Single-well genotyping of diallelic sequence variations by a two-color ELISA-based oligonucleotide ligation assay.

Single nucleotide substitutions and unique insertions/deletions are the most common form of DNA sequence variation and disease-causing mutation in the human genome. Because of the biological and medical importance of these variations, a wide array of methods have been developed for their typing. We have applied an approach that combines the amplification of polymorphic regions by the polymerase chain reaction (PCR) with a system for typing diallelic variants using an oligonucleotide ligation assay (OLA). In this report, we describe a significant advance in this technology that permits the typing of two alleles in a single microtiter well. By marking each of the allele-specific primers with a unique hapten, i.e. digoxigenin and fluorescein, each OLA reaction can be detected by using hapten specific antibodies that are labeled with different enzyme reporters, alkaline phosphatase or horseradish peroxidase. This system permits the detection of the two alleles using a high throughput format that leads to the production of two different colors. We demonstrate the specificity, sensitivity and ease of data interpretation with this system. Furthermore, we show that multiplex PCR/OLA not only increases the throughput of DNA typing but also increases its accuracy in typing diallelic sequence variations using an approach that can be broadly applied for human genome analysis (in evaluating genotype/phenotype links), in typing infectious agents and in forensic analysis.     

Multiplexed single nucleotide polymorphism genotyping by oligonucleotide ligation and flow cytometry

BACKGROUND: We have developed a rapid, high throughput method for single nucleotide polymorphism (SNP) genotyping that employs an oligonucleotide ligation assay (OLA) and flow cytometric analysis of fluorescent microspheres. METHODS: A fluoresceinated oligonucleotide reporter sequence is added to a "capture" probe by OLA. Capture probes are designed to hybridize both to genomic "targets" amplified by polymerase chain reaction and to a separate complementary DNA sequence that has been coupled to a microsphere. These sequences on the capture probes are called "ZipCodes". The OLA-modified capture probes are hybridized to ZipCode complement-coupled microspheres. The use of microspheres with different ratios of red and orange fluorescence makes a multiplexed format possible where many SNPs may be analyzed in a single tube. Flow cytometric analysis of the microspheres simultaneously identifies both the microsphere type and the fluorescent green signal associated with the SNP genotype. RESULTS: Application of this methodology is demonstrated by the multiplexed genotyping of seven CEPH DNA samples for nine SNP markers located near the ApoE locus on chromosome 19. The microsphere-based SNP analysis agreed with genotyping by sequencing in all cases. CONCLUSIONS: Multiplexed SNP genotyping by OLA with flow cytometric analysis of fluorescent microspheres is an accurate and rapid method for the analysis of SNPs.     

Improved single-strand conformation polymorphism analysis by asymmetric polymerase chain reaction with end-labeled primers

An improved form of single-strand conformation polymorphism (SSCP) assay has been developed for the analysis of bovine major histocompatibility complex class II alleles. The method uses asymmetric polymerase chain reaction (PCR) amplification from each of two end-labeled primers to generate individual single-stranded products that are analyzed by electrophoresis in nondenaturing polyacrylamide gels. This technique gives good resolution of labeled single strands derived from 392-bp bovine DRB exon-2 PCR products, without interference from double-stranded products, and enables assignment of SSCP bands to the individual strands of the template DNA. The allelic groupings defined by this method in a panel of test animals were confirmed by independent typing by restriction fragment-length polymorphism.     

Automatable screening of yeast artificial-chromosome libraries based on the oligonucleotide-ligation assay.

The systematic screening of yeast artificial-chromosome (YAC) libraries is the limiting step in many physical mapping projects. To improve the screening throughput for a human YAC library, we designed an automatable strategy to identify YAC clones containing a specific segment of DNA. Our approach combines amplification of the target sequence from pooled YAC DNA by the polymerase chain reaction (PCR) with detection of the sequence by an ELISA-based oligonucleotide-ligation assay (OLA). The PCR-OLA approach eliminates the use of radioactive isotopes and gel electrophoresis, two of the major obstacles to automated YAC screening. Furthermore, the use of the OLA to test for the presence of sequences internal to PCR primers provides an additional level of sensitivity and specificity in comparison to methods that rely solely on the PCR.     

