Microarray-based method for genotyping of functional single nucleotide polymorphisms using dual-color fluorescence hybridization

Genetic mechanisms of neurodevelopmental disorders

Neurodevelopmental disorders encompass a broad range of conditions, which include autism, epilepsy, and intellectual disability. These disorders are relatively common and have associated clinical and genetic heterogeneity. Technology has driven much of our understanding of these diseases and their genetic underlying mechanisms, particularly highlighted by the study of large cohorts with comparative genomic hybridization and the more recent implementation of next-generation sequencing (NGS). The mapping of copy number variants throughout the genome has highlighted the recurrent, highly penetrant, de novo variation in syndromic forms of neurodevelopmental disease. NGS of affected individuals and their parents led to a dramatic shift in our understanding as these studies showed that a significant proportion of affected individuals carry rare, de novo variants within single genes that explain their disease presentation. Deep sequencing studies further implicate mosaicism as another mechanism of disease. However, it has also become clear that while rare variants explain a significant proportion of sporadic neurodevelopmental disease, rare variation still does not fully account for the familial clustering and high heritability observed. Common variants, including those within these known disease genes, are also shown to contribute significantly to overall risk. There is also increasing awareness of the important contribution of epigenetic factors and gene-environment interactions.

A Review of the Genomic Analysis of Children Presenting with Developmental Delay/Intellectual Disability and Associated Dysmorphic Features

This review describes the clinical criteria of developmental delay (DD)/intellectual disability (ID) as well as the various techniques that are currently implemented to diagnose neurodevelopmental disorders that typically present with associated dysmorphic features such as Angelman syndrome, Prader-Willi syndrome, and DiGeorge syndrome. These analyses include various forms of chromosomal microarray (CMA), which have proven to be superior to previously implemented techniques such as G-banded karyotyping and fluorescent in situ hybridization (FISH) analysis, as well as whole exome sequencing (WES), which is implemented as a secondary examination when CMA analysis is unrevealing. The clinical significance of identified variants and how it relates to facilitating the management of specific genetic disorders such as the above mentioned is also discussed. In addition, the importance of genomic databases and bioinformatics technologies as they relate to variant classification is also considered. Essentially, the discovery of pathogenic variants allows for enhanced management of a patient’s clinical phenotype, whereas the identification of variants of uncertain significance (VUS) has proven to have an increase in the number of associated conflicts as they typically generate more ambiguity in regard to the clinical manifestations present within the child. As a result, additional procedures need to be implemented to mitigate the issues that surround their identification. The concluding remarks are in regard to both the ethical and legal considerations of genetic testing as they relate to informed consent, testing of minors, how to handle secondary findings, as well as the anticipated future direction of genomic analysis.

A universal genotyping–microarray constructed by ligating a universal fluorescence-probe with SNP-encoded flaps cleaved from multiplex invasive reactions

The universal chip and fluorescence probe enable genotyping multiple SNPs more labor-saving and cost-saving.

Effect of oligonucleotide probes substituted by deoxyinosines on the specificity of SNP detection on the DNA microarray

One of the main factors that can affect the quality of microarray results is the microarray hybridization specificity. The key factor that affects hybridization specificity is the design of the probes. In this paper, we described a novel oligonucleotide probe containing deoxyinosines aimed at improving DNA hybridization specificity. We compared different probes to determine the distance between deoxyinosine base and SNPs site and the number of deoxyinosine bases. The new probe sequences contained two set of deoxyinosines (each set had two deoxyinosines), in which the interval between SNP site and each set of deoxyinosines was two bases. The new probes could obtain the highest hybridization specificity. The experimental results showed that probes containing deoxyinosines hybridized effectively to the perfectly matched target and improved the hybridization specificity of DNA microarray. By including a simple washing step after hybridization, these probes could distinguish matched targets from single-base-mismatched sequences perfectly. For the probes containing deoxyinosines, the fluorescence intensity of a match sequence was more than eight times stronger than that of a mismatch. However, the intensity ratio was only 1.3 times or less for the probes without deoxyinosines. Finally, using hybridization of the PCR product microarrays, we successfully genotyped SNP of 140 samples using these new labeled probes. Our results show that this is a useful new strategy for modifying oligonucleotide probes for use in DNA microarray analysis.

