Mouse mammary gland reconstitution with extrinsic gene-transferred mammary epithelial cells in vitro and in vivo

Cancer stem cells (CSCs) comprise a minor population of self-renewing, immortal tumor cells capable of differentiating into the various cell types found within the bulk tumor. However, whether CSCs are derived from normal stem or progenitor cells and the underlying mechanism whereby they are generated remain to be elucidated. To answer these queries and to investigate the process of carcinogenesis, we have developed a novel strategy to introduce genetic changes into a subset of mammary stem/progenitor cells in vitro and in vivo. We used retroviral vectors to introduce the enhanced green fluorescence protein (EGFP) reporter gene into the bulk of mouse mammary epithelial cells, and evaluated the tissue regenerative potential of these cells in vitro and in vivo. We showed that EGFP-transduced primary mouse mammary epithelial cells could regenerate duct-alveolar unit-like structures in 3-D Matrigel culture. However, we could not confirm clonogenic outgrowths of ectopic EGFP-expressing transplanted mammary epithelial cells in the recipient mouse. We present the preliminary results of these studies and discuss the significance of this model.