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.

Evidence for a multipotent mammary progenitor with pregnancy-specific activity

“…As expected, H2BGFP was not detected in mammary cells from single transgenic or uninduced double transgenic mice (data not shown). In contrast to a previous report that this MMTVrtTA transgene drives ubiquitous expression in MECs [21], H2BGFP expression was detected in only a fraction (18 ± 3.1%) of MECs from double transgenic mice (Figure 1a; also see Discussion).…”

“…Our observation that MMTVrtTA is active in mammary stem cells and pregnancy-activated progenitors conflicts with a previous report that the same strain of MMTVrtTA is expressed homogeneously in all MECs [21]. In that study, the MMTVrtTA transgene-induced expression of tetracycline-driven LacZ, and an enzymatic assay was used to detect transgene expression.…”

Evidence for a multipotent mammary progenitor with pregnancy-specific activity

“…As expected, H2BGFP was not detected in mammary cells from single transgenic or uninduced double transgenic mice (data not shown). In contrast to a previous report that this MMTVrtTA transgene drives ubiquitous expression in MECs [21], H2BGFP expression was detected in only a fraction (18 ± 3.1%) of MECs from double transgenic mice (Figure 1a; also see Discussion).…”

“…Our observation that MMTVrtTA is active in mammary stem cells and pregnancy-activated progenitors conflicts with a previous report that the same strain of MMTVrtTA is expressed homogeneously in all MECs [21]. In that study, the MMTVrtTA transgene-induced expression of tetracycline-driven LacZ, and an enzymatic assay was used to detect transgene expression.…”

P190-B Rho GTPase-Activating Protein Overexpression Disrupts Ductal Morphogenesis and Induces Hyperplastic Lesions in the Developing Mammary Gland

“…As expected, the HA-tagged p190-B transgene is localized to the mammary epithelial cells, which is consistent with the expression of the MMTV-rtTA within this compartment of the mammary gland ( Fig. 1F) (15).…”

Activation of nuclear factor kappa B in mammary epithelium promotes milk loss during mammary development and infection

“…Transgene expression was observed in mammary gland tissue but not in kidney, liver or heart. A lower level of transgene expression was observed in the salivary gland as has been previously reported for the MMTV-rtTA mouse model (Gunther et al, 2002). …”

Evidence for a multipotent mammary progenitor with pregnancy-specific activity

“…As expected, H2BGFP was not detected in mammary cells from single transgenic or uninduced double transgenic mice (data not shown). In contrast to a previous report that this MMTVrtTA transgene drives ubiquitous expression in MECs [21], H2BGFP expression was detected in only a fraction (18 ± 3.1%) of MECs from double transgenic mice (Figure 1a; also see Discussion).…”

“…Our observation that MMTVrtTA is active in mammary stem cells and pregnancy-activated progenitors conflicts with a previous report that the same strain of MMTVrtTA is expressed homogeneously in all MECs [21]. In that study, the MMTVrtTA transgene-induced expression of tetracycline-driven LacZ, and an enzymatic assay was used to detect transgene expression.…”

P190-B Rho GTPase-Activating Protein Overexpression Disrupts Ductal Morphogenesis and Induces Hyperplastic Lesions in the Developing Mammary Gland

“…As expected, the HA-tagged p190-B transgene is localized to the mammary epithelial cells, which is consistent with the expression of the MMTV-rtTA within this compartment of the mammary gland ( Fig. 1F) (15).…”

Activation of nuclear factor kappa B in mammary epithelium promotes milk loss during mammary development and infection

“…Transgene expression was observed in mammary gland tissue but not in kidney, liver or heart. A lower level of transgene expression was observed in the salivary gland as has been previously reported for the MMTV-rtTA mouse model (Gunther et al, 2002). …”

Evidence for a multipotent mammary progenitor with pregnancy-specific activity

“…As expected, H2BGFP was not detected in mammary cells from single transgenic or uninduced double transgenic mice (data not shown). In contrast to a previous report that this MMTVrtTA transgene drives ubiquitous expression in MECs [21], H2BGFP expression was detected in only a fraction (18 ± 3.1%) of MECs from double transgenic mice (Figure 1a; also see Discussion).…”

“…Our observation that MMTVrtTA is active in mammary stem cells and pregnancy-activated progenitors conflicts with a previous report that the same strain of MMTVrtTA is expressed homogeneously in all MECs [21]. In that study, the MMTVrtTA transgene-induced expression of tetracycline-driven LacZ, and an enzymatic assay was used to detect transgene expression.…”

P190-B Rho GTPase-Activating Protein Overexpression Disrupts Ductal Morphogenesis and Induces Hyperplastic Lesions in the Developing Mammary Gland

“…As expected, the HA-tagged p190-B transgene is localized to the mammary epithelial cells, which is consistent with the expression of the MMTV-rtTA within this compartment of the mammary gland ( Fig. 1F) (15).…”

Activation of nuclear factor kappa B in mammary epithelium promotes milk loss during mammary development and infection

“…Transgene expression was observed in mammary gland tissue but not in kidney, liver or heart. A lower level of transgene expression was observed in the salivary gland as has been previously reported for the MMTV-rtTA mouse model (Gunther et al, 2002). …”