Isolating single stranded DNA using a microfluidic dialysis device

Isolating a particular strand of DNA from a double stranded DNA duplex is an important step in aptamer generation as well as many other biotechnology applications. Here we describe a microfluidic, flow-through, dialysis device for isolating single-stranded DNA (ssDNA) from double-stranded DNA (dsDNA). The device consists of two channels fabricated in polydimethylsiloxane (PDMS) separated by a track etched polycarbonate membrane (800 nm pore size). To isolate ssDNA, dual-biotin labelled dsDNA was immobilized onto streptavidin-coated polystyrene beads. Alkaline treatment was used to denature dsDNA, releasing the non-biotinylated ssDNA. In the flow-through dialysis device the liberated ssDNA was able to cross the membrane and was collected in an outlet channel. The complementary sequence bound to the bead was unable to cross the membrane and was directed to a waste channel. The effect of NaOH concentration and flow rate on purity and yield were compared. >95% ssDNA purity was achieved at 25 mM NaOH. However, lower flow rates were necessary to achieve ssDNA yields approaching the 50% theoretical maximum of the concurrent-flow device. Under optimized conditions the microfluidic isolation achieved even higher purity ssDNA than analogous manual procedures.

Single nucleotide polymorphisms predict symptom severity of autism spectrum disorder

Autism is widely believed to be a heterogeneous disorder; diagnosis is currently based solely on clinical criteria, although genetic, as well as environmental, influences are thought to be prominent factors in the etiology of most forms of autism. Our goal is to determine whether a predictive model based on single-nucleotide polymorphisms (SNPs) can predict symptom severity of autism spectrum disorder (ASD). We divided 118 ASD children into a mild/moderate autism group (n = 65) and a severe autism group (n = 53), based on the Childhood Autism Rating Scale (CARS). For each child, we obtained 29 SNPs of 9 ASD-related genes. To generate predictive models, we employed three machine-learning techniques: decision stumps (DSs), alternating decision trees (ADTrees), and FlexTrees. DS and FlexTree generated modestly better classifiers, with accuracy = 67%, sensitivity = 0.88 and specificity = 0.42. The SNP rs878960 in GABRB3 was selected by all models, and was related associated with CARS assessment. Our results suggest that SNPs have the potential to offer accurate classification of ASD symptom severity.

SNP genotyping for the genetic monitoring of laboratory mice by using a microarray-based method with dualcolour fluorescence hybridisation

Ensuring the genetic homogeneity of the mice used in laboratory experiments contributes to the Reduction aspect of the Three Rs, by maximising the quality of the data obtained from any animals that are used for these purposes, and ultimately reducing the numbers of animals used. Single nucleotide polymorphism (SNP) genotyping is especially suitable for use in the analysis of the genetic purity of model organisms such as the mouse, because bi-allelic markers remain fully informative when used to characterise crosses between inbred strains. Here, we attempted to apply a microarray-based method for a SNP marker to monitor the genetic quality of inbred mouse strains, so as to validate the reliability, stability and applicability of this SNP genotyping panel. The amplified PCR products containing four different SNP loci from four inbred mouse strains were spotted and immobilised onto amino-modified glass slides to generate a microarray. This was then interrogated through hybridisation with dual-colour probes, to determine the SNP genotypes of each sample. The results indicated that this microarray-based method could effectively determine the genotypes of the four selected SNPs with a high degree of accuracy. We have developed a new SNP genotyping technique for effective use in the genetic monitoring of inbred mouse strains.

Analysis of the non-recombining Y chromosome defines polymorphisms in domestic pig breeds: ancestral bases identified by comparative sequencing

Sequences from 20 amplicons representing nine different loci and 11369bp from the short arm of the pig Y chromosome were compared using pools of DNA from different European and Chinese breeds. A total of 33 polymorphic sites were identified, including five indels and 28 single nucleotide polymorphisms (SNPs). Three high frequency SNPs within the coding regions of SRY were further analysed across 889 males representing 25 European and 25 Asian breeds or Lines, plus a European Line of Meishan. Two haplotypes seen to be associated with 'European' or 'Chinese' origin in the initial SNP discovery phase were found to be the most common in their respective groups of breeds in a more detailed genotyping study. Two further SRY haplotypes are relatively rare. One was found exclusively within Tamworth, at low frequency in Retinto, and in three Chinese breeds (Huai, Sahwutou and Xiaomeishan). The other uncommon haplotype is found exclusively in Bamajiang, two further Chinese breeds (Hangjiang Black and Longling) and two European rare breeds (Mangalica and Linderödssvin), but appears based on comparison with other suids to represent an ancestral sequence.

