Mammary stem cells and cancer: roles of Wnt signaling in plain view

The likely roles of Wnt signaling in regulating mammary stem cell behavior have been much discussed, in part because they may underlie the oncogenic effects of Wnt signaling in mammary tissue. Two recent papers add important data to this field. One tests directly the effects of purified Wnt protein on mouse mammary stem cells in culture and finds a specific increase in the proportion of cells with self-renewing stem cell phenotypes. The second identifies a novel target gene of canonical Wnt signaling that may be expressed in stem cells and is induced in both mouse and human mammary tumors associated with Wnt pathway activation.