Genetic Control of Ductal Morphology, Estrogen-Induced Ductal Growth, and Gene Expression in Female Mouse Mammary Gland

Abstract

The uterotropic response of the uterus to 17β-estradiol (E2) is genetically controlled, with marked variation observed depending on the mouse strain studied. Previous genetic studies from our laboratory using inbred mice that are high (C57BL6/J; B6) or low (C3H/HeJ; C3H) responders to E2 led to the identification of quantitative trait loci (QTL) associated with phenotypic variation in uterine growth and leukocyte infiltration. Like the uterus, phenotypic variation in the responsiveness of the mammary gland to E2 during both normal and pathologic conditions has been reported. In the current experiment, we utilized an E2-specific model of mammary ductal growth combined with a microarray approach to determine the degree to which genotype influences the responsiveness of the mammary gland to E2, including the associated transcriptional programs, in B6 and C3H mice. Our results reveal that E2-induced mammary ductal growth and ductal morphology are genetically controlled. In addition, we observed a paradoxical effect of mammary ductal growth in response to E2 compared with what has been reported for the uterus; B6 is a high responder for the uterus and was a low responder for mammary ductal growth, whereas the reverse was observed for C3H. In contrast, B6 was a high responder for mammary ductal side branching. The B6 phenotype was associated with increased mammary epithelial cell proliferation and apoptosis, and a distinct E2-induced transcriptional program. These findings lay the groundwork for future experiments designed to investigate the genes and mechanisms underlying phenotypic variation in tissue-specific sensitivity to systemic and environmental estrogens during various physiological and disease states.

Genetic variation in sensitivity to estrogens and breast cancer risk

“…Hierarchical clustering defined 4 patterns of development represented by C3H/HeJ, 129S1/SvlmJ, C57BL/6J and BALB/cByJ (Clusters 1–4, respectively). This is consistent with the differences in ductal growth between C57BL/6J and C3H/HeJ strains (Table 1) following acute treatment with 17β-estradiol (Wall et al 2014a). The analysis of mammary gland development identified 20 mammary ductal quantitative trait loci ( Mdq , Table 3).…”

“…Treatment with 17β-estradiol also stimulates expansion of the of ductal branching in mammary glands. The extent of development was nearly 2-fold greater in C57BL/6J mice compared to C3H/HeJ (Wall et al 2014a). Although estrogen stimulates increases in tissue mass in both the mammary epithelium and uterus, little overlap was observed in transcriptional profiles induced by 17β-estradiol in these tissues (Wall et al 2014b).…”

“…However, only 5 publications compared responses across strains of mice or rats and differed greatly in doses and duration of treatments. Acute exposure to 17β-estradiol for 4 days was evaluated in C57BL/6J and C3H/H3J mice that were ovariectomized prior to puberty (Wall et al 2014a). Branching of mammary ducts was greatest in C57BL/6J females, whereas C3H/HeJ exhibited a greater ductal length.…”

“…This was most notable in the pituitary and mammary tissues of BN and COP rats indicating an ability to attenuate signaling (Ding et al 2013; Gould et al 2000) but not in ACI and F344. In the case of mammary epithelium of C57BL/6J mice, proliferation in response to 17β-estradiol appeared to be balanced by an increase in apoptosis (Wall et al 2014a). In contrast, ACI rats have a persistent proliferative response to DES in mammary epithelium without a compensatory increase in apoptosis and was associated with extensive hyperplasia (Ding et al 2013).…”

Hormone-Sensing Mammary Epithelial Progenitors: Emerging Identity and Hormonal Regulation

“…This is consistent with a previous finding that silencing RUNX1 expression induced hyper-proliferation and abnormal organisation of the immortilised, non-transformed human MEC line, MCF10A [161], though these cells lack notable steroid receptor expression. Evidence of RUNX1 being associated with oestrogen-regulated phenotypic changes in mammary ductal length have been suggested based on quantitative trait loci analysis [162], however contrary to the association of RUNX1 with inhibiting MEC proliferation in genetic modification and functional studies, this later study identified a positive association of RUNX1 with oestrogen-induced ductal growth. The stark differences between methods of investigation could be the reason behind this discrepancy.…”