Dual-view imaging system using a wide-range dichroic mirror for simultaneous four-color single-molecule detection

A dual-view imaging system for simultaneous four-color single-molecule (SM) detection was developed. As for the detection procedure, four species of SM fluorophores, namely, Alexa 488, 555, 647, and 680, are immobilized on different slides and excited by evanescent-wave illumination. Fluorescence emitted from an SM fluorophore is split by a wide-range dichroic mirror (WR DM) in a dual-view optics and imaged as two SM fluorescence spots (SM spots) on an electron-multiplying charge-coupled device (EM-CCD) at 100 Hz. The transmittance of the WR DM changes gradually over the wavelength range of 500 to 700 nm so that the signal ratios of the two SM spots for the four fluorophore species differ. A method for classifying SM fluorophores into four species in accordance with their signal ratios was developed. It was used to classify 597 SM fluorophores at an accuracy of above 98% for all the species. This accuracy is comparable to that of a conventional four-color SM detection system. To classify four species, the conventional system disperses SM fluorescence with a prism and provides an elongated SM spot that uses more pixels of an EM-CCD chip than that of the developed system. The developed system can thus detect 1.5-fold more SM spots with the same-size EM-CCD chip, so it can achieve 1.5-fold higher throughput. Moreover, the developed system is based on a simple and practical approach, namely, replacing an ordinary dichroic mirror in a commercially available dual-view optics with a WR DM. This replacement transforms a dual-view imaging system for two-color detection into a system for four-color detection. The developed system is suitable for detection systems of next-generation DNA sequencers and DNA microarray-chip analyzers.

A novel automated assay with dual-color hybridization for single-nucleotide polymorphisms genotyping on gold magnetic nanoparticle array

A high-throughput and cost-effective single-nucleotide polymorphism (SNP) genotyping method based on a gold magnetic nanoparticle (GMNP) array with dual-color hybridization has been designed. Biotinylated single-strand polymerase chain reaction (PCR) products containing the SNP locus were captured by the GMNPs that were coated with streptavidin. The GMNP array was fabricated by immobilizing single-stranded DNA (ssDNA)-GMNP complexes onto a glass slide using a magnetic field, and SNPs were identified with dual-color fluorescence hybridization. Three different SNP loci from 24 samples were genotyped successfully using this platform. This procedure allows the user to directly analyze the bead fluorescence to determine the SNP genotype, and it eliminates the need for background subtraction for signal determination. This method also bypasses tedious PCR purification and concentration procedures, and it facilitates large-scale SNP studies by using a method that is highly sensitive, simple, labor-saving, and potentially automatable.

Association analysis between pseudorabies antibody and five single-nucleotide polymorphisms in pigs

Pseudorabies has become endemic and represents a widespread problem for pig production in the world, causing great economic losses associated with reproductive failure and neonatal mortality in the pig industry. Most diseases are the results of mutations of functional genes. Single-nucleotide polymorphisms (SNPs) from the coding regions of the mediators of pro-inflammatory responses or other candidate genes in pigs could indicate their potential involvement in susceptibility or resistance to PrV (pseudorabies virus) infection. There have been no previous association studies with candidate host genes that may influence PrV phenotypic traits. In order to perform association studies to identify genes contributing to PrV phenotypes, the genotypes of five SNPs from four genes (IL10, CXCL12, BAT2 and EHMT2) were determined for 178 sow samples using a high throughput microarray-based methodology. PrV antibodies were tested by enzyme-linked immunosorbent assay (ELISA) to determine whether there was an association between antibody levels and particular genotypes. The association between SNP genotypes and the PrV antibody levels were analysed using the Duncan method of one-way ANOVA procedure using the SAS (Statistical Analysis Systems) software package. The results showed that the glycoprotein E-ELISA antibody level of pigs with genotypes 11(AA) and 12(AG) was significantly higher than in pigs with genotype 22(GG) (P < 0.05) of SNP in the gene EHMT2-SNP2. The SNP of EHMT2 may be an effective potential tool to identify susceptible and resistant animals when used in conjunction with traditional selection methods.

Association study between BDNF gene polymorphisms and autism by three-dimensional gel-based microarray

Single nucleotide polymorphisms (SNPs) are important markers which can be used in association studies searching for susceptible genes of complex diseases. High-throughput methods are needed for SNP genotyping in a large number of samples. In this study, we applied polyacrylamide gel-based microarray combined with dual-color hybridization for association study of four BDNF polymorphisms with autism. All the SNPs in both patients and controls could be analyzed quickly and correctly. Among four SNPs, only C270T polymorphism showed significant differences in the frequency of the allele (χ² = 7.809, p = 0.005) and genotype (χ² = 7.800, p = 0.020). In the haplotype association analysis, there was significant difference in global haplotype distribution between the groups (χ² = 28.19, p = 3.44e-005). We suggest that BDNF has a possible role in the pathogenesis of autism. The study also show that the polyacrylamide gel-based microarray combined with dual-color hybridization is a rapid, simple and high-throughput method for SNPs genotyping, and can be used for association study of susceptible gene with disorders in large samples.

