The mouse mammary microenvironment redirects mesoderm-derived bone marrow cells to a mammary epithelial progenitor cell fate.

Mammary stem cells reside in protected tissue locales (niches), where their reproductive potency remains essentially unchanged through life. Disruption of the tissue leads to a reduced capacity of dispersed epithelial cells to recapitulate complete functional mammary structures. Previous studies demonstrate that during the reformation of mammary stem cell niches by dispersed epithelial cells in the mammary stroma, nonmammary cells of ectodermal germ origin may be sequestered and reprogrammed to perform mammary epithelial cell (MEC) functions, including those ascribed to mammary stem/progenitor cells. To test whether tissue cells from organs derived from different germ layers could respond to mammary epithelial-specific signals, we utilized fluorescence-activated cell sorting-purified Lin(-) and Lin(-)/cKit+adult male bone marrow cells to mix with MECs. Our evidence shows that the signals provided by the mammary microenvironment are capable of redirecting mesoderm-derived adult progenitor cells to produce functional MEC progeny.