The functionality of each organ in our body is determined by the structure and correct organisation of each tissue component. Tissue architecture is ensured by a perfect equilibrium between each individual cell, its neighbours and the physical environment. In particular, this is tightly regulated in epithelia that are constantly renewed through our lives thanks to stem cells and progenitors able to regenerate entire tissues. Stem cells have the capacity to renew and differentiate in other cells types and the ability to sense and cope with different external cues. Specifically, we focus our interest into the mechanobiology field that studies the set of mechanisms converting physical cues into chemical signals by a process called mechanotransduction.
The questions we want to address include how tissues remodel their cellular division and cell-fate patterns, and how the cell-cell and cell-matrix connections are adjusted to coordinate biological function and collectively react to external stress with the activation of specific transcription factor programs. We are investigating these biological questions in tissues that are naturally subjected to different mechanical perturbations such as the skin and the urinary tract. Understanding these fundamental principles will improve our basic understanding and have a high impact in the development of new regenerative medicine tools.
Using lineage tracing in mouse models, embryo tissue explants for live imaging during organ formation, transcriptomic and chromatin profiling at the single cell level, we study how mechanical stimuli are integrated by the cells and translated in signalling pathways that, providing positional information for cell fate decisions, directly shape tissue architecture.
Cellular components involved in mechanotransduction. Each cell is in perfect equilibrium with its microenvironment. Different external forces shape the structures and the functions of eukaryotic cells that will adjust their behaviour by the activation and repression of specific gene regulatory network.
Mechanisms regulating the response to stretching in the skin
The capacity of the skin to expand as a reaction to stretching is a property commonly exploited in plastic surgery to generate an excess of skin that can be used to repair birth defects, damaged tissues, scars and for breast reconstruction after mastectomy. Although this technique has been used for decades in reconstructive surgery, little is known about the cellular and molecular responses of cells to tissue stretching. For these reasons, the skin is a perfect tissue to study and model the effects of mechanical stimuli on cell behaviour in a clinically relevant context. We developed a mouse model in which the temporal consequences of stretching the skin epidermis can be studied in vivo. We discovered that stretching induces skin expansion by creating a transient bias in the renewal activity of epidermal stem cells, while a second subpopulation of basal progenitors remains committed to differentiation. By transcriptional and chromatin profiling and functional assays, we identified how cell states and gene regulatory networks are modulated by stretching in the epidermis. We are currently studying how the other skin compartments, mainly in the dermis, maintain themselves under mechanical stress, as well as how they coordinate their own homeostatic behavior with the different neighboring cell types.
A mouse model to study mechanotransduction in the skin. Several cell types constitute and maintain the barrier function of the skin. We are studying how they all ensure proper tissue architecture in response to mechanical cues such as mechanical stretching
Principles of cellular urinary tract homeostasis
It has become increasingly clear that not only stretching and compression are important physical cues that shape epithelia, but that also more broadly acting forces like fluid flow and hydrostatic pressure play substantial roles during morphogenesis and homeostasis. As complementary paradigm, we are studying the epithelium of the urinary tract that is under frequent mechanical loading and unloading due to the urine flow, providing a model in which we can interrogate the effect of fluid mechanics on epithelia biology. Additionally, from these body compartments, with the urine flow, we lose cells that need to be constantly replaced. However, it is still unknown whether this tissue is maintained by a single equipotent population of cells or by a defined cluster of stem cells and which degree of plasticity characterises these cells. By single-cell sequencing, lineage tracing and clonal analysis, we are studying the hierarchical organization and proliferation dynamics of cell lineages within the ureters and urethra epithelia.
Urinary tract tubulogenesis and development
With the tools and knowledge acquired by studying the urethral epithelium during homeostasis, we are interrogating the cellular mechanism of lumen formation during embryonic development. We are studying which are the driving forces that, from a single homogeneous group of cells, specify and pattern the different cell types to generate the adult tissue architecture. By culturing ex vivo mouse embryonic explants we are investigating the cellular dynamics that lead to tubulogenesis from a spatial and temporal perspective. To understand whether and how fluid mechanics affect the generation of the organ, we are correlating changes in cell-fates and in the remodelling of the actomyosin cytoskeleton with the measurements of the hydrostatic pressure and urine flow. By studying these processes, we will be able to shed light on the molecular mechanisms that could be responsible for congenital anomalies and disorders affecting the urinary tract.
Mechanotransduction in the urethral epithelium
To gain further insights in the molecular characterization of this biological system, we will implement currently available 3D organotypic cultures of human urinary tract tissue, and use them to analyze the cells dynamics in response to the pressure and shear stress generated by the urine flow. By live imaging on organoid cultures we will track the different cell fates, we will analyze the molecular mechanisms and the gene regulatory networks underlying cell behaviors, and we will describe in which specific cells different signaling pathways are activated or repressed.
Globally, we aim to understand how mechanical cues, morphogens, cell-cell interaction and competition, as well as other important determinants of the cell microenvironment and niche, locally regulate transcription to shape tissue architecture and how this impacts stem cell physiology and pathology. Our ultimate goal is to provide deep knowledge on how tissues are naturally built, in order to direct new approaches for regenerative and reconstructive therapies.
A mosaic of clones constitutes the epithelial skin barrier
Epidermal stem cell clones traced with the Confetti reporter (the four colour of the cassette are mCFP, YFP, nGFP, RFP) during wound healing.
Tissue geometry regulates proliferation
Epithelial cells cultured on a squared micro-patterned substrate. Colorimetric stacked images of BrdU incorporation, used to visualize spatial variations of proliferation in cell monolayers. The colour scale indicates the extent of cell proliferation in a given position of the monolayers.