Nucleic Acid Amplification Strategies for DNA Microarray-Based Pathogen Detection

DNA microarray-based screening and diagnostic technologies have long promised comprehensive testing capabilities. However, the potential of these powerful tools has been limited by front-end target-specific nucleic acid amplification. Despite the sensitivity and specificity associated with PCR amplification, the inherent bias and limited throughput of this approach constrain the principal benefits of downstream microarray-based applications, especially for pathogen detection. To begin addressing alternative approaches, we investigated four front-end amplification strategies: random primed, isothermal Klenow fragment-based, 29 DNA polymerase-based, and multiplex PCR. The utility of each amplification strategy was assessed by hybridizing amplicons to microarrays consisting of 70-mer oligonucleotide probes specific for enterohemorrhagic Escherichia coli O157:H7 and by quantitating their sensitivities for the detection of O157:H7 in laboratory and environmental samples. Although nearly identical levels of hybridization specificity were achieved for each method, multiplex PCR was at least 3 orders of magnitude more sensitive than any individual random amplification approach. However, the use of Klenow-plus-Klenow and 29 polymerase-plus-Klenow tandem random amplification strategies provided better sensitivities than multiplex PCR. In addition, amplification biases among the five genetic loci tested were 2- to 20-fold for the random approaches, in contrast to >4 orders of magnitude for multiplex PCR. The same random amplification strategies were also able to detect all five diagnostic targets in a spiked environmental water sample that contained a 63-fold excess of contaminating DNA. The results presented here underscore the feasibility of using random amplification approaches and begin to systematically address the versatility of these approaches for unbiased pathogen detection from environmental sources.     

Oligonucleotide Primers for PCR Amplification of Coelomate Introns

Abstract Seven novel oligonucleotide primer pairs for polymerase chain reaction amplification of introns from nuclear genes in coelomates were designed and tested. Each pair bound to adjacent exons that are separated by a single intron in most coelomate species. The primer sets amplified introns in species as widely separated by the course of evolution as oysters (Mollusca: Protostoma) and salmon (Chordata: Deuterostoma). Each primer set was tested on a further 6 coelomate species and found to amplify introns in most cases. These primer sets may therefore be useful tools for developing nuclear DNA markers in diverse coelomate species for studies of population genetics, phylogenetics, or genome mapping.     

Lna (Locked Nucleic Acid)

Abstract

LNA (Locked Nucleic Acid) forms duplexes with complementary DNA, RNA or LNA with unprecedented thermal affinities. CD spectra show that duplexes involving fully modified LNA (especially LNA:RNA) structurally resemble an A-form RNA:RNA duplex. NMR examination of an LNA:DNA duplex confirm the 3′-endo conformation of an LNA monomer. Recognition of double-stranded DNA is demonstrated suggesting strand invasion by LNA. Lipofectin-mediated efficient delivery of LNA into living human breast cancer cells has been accomplished.     

Locked Nucleic Acids: Promising Nucleic Acid Analogs for Therapeutic Applications

Locked Nucleic Acid (LNA) is a unique nucleic‐acid modification possessing very high binding affinity and excellent specificity toward complementary RNA or DNA oligonucleotides. The remarkable properties exhibited by LNA oligonucleotides have been employed in different nucleic acid‐based therapeutic strategies both in vitro and in vivo. Herein, we highlight the applications of LNA nucleotides for controlling gene expression.     

Locked Nucleic Acid Probe-Based Real-Time PCR Assay for the Rapid Detection of Rifampin-Resistant Mycobacterium tuberculosis

Drug-resistant Mycobacterium tuberculosis can be rapidly diagnosed through nucleic acid amplification techniques by analyzing the variations in the associated gene sequences. In the present study, a locked nucleic acid (LNA) probe-based real-time PCR assay was developed to identify the mutations in the rpoB gene associated with rifampin (RFP) resistance in M. tuberculosis. Six LNA probes with the discrimination capability of one-base mismatch were designed to monitor the 23 most frequent rpoB mutations. The target mutations were identified using the probes in a “probe dropout” manner (quantification cycle = 0); thus, the proposed technique exhibited superiority in mutation detection. The LNA probe-based real-time PCR assay was developed in a two-tube format with three LNA probes and one internal amplification control probe in each tube. The assay showed excellent specificity to M. tuberculosis with or without RFP resistance by evaluating 12 strains of common non-tuberculosis mycobacteria. The limit of detection of M. tuberculosis was 10 genomic equivalents (GE)/reaction by further introducing a nested PCR method. In a blind validation of 154 clinical mycobacterium isolates, 142/142 (100%) were correctly detected through the assay. Of these isolates, 88/88 (100%) were determined as RFP susceptible and 52/54 (96.3%) were characterized as RFP resistant. Two unrecognized RFP-resistant strains were sequenced and were found to contain mutations outside the range of the 23 mutation targets. In conclusion, this study established a sensitive, accurate, and low-cost LNA probe-based assay suitable for a four-multiplexing real-time PCR instrument. The proposed method can be used to diagnose RFP-resistant tuberculosis in clinical laboratories.     

