Expression and purification of Arisaema heterophyllum agglutinin in Escherichia coli

Recombinant Arisaema heterophyllum agglutinin (AHA) was expressed in Escherichia coli as N-terminal His-tagged fusions. After induction with isopropylthio-beta-D-galactoside, the recombinant AHA was purified by metal-affinity chromatography. The purified AHA protein was incorporated into artificial diet at 0.1% (w/v) concentration in insect bioassay trial and the result showed that artificial diet containing AHA could significantly inhibit the growth of the third-instar nymphs of peach potato aphid (Myzus persicae). This study suggested that AHA could be an effective candidate for the control of peach potato aphid, one of the most serious sap-sucking insect pests causing significant yield loss of crops.     

Optimized adaptor polymerase chain reaction method for efficient genomic walking

Genomic walking is one of the most useful approaches in genome-related research. Three kinds of PCR-based methods are available for this purpose. However, none of them has been generally applied because they are either insensitive or inefficient. Here we present an efficient PCR protocol, an optimized adaptor PCR method for genomic walking. Using a combination of a touchdown PCR program and a special adaptor, the optimized adaptor PCR protocol achieves high sensitivity with low background noise. By applying this protocol, the insertion sites of a gene trap mouse line and two gene promoters from the incompletely sequenced Xenopus laevis genome were successfully identified with high efficiency. The general application of this protocol in genomic walking was promising.     

An efficient and rapid method for gene cloning from eukaryotic genomic DNA using overlap-PCR: With an example of cattle Ghrelin gene

In this study, overlap-PCR, an efficient and rapid method, was used to clone cattle Ghrelin gene CDS (coding sequence) from genomic DNA. The procedure included seven primers and three-step PCRs. Cattle Ghrelin gene consists of four exons and the CDS contains 351 bps. In the first step three PCRs were performed to generate extended exon1, exon2, and exon3 that contained overlapped nucleotides and were used as the templates for second ligation PCR. Secondly, exon1 and exon2 were spliced together. And it was same with exon3 and exon4. Lastly, the four exons were linked together with outermost primers and the templates from the second step. Comparison analysis on the obtained CDS of Ghrelin gene and cDNA by RT-PCR showed that the two sequences were same. As an efficient and rapid method, overlap-PCR is feasible and acceptable for gene cloning from genomic DNA.     

Tandem gene amplification in vitro for rapid and efficient expression in animal cells

Plasmid vectors pHSG293 and pHSG747, suitable for in vitro gene amplification for subsequent animal-cell expression, were developed. A cosmid vector pHSG293 confers Km resistance to Escherichia coli host cells and G418 resistance to animal cells and contains a single BstXI recognition/cleavage site, CCACGGGG/CTGG, near the cos site (the recognition site is underlined). The cassette vector plasmid pHSG747 contains a multiple cloning site (MCS) between the simian virus 40 early promoter and the poly(A) signal sequence flanked by the same BstXI sites and confers Cm resistance to E. coli host cells. After inserting a coding fragment for human protein C or its derivative in the appropriate orientation in the MCS of pHSG747, the BstXI expression unit fragment was purified, mixed with BstXI-digested pHSG293 DNA at a molecular ratio of 20 to 40:1 and ligated. This allowed for tandem gene amplification due to asymmetric cohesive ends. Ligation products were packaged in lambda phage particles, amplified in E. coli cells as large cosmid molecules, and then introduced into CHO cells. G418R transformants were found to produce and secrete recombinant protein molecules at a high level. The plasmid vectors developed in this work will provide a rapid screening system useful for protein engineering in animal cells.     

快速检测NDM-1基因的环介导恒温扩增技术的建立与评价

基于DNA环介导恒温扩增技术 (Loop-mediated isothermal amplification,LAMP),探索建立一种应用于NDM-1基因 (New Metallo-β-Lactamase-1 Gene,NDM-1) 的快速检测方法,以适应临床实验室等的检测需求。利用LAMP技术,以NDM-1基因为靶序列,设计4组LAMP引物,并筛选最优引物组,建立LAMP反应体系与条件,进行灵敏度和特异性实验。结果表明整个检测过程仅需1 h,即可通过肉眼直接目测实验结果。在灵敏度试验中,NDM-1基因的最低检测限为6 拷贝/反应。在特异性实验中,以4株病原菌 (肺炎克雷伯氏菌、大肠埃希氏菌、金黄色葡萄球菌、肺炎链球菌) 以及肠道菌群元基因组DNA、土壤菌群元基因组DNA为模板对NDM-1基因进行检测,结果显示均没有发生非特异性扩增反应。文中建立的LAMP检测方法能够快速检测NDM-1基因,且可直接观察到实验结果,实现了检测结果的可视化。具有操作简单安全、检测灵敏度高、特异性高的特点,能够满足基层实验室、应急检测或现场监测等方面的使用需求,具有良好的应用价值。     

