Preparing long probes by an asymmetric polymerase chain reaction-based approach for multiplex ligation-dependent probe amplification

To clearly discriminate the results of simultaneous screening and quantification of up to 40 different targets–DNA sequences, long probes from 100 to 500 nt, rather than smaller or similar-sized synthetic ones, were adopted for multiplex ligation-dependent probe amplification (MLPA). To prepare the long probes, asymmetric polymerase chain reaction (PCR) was employed to introduce non-complementary stuffers in between the two parts of the MLPA probe with specially designed primers, then restriction enzymes were selected to digest the double-stranded DNAs, and finally polyacrylamide gel electrophoresis was used to purify the single-stranded DNAs (i.e., the long probes). By using this approach, 12 long probes were prepared and used to identify genetically modified (GM) maize. Our experimental results show that the prepared long probes were in full accordance with the designed ones and could be assembled in 4-, 7-, and 10-plex MLPA analysis without losing result specificity and accuracy, showing they were as effective and reliable in MLPA analysis as those prepared with M13-derived vectors. This novel asymmetric PCR-based approach does not need expensive equipment, special reagents, or complicated operations when compared with previous methods. Therefore, our new approach could make MLPA analysis more independent, efficient, and economical.     

Polymerase chain reaction-based methods of DNA methylation analysis

DNA methylation is the main epigenetic modification in humans, and changes in methylation patterns play an important role in tumorigenesis. Hypermethylation of normally unmethylated CpG islands in the promoter regions often occurs in important tumor suppressor genes, DNA repair genes, and metastasis inhibitor genes. The changes of methylation status of various gene promoters seem to be a common feature of malignant cells and these changes can occur early in the progression process. Therefore detection of aberrant promoter hypermethylation of cancer-related genes may be useful for cancer diagnosis or detection of cancer recurrence. The purpose of this review is to provide a summary of the most commonly used techniques for the study of DNA methylation. Current scientific literature involving methylation detection methods was reviewed with an emphasis on polymerase chain reaction (PCR)-based detection methods. The current methodologies may be broadly classed into PCR-based methylation assays and non-PCR-based methylation assays. The problems and advantages of the different methods for detecting aberrant methylation are discussed. As the number of genes known to be hypermethylated in cancer is growing, the detection of aberrant promoter region methylation will be a promising approach for using DNA-based markers for the early detection of human cancers. Many techniques, especially PCR-based methylation assay techniques, make it practical to use these new methylation biomarkers in early cancer diagnosis.     

mPSQed: a software for the design of multiplex pyrosequencing assays

Molecular-based diagnostic assays are the gold standard for infectious diseases today, since they allow a rapid and sensitive identification and typing of various pathogens. While PCR can be designed to be specific for a certain pathogen, a subsequent sequence analysis is frequently required for confirmation or typing. The design of appropriate PCR-based assays is a complex task, especially when conserved discriminating polymorphisms are rare or if the number of types which need to be differentiated is high. One extremely useful but underused method for this purpose is the multiplex pyrosequencing technique. Unfortunately there is no software available to aid researchers in designing multiplex pyrosequencing assays. Here, we present mPSQed (Multiplex PyroSeQuencing EDitor), a program targeted at closing this gap. We also present the design of an exemplarily theoretical assay for the differentiation of human adenovirus types A-F using two pyrosequencing primers on two distinct PCR products, designed quickly and easily using our software.     

Digital Detection of Multiple Minority Mutants and Expression Levels of Multiple Colorectal Cancer-Related Genes Using Digital-PCR Coupled with Bead-Array

To simultaneously analyze mutations and expression levels of multiple genes on one detection platform, we proposed a method termed “multiplex ligation-dependent probe amplification–digital amplification coupled with hydrogel bead-array” (MLPA–DABA) and applied it to diagnose colorectal cancer (CRC). CRC cells and tissues were sampled to extract nucleic acid, perform MLPA with sequence-tagged probes, perform digital emulsion polymerase chain reaction (PCR), and produce a hydrogel bead-array to immobilize beads and form a single bead layer on the array. After hybridization with fluorescent probes, the number of colored beads, which reflects the abundance of expressed genes and the mutation rate, was counted for diagnosis. Only red or green beads occurred on the chips in the mixed samples, indicating the success of single-molecule PCR. When a one-source sample was analyzed using mixed MLPA probes, beads of only one color occurred, suggesting the high specificity of the method in analyzing CRC mutation and gene expression. In gene expression analysis of a CRC tissue from one CRC patient, the mutant percentage was 3.1%, and the expression levels of CRC-related genes were much higher than those of normal tissue. The highly sensitive MLPA–DABA succeeds in the relative quantification of mutations and gene expressions of exfoliated cells in stool samples of CRC patients on the same chip platform. MLPA–DABA coupled with hydrogel bead-array is a promising method in the non-invasive diagnosis of CRC.     

