By dividing asymmetrically, stem cells can generate two daughter cells with distinct fates. However, evidence is limited in mammalian systems for the selective apportioning of subcellular contents between daughters. We followed the fates of old and young organelles during the division of human mammary stem-like cells and found that such cells apportion aged mitochondria asymmetrically between daughter cells. Daughter cells that received fewer old mitochondria maintained stem cell traits. Inhibition of mitochondrial fission disrupted both the age-dependent sub-cellular localization and segregation of mitochondria, and caused loss of stem cell properties in the progeny cells. Hence, mechanisms exist for mammalian stem-like cells to asymmetrically sort aged and young mitochondria, and these are important for maintaining stemness properties.

Hutchinson-Gilford progeria syndrome (HGPS) is the result of a defective form of the lamin A protein called progerin. While progerin is known to disrupt the properties of the nuclear lamina, the underlying mechanisms responsible for the pathophysiology of HGPS remain less clear. Previous studies in our laboratory have shown that progerin expression in murine epidermal basal cells results in impaired stratification and halted development of the skin. Stratification and differentiation of the epidermis is regulated by asymmetric stem cell division. Here, we show that expression of progerin impairs the ability of stem cells to maintain tissue homeostasis as a result of altered cell division. Quantification of basal skin cells showed an increase in symmetric cell division that correlated with progerin accumulation in HGPS mice. Investigation of the mechanisms underlying this phenomenon revealed a putative role of Wnt/b-catenin signaling. Further analysis suggested an alteration in the nuclear translocation of b-catenin involving the inner and outer nuclear membrane proteins, emerin and nesprin-2. Taken together, our results suggest a direct involvement of progerin in the transmission of Wnt signaling and normal stem cell division. These insights into the molecular mechanisms of progerin may help develop new treatment strategies for HGPS.In situ hybridization K15 transcripts were detected using RNAscope (Advanced Cell Diagnostic, Newark, CA) in accordance with the manufacturer's protocol. Few modifications were made: target A Sola-Carvajal et al.

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Epithelial attachment to the basement membrane (BM) is essential for mammary gland development, yet the exact roles of specific BM components remain unclear. Here, we show that Laminin α5 (Lama5) expression specifically in the luminal epithelial cells is necessary for normal mammary gland growth during puberty, and for alveologenesis during pregnancy. Lama5 loss in the keratin 8-expressing cells results in reduced frequency and differentiation of hormone receptor expressing (HR+) luminal cells. Consequently, Wnt4-mediated crosstalk between HR+ luminal cells and basal epithelial cells is compromised during gland remodeling, and results in defective epithelial growth. The effects of Lama5 deletion on gland growth and branching can be rescued by Wnt4 supplementation in the in vitro model of branching morphogenesis. Our results reveal a surprising role for BM-protein expression in the luminal mammary epithelial cells, and highlight the function of Lama5 in mammary gland remodeling and luminal differentiation.

28Epithelial attachment to the basement membrane (BM) is essential for mammary 29 gland development, yet the exact roles of specific BM components remain unclear. 30Here, we demonstrate that expression of distinct laminin α-isoforms by luminal and 31 basal mammary epithelial cells enforces lineage identity that is necessary for 32 normal mammary gland growth and function. Laminin α5 (LMα5) is mainly 33 expressed by the luminal epithelial cells, and it is necessary for pubertal mammary 34 gland growth, pregnancy induced gland remodeling, and for alveolar 35 function. Adhesion to LMα5 containing laminin promotes luminal traits in both 36 luminal and basal epithelial cells, and reduces progenitor activity of basal epithelial 37 cells. Mechanistically, we show that Lama5 loss interferes with differentiation of 38 hormone receptor positive luminal cells, which results in reduced Wnt4 expression 39 and defective crosstalk between luminal and basal epithelial cells during gland 40 remodeling. Our results reveal a novel BM-mediated mechanism, which regulates 41 mammary gland remodeling and function via specification of luminal epithelial 42 cells. 43 44 45 46 47 Yurchenco 2013). Laminins are heterotrimers consisting of a, b, and g subunits, 79 which are expressed in a tissue-specific and temporally controlled manner (Ahmed 80 and Ffrench-Constant 2016). Several laminin isoforms have been detected in the 81 mammary gland, and earlier studies suggest that Laminin-111 (LM-111; containing 82 a1, b1, and g1 subunits), LM-332 and LM-511/521 are the most common forms in 83 the adult glands (Gudjonsson et al. 2002; Prince et al. 2002; Goddard et al. 2016), 84 yet LM-211 and LM-411/421 are also found. A microarray profiling study showed 85 that mRNA expression of Lama1 and Lama3 subunits is higher in a population of 86 cells enriched for mammary stem cells (MaSC), whereas in mature luminal cells 87 the expression of Lama1 is reduced and Lama5 is increased (Lim et al. 2010). In 88 addition, recent data from single cell profiling studies confirm these results (Bach 89 et al. 2017; Tabula Muris et al. 2018). However, what are the spatial and temporal 90 expression patterns of these LMs within intact tissue and what are their exact roles 91 in maintenance and function of luminal and basal mammary epithelial cells is 92 unclear. 93 94 We set out to study the expression pattern of different LM isoforms in the mouse 95 mammary gland during pubertal expansion, pregnancy and adult homeostasis in 96 vivo. Different LM isoforms exhibited surprisingly discrete and cell type-restricted 97 expression patterns in the mammary gland, and unexpectedly, we found strong 98 expression of LMα5 in the luminal epithelial cells. We demonstrate that LMα5 99 produced by luminal cells enforces luminal identity, and is necessary for normal 100 mammary gland growth and development both during puberty and pregnancy. 101 Mechanistically, we show that LMα5 enhanced luminal differentiation is necessary 102 for Wnt4 mediated interactions between luminal and basal ...