Development of new substrates for high-sensitive genotyping of minority mutated alleles

An unsurpassed level of sensitivity was reached in the detection of minority mutated alleles. A low-density microarray was printed on a substrate specifically designed to provide an interference effect which amplifies the collection of the light emitted on the support and reinforces the intensity of excitation light. Optimal performance of the array was obtained by maximizing the probe density and the binding efficiency to the target through a polymeric coating made by the adsorption of a copolymer of N,N-dimethylacrylamide (97% of moles), N,N-acryloyloxysuccinimide (2%) and 3-(trimethoxysilyl)propyl methacrylate (1%) synthesized by free radical copolymerization. The new substrate was used in the identification of fetal mutations in the maternal plasma DNA. Amino-modified amplicons from genomic DNA corresponding to the locus of eight beta-thalassemia mutations were immobilized and interrogated with dual-color oligonucleotide targets. Compared with the conventional glass substrates, the new substrate showed a great enhancement of fluorescence signals thanks to the combination of the optics with the highly efficient polymeric coating, allowing specific detection of all mutations. The high sensitivity and selectivity obtained made it possible to develop assays for the identification of paternally inherited mutations on fetal DNA in the maternal plasma in couples at risk for beta-thalassemia.

Array-based high-throughput DNA markers for crop improvement

The last two decades have witnessed a remarkable activity in the development and use of molecular markers both in animal and plant systems. This activity started with low-throughput restriction fragment length polymorphisms and culminated in recent years with single nucleotide polymorphisms (SNPs), which are abundant and uniformly distributed. Although the latter became the markers of choice for many, their discovery needed previous sequence information. However, with the availability of microarrays, SNP platforms have been developed, which allow genotyping of thousands of markers in parallel. Besides SNPs, some other novel marker systems, including single feature polymorphisms, diversity array technology and restriction site-associated DNA markers, have also been developed, where array-based assays have been utilized to provide for the desired ultra-high throughput and low cost. These microarray-based markers are the markers of choice for the future and are already being used for construction of high-density maps, quantitative trait loci (QTL) mapping (including expression QTLs) and genetic diversity analysis with a limited expense in terms of time and money. In this study, we briefly describe the characteristics of these array-based marker systems and review the work that has already been done involving development and use of these markers, not only in simple eukaryotes like yeast, but also in a variety of seed plants with simple or complex genomes.

Rice molecular breeding laboratories in the genomics era: Current status and future considerations

Using DNA markers in plant breeding with marker-assisted selection (MAS) could greatly improve the precision and efficiency of selection, leading to the accelerated development of new crop varieties. The numerous examples of MAS in rice have prompted many breeding institutes to establish molecular breeding labs. The last decade has produced an enormous amount of genomics research in rice, including the identification of thousands of QTLs for agronomically important traits, the generation of large amounts of gene expression data, and cloning and characterization of new genes, including the detection of single nucleotide polymorphisms. The pinnacle of genomics research has been the completion and annotation of genome sequences for indica and japonica rice. This information-coupled with the development of new genotyping methodologies and platforms, and the development of bioinformatics databases and software tools-provides even more exciting opportunities for rice molecular breeding in the 21st century. However, the great challenge for molecular breeders is to apply genomics data in actual breeding programs. Here, we review the current status of MAS in rice, current genomics projects and promising new genotyping methodologies, and evaluate the probable impact of genomics research. We also identify critical research areas to "bridge the application gap" between QTL identification and applied breeding that need to be addressed to realize the full potential of MAS, and propose ideas and guidelines for establishing rice molecular breeding labs in the postgenome sequence era to integrate molecular breeding within the context of overall rice breeding and research programs.