Dinucleotide Repeat Loci Contribute Highly Informative Genetic Markers to the Human Chromosome 2 Linkage Map

Microsatellite repeat loci can provide informative markers for genetic linkage. Currently, the human chromosome 2 genetic linkage map has very few highly polymorphic markers. Being such a large chromosome, it will require a large number of informative markers for the dense coverage desired to allow disease genes to be mapped quickly and accurately. Dinucleotide repeat loci from two anonymous chromosome 2 genomic DNA clones were sequenced so that oligonucleotide primers could be designed for amplifying each locus using the polymerase chain reaction (PCR). Five sets of PCR primers were also generated from nucleotide sequences in the GenBank Database of chromosome 2 genes containing dinucleotide repeats. In addition, one PCR primer pair was made that amplifies a restriction fragment length polymorphism on the TNP1 gene (Hoth and Engel, 1991). These markers were placed on the CEPH genetic linkage map by screening the CEPH reference DNA panel with each primer set, combining these data with those of other markers previously placed on the map, and analyzing the combined data set using CRI-MAP and LINKAGE. The microsatellite loci are highly informative markers and the TNP1 locus, as expected, is only moderately informative. A map was constructed with 38 ordered loci (odds 1000:1) spanning 296 cM (male) and 476 cM (female) of chromosome 2 compared with 306 cM (male) and 529 cM (female) for a previous map of 20 markers.     

Linkage mapping of D21S171 to the distal long arm of human chromosome 21 using a polymorphic (AC)n dinucleotide repeat

Summary An (AC)_n repeat within the anonymous DNA sequence D21S171 was shown to be highly polymorphic in members of the 40 Centre d'Etude du Polymorphisme Humain (CEPH) families. Ten different alleles at this marker locus were detected by electrophoresis on polyacrylamide gels of DNA amplified by the polymerase chain reaction (PCR) using primers flanking the (AC)_n repeat. The observed heterozygosity was 66%. PCR amplification of DNA from somatic cell hybrids mapped D21S171 to human chromosome 21, and linkage analysis localized this marker close to the loci CD18, PFKL, D21S113 and D21S112 in chromosomal band 21q22.3. In CEPH family 12 a de novo allele has been observed in a maternally derived chromosome.     

Overall Informativity,OI, in DNA Polymorphisms Revealed by inter-AluPCR: Detection of Genomic Rearrangements

We studied two systems of multilocus markers revealed by PCR using primers directing amplification betweenAlurepeats in a tail-to-tail orientation. Genomic polymorphisms were detected as the presence or absence of the electrophoretic bands representing DNA fragments of a given length. A total of 104 such fragments segregating as Mendelian markers in a panel of eight CEPH families were analyzed by two-point linkage analysis. Fifty-one of these fragments were localized with respect to CEPH markers; they represented 33 loci, 7 of which were multiallelic. Locus-specific oligonucleotides were developed and used as hybridization probes to identify the mapped loci within a complex pattern of inter-AluPCR products. A great proportion of inter-AluPCR polymorphisms represented length variants within amplified DNA segments, while others were presumably due to mutations within the priming sites. To describe the expected number of informative loci per typing experiment we introduced a parameter called overall informativity (OI), which provides a single measure of the multiplex ratio and the informativity of markers contributing to a multilocus system (OIof a single locus is equivalent to its heterozygosity and cannot exceed 0.5 for a biallelic codominant marker). HighOIvalues (5.8 and 11.5) of the two presented systems of inter-AluPCR markers of random chromosomal distribution render them suitable for mapping genomic rearrangements such as genomic deletions in tumoral tissues. This was illustrated by the detection of loss of heterozygosity in the 9q22–qter region in sporadic colon cancer.     

