Developmental changes in the in vitro activated regenerative activity of primitive mammary epithelial cells. Mus musculus

Many normal adult tissues contain rare stem cells with extensive self-maintaining regenerative potential. During development, the stem cells of the hematopoietic and neural systems undergo intrinsically specified changes in their self-renewal potential. In the mouse, mammary stem cells with transplantable regenerative activity are first detectable a few days before birth. They share some phenotypic properties with their adult counterparts but are enriched in a subpopulation that displays a distinct gene expression profile. Here we show that fetal mammary epithelial cells have a greater direct and inducible growth potential than their adult counterparts. The latter feature is revealed in a novel culture system that enables large numbers of mammary stem cells with serially transplantable activity as well as in vitro clonogenic progenitors to be produced within 7 days from single fetal or adult input cells. We further show that these responses are highly dependent on novel factors produced by fibroblasts. These findings provide new avenues for elucidating mechanisms that regulate normal mammary epithelial stem cell properties at the single-cell level, how these change during development, and how their perturbation may contribute to transformation. We used microarrays to compare the transcriptome of E18.5 fetal and adult MRU-enriched mammary cells. Overall design: Three biological replicates each of CD31-CD45-Ter119-BP-1-EpCAM+CD49f+ adult basal cells and CD31-CD45-Ter119-EpCAM++CD49f+ fetal cells were sorted. RNA was extracted and hybridized to the Agilent One-Color Gene Expression Arrays .