Experimental approaches to study mammary epithelial stem cells: Role of the ETS gene PEA3 during stem cell differentiation

The paradigm of cancer stem cells and their contribution to certain types of human tumors is now well established. However, the molecular mechanisms that regulate formation, self-renewal, and differentiation of stem cells remain poorly understood. Exploiting the full potential of such cells will require a detailed understanding of the spectrum of genetic factors that control stem cell processes. The main objective of this dissertation is to facilitate understanding of the ontology and etiology of mammary epithelial stem cells. I first investigated the role of the pea3 transcription factor gene during mammary epithelial stem cell differentiation. To generate a renewable source of mammary epithelial stem and progenitor cells and to facilitate the studies of Pea3 during stem cell differentiation, I made use of previously described method for culturing neuronal stem and progenitor cell in vitro. Indeed, culturing mammary epithelial cells as non-adherent mammospheres presents a renewable source of functional bona fide stem and progenitor cell types for molecular studies. I further report that culturing mouse mammary tumor cells as non-adherent tumorspheres affords a rich source of tumor-initiating cells and may help in their identification and characterization. Importantly, I report that mouse mammary tumors contain entirely of cancer stem cells, in apparent contrast to the frequency of such cells in human breast tumors. Hence mouse mammary tumors may offer a rich source of cancer stem cells and in parallel with an in vitro sphere formation as an assay for stem cells, may provide a model system to understand these cells.