Multiple-locus variable-number tandem repeat analysis of Legionella pneumophila using multi-colored capillary electrophoresis

Several methods for typing of Legionella pneumophila exist, one of which is an 8-locus variable-number of tandem repeats analysis (MLVA). This method is based on separating and sizing amplified VNTR PCR products by agarose gel electrophoresis. In the present work, the existing L. pneumophila MLVA-8 assay is adapted to capillary electrophoresis. The assay was multiplexed by using multiple fluorescent labeling dyes and tested on a panel of L. pneumophila strains with known genotypes. The results from the capillary electrophoresis-based assay are shown to be equivalent to, and in a few cases more sensitive than, the gel-based genotyping assay. The assay presented here allows for a swift, automated and precise typing of L. pneumophila from patient or environmental samples and represents an improvement over the current gel-based method.     

Genetic mapping of four dinucleotide repeat loci, DXS453, DXS458, DXS454, and DXS424, on the X chromosome using multiplex polymerase chain reaction.

Dinucleotide CA repeat sequences in the human genome have been shown to be highly polymorphic due to variation in the length of the repeat-containing segment. Therefore, these markers can serve as anchor loci in the construction of a high-resolution genetic map of the human genome. In this study, we improved the efficiency of typing dinucleotide repeats using multiplex polymerase chain reaction (PCR). Dinucleotide repeat sequences of four previously identified markers (DXS453, DXS458, DXS454, and DXS424) on the long arm of the X chromosome were simultaneously amplified in a single PCR reaction. This multiplex PCR was applied to genotype individuals from the 40 CEPH reference families, and the genotypic data were used to determine the map position of the four loci with respect to eight reference markers in the Xq region by linkage analysis.     

A single multiplex PCR and SNaPshot minisequencing reaction of 42 SNPs to classify admixture populations into mitochondrial DNA haplogroups

SNaPshot minisequencing reaction is in increasing use because of its fast detection of many polymorphisms in a single assay. In this work we described a highly sensitive single nucleotide polymorphisms (SNPs) typing method with detection of 42 mitochondrial DNA (mtDNA) SNPs in a single PCR and SNaPshot multiplex reaction, in order to allow haplogroup classification in Latin American admixture population. We validated the panel typing 160 Brazilian individuals. Complete SNP profiles were obtained from 10 pg of total DNA. We conclude that it is possible to build and genotype more than forty mtDNA SNPs in a single multiplex PCR and SNaPshot reaction, with sensitivity and reliability, resolving haplogroup classification in admixture populations.     

Genetic mapping of the beta 1 GABA receptor gene to human chromosome 4, using a tetranucleotide repeat polymorphism.

As more coding loci for functional human genes are described, there is a growing need to identify DNA polymorphisms in specific genes. By examining DNA sequences within the introns of the beta 1 subunit of the gamma-aminobutyric acid receptor gene, GABARB1, we found a tetranucleotide repeat sequence (GATA). Amplification of this region by using PCR revealed seven alleles and a high degree of polymorphism (PIC = .75) in human populations. DNAs from the CEPH families were typed for the GABARB1 intron polymorphism and were analyzed with respect to 20 linked markers on chromosome 4. The results permit placement of GABARB1 on the linkage map of chromosome 4, between D4S104 and ALB. These results affirm that sequence analysis of noncoding segments included within or adjacent to functional genes has value as a strategy to detect highly informative polymorphisms.     

基于荧光定量PCR扩增反应的SNP测定法

建立一种利用荧光定量PCR扩增反应进行单核苷酸多态性(SNP)快速测定的方法.以人β肾上腺素受体2基因中的Arg16Gly为研究对象,利用荧光染料SYBRGreenⅠ标记定量PCR产物,通过PCR生长曲线和融解曲线分析结果进行SNP分型.为提高SNP测定的特异性,分别在野生型和突变型等位基因的特异性引物3′端倒数第3个碱基位置,引入了一个人为错配碱基,使引物的错误延伸率显著降低,大大提高了SNP分析的准确性.通过DNA测序验证荧光定量PCR对β肾上腺素受体2基因中Arg16Gly分型结果的准确率.实验结果表明,所建立的方法操作简便,结果准确,适合进行大规模样品的SNP检测工作.     

