Periodic Reporting for period 1 - SkinForce (Mechanisms of epidermal stratification and force-mediated regulation of stem cell fate and positioning)
Reporting period: 2021-03-01 to 2023-02-28
Understanding how mammalian tissues are formed during embryonic development is fundamental to understand mechanisms of human disease. In this project, we have addressed the central question of how tissue morphogenesis and cell state transitions are coordinated in time and space to produce a functional tissue. The tissue of interest in this study is the skin epidermis, the epithelial component of the skin. It forms a life-essential barrier that prevents pathogens and toxins from entering our bodies and water from being lost due to the temperature difference between our body and the external environment. The epidermis also contains the hair follicles that generate the hair coat. The epidermis and hair follicles form during embryogenesis from a single stem cell layer and they continue to constantly self-renew to replace differentiated, dying or damaged cells throughout adulthood. Disturbances in this self-renewal are associated with cancer, inflammatory skin diseases, as well as age-related tissue degeneration. The central objective of this study was to combine state-of-the-art cell biology, cutting-edge quantitative image analysis methods and physical modelling approaches to understand epidermis development and to unravel the role of mechanical tissue properties in stem cell fate regulation and barrier establishment. The specific aims were to establish principles by which tissue geometry and cell shape/volume changes control stem cell behavior (WP1) and discover molecular mechanisms of force-mediated regulation of epidermal stem cell fate (WP2). Overall, this project has been stupendous for the researcher career. The objective associated to the WP1 of this project has been completed, the resulting study is published as a preprint, and the submitted manuscript is under revision at NCB. The objective associated to the WP2 is nearly complete and a manuscript will be submitted end 2023.
Objective 1: Decipher dynamic cell shape changes and tissue fluidization in epidermal stratification
In this objective, a new mechanism of how coordination of compressive and contractile forces drives cell shape and fate changes to generate the epidermal hair follicle placode was discovered. Specifically, the researcher identified a key role for coordinated mechanical forces stemming from contractile, proliferative, and proteolytic activities across the epithelial and mesenchymal compartments in generating the placode structure. A ring of fibroblast cells gradually wraps around the placode cells to generate centripetal contractile forces, which in collaboration with polarized epithelial myosin activity promote elongation and local tissue thickening. Subsequently, proteolytic remodeling locally softens the basement membrane to facilitate release of pressure on the placode, enabling localized cell divisions, tissue fluidification, and epithelial invagination into the underlying mesenchyme. Together, the experimental data and modeling identify dynamic cell shape transformations and tissue-scale mechanical co-operation as key factors for orchestrating organ formation. This work is published as a preprint (https://www.biorxiv.org/content/10.1101/2022.12.12.519937v1(opens in new window)) has been presented as poster and oral presentation at a number of conferences, and is currently under revision in a peer-reviewed journal.
Objective 2: Unravelling molecular mechanism of force-mediated regulation of stem cell fate
Here, the researcher has addressed the mechanism by which the epidermal stem cells commit to differentiation to form the life-essential skin barrier. Using single-cell RNA sequencing, the researcher discovered a committed stem cell population in the basal compartment that emerges during development, when tissue compartmentalization in the epidermis is being established. The emergence of the committed cell that will eventually delaminate coincides with profound changes in tissue packing and maturation of the extracellular matrix and adhesion. Additional analyses have indicated a signaling mechanism that triggers the differentiation of the stem cells. Remaining work aims at investigating how the mechanical properties of the tissue and cells coordinate this signaling activity to drive cell fate commitment. Understanding this connection will generate fundamental knowledge on how tissue growth and differentiation are coordinated. The work is expected to be complete end of 2023, after which it will be published as a preprint and submitted to a peer-reviewed journal.
In this objective, a new mechanism of how coordination of compressive and contractile forces drives cell shape and fate changes to generate the epidermal hair follicle placode was discovered. Specifically, the researcher identified a key role for coordinated mechanical forces stemming from contractile, proliferative, and proteolytic activities across the epithelial and mesenchymal compartments in generating the placode structure. A ring of fibroblast cells gradually wraps around the placode cells to generate centripetal contractile forces, which in collaboration with polarized epithelial myosin activity promote elongation and local tissue thickening. Subsequently, proteolytic remodeling locally softens the basement membrane to facilitate release of pressure on the placode, enabling localized cell divisions, tissue fluidification, and epithelial invagination into the underlying mesenchyme. Together, the experimental data and modeling identify dynamic cell shape transformations and tissue-scale mechanical co-operation as key factors for orchestrating organ formation. This work is published as a preprint (https://www.biorxiv.org/content/10.1101/2022.12.12.519937v1(opens in new window)) has been presented as poster and oral presentation at a number of conferences, and is currently under revision in a peer-reviewed journal.
Objective 2: Unravelling molecular mechanism of force-mediated regulation of stem cell fate
Here, the researcher has addressed the mechanism by which the epidermal stem cells commit to differentiation to form the life-essential skin barrier. Using single-cell RNA sequencing, the researcher discovered a committed stem cell population in the basal compartment that emerges during development, when tissue compartmentalization in the epidermis is being established. The emergence of the committed cell that will eventually delaminate coincides with profound changes in tissue packing and maturation of the extracellular matrix and adhesion. Additional analyses have indicated a signaling mechanism that triggers the differentiation of the stem cells. Remaining work aims at investigating how the mechanical properties of the tissue and cells coordinate this signaling activity to drive cell fate commitment. Understanding this connection will generate fundamental knowledge on how tissue growth and differentiation are coordinated. The work is expected to be complete end of 2023, after which it will be published as a preprint and submitted to a peer-reviewed journal.
Collectively these studies have identified how mechanical cross-talk across compartments is essential to propagate symmetry breaking and the emergence of tissue patterns. Specifically, this work identifies dynamic cell shape transformations and tissue-scale mechanical co-operation as key factors for orchestrating development of the skin epidermis and the associated hair follicle. The mechanical forces that are required for tissue formation stem from contractile, proliferative, and proteolytic activities across the epithelial and mesenchymal compartments. Interestingly, the distinct role of skin fibroblasts in generating forces and adjusting pressure within the skin epidermis through remodeling the ECM recapitulate features observed between cancer-associated fibroblasts and tumor cells during cancer progression. These common features between epidermal hair follicle development/budding and cancer progression, are consistent with observations on cancer cells hijacking embryonal pathways to promote aggression. This suggest that the mechanisms discovered in this study as well as the modeling approaches developed could be of broad relevance for various biological processes.