Wnt Proteins Are Self-Renewal Factors for Mammary Stem Cells and Promote Their Long-Term Expansion in Culture

Howard Hughes Medical Institute, Department of Developmental Biology, Stanford University, School of Medicine, Stanford, CA 94305-5323, USA.
Cell stem cell (Impact Factor: 22.27). 06/2010; 6(6):568-77. DOI: 10.1016/j.stem.2010.03.020
Source: PubMed


Adult stem cells have the ability to self-renew and to generate specialized cells. Self-renewal is dependent on extrinsic niche factors but few of those signals have been identified. In addition, stem cells tend to differentiate in the absence of the proper signals and are therefore difficult to maintain in cell culture. The mammary gland provides an excellent system to study self-renewal signals, because the organ develops postnatally, arises from stem cells, and is readily generated from transplanted cells. We show here that adult mammary glands contain a Wnt-responsive cell population that is enriched for stem cells. In addition, stem cells mutant for the negative-feedback regulator Axin2 and therefore sensitized to Wnt signals have a competitive advantage in mammary gland reconstitution assays. In cell culture experiments, exposure to purified Wnt protein clonally expands mammary stem cells for many generations and maintains their ability to generate functional glands in transplantation assays. We conclude that Wnt proteins serve as rate-limiting self-renewal signals acting directly on mammary stem cells.

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    • "As seen using our genetic approach to delete Rank, mice treated with RANK-Fc exhibited a blunted progesteroneinduced expansion of both the luminal (CD24 + CD49f lo ) and basal (CD24 + CD49f hi ) populations, and also suppressed lobuloalveologenesis (Figures 4B–4D). Previous studies using WNT reporter mice have documented the presence of WNT-responsive cells ($5%) within basal, but not luminal cells, of adult virgin mice (van Amerongen et al., 2012; Zeng and Nusse, 2010). During pregnancy, however, lineage tracing experiments have identified WNT-responsive luminal cells adjacent to basal cells within alveolar structures, suggesting their origin from a common bipotent progenitor (van Amerongen et al., 2012). "
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    ABSTRACT: Systemic and local signals must be integrated by mammary stem and progenitor cells to regulate their cyclic growth and turnover in the adult gland. Here, we show RANK-positive luminal progenitors exhibiting WNT pathway activation are selectively expanded in the human breast during the progesterone-high menstrual phase. To investigate underlying mechanisms, we examined mouse models and found that loss of RANK prevents the proliferation of hormone receptor-negative luminal mammary progenitors and basal cells, an accompanying loss of WNT activation, and, hence, a suppression of lobuloalveologenesis. We also show that R-spondin1 is depleted in RANK-null progenitors, and that its exogenous administration rescues key aspects of RANK deficiency by reinstating a WNT response and mammary cell expansion. Our findings point to a novel role of RANK in dictating WNT responsiveness to mediate hormone-induced changes in the growth dynamics of adult mammary cells. Copyright © 2015 The Authors. Published by Elsevier Inc. All rights reserved.
    Stem Cell Reports 06/2015; 9(1). DOI:10.1016/j.stemcr.2015.05.012 · 5.37 Impact Factor
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    • "). Additionally, Lbh expression was compared with expression of ERα , which primarily marks differentiated luminal cells (Asselin-Labat et al., 2007; Lim et al., 2010), the WNT target gene and basal MaSC marker Axin2 (Jho et al., 2002; Zeng and Nusse, 2010), as well as with expression of the luminal and basal lineage-specific isoforms of epithelial transcription factor p63, TAp63 (Trp63 – Mouse Genome Informatics) and ΔNp63, respectively (Li et al., 2008; Nylander et al., 2002). Notably, Lbh was predominantly expressed in the "
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    ABSTRACT: The identification of multipotent mammary stem cells (MaSCs) has provided an explanation for the unique regenerative capacity of the mammary gland throughout adult life. However, it remains unclear what genes maintain MaSCs and control their specification into the two epithelial lineages: luminal and basal. LBH is a novel transcription co-factor in the WNT pathway with hitherto unknown physiological function. LBH is expressed during mammary gland development and aberrantly overexpressed in aggressive 'basal' subtype breast cancers. Here, we have explored the in vivo role of LBH in mammopoiesis. We show that in postnatal mammary epithelia, LBH is predominantly expressed in the Lin(-)CD29(high)CD24(+) basal MaSC population. Upon conditional inactivation of LBH, mice exhibit pronounced delays in mammary tissue expansion during puberty and pregnancy, accompanied by increased luminal differentiation at the expense of basal lineage specification. These defects could be traced to a severe reduction in the frequency and self-renewal/differentiation potential of basal MaSCs. Mechanistically, LBH induces expression of key epithelial stem cell transcription factor ΔNp63 to promote a basal MaSC state and repress luminal differentiation genes, mainly that encoding estrogen receptor α (Esr1/ERα). Collectively, these studies identify LBH as an essential regulator of basal MaSC expansion/maintenance, raising important implications for its potential role in breast cancer pathogenesis. © 2015. Published by The Company of Biologists Ltd.
    Development 02/2015; 142(5). DOI:10.1242/dev.110403 · 6.46 Impact Factor
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    • "Bulb-shaped terminal end buds (TEBs) drive development during puberty, where an outer layer of stem-like cap cells and an inner layer of body cells lay the foundation for the epithelial constituents that make up the ductal network (Smalley and Ashworth, 2003; Srinivasan et al., 2003). Wnt/-catenin signaling is essential for orchestrating self-renewal cues required for stem cell maintenance and cell fate decisions in multiple embryonic and postnatal tissues (Zeng and Nusse, 2010; van Amerongen et al., 2012a). The Wnt/ -catenin pathway is required at the earliest stage of mammary development in the embryo for the specification of the mammary placode and initiation of mammary morphogenesis (Chu et al., 2004) and in postnatal development for proper stem cell maintenance , branching morphogenesis, and alveolar development (Hatsell et al., 2003; Lindvall et al., 2006; Badders et al., 2009). "
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    ABSTRACT: Wnt signaling encompasses beta-catenin-dependent and -independent networks. How receptor context provides Wnt specificity in vivo to assimilate multiple concurrent Wnt inputs throughout development remains unclear. Here, we identified a refined expression pattern of Wnt/receptor combinations associated with the Wnt/beta-catenin-independent pathway in mammary epithelial subpopulations. Moreover, we elucidated the function of the alternative Wnt receptor Ror2 in mammary development and provided evidence for coordination of this pathway with Wnt/beta-catenin-dependent signaling in the mammary epithelium. Lentiviral short hairpin RNA (shRNA)-mediated depletion of Ror2 in vivo increased branching and altered the differentiation of the mammary epithelium. Microarray analyses identified distinct gene level alterations within the epithelial compartments in the absence of Ror2, with marked changes observed in genes associated with the actin cytoskeleton. Modeling of branching morphogenesis in vitro defined specific defects in cytoskeletal dynamics accompanied by Rho pathway alterations downstream of Ror2 loss. The current study presents a model of Wnt signaling coordination in vivo and assigns an important role for Ror2 in mammary development.
    The Journal of Cell Biology 02/2015; 208(3):351-66. DOI:10.1083/jcb.201408058 · 9.83 Impact Factor
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