Luminal Progenitors Restrict Their Lineage Potential during Mammary Gland Development

Abstract

The hierarchical relationships between stem cells and progenitors that guide mammary gland morphogenesis are still poorly defined. While multipotent basal stem cells have been found within the myoepithelial compartment, the in vivo lineage potential of luminal progenitors is unclear. Here we used the expression of the Notch1 receptor, previously implicated in mammary gland development and tumorigenesis, to elucidate the hierarchical organization of mammary stem/progenitor cells by lineage tracing. We found that Notch1 expression identifies multipotent stem cells in the embryonic mammary bud, which progressively restrict their lineage potential during mammary ductal morphogenesis to exclusively generate an ERαneg luminal lineage postnatally. Importantly, our results show that Notch1-labelled cells represent the alveolar progenitors that expand during pregnancy and survive multiple successive involutions. This study reveals that postnatal luminal epithelial cells derive from distinct self-sustained lineages that may represent the cells of origin of different breast cancer subtypes.

Quantitative lineage tracing strategies to resolve multipotency in tissue-specific stem cells

“…Using this method, we showed that the Cre used to support multipotency during MG development and homeostasis, although preferentially labeling BCs, also initially and independently labeled some LCs, as evidenced by the presence of isolated marked LCs just after Cre-mediated recombination and the fact that the frequency of these unicolor doublets was not statistically enriched over bicolor doublets. The frequency of these events corresponds to what would be observed by chance if the Cre were labeling two neighboring cells, further suggesting that MG development and adult remodeling are not mediated by multipotent SCs but rather by two independent lineages (Van Keymeulen et al 2011;Lafkas et al 2013;Prater et al 2014;Tao et al 2014;Rodilla et al 2015). Different transgenic mice using a similar human K14 promoter fragment lead to very different targeting efficiency and specificity of labeling in the MG.…”

“…These two tissues present interesting similarities. They both originate from multipotent embryonic progenitors, which are replaced in adult tissue by unipotent basal and luminal SCs (Van Keymeulen et al 2011;Choi et al 2012;Ousset et al 2012;Wang et al 2013;Prater et al 2014;Rodilla et al 2015). The main difference between the prostate and the mammary BCs is the timing of the switch from multipotency to unipotency.…”

“…Different lineage tracing studies demonstrated that unipotent myoepithelial cells under normal physiological conditions are multipotent in transplantation assays (Van Keymeulen et al 2011;Prater et al 2014). Other studies tracing either BCs (Lgr5, Axin2, and Ad-K14-Cre) or LCs (Notch1, Notch3, Lgr5, Axin2, and Ad-K8-Cre) further supported the notion that both lineages in the MG are self-sustained by unipotent SCs in vivo during MG postnatal development and homeostasis and adult remodeling (Van Keymeulen et al 2011;de Visser et al 2012;van Amerongen et al 2012;Lafkas et al 2013;Prater et al 2014;Tao et al 2014;Rodilla et al 2015). However, two recent studies using new K14 and K5 transgenic and Procr-CreER knock-in mice suggested instead that BCs contain multipotent SCs (Rios et al 2014;Wang et al 2015).…”

“…6A, top panel) or whether the luminal lineage consists of committed progenitors with shortterm self-renewal potential that are replaced by basal SCs (Fig. 6A, bottom panel; Van Keymeulen et al 2011;de Visser et al 2012;van Amerongen et al 2012;Lafkas et al 2013;Malhotra et al 2014;Rios et al 2014;Tao et al 2014;Rodilla et al 2015).…”

“…We performed these experiments in the mammary gland (MG) and the prostate, two ductal epithelial tissues composed of basal cells (BCs) and luminal cells (LCs) for which, despite dozens of independent lineage tracing investigations, the actual fate of their SCs (unipotent, bipotent, or both) remains unclear (Wang et al , 2013(Wang et al , 2015Liu et al 2011;Van Keymeulen et al 2011;Choi et al 2012;de Visser et al 2012;van Amerongen et al 2012;Lafkas et al 2013;Lu et al 2013;Malhotra et al 2014;Prater et al 2014;Rios et al 2014;Tao et al 2014;Rodilla et al 2015). Our analysis clearly shows that, while the prostate develops from multipotent SCs, only unipotent SCs mediate MG pubertal expansion and adult tissue remodeling.…”