Microarrays and Crohn's disease: collecting reliable information.
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Biomarkers↗
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Results for “Oligonucleotide Array Sequence Analysis”
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High-density arrays and insights into genome function.
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Algorithms↗
Kinetics of hybridization on the oligonucleotide microchips with gel pads.
The kinetics of hybridization on the oligonucleotide microchip with gel pads is studied both theoretically and experimentally. The monitoring of kinetics was performed with the measurements of fluorescence intensity produced by the labeled target oligonucleotides. As is shown, the hybridization time depends on the stability of the formed duplexes, the concentrations of target and probe oligonucleotides, and the diffusion of target oligonucleotides in solution and gel pad. The initial stage of hybridization is determined by the flow of target oligonucleotides from solution, then, followed by the diffusive propagation with approximately constant concentration of oligonucleotides at the boundary of gel pad and, finally, by the exponential saturation. The theoretical predictions of hybridization kinetics reveal a good correspondence with the experimental results and may be used for the choice of the optimal hybridization conditions. The possible applications of kinetic hybridization curves to the discrimination problems and assessment of diffusion coefficients in gel pads are briefly discussed. Finally, we discuss the relationships between the binding kinetics and the general functioning of biomolecular microchips.
Algorithms↗
Discrimination between perfect and mismatched duplexes with oligonucleotide gel microchips: role of thermodynamic and kinetic effects during hybridization.
The efficiency of discrimination between perfect and mismatched duplexes during hybridization on microchips depends on the concentrations of target DNA in solution and immobilized probes, buffer composition, and temperature of hybridization and is determined by both thermodynamic relationships and hybridization kinetics. In this work, optimal conditions of discrimination were studied using hybridization of fluorescently labeled target DNA with custom-made gel-based oligonucleotide microchips. The higher the concentration of immobilized probes and the higher the association constant, the higher the concentration of the formed duplexes and the stronger the corresponding fluorescence signal, but, simultaneously, the longer the time needed to reach equilibrium. Since mismatched duplexes hybridize faster than their perfect counterparts, perfect-to-mismatch signal ratio is lower in transient regime, and short hybridization times may hamper the detection of mutations. The saturation time can be shortened by decreasing the probe concentration or augmenting the gel porosity. This improves the detection of mutations in transient regime. It is shown that the decrease in the initial concentration of oligonucleotide probes by an order of magnitude causes only 1.5-2.5-fold decrease of fluorescence signals after hybridization of perfect duplexes for 3-12 h. At the same time, these conditions improve the discrimination between perfect and mismatched duplexes more than two-fold. A similar improvement may be obtained using an optimized dissociation procedure.
Base Composition↗
Gene silencing nucleic acids designed by scanning arrays: anti-EGFR activity of siRNA, ribozyme and DNA enzymes targeting a single hybridization-accessible region using the same delivery system.
Gene silencing nucleic acids such as ribozymes, DNA enzymes (DNAzymes), antisense oligonucleotides (ODNs), and small interfering (si)RNA rely on hybridization to accessible sites within target mRNA for activity. However, the accurate prediction of hybridization accessible sites within mRNAs for design of effective gene silencing reagents has been problematic. Here we have evaluated the use of scanning arrays for the effective design of ribozymes, DNAzymes and siRNA sequences targeting the epidermal growth factor receptor (EGFR) mRNA. All three gene silencing nucleic acids designed to be complementary to the same array-defined hybridization accessible-site within EGFR mRNA were effective in inhibiting the growth of EGFR over-expressing A431 cancer cells in a dose dependent manner when delivered using the cationic lipid (Lipofectin) delivery system. Effects on cell growth were correlated in all cases with concomitant dose-dependent reduction in EGFR protein expression. The control sequences did not markedly alter cell growth or EGFR expression. The ribozyme and DNAzyme exhibited similar potency in inhibiting cell growth with IC50 values of around 750 nM. In contrast, siRNA was significantly more potent with an IC50 of about 100 nM when delivered with Lipofectin. The potency of siRNA was further enhanced when Oligofectamine was used to further improve both the cellular uptake and subcellular distribution of fluorescently labelled siRNA. Our studies show that active siRNAs can be designed using hybridization accessibility profiles on scanning arrays and that siRNAs targeting the same array-designed hybridization accessible site in EGFR mRNA and delivered using the same delivery system are more potent than ribozymes and DNAzymes in inhibiting EGFR expression in A431 cells.
