、20min孵育时间和30s采集时间,就可得出其中有12例存在点突变,点突变率为92.3%。本方法操作简便、安全、快速、灵敏,可用于检测任何一种导致限制性内切酶位点改变的基因点突变。     

电化学发光PCR定量检测H-ras癌基因点突变

提出了一种电化学发光PCR(ECL-PCR)分析方法,该法可用于定量检测基因点突变.其检测H-ras癌基因PCR扩增产物的灵敏度可达100fmol;线性范围为0.1-500pmol.用ECL-PCR分析法对膀胱癌组织中H-ras癌基因进行突变检测,只需要10μL样品,20min的孵育时间和30s的采集时间,得出20例膀胱癌样品中有7例存在点突变,通过标准曲线方程定量计算出突变样品的量.ECL-PCR分析方法在灵敏度、线性范围、分析时间等方面都优于传统的检测方法,是一种安全、快速、灵敏、定量检测基因点突变的分析方法.     

未修饰的纳米金结合等位特异性扩增来检测K-ras基因点突变

将等位基因特异性扩增的特异性与纳米金特殊的光学性质相结合, 发展了一种新的基因点突变检测方法. 以肿瘤中常见的K-ras癌基因第12位密码子作为点突变检测对象, 采用突变型引物对待测序列进行等位特异性扩增. 突变型样品扩增产物中大部分是双链DNA; 而野生型样品由于不能被顺利扩增, 产物中大部分是单链DNA. 以纳米金颗粒作为报告基团, 向两种不同基因型扩增产物中依次加入纳米金胶和盐溶液, 野生型基因扩增产物中的单链引物被吸附到纳米金颗粒表面, 使得纳米金在适宜浓度的盐溶液中不发生聚集; 突变型样品扩增产物中的双链DNA由于与纳米金颗粒间存在静电斥力而不能被吸附到纳米金颗粒表面, 纳米金在该浓度的盐溶液中发生聚集, 导致两种基因型的混合液在吸收光谱和颜色方面均存在显著差异, 从而实现了检测基因点突变的目的. 该检测方法直观、快速、简便, 实验成本低, 能够检测到pmol量级的样品, 为点突变检测提供了一种实用的新方法.     

Detection of single-base mutation by affinity capillary electrophoresis using a DNA-polyacrylamide conjugate

We have developed an affinity capillary electrophoresis (ACE) method for detection of gene point mutations using a DNA-polyacrylamide conjugate as a pseudostationary affinity phase. In this study, the target DNA was prepared by mixing two PCR products: the wild type of K-ras gene and its codon 12 point mutant. The ligand DNA was designed to be complementary to codons 11 and 12 of the wild type. The target DNA was denatured by the addition of formamide and by heating at 95 degrees C for 5 min, and then electrophoretically separated by difference in affinity to the pseudoimmobilized ligand DNA. The method successfully separated a mixture of the wild-type DNA and each of six codon 12 point mutants by the same ligand DNA. The limit of mutation detection was determined by mixing the wild-type DNA with decreasing concentrations of the mutant DNA. The lowest level of detection was 10% mutant DNA in a background of the wild type. The practicability of this method has been confirmed using a colorectal carcinoma cell line. This study is the first demonstration of detection of gene point mutation in polymerase chain reaction (PCR) products using ACE, and opens up a new possibility of CE-based gene diagnosis.     

An improved electrochemiluminescence polymerase chain reaction method for the detection of Fusarium wilts

An improved electrochemiluminescence polymerase chain reaction （ECL-PCR） method was developed and applied to detect Fusarium wilt. Briefly, the internal transcribed spacer （ITS） sequence of Fusarium oxysporumf, sp Cubense （FOC） was amplified by PCR. Two universal fragments, which were complimentary to Ru（bpy）3^2＋ （TBR） labeled probe and Biotin labeled probe, respectively, were connected to the tail of primers so that all the PCR products got universal sequences. Then biotin labeled probes and TBR labeled probes were hybridized with the PCR products at the same time. Through the specific interaction between biotin and streptavidin, the PCR products were captured by streptavidin coated magnetic bead and then detected by ECL assay. The experiment results showed that the healthy banana samples and infected ones can be discriminated by this ECL-PCR method. This improved ECL-PCR approach is useful in Fusarium wilt detection due to its high sensitivity, simplicity and stability.     

