Targeting reverse tetracycline-dependent transactivator to murine mammary epithelial cells that express the progesterone receptor

Abstract

Through an established gene-targeting strategy, reverse tetracycline-dependent transactivator (rtTA) was targeted downstream of the murine progesterone receptor (PR) promoter. Mice were generated in which one (PR+/rtTA) or both (PRrtTA/rtTA) PR alleles harbor the rtTA insertion. The PR+/rtTA and PRrtTA/rtTA knockins exhibit phenotypes identical to the normal and the progesterone receptor knockout mouse, respectively. Crossed with the TZA reporter, which carries the TetO-LacZ responder transgene, the PR+/rtTA/TZA and PR rtTA/rtTA/TZA bigenics exhibit doxycycline-induced β-galactosidase activity specifically in progesterone responsive target tissues such as the mammary gland, uterus, ovary, and pituitary gland. In the case of the PR+/rtTA/TZA mammary epithelium, dual immunofluorescence demonstrated that PR expression and doxycycline-induced β-galactosidase activity colocalized; β-galactosidase was not detected in the absence of doxycycline. Although both the PR+/rtTA and PRrtTA/rtTA knockins represent innovative animal models with which to further query progesterone's mechanism of action in vivo, the PRrtTA/rtTA mouse in particular promises to provide unique insight into the paracrine mechanism of action, which underpins progesterone's involvement in mammary morphogenesis with obvious implications for extending our understanding of this steroid's role in breast cancer progression. © 2007 Wiley-Liss, Inc.