Identification of multipotent mammary stem cells by protein C receptor expression

Using transplantation and lineage-tracing strategies, protein C receptor is identified as a marker of mammary stem cells in mice, with potential implications for understanding the initiation of breast cancer. Procr link to mammary stem cell multipotency Using transplantation and lineage tracing strategies, Yi Zeng and colleagues have identified protein C receptor (Procr), a target for Wnt signalling proteins in the mammary gland, as a marker of mammary stem cells. Procr is exclusively expressed in a small subset of the basal/stem cell-enriched but not the luminal cell population of mouse mammary glands. The authors suggest that the identification of this new population of multipotent mammary stem cells could be important in the understanding of initiation of breast cancer. The mammary gland is composed of multiple types of epithelial cells, which are generated by mammary stem cells (MaSCs) residing at the top of the hierarchy 1 , 2 . However, the existence of these multipotent MaSCs remains controversial and the nature of such cells is unknown 3 , 4 . Here we demonstrate that protein C receptor (Procr), a novel Wnt target in the mammary gland, marks a unique population of multipotent mouse MaSCs. Procr-positive cells localize to the basal layer, exhibit epithelial-to-mesenchymal transition characteristics, and express low levels of basal keratins. Procr-expressing cells have a high regenerative capacity in transplantation assays and differentiate into all lineages of the mammary epithelium by lineage tracing. These results define a novel multipotent mammary stem cell population that could be important in the initiation of breast cancer.