Evaluation of the gene expression changes induced by 17-α-ethynyl estradiol in the immature uterus/ovaries of the rat using high density oligonucleotide arrays

BACKGROUND: In a previous study, we determined the effects of 17‐α‐ethynyl estradiol (EE) on gene expression using microarrays that represented approximately 9,000 genes, which was the state of‐the‐art. Higher content arrays with almost double the number of genes have since become available. In order to better determine whether common sets of gene expression changes can be predictive of estrogenic activity, we have replicated the previous experiment using the more comprehensive microarray. METHODS: Immature 20‐day‐old Sprague‐Dawley rats were exposed to 0.1, 1, and 10 µg EE/kg/day ( subcutaneously [s.c.]), for four days, dosing from postnatal day (PND) 20–23). Changes in a more comprehensive expression level of 15,923 rat annotated genes and expressed sequence tags were evaluated on PND 24. RESULTS: By comparing the response of the treatment groups versus controls using various statistical parameters, we determined that the expression of 1,394 genes showed a significant change with respect to control (p≤0.0001), to at least one of the EE dosages. The tissues from animals exposed to 0.1 µg EE/kg/day showed changes in the expression of only 33 genes, whereas when they were exposed to 1 or 10 µg EE/kg/day, the expression of 409 and 548 genes was modified, respectively. A dose‐dependent analysis indicated that 592 genes showed a robust and significant response to EE exposure (increased or decreased). Our analysis confirmed the regulation of previously identified estrogen‐sensitive genes, and clearly identified novel mediators of estrogen actions, both in the uterus as well as in the ovary. CONCLUSIONS: This compendium of genes represents the largest compilation of estrogen‐responsive genes that has ever been identified for the immature uterus and ovary of any species, and can be used to generate testable hypothesis to improve the understanding of the molecular pathways associated with physiological and pathophysiological responses to exposure to chemicals with estrogenic properties. Birth Defects Res B 74:164–184, 2005. © 2005 Wiley‐Liss, Inc.