Serially transplantable mammary epithelial cells express the Thy-1 antigen

Background: Recent studies in murine mammary tissue have identified functionally distinct cell populations that may be isolated by surface phenotype or lineage tracing. Previous groups have shown that CD24(med)CD49f(high) cells enriched for long-lived mammary epithelial cells can be serially transplanted. Methods: Flow cytometry-based enrichment of distinct phenotypic populations was assessed for their gene expression profiles and functional proliferative attributes in vitro and in vivo. Results: Here, we show Thy-1 is differentially expressed in the CD24(med)CD49f(high) population, which allowed us to discern two functionally different populations. The Thy-1(+)CD24(med)CD49f(high) phenotype contained the majority of the serially transplantable epithelial cells. The Thy-1(-)CD24(med)CD49f(high) phenotype contains a rare progenitor population that is able to form primary mammary outgrowths with significantly decreased serial in vivo transplantation potential. Conclusions: Therefore, Thy-1 expression in the immature cell compartment is a useful tool to study the functional heterogeneity that drives mammary gland development and has implications for disease etiology.