Inhibition of lobuloalveolar development by FOXC1 overexpression in the mouse mammary gland

Bowen Gao,Ying Qu,Yoshiko Nagaoka,Liting Jin,Xiaojiang Cui,Nan Deng,Bingchen Han,Makoto Katsumata,Armando E Giuliano,Shikha Bose

doi:10.1038/s41598-017-14342-8

Abstract

The forkhead box transcription factor FOXC1 plays a critical role in embryogenesis and the development of many organs. Its mutations and high expression are associated with many human diseases including breast cancer. Although FOXC1 knockout mouse studies showed that it is not required for mammary gland development during puberty, it is not clear whether its overexpression alters normal mammary development in vivo. To address this question, we generated transgenic mice with mammary-specific FOXC1 overexpression. We report that transgenic FOXC1 overexpression suppresses lobuloalveologenesis and lactation in mice. This phenotype is associated with higher percentages of estrogen receptor-, progesterone receptor-, or ki67-positive mammary epithelial cells in the transgenic mice at the lactation stage. We also show that expression of the Elf5 transcription factor, a master regulator of mammary alveologenesis and luminal cell differentiation, is markedly reduced in mammary epithelial cells of transgenic mice. Likewise, levels of activated Stat5, another inducer of alveolar expansion and a known mediator of the Elf5 effect, are also lowered in those cells. In contrast, the cytokeratin 8-positive mammary cell population with progenitor properties is elevated in the transgenic mice at the lactation stage, suggesting inhibition of mammary cell differentiation. These results may implicate FOXC1 as a new important regulator of mammary gland development.

Highlights

Mammary gland development is a highly dynamic and complex physiological process in mammals that involves periodic cycles of mammary epithelium proliferation, differentiation, apoptosis, and morphogenesis throughout a female’s life[1]
The forkhead box C1 (FOXC1) transgene was not detected in these tissues as opposed to mammary tissue. These results indicate that the mammary tumor virus (MMTV)-FOXC1 transgenic mice express the transgene in the luminal epithelium of the mammary gland
Wildtype controls displayed reduced Ki67+ staining at the lactation stage when mammary cells undergo lactogenesis, whereas the percentages of Ki67+ mammary cells were similar between pregnancy day 11.5 and lactation day 2 in transgenic mice (Figure S2). These results suggest that FOXC1 overexpression may alter the proportions of estrogen receptor (ER), progesterone receptor (PR), and Ki67-expressing mammary epithelial cells during the lactation stage, consistent with the whole mount staining showing that the FOXC1 transgene disrupts lobuloalveolar development

Summary

Introduction

Mammary gland development is a highly dynamic and complex physiological process in mammals that involves periodic cycles of mammary epithelium proliferation, differentiation, apoptosis, and morphogenesis throughout a female’s life[1]. These results suggest that FOXC1 overexpression may alter the proportions of ER-, PR-, and Ki67-expressing mammary epithelial cells during the lactation stage, consistent with the whole mount staining showing that the FOXC1 transgene disrupts lobuloalveolar development. Elf[5] expression is suppressed in mammary epithelial cells of transgenic mice at lactation.

Results

Conclusion