Metabolomics,Unknown,Transcriptomics,Genomics,Proteomics

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Transcription profiling of human cancer cells using different washing cycles after hybridization

ABSTRACT: Post-hybridization washing is an essential part of microarray experiments. Both, the quality of the experimental washing protocol and the adequate consideration of washing in intensity calibration ultimately affect the quality of the expression estimates extracted from the microarray intensities. We conducted experiments on GeneChip microarrays with altered protocols for washing, scanning and staining to study the probe-level intensity changes as a function of washing cycles. Particularly, three Affymetrix GeneChip HGU133plus2 arrays were hybridized and equilibrated for 16 hours in the hybridization oven. For one of the three arrays washing and staining was performed according to the manufacturer’s instructions. For another array the first scan was done immediately after low stringent wash and staining without intermitting stringent washing. Then, the array was stringently washed and scanned in alternating order three more times where each washing step consists of a definite number of washing cycles. The third array was low stringently washed followed by two stringent washing cycles and staining before the first scan. Subsequently it was analogously processed as array A. All three chips are repeatedly processed in a second series of alternating wash/scan-cycles which was performed using the same protocol for each chip as in the first series as described above. As in the first series the arrays were also stained a second time to compensate for any loss of bleached fluorescent dye. Analysis of the washing kinetics shows that the signal-to-noise ratio doubles roughly every ten stringent washing cycles. Washing can be characterized by time-dependent rate constants which reflect the heterogeneous character of target binding to microarray probes. We propose an empirical washing function which estimates the survival of probe bound targets. The washing function allows calibrating probe intensities for the effect of washing. On a relative scale, proper calibration for washing markedly increases expression measures especially in the limit of small and large values. Experiment Overall Design: The aim of the study was to understand the probe-level intensity changes as a function of washing cycles. For this experiment RNA was prepared from a cancer cell line and used for probe synthesis. Hybridisation to three Affymetrix microarrays was identically performed with aliquotes of one hybridization mix from a single RNA sample. The protocols for washing, scanning and staining were altered.

ORGANISM(S): Homo sapiens

SUBMITTER: Knut Krohn

PROVIDER: E-GEOD-18161 | biostudies-arrayexpress |

REPOSITORIES: biostudies-arrayexpress

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Project description:Post-hybridization washing is an essential part of microarray experiments. Both, the quality of the experimental washing protocol and the adequate consideration of washing in intensity calibration ultimately affect the quality of the expression estimates extracted from the microarray intensities. We conducted experiments on GeneChip microarrays with altered protocols for washing, scanning and staining to study the probe-level intensity changes as a function of washing cycles. Particularly, three Affymetrix GeneChip HGU133plus2 arrays were hybridized and equilibrated for 16 hours in the hybridization oven. For one of the three arrays washing and staining was performed according to the manufacturer’s instructions. For another array the first scan was done immediately after low stringent wash and staining without intermitting stringent washing. Then, the array was stringently washed and scanned in alternating order three more times where each washing step consists of a definite number of washing cycles. The third array was low stringently washed followed by two stringent washing cycles and staining before the first scan. Subsequently it was analogously processed as array A. All three chips are repeatedly processed in a second series of alternating wash/scan-cycles which was performed using the same protocol for each chip as in the first series as described above. As in the first series the arrays were also stained a second time to compensate for any loss of bleached fluorescent dye. Analysis of the washing kinetics shows that the signal-to-noise ratio doubles roughly every ten stringent washing cycles. Washing can be characterized by time-dependent rate constants which reflect the heterogeneous character of target binding to microarray probes. We propose an empirical washing function which estimates the survival of probe bound targets. The washing function allows calibrating probe intensities for the effect of washing. On a relative scale, proper calibration for washing markedly increases expression measures especially in the limit of small and large values.

