Phenotypic and functional characterisation of the luminal cell hierarchy of the mammary gland

Abstract

IntroductionThe organisation of the mammary epithelial hierarchy is poorly understood. Our hypothesis is that the luminal cell compartment is more complex than initially described, and that an understanding of the developmental relationships within this lineage will help in understanding the cellular context in which breast tumours occur.MethodsWe used fluorescence-activated cell sorting along with in vitro and in vivo functional assays to examine the growth and differentiation properties of distinct subsets of human and mouse mammary epithelial cells. We also examined how loss of steroid hormones influenced these populations in vivo. Gene expression profiles were also obtained for all the purified cell populations and correlated to those obtained from breast tumours.ResultsThe luminal cell compartment of the mouse mammary gland can be resolved into nonclonogenic oestrogen receptor-positive (ER+) luminal cells, ER+ luminal progenitors and oestrogen receptor-negative (ER-) luminal progenitors. The ER+ luminal progenitors are unique in regard to cell survival, as they are relatively insensitive to loss of oestrogen and progesterone when compared with the other types of mammary epithelial cells. Analysis of normal human breast tissue reveals a similar hierarchical organisation composed of nonclonogenic luminal cells, and relatively differentiated (EpCAM+CD49f+ALDH-) and undifferentiated (EpCAM+CD49f+ALDH+) luminal progenitors. In addition, approximately one-quarter of human breast samples examined contained an additional population that had a distinct luminal progenitor phenotype, characterised by low expression of ERBB3 and low proliferative potential. Parent-progeny relationship experiments demonstrated that all luminal progenitor populations in both species are highly plastic and, at low frequencies, can generate progeny representing all mammary cell types. The ER- luminal progenitors in the mouse and the ALDH+ luminal progenitors in the human appear to be analogous populations since they both have gene signatures that are associated with alveolar differentiation and resemble those obtained from basal-like breast tumours.ConclusionThe luminal cell compartment in the mammary epithelium is more heterogeneous than initially perceived since progenitors of varying levels of luminal cell differentiation and proliferative capacities can be identified. An understanding of these cells will be essential for understanding the origins and the cellular context of human breast tumours.

The WNT-controlled transcriptional regulator LBH is required for mammary stem cell expansion and maintenance of the basal lineage

“…6C,D). Conversely, the ERα −/low (Sca − CD49b + ) LP population, which likely represents immature alveolar progenitor cells (Shehata et al, 2012), was reduced by approximately the same amount (28% versus 46%; P=0.003) (Fig. 6D).…”

A strategy for tissue self-organization that is robust to cellular heterogeneity and plasticity

“…For example, neighboring cells in healthy tissue can differ markedly with respect to their expression of adhesion molecules, cytoskeletal proteins, hormone receptors, and the activation of specific signaling pathways (14)(15)(16)(17). Such heterogeneity can affect the distribution of cell-cell cohesive properties among different cell types, thus confounding the ordered hierarchy of interactions necessary to drive self-organization robustly (6).…”

R-spondin1 is a novel hormone mediator for mammary stem cell self-renewal

“…Hormone receptor-positive luminal cells can be further separated by their Sca1 expression (Regan et al 2012;Shehata et al 2012). We next investigate the expression of luminal Wnts and Rspo1 in the FACS-isolated Sca1 + and Sca1 À subpopulation (Fig.…”