Unknown,Transcriptomics,Genomics,Proteomics

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The impact of quantitative microarray optimization on gene expression analysis

ABSTRACT: Background: With the growing availability of entire genome sequences, an increasing number of scientists can exploit oligonucleotide microarrays for genome-scale expression studies. While probe-design is a major research area, relatively little work has been reported on the optimization of microarray protocols. Results: As shown in this study, suboptimal conditions can have considerable impact on biologically relevant observations. For example, deviation from the optimal temperature by one degree Celsius lead to a loss of 44% of differentially expressed genes identified. While genes from thousands of Gene Ontology categories were affected, transcription factors and other low-copy-number regulators were disproportionately lost. Calibrated protocols are thus required in order to take full advantage of the large dynamic range of microarrays. For an objective optimization of protocols we introduce an approach that maximizes the amount of information obtained per experiment. A comparison of two typical samples is sufficient for this calibration. We ensure, however, that optimization results are independent of the samples and the specific measures used for calibration. Both simulations and spike-in experiments confirm an unbiased determination of generally optimal experimental conditions. Conclusions: Well calibrated hybridization conditions are thus easily achieved and necessary for the efficient detection of differential expression. They are essential for the sensitive profiling of low-copy-number molecules. This is particularly critical for studies of transcription factor expression, or the inference and study of regulatory networks. Supporting material, including source code and data, is available at http://bioinf.boku.ac.at/pub/optMA2010/. Optimization of hybridization temperature via an assessment of differential expression between two samples (male vs female Drosophila melanogaster) in 6 technical replicates (3 regular + 3 dye-swaps) for hybridizations at different temperatures (in two batches of 50, 52, 54, and 56; and 47, 49, 50, and 51 degree Celsius, with the repeated hybridization at 50 degree Celsius serving to demonstrate batch-to-batch stability).

ORGANISM(S): Drosophila melanogaster

SUBMITTER: D Kreil

PROVIDER: E-GEOD-25625 | biostudies-arrayexpress |

REPOSITORIES: biostudies-arrayexpress

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Project description:Prenatal Human Cytomegalovirus (HCMV) infection often causes CNS maldevelopment. In a murine model, we detect Murine Cytomegalovirus (MCMV) in brain following intra-peritoneal inoculation at birth. Infected mice show impaired cerebellar development and impaired neurologic function on a beam balance test as adults. Among developmental genes differentially regulated, hindbrain expression of the homeodomain transcription factor HOXa5 was reduced with infection, and fewer HOXa5 expressing neurons were found in vestibular nuclei. Based on the hypothesis that immune activation connects focal viral infection and global CNS maldevelopment, we defined the components of CNS immune response. Flow cytometry showed a large increase in both number and activation of CNS monocytes. Monocytes were found in close association with infected cells by immunohistochemistry (IHC). Oligonucleotide microarrays contained herein identified many differentially expressed genes related to innate immune response. Chemokines, cytokines, cell surface receptors, and proteases are some of the many immunological genes shown to be differentially regulated by MCMV infection. These results together show that MCMV infection induces a complex immune response associated with changes in developmental gene expression and lasting neurologic defecit. Keywords: disease state comparison (virus infection) and competetive hybridization for expression analysis Previous work empirically determined the kinetics of viral spread to and replication in the Balb-C murine CNS. Balb-C mice were inoculated intra-peritoneally at birth, and harvested at 5, 8, 12, and 21 days post inoculation for cerebellar experiments. Controls were mock infected with vehicle (DMEM cell growth media) and harvested at the same timepoints. Each microarray was a two channel MEEBO array, upon which labeled and reverse transcribed cDNA from 3 pooled infected cerebella and three pooled uninfected cerebella competetively hybridized. Three unique biological replicates were performed with day 5 cDNA, 5 unique biological replicates at day 8, 5 unique biological replicates at day 12, and 4 unique biological replicates at day 21. For the analysis, colors channels were seperated and treated as independent hybridizations. However, since the experiments were dual channel, the primary data may be employed to generate ratio based measurements, and each sample is provided a corresponding number that can be used to pair the processed data and derive ratios (mock 3, infected 3). Mice were similarly inoculated and harvested at 5, 15, and 21 days post natal for liver tissue analysis. Inoculation was performed by injection with a microsyringe of 50ul titered virus delivering 500-1000 PFU per animal.

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The impact of quantitative microarray optimization on gene expression analysis

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