实时荧光等位基因特异性扩增法快速检测K-ras癌基因点突变

将荧光定量PCR技术与等位基因特异性扩增(Allele specific amplification, ASA)方法相结合, 发展了一种可以快速检测基因点突变的实时荧光等位基因特异性扩增(Real-time ASA)方法. 将该法用于检测K-ras癌基因第12位密码子发生的点突变, 分别采用针对其不同点突变方式(GAT, GTT, CGT)设计的突变型引物对待测样品进行ASA, 只有突变型样品能被顺利扩增出双链DNA产物, 该产物才能与双链DNA染料SYBR Green Ⅰ结合, 发出荧光信号从而被检测到. 用该法检测31例结肠癌组织中的K-ras癌基因点突变, 其中有15例样品检出为突变型. Real-time ASA法可检测到样品中含量为1/1000的突变型基因, 具有灵敏、快速、简便、安全、高通量和低成本等优点, 可望用于大量临床样本的点突变筛查.     

An improved electrochemiluminescence polymerase chain reaction method for highly sensitive detection of plant viruses

Recently, we have reported an electrochemiluminescence polymerase chain reaction (ECL-PCR) method for detection of genetically modified organisms. The ECL-PCR method was further improved in the current study by introducing a multi-purpose nucleic acid sequence that was specific to the tris(bipyridine) ruthenium (TBR) labeled probe, into the 5′ terminal of the primers. The method was applied to detect plant viruses. Conserved sequence of the plant viruses was amplified by PCR. The product was hybridized with a biotin labeled probe and a TBR labeled probe. The hybridization product was separated by streptavidin-coated magnetic beads, and detected by measuring the ECL signals of the TBR labeled. Under the optimized conditions, the experiment results show that the detection limit is 50 fmol of PCR products, and the signal-to-noise ratio is in excess of 14.6. The method was used to detect banana streak virus, banana bunchy top virus, and papaya leaf curl virus. The experiment results show that this method could reliably identity viruses infected plant samples. The improved ECL-PCR approach has higher sensitivity and lower cost than previous approach. It can effectively detect the plant viruses with simplicity, stability, and high sensitivity.     

结直肠癌组织中K-ras基因突变的毛细管电泳检测

通过对PCR扩增的76例结直肠癌组织及癌旁正常组织DNA基因组共152个样本纯化变性后,采用毛细管电泳-激光诱导荧光检测(CE-LIF)结合单链构象多态性(SSCP)分析方法检测了人结直肠癌组织及癌旁正常组织中K-ras基因第12/13位密码子突变。所检测的76例结直肠癌患者中有30例患者存在基因突变,并对异常片段进行测序验证,测序证实以碱基G→A点突变为主。结果表明所建立的CE-LIF技术结合SSCP分析检测K-ras基因突变的方法高效、快速、灵敏、准确,适合于临床上大样本结直肠癌中K-ras基因突变分析,对选择抗结直肠癌药物有一定的指导作用。     

Approaching real-time molecular diagnostics: single-pair fluorescence resonance energy transfer (spFRET) detection for the analysis of low abundant point mutations in K-ras oncogenes