Designing a simple multiplex ligation-dependent probe amplification （MLPA） assay for rapid detection of copy number variants in the genome

Copy number variants （CNVs） are pervasive in the human genome and are responsible for many Mendelian diseases and genomic disorders. The detection of CNVs is an essential element of a complete mutation screening strategy. Many techniques have been developed for gene dosage testing. Multiplex ligation-dependent probe amplification （MLPA） is a robust, easy and flexible technique that can detect both deletions and duplications for more than 40 loci in one assay. It has been widely used in research and diagnostic laboratories. We routinely develop our own MLPA assays for quick validation of array comparative genomic hybridization （CGH） findings. Here we discuss the general principles and critical aspects of MLPA assay development and validation using all synthetic MLPA probes. We believe that MLPA will play important roles in the rapid detection of genomic disorders associated with genomic imbalances, the confirmation of pathogenic mutations involving exonic deletions/duplications, CNV genotyping and population frequency analysis of CNVs.     

Methylation-specific multiplex ligation-dependent probe amplification analysis of subjects with chromosome 15 abnormalities

Prader-Willi syndrome (PWS) and Angelman syndrome (AS) are neurodevelopmental disorders caused by loss of expression of imprinted genes from the 15q11-q13 region. They arise from similar defects in the region but differ in parent of origin. There are two recognized typical 15q11-q13 deletions depending on size and several diagnostic assays are available but each has limitations. We evaluated the usefulness of a methylation-specific multiplex ligation-dependent probe amplification (MLPA) kit consisting of 43 probes to detect copy number changes and methylation status in the region. We used the MLPA kit to genotype 82 subjects with chromosome 15 abnormalities (62 PWS, 10 AS and 10 individuals with other chromosome 15 abnormalities) and 13 with normal cytogenetic findings. We developed an algorithm for MLPA probe analysis which correctly identified methylation abnormalities associated with PWS and AS and accurately determined copy number in previously assigned genetic subtypes including microdeletions of the imprinting center. Furthermore, MLPA analysis identified copy number changes in those with distal 15q deletions and ring 15s. MLPA is a relatively simple, cost-effective technique found to be useful and accurate for methylation status, copy number and analysis of genetic subtype in PWS and AS, as well as other chromosome 15 abnormalities.     

Simultaneous MLPA-based multiplex point mutation and deletion analysis of the <Emphasis Type="Italic">Dystrophin</Emphasis> gene

The Multiplex Ligation-dependent Probe Amplification assay (MLPA) is the method of choice for the initial mutation screen in the analysis of a large number of genes where partial or total gene deletion is part of the mutation spectrum. Although MLPA dosage probes are usually designed to bind to normal DNA sequence to identify dosage imbalance, point mutation-specific MLPA probes can also be made. Using the dystrophin gene as a model, we have designed two MLPA probe multiplexes that are specific to a number of commonly listed point mutations in the Leiden dystrophin point mutation database (http://www.dmd.nl). The point mutation probes are designed to work simultaneously with two widely used dystrophin MLPA multiplexes, allowing both full dosage analysis and partial point mutation analysis in a single test. This approach may be adapted for other syndromes with well defined common point mutations or polymorphisms.     

Multiplex ligation-dependent probe amplification using a completely synthetic probe set

The recent development of multiplex ligation-dependent probe amplification (MLPA) has provided an efficient and reliable assay for dosage screening of multiple loci in a single reaction. However, a drawback to this method is the time-consuming process of generating a probe set by cloning in single-stranded bacteriophage vectors. We have developed a synthetic probe set to screen for deletions in a region spanning 18.5 Mb within chromosome 3q. In a pilot study, we tested 15 synthetic probes on 4 control samples and on 2 patients previously found to possess a heterozygous deletion in the region 3q26-q28. These synthetic probes detected deletions at all previously known deleted loci. Furthermore, using synthetic probes, the variability of results within samples was similar to that reported for commercially available M13-derived probes. Our results demonstrate that this novel approach to MLPA provides a generic solution to the difficulties of probe development by cloning; such synthetically generated probes may be used to screen a large number of loci in a single reaction. We conclude that the use of synthetic probes for MLPA is a rapid, robust, and efficient alternative for research (and potentially diagnostic) deletion and duplication screening of multiple genomic loci.     