Association of four new single-nucleotide polymorphisms in follicle-stimulating hormone receptor and zona pellucida glycoprotein with reproductive traits in pigs

Two new single-nucleotide polymorphisms (SNPs) (C1166T and G1190A) were discovered in the follicle-stimulating hormone receptor (FSHR) gene and two (G261A and T302C) in the zona pellucida glycoprotein (ZP3) gene. These SNPs were genotyped in three Chinese domestic purebred sow lines (42 Small Meishan, 46 Qingping and 41 Jinhua sows) and three European purebred sow lines (225 Duroc, 195 Large White and 65 Landrace sows) by using SNP chips. Phenotypic data including the functional teat number (i.e. milk-producing teats, TN) and number of piglets born alive per litter (NBA). These traits were tested for association with the genotypes of four SNPs. The association analysis revealed genotype of G261A in the ZP3 gene was significantly (P < 0.01) associated with overall NBA and NBA at later parities (NBA2+) but not with NBA at first parity (NBA1). There was a significant (P < 0.05) difference between sows with genotype GG (14.83 ± 0.18) and AA (14.26 ± 0.09) in TN at position 261 in the ZP3 gene. No significant associations were observed for the SNPs in the FSHR gene with NBA or TN in our populations. The results showed that the new SNPs in the ZP3 gene may be an effective potential marker to be used in conjunction with traditional selection methods.

Gel immobilization of acrylamide-modified single-stranded DNA template for pyrosequencing

A novel two-step process was developed to prepare ssDNA templates for pyrosequencing. First, PCR-amplified DNA templates modified with an acrylamide group and acrylamide monomers were copolymerized in 0.1 M NaOH solution to form polyacrylamide gel spots. Second, ssDNA templates for pyrosequencing were prepared by removing electrophoretically unbound complementary strands, unmodified PCR primers, inorganic pyrophosphate (PPi), and excess deoxyribonucleotides under alkali conditions. The results show that the 3-D polyacrylamide gel network has a high immobilization capacity and the modified PCR fragments are efficiently captured. After electrophoresis, gel spots copolymerized from 10 microL of the crude PCR products and the acrylamide monomers contain template molecules on the order of pmol, which generate enough light to be detected by a regular photomultiplier tube. The porous structure of gel spots facilitated the fast transportation of the enzyme, dNTPs and other reagents, and the solution-mimicking microenvironment guaranteed polymerase efficiency for pyrosequencing. Successful genotyping from the crude PCR products was demonstrated. This method can be applied in any laboratory; it is cheap, fast, simple, and has the potential to be incorporated into a DNA-chip format for high-throughput pyrosequencing analysis.

PCR amplification on magnetic nanoparticles: application for high-throughput single nucleotide polymorphism genotyping

A novel approach for the genotyping of single nucleotide polymorphisms (SNPs) based on solidphase PCR on magnetic nanoparticles (MNPs) is described. PCR products were amplified directly on MNPs. The genotypes of a given SNP were differentiated by hybridization with a pair of allele-specific probes labeled with dual-color fluorescence (Cy3, Cy5). The results were analyzed by scanning the microarray printed with the denatured fluorescent probes on an unmodified glass slide. Electrophoresis analysis indicated that PCR could proceed successfully when MNPs-bound primers were used. Furthermore, nine different samples were genotyped and their fluorescent signals were quantified. Genotyping results showed that three genotypes for the locus were very easily discriminated. The fluorescent ratios (match probe:mismatch probe signal) of homozygous samples were over 9.3, whereas heterozygous samples had ratios near 1.0. Without any purification and concentration of PCR products, this new MNP-PCR based genotyping assay potentially provides a rapid, labor-saving method for genotyping of a large number of individuals.

High-throughput SNP genotyping based on solid-phase PCR on magnetic nanoparticles with dual-color hybridization

Single-nucleotide polymorphisms (SNPs) are one-base variations in DNA sequence that can often be helpful when trying to find genes responsible for inherited diseases. In this paper, a microarray-based method for typing single nucleotide polymorphisms (SNPs) using solid-phase polymerase chain reaction (PCR) on magnetic nanoparticles (MNPs) was developed. One primer with biotin-label was captured by streptavidin coated magnetic nanoparticles (SA-MNPs), and PCR products were directly amplified on the surface of SA-MNPs in a 96-well plate. The samples were interrogated by hybridization with a pair of dual-color probes to determine SNP, and then genotype of each sample can be simultaneously identified by scanning the microarray printed with the denatured fluorescent probes. The C677T polymorphisms of methylenetetrahydrofolate reductase (MTHFR) gene from 126 samples were interrogated using this method. The results showed that three different genotypes were discriminated by three fluorescence patterns on the microarray. Without any purification and reduction procedure, and all reactions can be performed in the same vessel, this approach will be a simple and labor-saving method for SNP genotyping and can be applicable towards the automation system to achieve high-throughput SNP detection.