The aim of this study was to develop new strategies for analyzing molecular signatures of disease states approaching real-time using single pair fluorescence resonance energy transfer (spFRET) to rapidly detect point mutations in unamplified genomic DNA. In addition, the detection process was required to discriminate between normal and mutant (minority) DNAs in heterogeneous populations. The discrimination was carried out using allele-specific primers, which flanked the point mutation in the target gene and were ligated using a thermostable ligase enzyme only when the genomic DNA carried this mutation. The allele-specific primers also carried complementary stem structures with end-labels (donor/acceptor fluorescent dyes, Cy5/Cy5.5, respectively), which formed a molecular beacon following ligation. We coupled ligase detection reaction (LDR) with spFRET to identify a single base mutation in codon 12 of a K-ras oncogene that has high diagnostic value for colorectal cancers. A simple diode laser-based fluorescence system capable of interrogating single fluorescent molecules undergoing FRET was used to detect photon bursts generated from the molecular beacon probes formed upon ligation. LDR-spFRET provided the necessary specificity and sensitivity to detect single-point mutations in as little as 600 copies of human genomic DNA directly without PCR at a level of 1 mutant per 1000 wild type sequences using 20 LDR thermal cycles. We also demonstrate the ability to rapidly discriminate single base differences in the K-ras gene in less than 5 min at a frequency of 1 mutant DNA per 10 normals using only a single LDR thermal cycle of genomic DNA (600 copies). Real-time LDR-spFRET detection of point mutations in the K-ras gene was accomplished in PMMA microfluidic devices using sheath flows.     

Effect of polymer matrix and glycerol on rapid single-strand conformation polymorphism analysis by capillary and microchip electrophoresis for detection of mutations in K-ras gene

We present the rapid single-strand conformation polymorphism (SSCP) analysis by capillary and microchip electrophoresis to detect the mutations in K-ras gene. Parameters that might affect the analysis of mutation in K-ras gene, such as the polymer and the additive in the sieving matrix, have been studied systematically. Under the optimal conditions, the analysis of seven mutants of K-ras gene could be finished within 10 min by capillary electrophoresis (CE). Furthermore, with the wild-type gene as the inner standard, the analysis accuracy of mutations could be improved. In addition, by studying the properties of polymer solutions, the matrix suitable for microchip electrophoresis was found, and the detection of mutations in K-ras gene could be further shortened to 1 min.     

基于DNA聚合酶I的新型电化学传感器及其胰腺癌K-ras基因点突变检测

本文构建DNA聚合酶I的新型DNA电化学传感器,将捕获探针通过Au-S键固定于Au基底表面,与互补靶序列杂交至点突变前一个碱基,通过DNA聚合酶Ⅰ将dUTP-biotin连接在目标DNA的检测位点,再与avidin-HRP反应,而后测定在TMB溶液中的电化学特性. 结果表明,DNA电化学传感电极的检测电流值与K-ras突变型基因浓度（1.0×10^-15 ~ 1.0×10^-10 mol·L^-1）对数呈良好的线性关系,且灵敏度高,特异性较佳.     

Applications of homemade kit in mutation detection of genes

With the accomplishment of Human Genome Project (HGP), single nucleotide polymorphism (SNP) and mutation detection in human genome are becom-ing a new researching focus. These researches can help us to understand the phenotype diversity of indi-vidual, disease susceptibility and drug resistance of different colonies. Traditional method used for muta-tion detection is slab gel electrophoresis, which re-mains labor-intensive and time-consuming because of the requirement of radioactivity or te…     

Detection of K-ras exon 1 mutations by constant denaturant capillary electrophoresis

Among various mutation detection methods, constant denaturant capillary electrophoresis (CDCE) is one of the most common techniques for rapid identification of known or unknown mutations. In this report, a CDCE analysis method with homemade linear polyacrylamide (LPA) kit was developed on ABI 310 genetic analyzer, the effect and relationship of various denaturing factors in CDCE analysis were investigated and K-ras gene mutations of 31 coloerctal cancer patients were detected. Results indicate that, with the increase of chemical danaturant concentration, the optimum temperature was lowered, and when the concentration of urea (formamide) was higher than 7 M (40%), the homoduplex and heteroduplex of mutant samples were separated with difficulty. Detection results of K-ras gene in colorectal samples indicated that mutations were present in eight (26%) of 31 patients; most mutations were localized in codon 12, which is thought to be a critical step and plays an important role in human colorectal carcinogenesisas.     