Principle of LAMP method--a simple and rapid gene amplification method

So far nucleic acid test (NAT) has been employed in various fields, including infectious disease diagnoses. However, due to its complicated procedures and relatively high cost, it has not been widely utilized in many actual diagnostic applications. We have therefore developed a simple and rapid gene amplification technology, Loop-mediated Isothermal Amplification (LAMP) method, which has shown prominent results of surpassing the performance of the conventional gene amplification methods. LAMP method acquires three main features: (1) all reaction can be carried out under isothermal conditions; (2) the amplification efficiency is extremely high and tremendous amount of amplification products can be obtained; and (3) the reaction is highly specific. Furthermore, developed from the standard LAMP method, a rapid LAMP method, by adding in the loop primers, can reduce the amplification time from the previous 1 hour to less than 30 minutes. Enormous amount of white precipitate of magnesium pyrophosphate is produced as a by-product of the amplification, therefore, direct visual detection is possible without using any reaction indicators and detection equipments. We believe LAMP technology, with the integration of these features, can rightly apply to clinical genetic testing, food and environmental analysis, as well as NAT in different fields.     

A rapid method for detection of plant genomic instability using unanchored-microsatellite primers

In order to assess the feasibility of microsatellite primers as markers for genomic instability, we conducted a study of DNA stability in cauliflower callus. A protocol is described for the rapid screening of a large number of putative variant calli and plants. Genomic DNA is isolated and screened by microsatellite primers. We believe that inter-simple sequence repeat PCRs can conveniently detect and measure common genetic events underlying plant genomic instability. These include deletions, amplifications, translocations, insertions, recombination or chemical alterations. Our results indicate that instability occurred in an early step in the process of callogenesis. The technique is fast, reproducible, and is a new application for ISSR markers.     

An efficient and rapid transgenic pollen screening and detection method using flow cytometry

Assaying for transgenic pollen, a major vector of transgene flow, provides valuable information and essential data for the study of gene flow and assessing the effectiveness of transgene containment. Most studies have employed microscopic screening methods or progeny analyses to estimate the frequency of transgenic pollen. However, these methods are time-consuming and laborious when large numbers of pollen grains must be analyzed to look for rare transgenic pollen grains. Thus, there is an urgent need for the development of a simple, rapid, and high throughput analysis method for transgenic pollen analysis. In this study, our objective was to determine the accuracy of using flow cytometry technology for transgenic pollen quantification in practical application where transgenic pollen is not frequent. A suspension of non-transgenic tobacco pollen was spiked with a known amount of verified transgenic tobacco pollen synthesizing low or high amounts of green fluorescent protein (GFP). The flow cytometric method detected approximately 75% and 100% of pollen grains synthesizing low and high amounts of GFP, respectively. The method is rapid, as it is able to count 5000 pollen grains per minute-long run. Our data indicate that this flow cytometric method is useful to study gene flow and assessment of transgene containment.     

An improved single-cell cDNA amplification method for efficient high-density oligonucleotide microarray analysis

A systems-level understanding of a small but essential population of cells in development or adulthood (e.g. somatic stem cells) requires accurate quantitative monitoring of genome-wide gene expression, ideally from single cells. We report here a strategy to globally amplify mRNAs from single cells for highly quantitative high-density oligonucleotide microarray analysis that combines a small number of directional PCR cycles with subsequent linear amplification. Using this strategy, both the representation of gene expression profiles and reproducibility between individual experiments are unambiguously improved from the original method, along with high coverage and accuracy. The immediate application of this method to single cells in the undifferentiated inner cell masses of mouse blastocysts at embryonic day (E) 3.5 revealed the presence of two populations of cells, one with primitive endoderm (PE) expression and the other with pluripotent epiblast-like gene expression. The genes expressed differentially between these two populations were well preserved in morphologically differentiated PE and epiblast in the embryos one day later (E4.5), demonstrating that the method successfully detects subtle but essential differences in gene expression at the single-cell level among seemingly homogeneous cell populations. This study provides a strategy to analyze biophysical events in medicine as well as in neural, stem cell and developmental biology, where small numbers of distinctive or diseased cells play critical roles.     

