Identification, quantification and transcriptional profile of potential stem cells in bovine mammary gland

Mammary gland is an organ with remarkable regenerative capacity apparent during successive reproductive cycles. It is implicated that this regenerative capacity is caused by existence of competent mammary stem cells (MaSCs), which provide for expansion of cell populations, cell renewal, and replacement. Although stem cell research has often focused on mammary development, information regarding bovine mammary stem/progenitor cell population is still scarce. The aim of our study was to estimate the size of bovine mammary gland stem/progenitor cell population using morphological, biochemical and molecular markers. Mammary glands of non-pregnant 2-year-old Holstein–Friesian heifers were used in the experiments. Quantitative analysis of stem/progenitor cells was done using flow and scanning cytometry. FACS analysis of Hoechst dye-effluxing side population (SP) revealed that the bovine mammary population of cells with stem-like characteristics amounts 0.48%. Additionally it was noted that stem cell antigen-1 (Sca-1) is expressed on a small percentage of cells (2.14%) localized mainly in the basal layer of mammary epithelium. The Sca-1pos cells do not express ER, but show down-regulation of genes connected with differentiation of mammary epithelium, and up-regulation of genes characteristic for cells of hematopoietic origin. Therefore we hypothesize that the Sca-1pos cells found in bovine mammary gland can represent a population of cells of non-epithelial lineage, which inhabit the stem cell niche, enriching the stem/progenitor cell population in the mammary gland.