Rapid genetic characterization of poly(hydroxyalkanoate) synthase and its applications

Microorganisms containing short-chain-length (scl-) or medium-chain-length (mcl-) poly(hydroxyalkanoates) (PHAs) are commonly screened by applying rapid staining methods using lipophilic reagents. These methods provide powerful means for general screening of organisms actively producing and accumulating PHAs. The Southern blot hybridization method additionally allows the identification of potential PHA-producing microorganisms. Polymerase chain reaction (PCR)-based detection methods further afford rapid and sensitive means to screen for PHA biosynthesis genes. Specific PCR assays had been developed for the simultaneous or individual detection of the class II mcl-PHA synthase genes of Pseudomonas. The amplicons (approximately 0.54 kb) can be directly sequenced or used as probes for hybridization studies. The sequence information can further be used to initiate chromosome walking for an eventual cloning of the complete PHA biosynthesis operon. In addition, the amplification pattern and sequence data can be used to differentiate subgroups of organisms, as demonstrated for P. corrugata and P. mediterranea. Other researchers reported PCR methods for the detection of scl-PHA synthase genes and those of Bacillus spp., thus greatly expanding the types of PHA synthase gene and the organisms that can be characterized by this approach. The vast sequence information obtainable through PCR-based studies of various PHA synthase operons should facilitate the identification or construction of new PHA synthases capable of synthesizing novel PHAs.     

Detection of bacterial pathogens in environmental samples using DNA microarrays

Polymerase chain reaction (PCR) is an important tool for pathogen detection, but historically, it has not been possible to accurately identify PCR products without sequencing, Southern blots, or dot-blots. Microarrays can be coupled with PCR where they serve as a set of parallel dot-blots to enhance product detection and identification. Microarrays are composed of many discretely located probes on a solid substrate such as glass. Each probe is composed of a sequence that is complimentary to a pathogen-specific gene sequence. PCR is used to amplify one or more genes and the products are then hybridized to the array to identify species-specific polymorphism within one or more genes. We illustrate this type of array using 16S rDNA probes suitable for distinguishing between several salmonid pathogens. We also describe the use of microarrays for direct detection of either RNA or DNA without the aid of PCR, although the sensitivity of these systems currently limits their application for pathogen detection. Finally, microarrays can also be used to "fingerprint" bacterial isolates and they can be used to identify diagnostic markers suitable for developing new PCR-based detection assays. We illustrate this type of array for subtyping an important food-borne pathogen, Listeria monocytogenes.     

Discovery of biomarkers for gastric cancer: a proteomics approach

Gastric cancer is the second leading cause of cancer-related deaths worldwide. Although many treatment options exist for patients with gastric tumors, the incidence and mortality rate of gastric cancer are on the rise. The early stages of gastric cancer are non-symptomatic, and the treatment response is unpredictable. This situation is further aggravated by a lack of diagnostic biomarkers that can aid in the early detection and prognosis of gastric cancer and in the prediction of chemoresistance. Moreover, clinical surgical specimens are rarely obtained, and traditional biomarkers of gastric cancer are not very effective. Many studies in the field of proteomics have contributed to the discovery and establishment of powerful diagnostic tools (e.g., ProteinChip array) in the management of cancer. The evolution in proteomic technologies has not only enabled the screening of a large number of samples but also enabled the identification of pathologically significant proteins, such as phosphoproteins, and the quantitation of difference in protein expression under different conditions. Multiplexed assays are used widely to accurately fractionate various complex samples such as blood, tissue, cells, and Helicobacter pylori-infected specimens to identify differentially expressed proteins. Biomarker detection studies have substantially contributed to the areas of secretome, metabolome, and phosphoproteome. Here, we review the development of potential biomarkers in the natural history of gastric cancer, with specific emphasis on the characteristics of target protein convergence.     

