Distinct Stem Cells Contribute to Mammary Gland Development and Maintenance

The 2011 study investigated the cellular hierarchy of the mammary gland in mice, revealing that the gland is maintained by long-lived unipotent stem cells within both luminal and myoepithelial lineages. These cells have extensive renewing capacities and can expand clonally during morphogenesis, adult life, and across multiple pregnancy cycles. The research, which included genetic lineage-tracing experiments and mammary reconstitution assays, showed that these unipotent stem cells are self-renewing and are not replaced by multipotent stem cells under normal physiological conditions. However, the transplantation process can affect the differentiation potential of these cells. The study's findings challenge the previously held belief that the mammary gland is maintained by rare multipotent stem cells and have implications for understanding mammary gland physiology and breast cancer origins. The study analyzed at least 526 clones from three different mice at each time point, and at least 2 mice per time point for other measurements, providing a substantial amount of data to support its conclusions.