Embryonic cells contribute directly to the quiescent stem cell population in the adult mouse mammary gland

Abstract

IntroductionStudies have identified multi-potent stem cells in the adult mammary gland. More recent studies have suggested that the embryonic mammary gland may also contain stem/progenitor cells that contribute to initial ductal development. We were interested in determining whether embryonic cells might also directly contribute to long-lived stem cells that support homeostasis and development in the adult mammary gland.MethodsWe used DNA-label retention to detect long label-retaining cells in the mammary gland. Mouse embryos were labeled with 5-ethynl-2′-deoxyuridine (EdU) between embryonic day 14.5 and embryonic day 18.5 and were subsequently sacrificed and examined for EdU retention at various intervals after birth. EdU retaining cells were co-stained for various lineage markers and identified after fluorescence activated cell sorting analysis of specific epithelial subsets. EdU-labeled mice were subjected to subsequent 5-bromo-2′-deoxyuridine administration to determine whether EdU-labeled cells could re-enter the cell cycle. Finally, EdU-labeled cells were grown under non-adherent conditions to assess their ability to form mammospheres.ResultsWe demonstrate embryonically-derived, long label-retaining cells (eLLRCs) in the adult mammary gland. eLLRCs stain for basal markers and are enriched within the mammary stem cell population identified by cell sorting. eLLRCs are restricted to the primary ducts near the nipple region. Interestingly, long label retaining cells (labeled during puberty) are found just in front of the eLLRCs, near where the ends of the ducts had been at the time of DNA labeling in early puberty. A subset of eLLRCs becomes mitotically active during periods of mammary growth and in response to ovarian hormones. Finally, we show that eLLRCs are contained within primary and secondary mammospheres.ConclusionsOur findings suggest that a subset of proliferating embryonic cells subsequently becomes quiescent and contributes to the pool of long-lived mammary stem cells in the adult. eLLRCs can re-enter the cell cycle, produce both mammary lineages and self-renew. Thus, our studies have identified a putative stem/progenitor cell population of embryonic origin. Further study of these cells will contribute to an understanding of how quiescent stem cells are generated during development and how fetal exposures may alter future breast cancer risk in adults.Electronic supplementary materialThe online version of this article (doi:10.1186/s13058-014-0487-6) contains supplementary material, which is available to authorized users.

Single-cell lineage tracing in the mammary gland reveals stochastic clonal dispersion of stem/progenitor cell progeny

“…Thus, promiscuous labelling and subsequent expansion of even a single lineage-restricted MaSC could resemble clonal expansion of a bipotent MaSC26. In this context it is important to note that the expression of K14 and K18 is differentially regulated in the pre-pubertal mammary gland with some luminal cells unexpectedly expressing K14 (refs 30, 31). Similar difficulties arise with the K8 promoter that is expressed at low levels in a subset of cells, leading to the disparate labelling of luminal cell populations in fate-mapping studies16.…”

Form and Function: how Estrogen and Progesterone Regulate the Mammary Epithelial Hierarchy

“…In lineage tracing experiments marking luminal or basal/ME cells, some studies have shown that lineage restricted progenitor cells maintain the separate epithelial lineages after birth [82–84]. Luminal progenitor cells gave rise to mature luminal cells without contribution from a putative stem cell in the basal lineage (Fig.…”

“…For example, in both humans and mice, rare ERα + cells have been identified that co-label with markers of proliferation, [10–12,126]. Long-term label-retaining studies, which identify slower cycling stem cells or those that undergo asymmetric division, have also identified ERα + cells that retain label [60,84,127,128], suggesting the possibility of an ERα + progenitor cell. Human ERα + long-term label-retaining cells are also enriched for p21 cip , msi-1, and CK19, which have been shown to be putative stem cell markers [128,129].…”

New Insights of Mammary Gland During Different Stages of Development

“…Studies suggest the origin of mammary stem cells in adult stage is from the proliferating embryonic stem cells of the mammary gland during embryogenesis which has become quiescent in the adult stage [73].…”