A polymorphic (CA)n repeat element maps the human glucokinase gene (GCK) to chromosome 7p.

A compound imperfect dinucleotide repeat element, [CA]4TTTGT[CT]7[CA]9AA[CA]4CCACATA[CA]3, was found approximately 10 kb 3' to the human glucokinase gene (GCK) from analysis of contiguous genomic DNA obtained from a bacteriophage lambda chromosome walk. Direct human genomic sequencing revealed the source of polymorphism to be variable numbers of CT and CA repeats. Altogether six alleles that range in length from +10 to -15 nucleotides compared to the most common (Z) allele have been identified. Alleles Z, Z + 2, and Z + 4 were present in American Blacks, Pima Indians, and Caucasians, with somewhat varied frequencies among the groups. Two alleles, Z + 10 and Z - 15, appear to be unique to American Blacks, while a Z + 6 allele was observed only in the Caucasian population studied. Observed heterozygosity of the polymorphism in the CEPH reference pedigree collection is 44% and the PIC 0.44. The polymorphism is assayed by PCR amplification and resolution of 32P-end-labeled products (ranging in length from 180 to 205 bp) on denaturing polyacrylamide sequencing gels. Using the PCR assay, the human glucokinase gene was physically localized to chromosome 7 in a panel of rodent/human somatic cell lines. Genetic analysis in CEPH pedigrees placed the dinucleotide repeat element, and thereby the human glucokinase gene, on chromosome 7p between TCRG and a RFLP locus D7S57. The glucokinase dinucleotide repeat genetic marker can now be used to assess the role of the glucokinase gene in diabetes by population association studies. In addition, this repeat marker and others flanking it on chromosome 7 can be used in linkage studies with families segregating the disorder.     

Allelic discrimination using fluorogenic probes and the 5′ nuclease assay

Large-scale screening for known polymorphisms will require techniques with few steps and the ability to automate each of these steps. In this regard, the 5′ nuclease, or TaqMan, PCR assay is especially attractive. A fluorogenic probe, consisting of an oligonucleotide labeled with both a fluorescent reporter dye and a quencher dye, is included in a typical PCR. Amplification of the probe-specific product causes cleavage of the probe, generating an increase in reporter fluorescence. By using different reporter dyes, cleavage of allele-specific probes can be detected in a single PCR. The 5′ nuclease assay has been successfully used to discriminate alleles that differ by a single base substitution. Guidelines have been developed so that an assay for any single nucleotide polymorphism (SNP) can be quickly designed and implemented. All assays are performed using a single reaction buffer and single thermocycling protocol. Furthermore, a standard method of analysis has been developed that enables automated genotype determination. Applications of this assay have included typing a number of polymorphisms in human drug metabolism genes.     

Single-nucleotide polymorphism genotyping identifies a locally endemic clone of methicillin-resistant Staphylococcus aureus

We developed, tested, and applied a TaqMan real-time PCR assay for interrogation of three single-nucleotide polymorphisms that differentiate a clade (termed 't003-X') within the radiation of methicillin-resistant Staphylococcus aureus (MRSA) ST225. The TaqMan assay achieved 98% typeability and results were fully concordant with DNA sequencing. By applying this assay to 305 ST225 isolates from an international collection, we demonstrate that clade t003-X is endemic in a single acute-care hospital in Germany at least since 2006, where it has caused a substantial proportion of infections. The strain was also detected in another hospital located 16 kilometers away. Strikingly, however, clade t003-X was not found in 62 other hospitals throughout Germany nor among isolates from other countries, and, hence, displayed a very restricted geographical distribution. Consequently, our results show that SNP-typing may be useful to identify and track MRSA clones that are specific to individual healthcare institutions. In contrast, the spatial dissemination pattern observed here had not been resolved by other typing procedures, including multilocus sequence typing (MLST), spa typing, DNA macrorestriction, and multilocus variable-number tandem repeat analysis (MLVA).     