A genomic walking method for screening sequence length polymorphism

We adapted a recently developed nonrestrictional, nonligational genome walking method, Universal Fast Walking (UFW), for detection of length polymorphism in the proximal promoter region of genes. We demonstrate its efficacy at discovering naturally occurring transposition into heat‐shock genes of wild Drosophila and show that it surmounts limitations of simple polymerase chain reaction (PCR) approaches. We further present modifications to the standard UFW protocol and provide some guidelines to improve specificity. Although the resultant banding pattern of a standard UFW can be regarded as a DNA fingerprint, many amplicons result from false priming and not real polymorphisms. We describe ways to distinguish between UFW amplicons and false priming products in a high‐throughput assay.     

一种快速提取基因组DNA的方法

采采用氧化硅超顺磁性纳米磁珠和自己设计的试剂体系及提取流程,建立了一种基因组DNA的快速提取方法,该方法以氧化硅磁珠为固相吸附载体,盐酸胍、 -巯基乙醇和SDS为主要裂解吸附试剂。以全血或培养细胞为实验材料进行基因组DNA的提取结果显示用本文建立的方法提取100 L小鼠抗凝血,可得2～3 g基因组DNA, OD260/OD280为1.8 ± 0.05,其纯度可满足后续的酶切和PCR生物操作要求。该方法整个提取过程只需12分钟,不需特殊实验条件同时可省略蛋白酶K的消化过程和离心操作,适用于一般实验室的需求,是一种操作简便、快速高效的提取方法。     

SiteFinding-PCR: a simple and efficient PCR method for chromosome walking

In this paper, we present a novel PCR method, termed SiteFinding-PCR, for gene or chromosome walking. The PCR was primed by a SiteFinder at a low temperature, and then the target molecules were amplified exponentially with gene-specific and SiteFinder primers, and screened out by another gene-specific primer and a vector primer. However, non-target molecules could not be amplified exponentially owing to the suppression effect of stem–loop structure and could not be screened out. This simple method proved to be efficient, reliable, inexpensive and time-saving, and may be suitable for the molecules for which gene-specific primers are available. More importantly, large DNA fragments can be obtained easily using this method. To demonstrate the feasibility and efficiency of SiteFinding-PCR, we employed this method to do chromosome walking and obtained 16 positive results from 17 samples.     

An efficient method for gene disruption in Neurospora crassa

The frequency with which transforming DNA undergoes homologous recombination at a chromosomal site can be quite low in some fungal systems. In such cases, strategies for gene disruption or gene replacement must either select against ectopic integration events or provide easy screening to identify homologous site, double-crossover insertion events. A protocol is presented for efficient isolation of Neurospora crassa strains carrying a definitive null allele in a target gene. The protocol relies on the presence of a selectable marker flanking a disrupted plasmid-borne copy of the gene, and in the case presented led to a seven-fold enrichment for putative homologous site replacement events. In addition, a polymerase chain reaction assay is utilized for rapid identification of homologous recombinants among the remaining candidates. This protocol was used to identify 3 isolates, out of 129 primary transformants, which have a disruption in the Neurospora ccg-1 gene. The method should be applicable to a variety of fungal systems in which two selectable markers can be expressed, including those in which homologous recombination rates are too low to allow easy identification of homologous site insertions by the more traditional molecular method of Southern analysis. In addition to disrupting target genes for the purpose of generating null mutations, this method is useful for the targeting of reporter gene fusions to a native chromosomal site for the purpose of studying gene regulation.     

Sequence requirements for the stimulation of gene amplification by a mammalian genomic element

HSAG-1 is a 3.4-kb genomic element from a human chronic lymphocytic leukemia--Chinese hamster ovary (CHO) hybrid cell line shown to stimulate the amplification of expression vectors in cis when transfected into a variety of cell lines [McArthur and Stanners, J. Biol. Chem. 266 (1991) 6000-6005]. Subfragments of HSAG-1 were tested for amplification activity by insertion into the vector, pSV2DHFR. The results suggest that multiple positive- and negative-acting elements were present that influenced amplification activity. The deletion of regions believed to contain positive-acting elements decreased or abolished the amplification stimulatory activity of the most active 1.45-kb fragment, supporting this hypothesis. The construction of composite sequences containing multiple positive elements and lacking negative elements, however, failed to enhance the activity; maximum activity was obtained only with the original intact configuration of elements. Two of two CHO HSAG-1-like elements tested had an activity equivalent to HSAG-1, while one of 24 random CHO genomic fragments tested had an activity as high as HSAG-1. The combination of sequence and structural features needed to affect the frequency of gene amplification may therefore be quite common in the mammalian genome.     