Blotting, Western↗
Identification of transcriptional biomarkers induced by SERMS in human endometrial cells using multivariate analysis of DNA microarrays.
Functional genomic tools such as DNA microarrays are having a major impact on the drug-discovery process. Potentially, compounds with toxic responses can be identified and removed at a relatively early stage in the drug-development process before tests on animals or humans, solely on the gene expression profiles produced in cell culture. The study examined the expression profiles of primary cultured human endometrial cells treated with 17beta-oestradiol and the SERMs (selective oestrogen receptor modulators) tamoxifen and raloxifene. Primary cultures from three individuals were split into glandular epithelial cells and stromal cell types. Principal components and partial least-squares-discriminate analyses were employed to examine the transcript profile as a whole, identifying genes responsible for patient separation and those that might have an important role in tamoxifen-associated carcinogenesis. Using multivariate data analysis, transcriptional responses were identified in epithelial cells but not in stromal cells for the three SERMs examined. However, it was demonstrated that a major problem associated with using primary cultures derived from human patients is the large transcriptional differences that might exist between the different cultures.
Analysis of Variance↗
A graphical approach for quality control of oligonucleotide array data.
In studies of quality control of oligonucleotide array data, one objective is to screen out ineligible arrays. Incomparable arrays (one type of ineligible arrays) arise as the experimental factors are poorly controlled. Due to the high volume of data in gene arrays, examination of array comparability requires special treatments to reduce data dimension without distortion. This paper proposes a graphical approach to address these issues. The proposed approach uses percentile methods to group data, and applies the 2D image plot to display the grouped data. Moreover, an invariant band is employed to quantify degrees of array comparability. We use two publicly available oligonucleotide array datasets from Affymetrix GeneChip System for evaluation. The results demonstrate the utility of our approach to examine data quality and also as an exploratory tool to verify differentially expressed genes selected by vigorous statistical methods.
Algorithms↗
The use and evaluation of 2 + 2 photoaddition in immobilization of oligonucleotides on a three dimensional hydrogel matrix.
Photochemical attachment of synthetic oligonucleotides on the three dimensional surface of a polyacrylamide based hydrogel was used in the specific detection of target oligonucleotides. Covalent attachment of the oligonucleotide to the hydrogel was mediated by the incorporation of a 2 + 2 photo-attachable functional group in both the hydrogel and the oligonucleotide probe. Expression and SNP assays were used to evaluate this platform.
Acrylic Resins↗
Preparation of DNA chips using polyamine-oligonucleotide conjugates.
A convenient and efficient method for three-dimensional immobilizing oligonucleotides on glass was developed using oligonucleotide derivatives bearing a polyamine linker (PA-oligo conjugates). Polyamine (polylysine, poly(lysine, phenylalanine), polyethyleneimine) residues stipulate durable fixation of such conjugates to the glass surface with a high yield (90-95%). A DNA fragment (414-mer) is hybridized specifically to an immobilized oligonucleotide.
Base Sequence↗
Recent highlights on photolithic oligonucleotide array in situ synthesis.
Light directed synthesis of high-density oligonucleotide microarrays is currently performed using either ortho-nitro-benzyl-type [MeNPOC] (Pease, A.C.; Solas, D.; Sullivan, E.J.; Cronin, T.M.; Holmes, C.P.; Fodor, S.P.A. Proc. Natl. Acad Sci U.SA. 1994, 91, 6333.) or ortho-nitrophenylethyl-type [NPPOC] (Hasan, A.; Stengele, K.P.; Giegrich, H.; Cornwell, P.; Isham, K.R.; Sachleben, R.A.; Pfleiderer, W.; Foote, R.S. Tetrahedron 1997, 53, 424Z) protecting groups as the 5'-O-carbonate ester of the phosphoramidite building block. The synthesis cycle uses a combinatorial approach attaching one specific base per cycle, thus as many as 100 cycles need to be run to make an array of 25-mers. Time needed for deprotection/activation of the growing oligo chain determines overall manufacturing time and consequently also cost. In this report we demonstrate the development of photoprotected posphoramidite monomers for light directed array synthesis with increasing sensitivity to the UV light used. If combined with maskless array synthesis, this technology allows for synthesis of arrays with >780,000 different 25-mer oligonucleotides in about one hour and allows for high flexibility in array design and reiterative redesign. The arrays synthesized show high quality and reproducibility in our standard hybridization based assay.
Combinatorial Chemistry Techniques↗
Disruption of LTBP-4 function reduces TGF-beta activation and enhances BMP-4 signaling in the lung.
