WNT-Mediated Regulation of FOXO1 Constitutes a Critical Axis Maintaining Pubertal Mammary Stem Cell Homeostasis

Abstract

Summary Puberty is characterized by dynamic tissue remodeling in the mammary gland involving ductal elongation, resolution into the mature epithelial bilayer, and lumen formation. To decipher the cellular mechanisms underlying these processes, we studied the fate of putative stem cells, termed cap cells, present in terminal end buds of pubertal mice. Employing a p63CreERT2-based lineage-tracing strategy, we identified a unipotent fate for proliferative cap cells that only generated cells with basal features. Furthermore, we observed that dislocated ‘cap-in-body’ cells underwent apoptosis, which aided lumen formation during ductal development. Basal lineage-specific profiling and genetic loss-of-function experiments revealed a critical role for FOXO transcription factors in mediating these proliferative versus apoptotic fates. Importantly, these studies revealed a mode of WNT signaling-mediated FOXO1 inhibition, potentially mediated through AKT. Together, these data suggest that the WNT pathway confers proliferative and survival advantages on cap cells via regulation of FOXO1 localization.

Mammary mechanobiology: mechanically-activated ion channels in lactation and involution

“…To induce recombination in WAPCre mice, animals were taken through one full pregnancy-lactation-involution cycle. Pups (average 8; range [6][7][8][9][10] were weaned on postnatal day 21. Mothers were mated one week later in their second (experimental) mating.…”

“…The adult mammary epithelium consists of an arborized ductal network embedded within an adipose stroma (1). The ductal epithelium contains both luminal and basal cells, which are produced and maintained postnatally by lineage-restricted precursors (2)(3)(4)(5)(6)(7). During gestation, a coordinated program of epithelial proliferation, side-branching, differentiation and tissue remodeling takes place (1,8), resulting in the generation of thousands of alveolar structures that adorn the central ductal epithelium in lobular clusters (9).…”

Neutral lineage tracing of proliferative embryonic and adult mammary stem/progenitor cells

“…Recently, genetic lineage-tracing studies in the mouse mammary gland have achieved in vivo indelible marking of specific populations of cells (characterised by their expression of nominated genes at specific developmental stages) and the subsequent analysis of the progeny of proliferative labelled cells after an appropriate chase ( Sale and Pavelic, 2015 ). Targeted cell populations include those temporally or stably expressing: keratin (K) 5 ( Rios et al, 2014 ; Van Keymeulen et al, 2011 ), K14 ( Rios et al, 2014 ; Tao et al, 2014 ; Van Keymeulen et al, 2011 ; Wuidart et al, 2016 ), K8 ( Tao et al, 2014 ; Van Keymeulen et al, 2011 ; Wuidart et al, 2016 ), K18 ( Van Keymeulen et al, 2011 ), K19 ( Wuidart et al, 2016 ), Elf5 ( Rios et al, 2014 ), Lgr5 ( de Visser et al, 2012 ; Fu et al, 2017 ; Rios et al, 2014 ; Van Keymeulen et al, 2011 ; Wuidart et al, 2016 ), Lgr6 ( Blaas et al, 2016 ; Wuidart et al, 2016 ), Sox9 ( Wang et al, 2017 ; Wuidart et al, 2016 ), Axin2 ( van Amerongen et al, 2012 ), Notch1 ( Rodilla et al, 2015 ), Notch2 ( Šale et al, 2013 ), Notch3 ( Lafkas et al, 2013 ), WAP ( Chang et al, 2014 ), Acta2 ( Prater et al, 2014 ), p63 ( Sreekumar et al, 2017 ), Procr ( Wang et al, 2015 ), prominin 1 ( Wang et al, 2017 ) and ER ( Van Keymeulen et al, 2017 ). However, although providing valuable information on mammary development and the epithelial differentiation hierarchy, these models have relied on prior assumptions regarding the specificity and consistency of the expression of the chosen gene promoters, and have generated conflicting results.…”

Transcriptional regulation of normal human mammary cell heterogeneity and its perturbation in breast cancer

“…ZEB1 was also recently reported to have a protective role against oncogene‐induced DNA damage in normal human mammary epithelial cells (Morel et al, ). Other TFs involved in mammary stem cell function include FOXO1 (Sreekumar et al, ), RUNX2 (Ferrari et al, ), MYC (Hynes & Stoelzle, ; Moumen et al, ), CEBPB (C/EBPβ; LaMarca et al, ), BCL11A (Khaled et al, ), and BCL11B (Miller et al, ).…”