One New Method of Nucleic Acid Amplification-Loop-mediated Isothermal Amplification of DNA

Loop-mediated isothermal amplification (LAMP) is a novel nucleic acid amplification method, which amplifies DNA with high specificity, sensitivity, rapidity and efficiency under isothermal conditions using a set of four specially designed primers and a Bst DNA polymerase with strand displacement activity. The basic principle, characteristics, development of LAMP and its applications are summarized in this article.     

核酸体外扩增技术

核酸体外扩增是分子生物学研究的基础。随着生物技术的发展 ,出现了越来越多的核酸体外扩增技术。根据其特点可分为两类 :一类是靶核酸的直接扩增 ,如聚合酶链式反应、链替代扩增、连接酶链式反应、核酸依赖的扩增、Qβ复制、转录介导的扩增和滚环扩增等 ;另一类是信号放大扩增 ,如支链DNA、侵染探针等。就现有的核酸扩增技术的原理、特点及应用进行介绍。     

PCR增强剂在核酸体外扩增检测技术的研究进展

在各种高致病性病原体、禽流感病毒、食源性微生物等引起的疾病随时大规模流行的背景下,利用聚合酶链式反应（polymerase chain reaction,PCR）技术对第一例或第一波病例的快速实验室诊断显得尤为重要,同时发展出多种以PCR技术为基础的检测技术以便更加快速、高通量、敏感地对疾病进行诊断、预防或预测。然而,在实际病原体检测中,常常出现灵敏度低、准确性差的结果。PCR增强剂是在PCR及PCR衍生技术中添加的一类物质,其可从产率、特异性、灵敏度等方面提高核酸扩增性能,从而优化核酸检测,解决病原体检测的应用瓶颈,为第一例病原体检出节约宝贵的时间。结合以PCR为基础的核酸体外扩增检测技术对PCR增强剂在其中的应用、优缺点、作用机理进行介绍,以期为病原体核酸检测的实际应用提供一些参考。     

利用PCR方法从人染色体DNA中扩增G-CSF基因

利用PCR技术从染色体基因组DNA中扩增大DNA片段具有相当大的难度。本试验采用碱变性模板以及热启动等方法,成功地扩增出1.5kb的人基因组DNA,并讨论了影响扩增大DNA片段特异性和产量的因素。     

The Solution Structure of a Locked Nucleic Acid (LNA) Hybridized to DNA

Abstract

LNA (Locked Nucleic Acids) is a novel oligonucleotide analogue containing a conformationally restricted nucleotide with a 2′-0, 4′-C-methylene bridge that induces unprecedented thermal affinities when mixed with complementary single stranded DNA and RNA. We have used two-dimensional'H NMR spectroscopy obtained at 750 and 500 MHz to determine a high resolution solution structure of an LNA oligonucleotide hybridized to the complementary DNA strand. The determination of the structure was based on a complete relaxation matrix analysis of the NOESY cross peaks followed by restrained molecular dynamics calculations. Forty final structures were generated for the duplex from A-type and B-type dsDNA starting structures. The root-mean-square deviation (RMSD) of the coordinates for the forty structures of the complex was 0.32Å. The structures were analysed by use of calculated helix parameters. This showed that the values for rise and buckle in the LNA duplex is markedly different from canonical B-DNA at the modification site. A value of twist similar to A-DNA is also observed at the modification site. The overall length of the helix which is 27.3Å. The average twist over the sequence are 35.9° ± 0.3°. Consequently, the modification does not cause the helix to unwind. The bis-intercalation of the thiazole orange dye TOTO to the LNA duplex was also investigated by ¹H NMR spectroscopy to sense the structural change from the unmodified oligonucleotide. We observed that the bis-intercalation of TOTO is much less favourable in the 5′-CT^LAG-3′ site than in the unmodified 5′-CT^LAG-3′ site. This was related to the change in the base stacking of the LNA duplex compared to the unmodified duplex.     

应用改进的通用荧光PCR引物进行多重STR分型

通过设计通用荧光PCR引物并结合DNA测序系统建立了小鼠的多重STR分型方案.实验针对小鼠基因组设计了两对不同的通用引物序列,标记了FAM荧光的通用序列和"加尾"的位点特异性引物共同用于小鼠的多重PCR的STR基因分型.本研究优化了通用引物和特异性引物间的比例,优化了多重STR-PCR的反应条件,并最终利用该技术方案实现了五重STR分型.实验验证了该方案在多重STR分型中的可行性.与传统的荧光检测PCR产物方案相比,应用通用方案完成多重PCR反应大大节省了实验时间与经费.     