Quartz crystal microbalance detection of DNA single-base mutation based on monobase-coded cadmium tellurium nanoprobe

A new method for the detection of point mutation in DNA based on the monobase-coded cadmium tellurium nanoprobes and the quartz crystal microbalance (QCM) technique was reported. A point mutation (single-base, adenine, thymine, cytosine, and guanine, namely, A, T, C and G, mutation in DNA strand, respectively) DNA QCM sensor was fabricated by immobilizing single-base mutation DNA modified magnetic beads onto the electrode surface with an external magnetic field near the electrode. The DNA-modified magnetic beads were obtained from the biotin-avidin affinity reaction of biotinylated DNA and streptavidin-functionalized core/shell Fe(3)O(4)/Au magnetic nanoparticles, followed by a DNA hybridization reaction. Single-base coded CdTe nanoprobes (A-CdTe, T-CdTe, C-CdTe and G-CdTe, respectively) were used as the detection probes. The mutation site in DNA was distinguished by detecting the decreases of the resonance frequency of the piezoelectric quartz crystal when the coded nanoprobe was added to the test system. This proposed detection strategy for point mutation in DNA is proved to be sensitive, simple, repeatable and low-cost, consequently, it has a great potential for single nucleotide polymorphism (SNP) detection.     

基于热阻梯度加热系统的温度梯度芯片毛细管电泳用于DNA突变检测

建立了一种简单、可靠的空间温度梯度芯片毛细管电泳DNA突变分析系统, 制作了热阻呈梯度均匀变化的硅橡胶(PDMS)基片, 利用其热阻变化对热传导的影响, 在基片表面形成稳定的空间温度梯度. 通过改变PDMS基片的厚度差, 可得到范围不同的温度梯度, 且形成的温度梯度在6 h内保持稳定. 利用该温度梯度加热装置对玻璃微流控芯片进行加热, 在10 ℃温度梯度范围内对209 bp的DNA突变标准样品进行分离检测, 单次样品分析时间为8.3 min, 并成功用于3例大肠癌患者石蜡组织切片中K-ras基因突变的检测.     

High-sensitive fluorescent DNA sequencing and its application for detection and mass-screening of point mutations.

We describe a rapid and sensitive DNA sequencing method for an automated fluorescent DNA sequencer (AFDS) and its application for detection of point mutations. The method is based on an improved cycle sequencing procedure in which only 10-50 fmol of template DNA is required. Furthermore, it is able to use crude DNA preparation as a template as well as the purified one. Thus, the improved method provided a simplified procedure for sequencing of various types of DNA, including cosmid DNA, in which purification steps were unnecessary. We also developed a novel system for detection of point mutations using AFDS. A set of four lanes is used for the parallel analysis of single-base profiles of four different samples, instead of for the four-base profile of a sample. The AFDS exhibits the base profiles of the samples with four different colors in the analyzed data, which enables us to identify a mutation as an additional peak with a color specific for the lane. The feasibility of our system was tested by analyzing polymerase chain reaction (PCR)-amplified genomic DNAs from four individuals including a carrier of a mutation of C to T. The mutation was clearly identified as an additional "T" peak of a color specific for the carrier. The mutation was also detectable even if 16 individuals including the carrier were simultaneously analyzed on a set of four lanes (four individual samples for each lane). Thus, the novel system is useful for simultaneous detection of mutations in a large number of individual samples.     

Application of cycling gradient capillary electrophoresis to detection of APC, K-ras, and DCC point mutations in patients with sporadic colorectal tumors

A previously introduced technique of cycling gradient capillary electrophoresis (CGCE) was applied to monitoring of molecular changes during adenoma-carcinoma transition in progression of sporadic colorectal cancer. The purpose of this work was optimization of separation parameters for selected mutation regions in tumor suppressor genes involved in the early stages of colorectal carcinogenesis, followed by scanning for these mutations in clinical tissue samples from patients with adenomatous polyps and early carcinomas. A total of 47 colorectal tumors in various stages of progression were examined. Main emphasis was given to evaluation of mutation detection sensitivity and specificity required for effective early disease detection. A total of 7 different somatic mutations was identified among 32 K-ras mutant samples, 1 inherited mutation and 5 somatic mutations were identified among 15 adenomatous polyposis coli (APC) mutated samples. None of the two previously reported "deleted in colorectal carcinomas" (DCC) mutations was found in any of the clinical samples. In addition to simple optimization of running conditions, CGCE has demonstrated sensitivity and selectivity allowing detecting small mutant fractions as well as combination of multiple mutants within a single target sequence.     

