Session D24: Exploring New Frontiers: Measuring and Manipulating Mechanical Forces in Development and Disease

Understanding the mechanobiology of cell competition during cancer initiation

Cell competition is a vital process wherein healthy cells collectively identify and eliminate mutant cells within the body to maintain the overall well-being and function of tissues. It also underlies an inherent anti-cancer process, known as the epithelial defense against cancer (EDAC), which plays a crucial role in preventing the development of tumors. Despite its importance, the precise mechanisms governing EDAC have remained largely unknown. We are working to uncover how cellular forces and tissue mechanics influence EDAC. In our investigations, we initially observed that the stiffness of the extracellular matrix is a crucial factor in determining the effectiveness of EDAC. We found that when the matrix becomes stiffer, it impairs the body's ability to defend against the mutant cells. Additionally, we made the intriguing discovery that, before the removal of transformed cells, they experience compressive stress. Notably, this stress is not driven by differences in cell proliferation but rather by variations in mechanical properties, creating a competitive environment between normal and mutant cells. Furthermore, our research is delving into the role of nuclear mechanics in this intricate process. In summary, our findings are challenging the traditional paradigm of cancer research by emphasizing the significance of mechanobiology in understanding the initiation of cancer.   

Mechanical characterization of neural organoids using ferrofluid droplets

The ability of neurons to self-organize into networks has been shown to be influenced by both biochemical and mechanical signals. However, the quantification of mechanics within brain tissue remains an experimental challenge due to its limited accessibility. Neural organoids mimic aspects of the human brain, making the exploration of network formation and function accessible in vitro. The remaining challenge is to probe tissue mechanics in situ to ultimately link neuronal function to mechanical cues.

My group is developing tools for the mechanical and electrophysiological characterization of neuronal organoids. To extract Calcium signals in 3D at high spatiotemporal resolution, we have constructed a custom lightsheet microscope. We quantify neuronal network activity with a minimal set of parameters by applying statistical physics concepts.

Changes in tissue mechanics represent a biophysical hallmark of both organogenesis and tumor formation. Using ferrofluid droplets as mechanical actuators, we record the mechanical properties of developing retinal organoids and tumor-invaded cerebral organoids.

Mechanical and electrophysiological measurements conducted in neural organoids might inform researchers about the interaction between mechanics and function in the development of the central nervous system.   

Cell-level modelling of active forces in early-stage development

Gastrulation is an essential, highly conserved process in the development of all vertebrate embryos, including humans. It involves large-scale cell and tissue movements. When not executed properly, it can lead to a wide range of congenital defects, or, in more extreme cases, cause abortion of development. Gastrulation requires the integration of critical cell behaviours such as cell differentiation, division, and movement through chemical and mechanical cell-cell signalling, to achieve the morphogenesis essential for proper functions. These interactions between signalling and cell behaviours create complex feedback loops between tissue, cell, and molecular length- and timescales that have evolved to enable the robust formation of complex multi-cellular structures. In this talk, using the vertex model for cell-level description of epithelial tissues, we will discuss how various active processes, such as mechano-chemical feedback, cell growth, division, ingression, etc. couple to cell mechanics and lead to pattern formation and flows in model tissues. We will also make qualitative comparisons to the primitive steak formation (i.e. the gastrulation) in chick embryos.   

Stress management: dissecting how epithelial tissues flow and fold inside developing embryos

During embryonic development, groups of cells reorganize into functional tissues with complex form and structure. Tissue reorganization can be rapid and dramatic, often occurring through striking embryo-scale flows or folds that are mediated by the coordinated actions of hundreds or thousands of cells. These types of tissue movements can be driven by internal forces generated by the cells themselves or by external forces. While much is known about the molecules involved in these cell and tissue movements, it is not yet clear how these molecules work together to coordinate cell behaviors, give rise to emergent tissue mechanics, and generate coherent tissue movements at the embryo scale. To gain mechanistic insight into this problem, my lab develops and uses optogenetic technologies for manipulating mechanical activities of cells in the developing Drosophila embryo. First, I will discuss how mechanical forces are regulated in space and time to drive tissue flows that rapidly and symmetrically elongate the head-to-tail body axis of the embryo. Second, I will discuss some of our recent findings on the biological and physical mechanisms underlying distinct modes of generating curvature and folds in epithelial tissue sheets.   

Cellular Sumo Wrestling: Emergent Dynamics following Heterotypic Monolayer Collisions

Epithelia are stationary under homeostatic conditions. However, it has been recognized for over a century that in response to creation of a wound, epithelial sheets migrate collectively into the empty space. As the wound heals, the two cell sheets collide. Following this collision, the cell layers can either mix or form a stable boundary, but the cellular and biophysical properties determining the behavior of the collective following this collision are not well understood. I will present our group's ongoing work showing a novel biophysical behavior following the heterotypic collision of two monolayers with distinct biophysical phenotypes. We generated a barrier-lift assay with distinct populations of epithelial cells on each side of the wound, one being initially solid-like and stationary, and the other being initially fluidizied and collectively migratory. Upon release of the barrier, the initially solid-like cells moved into the wound in an organized fashion, with wave-like propagation of movement from the leading edge into the bulk of the monolayer, while the initially fluid-like cells moved into the wound area quickly and chaotically. Following the collision of the two cell sheets, an unexpected behavior is observed, wherein the solid-like cells are initially compressed away from the collision site, but then change direction and begin to compress the fluid-like cells, reminiscent of a spring being compressed and then released. These behaviors are complex, emergent, and unexpected. Current work focuses on using traction force microscopy and monolayer stress microscopy to illuminate the underlying physical forces governing this novel phenomenon. I will discuss this project in the larger context of our ongoing efforts to understand how events at the single cell level become integrated to yield collective behavior.