Comparing two diagnostic laboratory tests for Williams syndrome: fluorescent in situ hybridization versus multiplex ligation-dependent probe amplification

Most people with Williams syndrome (WS) have a heterozygous 1.55 Mb deletion on chromosome 7q11.23. For diagnostic purposes, fluorescence in situ hybridisation (FISH) with commercial FISH probes is commonly used to detect this deletion. We investigated whether multiplex ligation-dependent probe amplification (MLPA) is a reliable alternative for FISH. The MLPA kit (SALSA P029) contains probes for eight genes in the WS critical region: FKBP6, FZD9, TBL2, STX1A, ELN, LIMK1, RFC2, and CYLN2. The experimental FISH assay that was used consists of four probes covering the WS critical region. A total number of 63 patients was tested; in 53 patients, a deletion was detected both with FISH and MLPA(P029), in 10 patients both techniques failed to demonstrate a deletion. In only one patient, a deletion was detected which was not previously detected by two commercial FISH probes. This patient appeared to carry a small, atypical deletion. We conclude that MLPA is a reliable technique to detect WS. Compared with FISH, MLPA is less time consuming and has the possibility to detect also smaller, atypical deletions and duplications in the WS critical region.     

Method for systematic targeted isolation of homologous cDNA fragments in a multiplex format

In this study, a two-step method for systematic multiplex cloning of homologous cDNAs from related species was developed. The first step, called MUCH (multiplex cloning of homologous genes), is cloning of partial but authentic cDNA fragments of homologous cDNAs by hybridization to arrayed cRNA probes of specified genes on a nylon membrane, followed by PCR amplification of the hybridized fragments. The second step is PCR-based screening of a library that contains longer cDNA inserts based on the sequences obtained in the first step. To evaluate this method, we tried to isolate mouse counterparts of 53 human large cDNAs by MUCH and could successfully isolate 32 mouse counterpart cDNAs from a single library. Complete sequencing of two mouse cDNAs isolated by PCR-based screening further demonstrated that this method enabled us to isolate multiple homologous cDNAs in parallel. We thus expect that this method could be applied to high-throughput cloning of homologous cDNAs in related species.     

Improved PCR-Based Detection of Soil Transmitted Helminth Infections Using a Next-Generation Sequencing Approach to Assay Design

BackgroundThe soil transmitted helminths are a group of parasitic worms responsible for extensive morbidity in many of the world’s most economically depressed locations. With growing emphasis on disease mapping and eradication, the availability of accurate and cost-effective diagnostic measures is of paramount importance to global control and elimination efforts. While real-time PCR-based molecular detection assays have shown great promise, to date, these assays have utilized sub-optimal targets. By performing next-generation sequencing-based repeat analyses, we have identified high copy-number, non-coding DNA sequences from a series of soil transmitted pathogens. We have used these repetitive DNA elements as targets in the development of novel, multi-parallel, PCR-based diagnostic assays.Conclusions/SignificanceThe utilization of next-generation sequencing-based repeat DNA analysis methodologies for the identification of molecular diagnostic targets has the ability to improve assay species-specificity and limits of detection. By exploiting such high copy-number repeat sequences, the assays described here will facilitate soil transmitted helminth diagnostic efforts. We recommend similar analyses when designing PCR-based diagnostic tests for the detection of other eukaryotic pathogens.     

Transgene integration in hair follicles and peripheral blood cells measured by in vitro DNA amplification and fluorescence in situ hybridization

Screening of animals to detect the presence of integrated DNA sequences is an essential component of transgenic mouse generation. Rapid and sensitive detection techniques to facilitate identification of transgenic animals for biological studies or subsequent breeding programs are desirable. Most transgenics are generated on F1 backgrounds, thus determination of the histocompatibility status of neonates provides important diagnostic information for establishing congenic colonies. We describe the application of two assays, in vitro DNA amplification using the polymerase chain reaction (PCR) and fluorescence in situ hybridization with biotinylated DNA probes, to facilitate rapid detection of transgenes and their chromosomal integration patterns in young mice. A noninvasive PCR-based assay to detect the transgene in DNA contained in detergent-extracted hair follicles was developed for rapid screening. A total of 147 mice derived from F2, F3, and F4 generations of C57BL x F1 (globin transgenics) were assayed to determine whether they carried a globin transgene. Characterization of animals by PCR-based amplification of the transgene was compared with that obtained using standard Southern analysis of DNA extracted from tails. Categorization of animals as positive (carrying the transgene) or negative using PCR was performed successfully in the initial assay with 95% of the animals. Fluorescence in situ hybridization with a DNA probe showing homology with a portion of the transgene was performed on metaphase and interphase cells to determine the integration pattern of the transgene. Our data showed that the transgene was integrated in a single chromosome. These techniques should facilitate rapid identification of transgenic animals and characterization of the genomic transgene integration patterns.     