An efficient and site-specific gene trimming method

Trimming a DNA strand into a precisely determined fragment can be carried out efficiently by an improved method involving a site-specific trim-primer and a single-stranded DNA template which is generated from a multifunctional vector, pTZ18R, and linearized by using an Eco RI-pTZ18R splinter. A complementary DNA strand is synthesized by DNA polymerase I (Klenow), and the 3'-end of the template upstream from the annealed primer is trimmed by subsequent T4 DNA polymerase reaction. An ATG translation initiator codon or a termination codon can be incorporated into the trim-primer, providing versatility to this single-stranded DNA-initiated gene trimming method that can be applied to subcloning and expression of any DNA fragment with known terminal sequences.     

An efficient method for variable region assembly in the construction of scFv phage display libraries using independent strand amplification

Phage display library technology is a common method to produce human antibodies. In this technique, the immunoglobulin variable regions are displayed in a bacteriophage in a way that each filamentous virus displays the product of a single antibody gene on its surface. From the collection of different phages, it is possible to isolate the virus that recognizes specific targets. The most common form in which to display antibody variable regions in the phage is the single chain variable fragment format (scFv), which requires assembly of the heavy and light immunoglobulin variable regions in a single gene.

In this work, we describe a simple and efficient method for the assembly of immunoglobulin heavy and light chain variable regions in a scFv format. This procedure involves a two-step reaction: (1) DNA amplification to produce the single strand form of the heavy or light chain gene required for the fusion; and (2) mixture of both single strand products followed by an assembly reaction to construct a complete scFv gene. Using this method, we produced 6-fold more scFv encoding DNA than the commonly used splicing by overlap extension PCR (SOE-PCR) approach. The scFv gene produced by this method also proved to be efficient in generating a diverse scFv phage display library. From this scFv library, we obtained phages that bound several non-related antigens, including recombinant proteins and rotavirus particles.     

An efficient method for variable region assembly in the construction of scFv phage display libraries using independent strand amplification

Phage display library technology is a common method to produce human antibodies. In this technique, the immunoglobulin variable regions are displayed in a bacteriophage in a way that each filamentous virus displays the product of a single antibody gene on its surface. From the collection of different phages, it is possible to isolate the virus that recognizes specific targets. The most common form in which to display antibody variable regions in the phage is the single chain variable fragment format (scFv), which requires assembly of the heavy and light immunoglobulin variable regions in a single gene. In this work, we describe a simple and efficient method for the assembly of immunoglobulin heavy and light chain variable regions in a scFv format. This procedure involves a two-step reaction: (1) DNA amplification to produce the single strand form of the heavy or light chain gene required for the fusion; and (2) mixture of both single strand products followed by an assembly reaction to construct a complete scFv gene. Using this method, we produced 6-fold more scFv encoding DNA than the commonly used splicing by overlap extension PCR (SOE-PCR) approach. The scFv gene produced by this method also proved to be efficient in generating a diverse scFv phage display library. From this scFv library, we obtained phages that bound several non-related antigens, including recombinant proteins and rotavirus particles.     

One-base excess adaptor ligation method for walking uncloned genomic DNA

This report describes a novel and efficient method for walking the sequence of a genomic deoxyribonucleic acid (DNA) from a known region to an unknown region based on an oligodeoxynucleotide (oligo) cassette-mediated polymerase chain reaction technique. In this method, genomic DNA is digested by a restriction enzyme that generates a sticky 5′-end, followed by ligation of a one-base excess oligo-adaptor using T4 DNA ligase. The adaptor consists of two complementary oligos that form the same sticky end as the digested genomic DNA fragments, except that the 5′-overhang base overlaps the corresponding 3′-end base of the restriction site. This overhanging terminal base prevents ligation between the adaptors, and the appropriate molar ratio of adaptor to genomic DNA enables specific amplification of the target sequence. T4 DNA ligase catalyzes both the ligation of the phosphorylated overhang base of the adaptor to genomic DNA and the excision of the corresponding 3′-terminal base of the genomic DNA. This sequence-specific exonuclease activity of T4 DNA ligase was confirmed by ligation of an alternative adaptor in which the 5′-terminal base was not consistent with the corresponding 3′-terminal base. Using this technique, the 3′- and 5′-flanking sequences of the catalase gene of the ciliate Paramecium bursaria were determined.