Disruption of latent TGF-beta binding protein (LTBP)-4 expression in the mouse leads to abnormal lung development and colorectal cancer. Lung fibroblasts from these mice produced decreased amounts of active TGF-beta, whereas secretion of latent TGF-beta was significantly increased. Expression and secretion of TGF-beta2 and -beta3 increased considerably. These results suggested that TGF-beta activation but not secretion would be severely impaired in LTBP-4 -/- fibroblasts. Microarrays revealed increased expression of bone morphogenic protein (BMP)-4 and decreased expression of its inhibitor gremlin. This finding was accompanied by enhanced expression of BMP-4 target genes, inhibitors of differentiation 1 and 2, and increased deposition of fibronectin-rich extracellular matrix. Accordingly, increased expression of BMP-4 and decreased expression of gremlin were observed in mouse lung. Transfection of LTBP-4 rescued the -/- fibroblast phenotype, while LTBP-1 was inefficient. Treatment with active TGF-beta1 rescued BMP-4 and gremlin expression to wild-type levels. Our results indicate that the lack of LTBP-4-mediated targeting and activation of TGF-beta1 leads to enhanced BMP-4 signaling in mouse lung.
Adaptor Proteins, Signal Transducing↗
Muscle-specific microRNA miR-206 promotes muscle differentiation.
Three muscle-specific microRNAs, miR-206, -1, and -133, are induced during differentiation of C2C12 myoblasts in vitro. Transfection of miR-206 promotes differentiation despite the presence of serum, whereas inhibition of the microRNA by antisense oligonucleotide inhibits cell cycle withdrawal and differentiation, which are normally induced by serum deprivation. Among the many mRNAs that are down-regulated by miR-206, the p180 subunit of DNA polymerase alpha and three other genes are shown to be direct targets. Down-regulation of the polymerase inhibits DNA synthesis, an important component of the differentiation program. The direct targets are decreased by mRNA cleavage that is dependent on predicted microRNA target sites. Unlike small interfering RNA-directed cleavage, however, the 5' ends of the cleavage fragments are distributed and not confined to the target sites, suggesting involvement of exonucleases in the degradation process. In addition, inhibitors of myogenic transcription factors, Id1-3 and MyoR, are decreased upon miR-206 introduction, suggesting the presence of additional mechanisms by which microRNAs enforce the differentiation program.
Animals↗
Hypoxia-induced neutrophil survival is mediated by HIF-1alpha-dependent NF-kappaB activity.
Neutrophils are key effector cells of the innate immune response and are required to migrate and function within adverse microenvironmental conditions. These inflammatory sites are characterized by low levels of oxygen and glucose and high levels of reductive metabolites. A major regulator of neutrophil functional longevity is the ability of these cells to undergo apoptosis. We examined the mechanism by which hypoxia causes an inhibition of neutrophil apoptosis in human and murine neutrophils. We show that neutrophils possess the hypoxia-inducible factor (HIF)-1alpha and factor inhibiting HIF (FIH) hydroxylase oxygen-sensing pathway and using HIF-1alpha-deficient myeloid cells demonstrate that HIF-1alpha is directly involved in regulating neutrophil survival in hypoxia. Gene array, TaqMan PCR, Western blotting, and oligonucleotide binding assays identify NF-kappaB as a novel hypoxia-regulated and HIF-dependent target, with inhibition of NF-kappaB by gliotoxin or parthenolide resulting in the abrogation of hypoxic survival. In addition, we identify macrophage inflammatory protein-1beta as a novel hypoxia-induced neutrophil survival factor.
Animals↗
A model for measurement error for gene expression arrays.
We introduce a model for measurement error in gene expression arrays as a function of the expression level. This model, together with analysis methods, data transformations, and weighting, allows much more precise comparisons of gene expression, and provides guidance for analysis of background, determination of confidence intervals, and preprocessing data for multivariate analysis.
Computational Biology↗
Integrative biological analysis of the APOE*3-leiden transgenic mouse.