Short Oligonucleotide Tandem Ligation Assay for Genotyping of Single-Nucleotide Polymorphisms in Y Chromosome

We propose a novel universal methodology, Short Oligonucleotide Tandem Ligation Assay (SOTLA), for SNP genotyping. SOTLA is based on using a tandem of short oligonucleotide (TSO) probes consisting of three fragments: the core oligonucleotide and two flanking oligomers, one of which is immobilized onto a solid support and another one contains the biotin label. TSO is self-associated on a complementary DNA template, forms the complex containing two nicks, which are efficiently ligated with DNA ligase giving biotinylated oligonucleotide covalently bound to polymer beads. No ligation of TSO on an imperfect DNA template bearing the base substitution in the core binding site is occurred. We used SOTLA for the highly selective SNP analysis in different DNA fragments of human Y chromosome. Comparison of SOTLA results with those of PCR-RFLP and allele-specific PCR techniques demonstrates that SOTLA ensures the univocal reliable SNP analysis in different PCR fragments varying in length and base composition. The fundamental difference between SOTLA and well known OLA approaches while using T4 DNA ligase is that the accuracy of SNP analysis in OLA is ensured only by the specificity of ligase while that in SOTLA is provided by the specificity of both ligation and hybridization of TSO probes.     

CEPH maps.

There are CEPH genetic maps on each homologous human chromosome pair. Genotypes for these maps have been generated in 88 laboratories that receive DNA from a reference panel of large nuclear pedigrees/families supplied by the Centre d'Etude du Polymorphisme Humain. These maps serve as useful tools for the localization of both disease genes and other genes of interest.     

Discrimination between alpha-satellite DNA sequences from chromosomes 21 and 13 by using polymerase chain reaction.

alpha-Satellite subfamilies from chromosomes 21 and 13 are almost identical in sequence and cannot be distinguished from each other by hybridization techniques. A general method based on membrane-bound PCR is described here, allowing the discrimination of alpha-satellite DNA sequences from each of these two chromosomes, after detection by Southern blot hybridization. The PCR conditions were developed using somatic hybrid DNAs. The method was tested in membrane-bound PCR by using the alpha-satellite bands from a Southern blot of a CEPH family. The chromosomal origin of these bands, previously determined by linkage analysis, was confirmed by this method.     

DNA typing of primate major histocompatibility complex (Mhc)-DQA1 locus by PCR and dot blot hybridization.

Non-human primates (NHPs) are increasingly utilized as models to investigate different aspects of immune responses against self (autoimmunity) and foreign antigens. These animals provide valuable models for testing the efficacy of candidate vaccines against pathogens such as human immunodeficiency virus (HIV) and also fertility regulating agents (immunocontraceptives). In order to fully understand the effects of vaccination, it may be necessary to elucidate the immunogenetic background of these animals. The major histocompatibility complex (Mhc) molecules play an important role in the generation of effective immune responses. Serological techniques have been used in the identification of human leukocyte antigens (HLA) necessary for cross-matching organs and tissues for transplantation. However, the application of this technique for typing monkey Mhc alleles has been hampered by unavailability of well characterized immunological reagents. Polymerase chain reaction (PCR)-based techniques such as restriction fragment length polymorphism (RFLP) and sequence-specific oligonucleotide probe hybridization (SSOP) have been extensively used for typing HLA-DP, DQ and DR alleles. A commercially available Kit (AmpliTypeR) designed for amplification and typing of HLA DQalpha alleles is routinely used in typing DNA samples for forensic casework. In the present study, we have evaluated this kit for possible application in routine typing of primate DQA1 alleles. Genomic DNA from ten African primate species (23 individuals) was isolated from peripheral blood lymphocytes and polymorphic second exon of DQA1 locus amplified using GH26 and GH27 PCR primers. The PCR products were hybridized on a nylon membrane containing immobilized sequence-specific oligonucleotide probes. Our results show seven of the nine probes hybridizing with primate DQA1 alleles, indicating that typing of equivalent primate alleles can be accomplished at lower stringency conditions. However, it may be necessary to design additional oligonucleotides probes (based on available primate DQA1 sequences) to improve the discriminating power of this kit for use in routine typing of Old World monkey DQA1 alleles.