Post-hybridisation by Electrophoresis for Reinforcing the Hybridization Result

In this paper, we developed an electrophoresis method for reinforcing hybridization efficiency, and distinguishing the perfectly matched sequences from the mismatched ones. The non-specific binding labeled targets in the hybridization were effectively removed by electrophoresis instead of the conventional washing procedure in the post-hybridisation process. During electrophoresis, the hybrids (the dual-spiral structures formed in hybridization) would be unchained when targets were continuously removed. In this case, not only the non-specific binding labeled targets, but also the targets participating in hybridization would be removed. Therefore, only the perfectly matched sequences had the distinct hybridization signals, the perfectly matched probes from the single-base mismatched ones could more easily be distinguished, and the single nucleotide polymorphisms (SNP) genotypes were also easily determined by dual-color fluorescence targets.

Novel microarray technology for post-genomic studies

There are great challenges of developing high-throughput analytic tools in the post-genomic era. The microarray technology, as one of the most poowerful high-throughput tools, has a lot of opportunities in meeting increasing enormous demands in the discovery of the molecular mechanisms of life systems. A number of the new concept microarrays will be developed and used in fundamental and medical researches in the near future. We developed several kinds of the new microarray chips for detecting DNA methylation patterns, double strands DNA microarray for sequence-specific DNA binding proteins (such as transcription factors), the PCR procduct microarray for screening disease related SNPs, a cap-array assay (lab-in-a-tube system), and quantitative detection microarray for mulit-viruses detection and clinical applications. In this presentation, I will give brief introductions on these biochip platforms developed in our laboratory recently. Our results show that the innovations in high-throughput tools could be promoted through the combination between life science and engineering researches.

Genetic data acquirement, construction and analysis based on microarray technology

Several novel microarray technology platforms to be applied to acquire both genetic and epigenetic data from biological systems have been developed. Genetic database and the related bioinformatics analytic tools are being constructed. Here, some on-going projects related to bioinformatics analysis based on the microarray technology, such as such as the high density microarray design, combinational analyses of the data based on microarrays for gene expressions, methylation of CG islands, trans-factor protein level and mutation detection, and the disease related SNPs in human genomes are presented.

TAMGeS: a Three-array Method for Genotyping of SNPs by a dual-colour approach

Background

Many of the most effective high-throughput protocols for SNP genotyping employ microarrays. Genotypes are assessed by comparing the signal intensities that derive from the hybridization of different allele-specific probes labelled either by using four fluorescent dyes, one for each base, or by using only two dyes and investigating the polymorphic alleles two by two on separate arrays. The employment of only two dyes makes it possible to use a dual-laser scanner, which has the advantage of being present in every microarray laboratory. However, this protocol may present some drawbacks. To infer all the six possible genotypes it is necessary to compare signals from two arrays, but this comparison not always is successful. A number of systematic errors in the experimental protocol, in fact, may differently affect signal intensities on separate arrays. Here we present TAMGeS (Three-Array Method for Genotyping of SNPs), an exhaustive method for SNP genotyping through SBE (Single Base Extension) and dual-colour microarrays, which makes the comparison of signals on distinct arrays reliable by using a third array and a data handling method for signal normalization based on bilinear regression theory.

Results

We tested the effectiveness of the proposed method by evaluating the results obtained from the direct comparison of the two arrays or by applying TAMGeS, both on experimental and synthetic data. With synthetic data, TAMGeS reduced the frequency of errors by an order of magnitude, when the incidence of systematic errors was not negligible. With the experimental data, produced by genotyping 25 SNPs in 437 subjects, TAMGeS reduced the percentage of missing genotypes from 54% (Two-Array Method) to 14.5%. Allelic and genotypic call rates were 99.3% and 99.5%, respectively. The normalization procedure takes into account also systematic errors, which can be generated by a time-delayed assay, thus making the protocol more flexible.

Conclusion

TAMGeS represents an innovative method, which proved to be very effective in producing reliable SNP genotyping data by dual-colour microarrays. The requirement of a third array is well balanced by the strong enhancement in data quality and by the greater flexibility of the experimental protocol.

