Project description:Uniquely among mammalian organs, skin is capable of dramatic size change in adults, yet the mechanisms underlying this striking capacity are unclear. Here, we utilize a system of controlled tissue expansion in mice to uncover cellular and molecular determinants of skin growth. Through machine learning-guided three-dimensional tissue reconstruction, we capture morphometric changes in growing skin. We find that most growth is driven by the proliferation of the epidermis in response to mechanical tension, with more limited changes in dermal and subdermal compartments. Epidermal growth is achieved through preferential activation and differentiation of not Lgr5+, but instead Lgr6+ stem cells of the interfollicular epidermis, driven in part by the Hippo pathway. By single-cell RNA sequencing, we uncover further changes in mechanosensitive and metabolic pathways underlying growth control in the skin. These studies point to therapeutic strategies to enhance skin growth and establish a platform for understanding organ size dynamics in adult mammals.
Project description:Uniquely among mammalian organs, skin is capable of dramatic size change in adults, yet the mechanisms underlying this striking capacity are unclear. Here, we utilize a system of controlled tissue expansion in mice to uncover cellular and molecular determinants of skin growth. Through machine learning-guided three-dimensional tissue reconstruction, we capture morphometric changes in growing skin. We find that most growth is driven by the proliferation of the epidermis in response to mechanical tension, with more limited changes in dermal and subdermal compartments. Epidermal growth is achieved through preferential activation and differentiation of not Lgr5+, but instead Lgr6+ stem cells of the interfollicular epidermis, driven in part by the Hippo pathway. By single-cell RNA sequencing, we uncover further changes in mechanosensitive and metabolic pathways underlying growth control in the skin. These studies point to therapeutic strategies to enhance skin growth and establish a platform for understanding organ size dynamics in adult mammals.
Project description:Uniquely among mammalian organs, skin is capable of marked size change in adults, yet the mechanisms underlying this notable capacity are unclear. Here, we use a system of controlled tissue expansion in mice to uncover cellular and molecular determinants of skin growth. Through machine learning-guided three-dimensional tissue reconstruction, we capture morphometric changes in growing skin. We find that most growth is driven by the proliferation of the epidermis in response to mechanical tension, with more limited changes in dermal and subdermal compartments. Epidermal growth is achieved through preferential activation and differentiation of Lgr6+ stem cells of the epidermis, driven in part by the Hippo pathway. By single-cell RNA sequencing, we uncover further changes in mechanosensitive and metabolic pathways underlying growth control in the skin. These studies point to therapeutic strategies to enhance skin growth and establish a platform for understanding organ size dynamics in adult mammals.
Project description:The renewing human epidermis constantly senses and adapts to a wide range of mechanical cues that are ubiquitous throughout life. The mechanisms of how mechanical forces are responded by interfollicular epidermal stem cells (IFESCs) and are transmitted directly into nucleus to modify gene expression remain incompletely defined. In vitro, human IFESCs were cultured on the collagen I coated silicon rubber membrane and then subjected to the mechanical stretched. Cyclic mechanical tension at 0.5 Hz sinusoidal curve at 10% elongation was applied using an FX-5000T™ Flexercell® Tension Plus™ unit (Flexcell International Corporation). In mechanical unloading groups, cells were cultured on the same plates in the same incubator with the mechanical stretched groups but not subjected to stretch. Combining genome-wide microarray and functional analyses, we made transcriptome analysis of samples from the mechanical unstretched or stretched isolated human IFESCs.
Project description:Stem cells support the lifelong maintenance of adult organs but their specific roles during injury are poorly understood. Here, we demonstrate that Lgr6 marks a regionally restricted population of epidermal stem cells that interact with nerves and specialize in wound re-epithelialization. Diphtheria toxin-mediated ablation of Lgr6 stem cells delays wound healing, and skin denervation phenocopies this effect. Using intravital imaging to capture stem cell dynamics after injury, we show that wound re-epithelialization by Lgr6 stem cells is diminished following the loss of nerves. This induces the recruitment of other stem cell populations, including hair follicle stem cells, which partially compensate to mediate the wound closure. Single-cell lineage tracing and gene expression analysis reveal that the fate of Lgr6 stem cells is shifted towards differentiation following the loss of their niche. We conclude that Lgr6 epidermal stem cells are primed for injury response and interact with nerves to regulate their fate
Project description:It has been a long-standing challenge to maintain the functions of hepatocytes in vitro. In the present study, we found that mechanical tension-induced yes-associated protein (Yap) activation triggered hepatocyte dedifferentiation. Alleviation of mechanical tension by confinement of cell spreading was sufficient to inhibit hepatocyte dedifferentiation. Based on this finding, we identified a small molecular cocktail LBDXL through reiterative chemical screening that could maintain hepatocyte functions over the long term and in vivo repopulation capacity by targeting actin polymerization and actomyosin contraction.
Project description:Mammalian epidermis consists of three self-renewing compartments: the hair follicle, sebaceous gland and interfollicular epidermis. We generated knock-in alleles of murine Lgr6, a close relative to the Lgr5 stem cell gene. Lgr6 was expressed in the earliest embryonic hair placodes. In adult hair follicles, Lgr6+ cells resided in a previously uncharacterized region directly above the follicle bulge. They expressed none of the known bulge stem cell markers. Prenatal Lgr6+ cells established the hair follicle, sebaceous gland and interfollicular epidermis. Postnatally, Lgr6+ cells generated sebaceous gland and interfollicular epidermis, while contribution to hair lineages gradually diminished with age. Adult Lgr6+ cells executed long-term wound repair, including the formation of new hair follicles. We conclude that Lgr6 marks the most primitive epidermal stem cell. For the Lgr5 and Lgr6 stem cell comparison RNA was isolated from sorted GFPhi cell fractions of dorsal skin from Lgr5-EGFP-ires-CreERT2 mice and Lgr6-EGFP-ires-CreERT2, respectively (3 mice per group per sort).