Serially transplantable mammary epithelial cells express the Thy-1 antigen

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^medCD49f^high cells enriched for long-lived mammary epithelial cells can be serially transplanted.

Flow cytometry-based enrichment of distinct phenotypic populations was assessed for their gene expression profiles and functional proliferative attributes in vitro and in vivo.

Here, we show Thy-1 is differentially expressed in the CD24^medCD49f^high population, which allowed us to discern two functionally different populations. The Thy-1⁺CD24^medCD49f^high phenotype contained the majority of the serially transplantable epithelial cells. The Thy-1^-CD24^medCD49f^high phenotype contains a rare progenitor population that is able to form primary mammary outgrowths with significantly decreased serial in vivo transplantation potential.

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.