Integrative (or systems biology) is a new approach to analyzing biological entities as integrated systems of genetic, genomic, protein, metabolite, cellular, and pathway events that are in flux and interdependent. Here, we demonstrate the application of intregrative biological analysis to a mammalian disease model, the apolipoprotein E3-Leiden (APO*E3) transgenic mouse. Mice selected for the study were fed a normal chow diet and sacrificed at 9 weeks of age-conditions under which they develop only mild type I and II atherosclerotic lesions. Hepatic mRNA expression analysis showed a 25% decrease in APO A1 and a 43% increase in liver fatty acid binding protein expression between transgenic and wild type control mice, while there was no change in PPAR-alpha expression. On-line high performance liquid chromatography-mass spectrometry quantitative profiling of tryptic digests of soluble liver proteins and liver lipids, coupled with principle component analysis, enabled rapid identification of early protein and metabolite markers of disease pathology. These included a 44% increase in L-FABP in transgenic animals compared to controls, as well as an increase in triglycerides and select bioactive lysophosphatidylcholine species. A correlation analysis of identified genes, proteins, and lipids was used to construct an interaction network. Taken together, these results indicate that integrative biology is a powerful tool for rapid identification of early markers and key components of pathophysiologic processes, and constitute the first application of this approach to a mammalian system.
Animals↗
Multiplexed screening assay for mRNA combining nuclease protection with luminescent array detection.
The principles and performance are described for the ArrayPlate mRNA assay, a multiplexed mRNA assay for high-throughput and high-content screening and drug development. THP-1 monocytes grown and subjected to compound treatments in 96-well plates were subjected to a multiplexed nuclease protection assay in situ. The nuclease protection assay destroyed all cell-derived mRNA, but left intact stoichiometric amounts of 16 target-specific oligonucleotide probes. Upon transfer of processed cell lysates to a microplate that contained a 16-element oligonucleotide array at the bottom of each well, the various probe species were separated by immobilization at predefined elements of the array. Quantitative detection of array-bound probes was by enzyme-mediated chemiluminescence. A high-resolution charge-coupled device imager was used for the simultaneous readout of all 1536 array elements in a 96-well plate. For the measurement of 16 genes in samples of 25000 cells, the average standard deviation from well to well within a plate was 8.6% of signal intensity and was 10.8% from plate to plate. Assay response was linear and reproducibility was constant for all detected genes in samples ranging from 1000 to 50000 cells. When THP-1 monocytes were differentiated with phorbol ester and subsequently activated with bacterial lipopolysaccharide that contained different concentrations of dexamethasone, dose-dependent effects of dexamethasone on the mRNA levels of several genes were observed.
Anti-Inflammatory Agents↗
SST versus EST in gene recognition.
The expressed sequence tag (EST) data provide a powerful tool for identification of transcribed DNA sequences. However, as EST are relatively short, many exons are poorly covered by EST, thus reducing the utility of EST data. Recently, signature sequence tag (SST) fingerprints were proposed as an alternative to EST fingerprints. Given a fingerprint set of probes, SST of a clone is a subset of probes from the fingerprint set that hybridize with the clone. We demonstrate that besides being a powerful technique for screening cDNA libraries, SST technology provides for very accurate gene predictions. Even with a small fingerprint set (600-800 probes), SST-based gene recognition outperforms many conventional and EST-based methods. The increase in the size of the fingerprint set to 1500 probes provides almost perfect gene recognition. Even more importantly, SST-based gene predictions miss very few exons and, therefore, provide an opportunity to bypass the cDNA sequencing step on the way from finished genomic sequence to mutation detection in gene-hunting projects. Because SST data can be obtained in a highly parallel and inexpensive way, SST technology has a potential of complementing EST technology for gene hunting.
Computational Biology↗
Selection of optimal DNA oligos for gene expression arrays.
MOTIVATION: High density DNA oligo microarrays are widely used in biomedical research. Selection of optimal DNA oligos that are deposited on the microarrays is critical. Based on sequence information and hybridization free energy, we developed a new algorithm to select optimal short (20-25 bases) or long (50 or 70 bases) oligos from genes or open reading frames (ORFs) and predict their hybridization behavior. Having optimized probes for each gene is valuable for two reasons. By minimizing background hybridization they provide more accurate determinations of true expression levels. Having optimum probes minimizes the number of probes needed per gene, thereby decreasing the cost of each microarray, raising the number of genes on each chip and increasing its usage. RESULTS: In this paper we describe algorithms to optimize the selection of specific probes for each gene in an entire genome. The criteria for truly optimum probes are easily stated but they are not computable at all levels currently. We have developed an heuristic approach that is efficiently computable at all levels and should provide a good approximation to the true optimum set. We have run the program on the complete genomes for several model organisms and deposited the results in a database that is available on-line (http://ural.wustl.edu/~lif/probe.pl). AVAILABILITY: The program is available upon request.
Algorithms↗