Project description:The aim of this study was to compare the gene expression profile changes of DMBA-induced rat breast tumors from an initial stage to the moment of sacrifice. To this end, a cDNA microarray was performed (Affymetrix’s Rat Genome 230 2.0 array). This gene expression study was carried out on the umor biopsy samples and compared with matched tumor biopsy samples once the study ended (7 weeks after initial biopsy). Breast tumors were induced with a single oral dosage of 7,12-dimethylbenz(alpha)anthracene (100 mg/kg body weight) in female Sprague-Dawley rats. Gene expression analysis was performed in paired samples as follows: DMBA final trucut tumor vs initial trucut tumor (DMBA final vs basal). For this assay, 5 samples were chosen according to histopathologic criteria (Bloom-Richardson grade II). Gene expression profiling was carried out using Affymetrix’s GeneChip technology, using the Rat Genome 230 2.0 array from this provider. All the protocols and apparatus were recommended by Affymetrix. Total RNA from frozen mammary tumors was extracted by RNeasy Mini kit and homogenized by QIAshredder columns according to manufacturer’s instructions. The quality and quantity of the obtained RNA was checked out through agarose electrophoresis and later spectrophotometry at 260/280 nm. Biotinylated cRNA was synthesized following the IVT labeling kit from Affymetrix and purified by the GeneChip Sample Cleanup Module from Affymetrix. The quality and quantity of the obtained cRNA was again checked out through agarose electrophoresis and posterior spectrophotometry at 260/280 nm. After hybridization, slides were washed and scanned following the manufacturer’s standard protocol. Intensity values were normalized by Robust Multichip Average method and subsequently these were filtered to remove the control sequences and those with a hybridization signal close to background. The spike controls were: BioB, BioC, BioD and Cre; because BioB was the least abundant in the samples, it was used to estimate the sensitivity of the experiment. The housekeeping control was GAPDH. After non-supervised clustering using Pearson correlation coefficient, statistical significance of gene expression was estimated by Student’s T test for paired samples, using GeneSpring GX 7.3 software (Agilent).

Project description:A series of two color gene expression profiles obtained using Agilent 44K expression microarrays was used to examine sex-dependent and growth hormone-dependent differences in gene expression in rat liver. This series is comprised of pools of RNA prepared from untreated male and female rat liver, hypophysectomized (‘Hypox’) male and female rat liver, and from livers of Hypox male rats treated with either a single injection of growth hormone and then killed 30, 60, or 90 min later, or from livers of Hypox male rats treated with two growth hormone injections spaced 3 or 4 hr apart and killed 30 min after the second injection. The pools were paired to generate the following 6 direct microarray comparisons: 1) untreated male liver vs. untreated female liver; 2) Hypox male liver vs. untreated male liver; 3) Hypox female liver vs. untreated female liver; 4) Hypox male liver vs. Hypox female liver; 5) Hypox male liver + 1 growth hormone injection vs. Hypox male liver; and 6) Hypox male liver + 2 growth hormone injections vs. Hypox male liver. A comparison of untreated male liver and untreated female liver liver gene expression profiles showed that of the genes that showed significant expression differences in at least one of the 6 data sets, 25% were sex-specific. Moreover, sex specificity was lost for 88% of the male-specific genes and 94% of the female-specific genes following hypophysectomy. 25-31% of the sex-specific genes whose expression is altered by hypophysectomy responded to short-term growth hormone treatment in hypox male liver. 18-19% of the sex-specific genes whose expression decreased following hypophysectomy were up-regulated after either one or two growth hormone injections. Finally, growth hormone suppressed 24-36% of the sex-specific genes whose expression was up-regulated following hypophysectomy, indicating that growth hormone acts via both positive and negative regulatory mechanisms to establish and maintain the sex specificity of liver gene expression. For full details, see V. Wauthier and D.J. Waxman, Molecular Endocrinology (2008)

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Rattus norvegicus

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