Stem cell characteristics of transplanted rat mammary clonogens

Rat mammary glands contain a subpopulation of clonogenic epithelial cells w ith large proliferation and differentiation potentials. When transplanted, the clonogens in monodispersed rat mammary epithelial cell suspensions give rise to either alveolar units (AUs) or ductal units (DUs) depending on the nature of the hormonal milieu in the graft recipient. Clonogens are also t he primary cells of origin of mammary cancer following exposure to ionizing radiation or chemical carcinogens. Given the other stem cell characteristi cs of mammary clonogens, it would be expected that the primary AUs and DUs to which they give rise when grafted and hormonally stimulated (a) would be derived from the same clonogenic cell subpopulation, (b) would contain all of the functionally differentiated cell types of homologous parts of compa rably stimulated mammary glands in situ, and (c) would also contain clonoge n subpopulations capable when subtransplanted of giving rise to secondary A Us and DUs of similar cell composition. The current experiments were design ed to test these expectations. The data are discussed in the context of res ults of previous studies with this and other experimental models. The resul ts further support the conclusion that rat mammary clonogens are multipoten t mammary stem cells. (C) 2000 Academic Press.