An improved gel-based DNA microarray method for detecting single nucleotide mismatch

3-D polyacrylamide gel-based DNA microarray platforms provide a high capacity for nucleic acids immobilization and a solution-mimicking environment for hybridization. However, several technological bottlenecks still remain in these platforms, such as difficult microarray preparation and high fluorescent background, which limit their application. In this study, two new approaches have been developed to improve the convenience in microarray preparation and to reduce the background after hybridization. To control the polymerization process, solutions containing acrylamide-modified oligonucleotide, acrylamide, glycerol and ammonium persulfate are spotted onto a functionalized glass slide, and then the slide is transferred to a vacuum chamber with TEMED, so that TEMED is vaporized and diffused into the spots to induce polymerization. By applying an electric field across a hybridized microarray to remove the nonspecifically bound labeled targets, this approach can solve the problem of high fluorescent background of the gel-based microarray after hybridization. Experimental results show that our immobilization method can be used to construct high quality microarrays and exhibits good reproducibility. Moreover, the polymerization is not affected by PCR medium, so that PCR products can be used for microarray construction without being treated by commercial purification cartridges. Electrophoresis can improve the signal-to-noise significantly and has the ability to differentiate single nucleotide variation between two homozygotes and a heterozygote. Our results demonstrated that this is a reliable novel method for high-throughput mutation analysis and disease diagnosis.

The common −318C/T polymorphism in the promoter region of CTLA4 gene is associated with reduced risk of ophthalmopathy in Chinese Graves' patients

Studies in the past have clearly established that CTLA4 is a susceptible gene for Graves' disease (GD). However, association studies between CTLA4 and the risk of developing Graves' ophthalmopathy (GO) in GD patients have shown conflicting results. In this study, associations of five CTLA4 single nucleotide polymorphisms (-1722A/G, -1661A/G, -318C/T, +49G/A, CT60) with GD risk and GO susceptibility in GD patients were investigated in a Chinese population. Our results showed that either +49A/G or CT60 polymorphism was associated with GD susceptibility in the Chinese population. Significant differences in the distribution of the genotypes or alleles evaluated between GD patients with and without clinically evident GO were only found for -318C/T polymorphism (P = 0.03). Multiple logistic regressions revealed that the -318T allele was negatively associated with GO under both additive and dominant genetic models (adjusted OR = 0.56, 95%CI 0.35-0.89, P = 0.014; adjusted OR = 0.51, 95%CI 0.30-0.84, P = 0.009, respectively). Stratification analysis according to gender demonstrated different scenarios concerning the role of the -318T allele in GO risk: a significant protective role for GO was only confirmed in male but not in female GD patients. Haplotype analyses showed that only the haplotypes containing the -318T allele played a protective role in GO. In conclusion, results from this study suggested that the -318T allele might play a protective role in GO susceptibility for GD patients at least in the Chinese population. However, extended analyses with larger sample size should be carried out in patients from different ethnic origins to further verify this association.

CTLA4 polymorphisms and ophthalmopathy in Graves' disease patients: association study and meta-analysis

Studies in the past have clearly established that cytotoxic T-lymphocyte antigen-4 (CTLA4) is a susceptible gene for Graves' disease (GD). However, association studies between the CTLA4 exon-1 +49A/G polymorphism and the risk of developing Graves' ophthalmopathy (GO) in GD patients have revealed conflicting results. In this study, associations of two CTLA4 polymorphisms (+49A/G and CT60) with GD risk and GO susceptibility in GD patients were investigated in a Chinese population. In addition, a meta-analysis was performed to better assess the purported association between the +49A/G polymorphism and GO susceptibility in GD patients. Our results demonstrated that both the +49A/G and CT60 polymorphisms were associated with GD susceptibility in the Chinese population. No significant association with GO susceptibility in GD patients was confirmed regardless of which polymorphism was tested individually. Similarly, the meta-analysis results provided minimal evidence about the role of the +49A/G polymorphism and GO risk in GD patients. Interestingly, haplotypic analysis demonstrated different scenarios concerning the role of CTLA4 in GO susceptibility in the Chinese GD patients. We found that the +49A-CT60G haplotype was marginally statistically associated with the increased risk of GO in GD patients (OR = 1.63, 95%CI 1.00-2.64, p = 0.05). In conclusion, our results suggested that CTLA4 might be involved in the susceptibility to GD in the Chinese population. Although neither +49A/G nor CT60 polymorphism was associated with the risk of GO in GD patients, the haplotypic analysis provided some evidence about its role in GO susceptibility in the Chinese GD patients. We suggest that more association studies recruiting haplotypic analysis should be performed to investigate the role of CTLA4 gene in GO susceptibility in patients from different nations.

