ABSTRACT: The growth and development of the uterus in response to 17β-estradiol (E2) is genetically controlled, with marked variation observed depending on the mouse strain studied. Previous work from our laboratory using inbred mice that are high (C57BL6/J; B6) or low (C3H/HeJ; C3H) responders to E2 has led to the identification of quantitative trait loci (QTL) associated with phenotypic variation in uterine growth and eosinophil infiltration. The mechanisms underlying differential responsiveness to E2, and the genes involved, are unknown. Therefore, we used a microarray approach to show association of distinct E2-regulated transcriptional signatures with genetically controlled high and low responses to E2. Among the 6,664 E2-responsive uterine transcripts, several reside within our previously identified QTL, including the ERα-tethering factor Runx1, demonstrated to enhance E2-mediated transcript regulation. The level of RUNX1 in uterine epithelial cells was shown to be 3.5-fold greater in B6 compared to C3H. Analysis of cellular functions in sets of strain-dependent E2-responsive transcripts indicated C3H-selective enrichment of apoptosis, consistent with a 7-fold increase in the apoptosis indicator CASP3, and a 2.4-fold decrease in the apoptosis inhibitor Naip1 in C3H vs. B6 following treatment with E2. Our novel insights into the mechanisms underlying the genetic control of tissue sensitivity to estrogen have great potential to advance understanding of individualized effects in physiological and disease states. Eight-week-old female B6, C3H, and (B6 × C3H)F1 (B6C3) hybrid mice were purchased from The Jackson Laboratory (Bar Harbor, ME). Animals were ovariectomized at NIEHS, rested for 1 to 2 wk, and then subjected to treatment with either E2 (40.0 μg/kg BW injected i.p.) in 0.1 ml saline containing 0.25% ethanol, or ethanol/saline vehicle. Animals were euthanized and tissue collected at 2 or 24 h after injection. Uterine tissue from 3 animals per treatment group was collected, and snap-frozen in liquid nitrogen for subsequent RNA isolation. Frozen uterine tissue from three animals per treatment group was pulverized, then homogenized in Trizol (Invitrogen, Carlsbad, CA), and RNA was prepared according to the manufacturer's protocol. Isolated RNA was then further purified using the QIAGEN (Valencia, CA) RNeasy mini prep kit clean-up protocol. Gene expression analysis was conducted using Agilent Whole Mouse Genome 4x44 Multiplex format oligo arrays (014868; Agilent Technologies, Santa Clara, CA) following the Agilent 1-color microarray-based gene expression analysis protocol. Starting with 500 ng of total RNA, Cy3-labeled cRNA was produced according to the manufacturer's protocol. For each sample, 1.65 ug of Cy3-labeled cRNAs were fragmented and hybridized for 17 hours in a rotating hybridization oven. Slides were washed and then scanned with an Agilent Scanner.
