Unknown,Transcriptomics,Genomics,Proteomics

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Gene Expression during the Egg Development of Drosophila melanogaster.

ABSTRACT: Despite the importance of egg development to the female life cycle in Drosophila, global patterns of gene expression have not been examined in detail primarily due to the difficulty of synchronizing developmental stages. Entry into vitellogenesis is however an key stage of oogenesis, and by delaying entry past this control point, we have been able to investigate some of the transcriptional dynamics apparent before and after early egg formation over a 72 hour period. A short-day photoperiod (10:14 light:dark photoperiod) and moderate temperatures (11Â°C) are required for the induction of ovarian diapause. For our microarray experiments, 0-4 hours post-eclosion females were immediately introduced to the restrictive environmental conditions. Females were subsequently collected for RNA extraction after 5-7 days, or were alternatively re-introduced to normal environmental conditions to continue egg development. Time-points were collected before and after the release of reproductive arrest at 24 hour intervals and hybridized in a balanced loop design, including dye-swaps. Eight biological replicates were subsequently performed for each treatment, including 3 day old male and female controls maintained under normal environmental conditions.

ORGANISM(S): Drosophila melanogaster

SUBMITTER: Dean Baker

PROVIDER: E-GEOD-13303 | biostudies-arrayexpress |

REPOSITORIES: biostudies-arrayexpress

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Project description:Analysis of differential gene expression in third instar Drosophila salivary glands in the absence versus presence of cohesin. ABSTRACT: Developmental abnormalities observed in Cornelia de Lange Syndrome (CdLS) have been genetically linked to mutations in the cohesin machinery. These findings raise the possibility that cohesin, in addition to its canonical function of mediating sister chromatid cohesion, might also be involved in regulating gene expression. We report that cleavage of cohesinM-CM-^Us kleisin subunit in post-mitotic Drosophila salivary glands induces major changes (both up and down) in the transcript levels of many genes. Kinetic analyses of changes in transcript levels upon cohesin cleavage reveal that a subset of genes responds to cohesin cleavage within a few hours. In addition, cohesin binds to most of these loci, suggesting that cohesin is directly regulating their expression. Amongst these genes are several that are regulated by the steroid hormone Ecdysone. Transcripts at EcR and Eip74EF, which encode an Ecdysone Receptor and an Ecdysone-regulated transcription factor, respectively, decline ten-fold within four hours of cohesin cleavage. Cytological visualization of transcription at selected Ecdysone-responsive genes reveals that puffing at Eip74EF ceases within an hour or two of cohesin cleavage, long before any decline in EcR associated with this locus. We conclude that cohesin regulates expression of a distinct set of genes, including those mediating the Ecdysone response. A heat-inducible transgene (hs-TEV) was used to induce TEV in terminally differentiated third instar Drosophila salivary glands expressing either wild type (+ cohesin) or TEV-cleavable myc10-tagged Rad21 protein (Rad21TEV, - cohesin). Total RNA was isolated from + and - cohesin salivary glands 10-12 hours after heat shock induction of TEV (7 independent biological samples each). RNA samples were converted to cDNA, labeled with Cy3 and Cy5 respectively (3x) and vice versa (4x; dye swaps), and hybridized to INDAC FL003 arrays. Analysis of seven arrays, each hybridized to an independently generated sample-pair revealed major differences in transcript levels between + and - cohesin samples.

Project description: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).

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Gene Expression during the Egg Development of Drosophila melanogaster.

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