Evidence for a novel multipotent mammary progenitor with pregnancy-specific activity

The mouse mammary gland has emerged as a model system for studying processes involved in the development of epithelial tissues. Current evidence suggests the existence of a differentiation hierarchy in the mammary gland, consisting of a stem cell capable of reconstituting the tissue, progenitors with the capacity to produce specific functional cell types, and differentiated cells with limited or no repopulation potential. Although markers for mammary stem cells and progenitors have been identified, these populations have not been isolated to purity and our understanding of how they function in different stages of mammary development remains incomplete.