Capillary and microelectrophoretic separations of ligase detection reaction products produced from low-abundant point mutations in genomic DNA

Capillary gel electrophoresis (CGE) and polymer-based microelectrophoretic platforms were investigated to analyze low-abundant point mutations in certain gene fragments with high diagnostic value for colorectal cancers. The electrophoretic separations were carried out on single-stranded DNA (ssDNA) products generated from an allele-specific ligation assay (ligase detection reaction, LDR), which was used to screen for a single base mutation at codon 12 in the K-ras oncogene. The presence of the mutation generated a ssDNA fragment that was >40 base pairs (bp) in length, while the primers used for the ligation assay were <30 bp in length. Various separation matrices were investigated, with the success of the matrix assessed by its ability to resolve the ligation product from the large molar excess of unligated primers when the mutant allele was lower in copy number compared to the wild-type allele. Using CGE, LDR product models (44 and 51 bp) could be analyzed in a cross-linked polyacrylamide gel with a 1000-fold molar excess of LDR primers (25 bp) in approximately 45 min. However, when using linear polyacrylamide gels, these same fragments could not be detected due to significant electrokinetic biasing during injection. A poly(methylmethacrylate) (PMMA) microchip of 3.5 cm effective column length was used with a 4% linear polyacrylamide gel to analyze the products generated from an LDR. When the reaction contained a 100-fold molar excess of wild-type DNA compared to a G12.2D mutant allele, the 44 bp ligation product could be effectively resolved from unligated primers in under 120 s, nearly 17 times faster than the CGE format. In addition, sample cleanup was simplified using the microchip format by not requiring desalting of the LDR prior to loading.     

High-throughput simultaneous detection of point mutations and large-scale rearrangements by CE

The detection of unknown mutations is important both in population genetics research and in diagnosis. At present, two different methods must be used to detect either point mutations or large-scale genetic rearrangements, which is costly and time-consuming. We describe here a new method for the simultaneous detection of these two types of mutations. It is based on electrophoretic heteroduplex analysis (HDA) using enhanced mismatch mutation analysis (EMMA) and semiquantitative multiplexed PCR conditions. The use of such conditions allows the simultaneous search of any kind of mutation in up to five different fragments per capillary, in a single or multi-CE system. The method was validated on patient samples with mutations in the breast predisposition gene BRCA1. It leads to highly reliable and high-throughput mutation detection at low cost, as compared with classical methods.     

Electrochemical biosensors for detection of point mutation based on surface ligation reaction and oligonucleotides modified gold nanoparticles

An electrochemical method for point mutation detection based on surface ligation reaction and oligonucleotides (ODNs) modified gold nanoparticles (AuNPs) was demonstrated. Point mutation identification was achieved using Escherichia coli DNA ligase. This system for point mutation detection relied on a sandwich assay comprising capture ODN immobilized on Au electrodes, target ODN and ligation ODN. Because of the sequence-specific surface reactions of E. coli DNA ligase, the ligation ODN covalently linked to the capture ODN only in the presence of a perfectly complementary target ODN. The presence of ligation products on Au electrode was detected using chronocoulometry through hybridization with reporter ODN modified AuNPs. The use of AuNPs improved the sensitivity of chronocoulometry in this approach, a detection limit of 0.9 pM complementary ODN was obtained. For single base mismatched ODN (smODN), a negligible signal was observed. Even if the concentration ratio of complementary ODN to smODN was decreased to 1:1000, a detectable signal was observed. This work may provide a specific, sensitive and cost-efficient approach for point mutant detection.