Project description:Goal of experiment: Identification of differentially expressed immune genes from male and female BWF1 lupus-prone mice. (Female incidence is higher than male--attempting to find sex hormone regulated genes that may contribute to this difference). Whole spleen was taken from pre-lupus (4 months old) BWF1 (females are lupus-prone) male and female mice. Preparation of cDNA. Double-stranded cDNA was synthesized from purified RNA. The first strand was synthesized by incubating 5 μg of RNA with 100 pg/ml T7-(dT)24 primer (HPLC purified DNA primer sequence: 5’-GGCCAGTGAATTGTAATACG ACTCACTATAGGGAGGCGG-(dT)24 -3’ Genset Corp, San Diego, CA) at 70°C for 10 minutes. Samples were incubated for 1 hour at 42°C with the following mix: 1X first strand buffer, 10 mM dithiothreitol, 500 μM each dNTP, 200 U SuperScript II in diethylpyrocarbonate (DEPC)-treated water up to 20 μl. Second strand synthesis was performed by incubating the first strand with the following mix for 2 hours at 16°C: 1X second strand reaction buffer, 200 μM dntps, 10 U E. coli DNA ligase, 40 U E coli DNA Polymerase I, 2 U of E. coli RNase H up to 150 μl with DEPC-treated water (all reagents were contained in SuperScript Choice System for cDNA Synthesis, Invitrogen). A phenol/chloroform extraction was performed on the ds-cDNA preparation before biotin-labeled cRNA was generated. Synthesis and fragmentation of biotin-labeled cRNA (in vitro transcription). The ENZO BioArrayTM HighYieldTM RNA Transcript Labeling Kit (T7) (Enzo diagnostics, Inc., Farmingdale, NY) was used to produce large amounts of hybridizable biotin-labeled RNA targets by in vitro transcription from the ds-cDNA. The following mix was incubated at 37°C for 5 hours: 1 μg of ds-cDNA, 1X HY reaction buffer, 1X biotin labeled ribonucleotides, 1X dithiothreitol, 1X T7 RNA Polymerase. Biotin-labeled cRNA was run over RNeasy spin columns (Qiagen), quantified, and run on an agarose gel to visualize the size distribution of labeled transcripts. Twenty micrograms of cRNA was incubated with 1X fragmentation buffer for 35 minutes at 94°C. (5X fragmentation buffer: 200 mM Tris-acetate, pH 8.1, 500 mM KOAc, 150 mM MgOAc). After fragmentation, the samples were stored at -20°C until the hybridization was performed. Sample hybridization. Oligonucleotide microarrays (MGU74v2 A, B, and C GeneChip probe arrays; Affymetrix) were hybridized with labeled cRNA derived from spleens from individual mice. For each array,15 μg of fragmented cRNA was mixed with a hybridization cocktail consisting of 1X hybridization buffer (2X hybridization buffer: 100 mM MES, 1 M [Na+], 20 mM EDTA, 0.01% Tween), 0.5 mg/ml acetylated BSA (Invitrogen), 0.1 mg/ml herring sperm DNA (Promega), and water (BioWhittaker) up to 300 μl). Biotin labeled cRNA transcripts of the E. coli and P1 bacteriophage genes, BioB, bioC, bioD, and cre (GeneChip Eukaryotic Hybridization control kit, Affymetrix) were spiked into each hybridization mix at 1.5, 5, 25, and 100 pM to evaluate sample hybridization efficiency for each array. The hybridization cocktail was heated to 99°C and then 45°C for 5 minutes each before it was centrifuged to remove any insoluble material. The array was equilibrated to room temperature, moistened with 1X hybridization buffer, and incubated for 10 minutes at 45°C with rotation. After incubation, the buffer solution was removed from the array. The array was filled with 300 μl of the hybridization cocktail, placed in a rotisserie box in a 45°C oven, and incubated for 16 hours while rotating at 60 rpm. Washing and staining of array. The hybridization cocktail was removed and the GeneChip Fluidics Station 400 (Affymetrix) with Microarray Suite software (Affymetrix) was used to wash and stain the probe arrays with the following protocol: 10 cycles of 2 mixes/cycle with wash buffer A at 25°C, 4 cycles of 15 mixes/cycle with wash buffer B at 50°C, 30 minute incubation with staining solution at 25°C, 10 cycles of 4 mixes/cycle with wash buffer A at 25°C. Wash buffer A -- non-stringent wash buffer (6X sodium chloride sodium phosphate + ethylenediaminetetraacetic acid (SSPE), 0.01% Tween-20). (20X SSPE: 3 M NaCl, 0.2 M NaH2PO4, 0.02 EDTA) (BioWhittaker). Wash buffer B – stringent wash buffer (100mM MES, 0.1 M [Na+], 0.1% Tween 20). Staining solution (1X 2-(N-Morpholino)ethanesulfonic Acid (MES) stain buffer, 2 mg/ml acetylated BSA, 10 μg/ml Streptavidin Phycoerythrin (SAPE), and water up to 600 μl). (12X MES stain buffer: 1.22 M MES, 0.89 M [Na+]). Analysis. After staining, the probe arrays were scanned using the GeneChip 3000 Scanner (Affymetrix) with Microarray Suite software (Affymetrix). Technical and assay variation between arrays was corrected for by multiplying or dividing the overall intensity of each array by a scaling factor so that the overall intensity of each array was equivalent to facilitate comparison analysis. Keywords = BWF1 total spleen Keywords: repeat sample

Project description:Untargeted metabolomics aims at obtaining quantitative information on the highest possible number of low-molecular biomolecules present in a biological sample. Rather small changes in mass spectrometric spectrum acquisition parameters may have a significant influence on the detectabilities of metabolites in untargeted global-scale studies by means of high-performance liquid chromatography-mass spectrometry (HPLC-MS). Employing whole cell lysates of human renal proximal tubule cells, we present a systematic global-scale study of the influence of mass spectrometric scan parameters on the number and intensity of metabolites detectable in whole cell lysates. Ion transmission and ion collection efficiencies in an Orbitrap-based mass spectrometer generally depend on the m/z range scanned, which, ideally, requires different instrument settings for the respective mass ranges investigated. Therefore, we split a full scan range of m/z 50-1000 relevant for metabolites into two separate segments (m/z 50-200 and m/z 200-1000), allowing an independent tuning of the ion transmission parameters for both mass ranges. Three different implementations, involving either scanning from m/z 50-1000 in a single scan, or scanning from m/z 50-200 and from m/z 200-1000 in two alternating scans, or performing two separate HPLC-MS runs with m/z 50-200 and m/z 200-1000 scan ranges were critically assessed. The most efficient approach in terms of feature number, which forms the basis for statistical analysis, identification, and for generating biological hypotheses, was the separate analysis of two different mass ranges. This lead to an increase in the number of detectable metabolite features, especially in the higher mass range (m/z greater than 400), by 2.5 (negative mode) to 6-fold (positive mode) as compared to analysis involving a single scan range. Application of the method to metabolite extracts prepared from whole cell lysates of human renal proximal tubule epithelial cells initially yielded up to 13,000 – 69,000 detectable features, which were subjected to rigorous background filtering and quality control in order to obtain reliable metabolite features for subsequent differential quantification.

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Transcription profiling of human cancer cells using different washing cycles after hybridization

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