Microarray-based methylation analysis using dual-color fluorescence hybridization

BACKGROUND

Aberrant DNA methylation of CpG sites is among the earliest and most frequent alterations in cancer. It is of great importance to develop simple, high-throughput and quantitative methods for methylation detection.

METHODS

A high-throughput methylation analysis method has been developed based on microarray and dual-color fluorescence hybridization. The genomic DNA was treated with bisulfite, resulting in conversion of non-methylated cytosine, but not methylated cytosine, into uracil within CpG islands of interest. PCR products of the treated genomic templates were spotted and immobilized onto a poly-l-lysine coated glass slide to fabricate a microarray and then interrogated by hybridization with dual-color probes to determine the methylation status. The hybridized signals were obtained with a scanner and the results were analyzed with the software Genepix Pro 3.0.

RESULTS

The methylation status of the CpG islands of IGFBP7 gene has been successfully evaluated by the microarray method for twenty-seven samples. All the investigated samples, including twenty human breast tumor tissues, six corresponding normal human breast tissues and one liver cell line, all CpG sites were found completely methylated.

CONCLUSIONS

The microarray technology has been proven to have potential for high-throughput detection of the methylation status for a given gene in multi-genomic samples, which could be a novel approach for rapidly screening DNA methylation marker for early stage cancer diagnosis.

Bisulfite-modified target DNA array for aberrant methylation analysis

Aberrant DNA methylation of CpG islands is among the earliest and most frequent alterations in cancer. It is of great importance to develop simple and high-throughput methods of methylation analysis for earlier cancer diagnosis or the detection of recurrence. In this study, bisulfite-modified target DNA arrays were prepared on positively charged nylon membrane with two different procedures: fixing PCR products and fixing genomic DNA. First, a bisulfite PCR product array was prepared through fixing PCR products amplified in bisulfite sequencing primers from the bisulfite-modified genomic DNA of different clinical samples on membrane. Furthermore, bisulfite-modified genomic DNA of the different samples was directly fixed on membrane to fabricate bisulfite genomic DNA arrays. The two kinds of arrays were hybridized by probes labeled with digoxigenin, and the hybridization signals were obtained through chemiluminescent detection. The methylation statuses of the IGFBP7 gene for breast tumor and normal tissue samples and for normal human blood cell samples were detected successfully by the two procedures. It was shown that the methods are reliable and sensitive and that they have high potential in screening molecular methylation markers from a large number of clinical samples.

Analysis of single nucleotide polymorphism sites in exon 4 of the p53 gene using high-performance liquid chromatography electrospray ionization mass spectrometry tandem mass spectrometry

Three groups of four oligonucleotides with special single nucleotide polymorphisms (SNP) sites in exon 4 of the p53 gene were analyzed with ion-pair reversed-phase high-performance liquid chromatography electrospray ionization mass spectrometry tandem mass spectrometry. The retention order of four oligonucleotides with SNPs was C < G < A < T, regardless of whether the polymorphisms were at the 3' end, the 5' end, or the middle of the oligonucleotides. The charge state of the molecular ion affects the MS/MS spectra of the oligonucleotides. SNPs at the 3' end can be easily identified from the fragmentation pattern of the 2- charge state, but not from the 3- charge state, especially from the w1 fragment. The single base may be taken as the symbol of the 5' end SNP site derived from [M3H]2, but not from the [M3H]2 charge state. The oligonucleotides with SNPs in the middle were also determined from the [M2H]2 precursor ion.

Validation of the high-throughput marker technology DArT using the model plant Arabidopsis thaliana

Diversity Arrays Technology (DArT) is a microarray-based DNA marker technique for genome-wide discovery and genotyping of genetic variation. DArT allows simultaneous scoring of hundreds of restriction site based polymorphisms between genotypes and does not require DNA sequence information or site-specific oligonucleotides. This paper demonstrates the potential of DArT for genetic mapping by validating the quality and molecular basis of the markers, using the model plant Arabidopsis thaliana. Restriction fragments from a genomic representation of the ecotype Landsberg erecta (Ler) were amplified by PCR, individualized by cloning and spotted onto glass slides. The arrays were then hybridized with labeled genomic representations of the ecotypes Columbia (Col) and Ler and of individuals from an F(2) population obtained from a Col x Ler cross. The scoring of markers with specialized software was highly reproducible and 107 markers could unambiguously be ordered on a genetic linkage map. The marker order on the genetic linkage map coincided with the order on the DNA sequence map. Sequencing of the Ler markers and alignment with the available Col genome sequence confirmed that the polymorphism in DArT markers is largely a result of restriction site polymorphisms.