Molecular tools for speciation and epidemiological studies of Acanthamoeba

Current diagnostic methods for Acanthamoeba identification rely heavily on light microscopic techniques that do not provide sufficient information about the identification of Acanthamoeba at the species level, thus delaying accurate identification of the infective agent. Here we report the use of polymerase chain reaction (PCR)-based restriction enzyme analyses to detect and speciate Acanthamoeba from both clinical and environmental sources by comparing their restriction endonuclease patterns. Significant diversity was observed between and within morphologically defined Acanthamoeba species. The usefulness of PCR-based assays and other available diagnostic methods is discussed. Received: 15 August 2001 / Accepted: 15 October 2001     

Identification of Prognostic Biomarkers by Combined mRNA and miRNA Expression Microarray Analysis in Pancreatic Cancer

Pancreatic cancer is the fourth leading cause for cancer-related death, and early diagnosis is one key to improve the survival rate of this disease. Molecular biomarkers are an important method for diagnostic use in pancreatic cancer. We used data from three mRNA microarray datasets and a microRNA dataset (GSE16515, GSE15471, GSE28735, and GSE41372) to identify potential key genes. Differentially expressed genes (DEGs) and microRNAs (DEMs) were identified. Functional, pathway enrichment, and protein-protein interaction analyses were performed on common DEGs across all datasets. The target genes of the DEMs were identified. DEMs targets that were also DEGs were further scrutinized using overall survival analysis. A total of 236 DEGs and 21 DEMs were identified. There were a total of four DEGs (ECT2, NR5A2, NRP2, and TGFBI), which were also predicted target genes of DEMs. Overall survival analysis showed that high expression levels of three of these genes (ECT2, NRP2, and TGFBI) were associated with poor overall survival for pancreatic cancer patients. The basic expression of DEGs in pancreas stood lower level in various organ tissues. The expression of ECT2 and NRP2 was higher in different pancreatic cancer cell lines than normal pancreas cell line. Knockout of ECT2 by Crispr Cas9 gene editing system decreased proliferation and migration ability in pancreatic cancer cell line MiaPaCa2. In conclusion, we think that data mining method can do well in biomarker screening, and ECT2 and NRP2 can play as potential biomarker or therapy target by Crispr Cas9 in pancreatic cancer.     

High-sensitivity hybridization assay for quantitation of residual E. coli DNA

Impurity assays for recombinant protein therapeutics are essential to ensure batch-to-batch consistency and to meet the FDA's criteria for a well-characterized biopharmaceutical. For determination of residual host cell DNA, membrane hybridization assays utilizing radiolabeled DNA probes prepared from the host cell's genomic DNA have traditionally been used for products derivedfrom bacterial expression systems to obtain the required low picogram sensitivity. Nonradioactive methods, while desirable to eliminate radioactive waste disposal and safety issues, typically suffer from poor sensitivity and high backgrounds. We report the development of a suitably sensitive, nonradioactive assay to quantitate residual E. coli DNA levels in purified protein drugs by means of a slot-blot hybridization method. The assay utilizes digoxigenin-labeled E. coli DNA probes and SuperSignal chemiluminescent substrate. The optimized chemiluminescent hybridization assay has both low background and high sensitivity, allowing routine detection of 2.5 pg E. coli DNA. The method can be tailored for detection/quantitation of DNA contamination in recombinant protein products expressed in E. coli or other bacterial expression systems.     

Quantitative analysis of DNA methylation after whole bisulfitome amplification of a minute amount of DNA from body fluids

Cell-free circulating DNA isolated from the plasma of individuals with cancer has been shown to harbor cancer-associated changes in DNA methylation, and thus it represents an attractive target for biomarker discovery. However, the reliable detection of DNA methylation changes in body fluids has proven to be technically challenging. Here we describe a novel combination of methods that allows quantitative and sensitive detection of DNA methylation in minute amounts of DNA present in body fluids (quantitative Methylation Analysis of Minute DNA amounts after whole Bisulfitome Amplification, qMAMBA). This method involves genome-wide amplification of bisulphite-modified DNA template followed by quantitative methylation detection using pyrosequencing and allows analysis of multiple genes from a small amount of starting DNA. To validate our method we used qMAMBA assays for four genes and LINE1 repetitive sequences combined with plasma DNA samples as a model system. qMAMBA offered high efficacy in the analysis of methylation levels and patterns in plasma samples with extremely small amounts of DNA and low concentrations of methylated alleles. Therefore, qMAMBA will facilitate methylation studies aiming to discover epigenetic biomarkers, and should prove particularly valuable in profiling a large sample series of body fluids from molecular epidemiology studies as well as in tracking disease in early diagnostics.