A novel doxycycline‐inducible system for the transgenic analysis of mammary gland biology

Abstract

Normal developmental events such as puberty, pregnancy, and parity influence the susceptibility of the mammary gland to tumorigenesis in both humans and rodent model systems. Unfortunately, constitutive transgenic mouse models that rely on mammary-specific promoters to control transgene expression have limited utility for studying the effect of developmental events on breast cancer risk since the hormonal signals governing these events also markedly influence transgene expression levels. A novel transgenic mouse system is described that uses the MMTV-LTR to drive expression of the reverse tetracycline-dependent transactivator rtTA. Transgenic mice expressing rtTA in the mammary epithelium were crossed with reporter lines bearing tet operator-controlled transgenes. We tested the ability to spatially, temporally, and quantitatively control reporter gene expression after administration of doxycycline to bitransgenic mice. Transgene expression using this system can be rapidly induced and deinduced, is highly mammary specific, can be reproducibly titrated over a wide range of expression levels, and is essentially undetectable in the uninduced state. Homogeneous transgene expression throughout the mammary epithelium can be achieved. This system permits transgene expression to be restricted to any desired stage of postnatal mammary gland development. We have developed a mammary-specific, doxycycline-inducible transgenic mouse model for studying the effect of mammary gland development on transgene-mediated phenotypes. Unlike other mammary-specific, transgenic systems that have been described, this system combines spatially homogeneous transgene expression in the mammary epithelium during puberty, pregnancy, lactation, and involution with the use of an orally administered, inexpensive, and widely available inducing agent. This system offers new opportunities for the transgenic analysis of mammary gland biology in vivo.

Transgenic overexpression of IGF-IR disrupts mammary ductal morphogenesis and induces tumor formation

“…This concentration of doxycycline has previously been demonstrated to induce near-maximal expression of the rtTA in the MTB mice (Gunther et al, 2002). Mammary tissue from MTB-IGFIR1 mice treated with doxycycline for either 21 days or 34 days contained elevated levels of IGF-IR compared to MTB, TRE-IGFIR1 and WT-treated mice (Figure 1a).…”

“…Mice MTB mice were provided by Dr L Chodosh (University of Pennsylvania, Philadelphia, PA, USA) and are described in Gunther et al (2002). TRE-IGFIR transgenic mice were generated by cloning the full-length human IGF-IR cDNA (provided by Dr R Baserga, Kimmel Cancer Institute, Philadelphia, PA, USA) downstream of the pTRE2 vector (Clontech, Palo Alto, CA, USA).…”

A temporal requirement for Hippo signaling in mammary gland differentiation, growth, and tumorigenesis

“…We tested this hypothesis through transgenic overexpression of human YAP under the control of a tetracycline response element (TRE) (Dong et al 2007). Crossing the TRE-YAP strain with the mammaryspecific MMTV-rtTA driver (Gunther et al 2002) allowed mammary-specific YAP overexpression in a doxycyclineregulated manner (Supplemental Fig. S5A).…”

Translating Lung Function Genome-Wide Association Study (GWAS) Findings

“…Inducible knock out mice can also be produced whereby gene expression can be turned on or off by doxycycline or tetracycline-regulated systems (Gunther et al, 2002;Shockett, Difilippantonio, Hellman, & Schatz, 1995). A way of producing lung specific inducible knockout mice is by exploiting the cell make-up of the airways, i.e.…”