Background

Although development of the mammary gland begins during embryonic development and a rudimentary epithelial structure is present at birth, the epithelial mammary tree undergoes extensive expansion postnatally. In response to hormonal changes, mammary epithelial cells proliferate and invade the mammary fat pad. During pregnancy, the mammary gland epithelium undergoes further differentiation and remodeling to prepare for milk production. Subsequently, these epithelial structures involute in response to weaning. These remodeling processes are driven by hormones, growth factors, cytokines and the extracellular matrix. In addition to remodeling in response to physiological processes, the mammary gland is subject to pathological processes such as neoplastic transformation. This complex biology together with the relatively ease of isolation make the mammary gland a useful experimental model. Experimental studies analyzing mammary gland biology or neoplastic transformation often employ mouse models to quantify the effect of gene deletion or overexpression on mammary gland development, remodeling and neoplastic transformation. Mammary gland whole mounts allow routine examination of these normal and disease processes on the entire 3D epithelial structure of the mammary gland (Plante et al., 2011; Inman et al., 2015; Tucker et al., 2016 and 2017; Kolla et al., 2017; Tolg et al., 2017). Furthermore, injection of mice with potential therapeutic compounds combined with whole mount analysis allows in vivo testing of future cancer treatment strategies. This protocol provides details of the procedure starting with removal of the mammary gland and ending with image analysis. A video of mammary gland isolation, photos, figures and referenced literature make it more complete compared to existing whole mount protocol.