不同纯化方法处理DNA合成引物对PCR扩增效率的影响

对ＤＮＡ合成的幽门螺杆菌尿素酶引物ＨＰ１、ＨＰ２、ＨＰ３、ＨＰ４进行了几种不同的纯化试验,分别采用无水乙醇沉淀法、ＮＴ柱及聚丙烯酰胺凝胶电泳方法,对其相应的纯化收率,ＰＣＲ扩增效率作了比较及分析。琼脂糖凝胶电泳结果证实,以无水乙醇沉淀纯化方法的ＰＣＲ扩增效果较为理想。该方法操作简便、稳定高效、省时省力、成本低。为此建议用该法处理ＤＮＡ合成引物。     

一种通用的基因组DNA提取方法

目的:探讨一种通厢的基因组DNA提取方法.方法:采用改良的膜法分别从动植物组织、外周血、细菌、细胞等标本提取基因组DNA,DNA样品经紫外吸收、琼脂糖凝胶电泳、PCR扩增和酶切进行榆测.结果:该方法提取的基因组DNA纯度较高,电泳条带清晰,DNA质量能满足下游分子生物学研究的需要.结论:该方法简便快速、适用范围广,是提取基因组DNA的一种有效方法.     

引物间同源性和裂口对PCR扩增的影响

采用ＰＣ／Ｇｅｎｅ软件对能扩增出特异睡不能扩增的ＰＣＲ引物进行同源性比较,同源间“裂口（ｇａｐｓ）”差数的统计,得出源率小于或等于３５％,“裂口”差数大于或等于３,是获得理想ＰＣＲ扩增效果的关键参数之一的结论,为引物设计提供了一条直观的依据。     

Isolation and PCR Amplification of Genomic DNA from Market Samples of Dry Tea

A simple procedure for DNA isolation from processed dried commercial samples of tea is described. The method involves a modified CTAB procedure employing extensive washing, use of 1% PVP to remove polyphenolics and a single phenol:chloroform extraction step. The average yield ranges from 164–494 g/g tea sample for various market samples. The DNA obtained from 11 different brands of tea using this procedure were consistently amplifiable (using both RAPD primers as well as defined sequences as primers) and digestible with restriction endonucleases.     

裸子植物DNA条形码ITS2高通用性引物的筛选

DNA条形码技术是利用标准DNA片段进行准确快速鉴定物种的一种方法,理想的DNA条形码片段应具有高通用性。虽然核糖体DNA内部转录间隔区II（ITS2）被建议作为种子植物有效的DNA条形码,但目前裸子植物还没有通用性高的引物可用。为获得高通用性的ITS2引物,本研究基于裸子植物55个属的5．8S基因的保守序列区设计了3个正向引物,与已有的ITS反向引物组合,组成了7对ITS2引物进行通用性的评价。选取了裸子植物8目、12科和40属的56个种用于本文的研究。引物组合5．8SR／ITS4、5．8SRa／ITS4和5．8SF2／S3R因为在科水平评价中通用性低或者产生的PCR产物有双带,因而排除在全部物种水平上进一步评价。其余4对引物（GYM-5．8SF1／ITS4、GYM-5．8SFl／S3R、GYM-5．8SF2／ITS4和S2F／S3R）在56个物种的PCR检测中,均有100％的扩增率。基于PCR产物的亮度、序列质量和正反向引物覆盖率的综合评价,建议引物GYM_5．8SF2／ITS4作为裸子植物条形码片段ITS2最好的通用引物。     

Universal Labeling Chemistry for Nucleic Acid Detection on DNA-Arrays

Abstract

We show here a new and efficient aqueous chemistry for labeling of any class of nucleic acids for their detection on DNA chip. The labels contain a diazo function as reactive moiety and biotin as detectable unit. The highly selective reaction of diazo group on the phosphate does not disrupt base pairing recognition and hybridization specificity.     

Universal Primers for Amplification of Mitochondrial Small Subunit Ribosomal RNA-Encoding Gene in Scleractinian Corals

We describe the construction of polymerase chain reaction primers designed to amplify a portion of the mitochondrial (mt) small subunit ribosomal (SSU) RNA-encoding genes in scleractinian corals. Combinations of cloning and sequencing show that the amplified fragments are between 694 and 896 bp in length. Alignment of the amplified DNA sequences to the published mt SSU rRNA genes of Metridium senile and Sarcophyton glaucum indicates several conserved regions among actiniarian, corallimorpharian, octocorallian, and scleractinians, suggesting this primer set can successfully amplify over 80% of the mt SSU rDNA region of scleractinian corals. Surveys of sequence variation and estimation of the rate of evolution show an extremely slow divergence of the SSU rRNA gene in the family Acroporidae. Received June 11, 1999; accepted October 4, 1999.     

高GC含量DNA模板的PCR扩增

目的：探索高GC含量DNA的PCR扩增条件,为扩增达托霉素生物合成基因簇及拼接奠定基础。方法：在PCR扩增体系中,使用高保真的聚合酶及添加不同浓度的DMSO、7-deaza-dGTP等增强剂,并选择合适的PCR循环程序,优化富含GC的DNA的PCR扩增条件。结果：向反应体系中额外添加1%~4%的DMSO可以显著提高富含GC的DNA的PCR扩增产物量,但会降低其特异性;7-deaza-dGTP可以提高扩增产物的特异性及保真度,但产量会有所下降。应用touch down PCR并在体系中添加7-deaza-dGTP能够提高扩增产物的特异性和产率,增加扩增的保真度。结论：应用优化的PCR扩增条件将所有达托霉素生物合成基因簇分段扩增出来,并可扩增出长达6 kb的片段,且序列完全正确,可以进行后续拼接。