Cellular Biophysics
(Dr. Mark Skamrahl, Tanmaya Sethi, Amaury Perez-Tirado, Marcel Jipp, Vanessa Theuer, Chin-Yao Chang)
Cellular Mechanics
Cellular mechanics plays a crucial role in many biological processes, such as cell migration, cell growth, embryogenesis, and oncogenesis. The cellular mechanisms to regulate the mechanical properties of the plasma membrane are important for cell survivability during cell division, changes in osmotic pressure, cell spreading, and other processes. The comparison between whole-cell experiments and experiments on isolated native membrane sheets on porous substrates allows the attribution of the mechanical changes to cortical changes or changes in the cell interior, giving a better understanding of underlying mechanisms.
Epithelial tissue responds to environmental cues, comprised of biochemical and physical stimuli, through defined changes in cell elasticity. For instance, cells respond to certain substrate properties such as viscoelasticity or topography by adapting their elasticity and shape accordingly. Resolving cell mechanics on various length scales and obtaining viscoelastic maps of the cell surface is therefore pivotal to our understanding of how cells respond to mechanical stress and how stress is transmitted across cell-cell boundaries, as during wound healing.
Forces in Tissues and Collective Migration
Collective cell migration is not only essential during vital processes such as embryogenesis but also crucial to close wounds in a cell layer. Our group has shown that even single-cell defects cause long-range mechanical responses during epithelial wound healing, highlighting the mechanical cooperativity of cells. We now aim to elucidate intercellular forces during wound closure across entire cell layers. For this, an array of long micropillars serves as a force sensor to detect the stress field within a cell layer. The deflection reports on local forces depending on the distance to the wound and allows to extract the stress pattern in differently sized cell collectives.
To gain a more comprehensive picture of epithelial wound healing, we apply the newly established MIET (metal-induced energy transfer) technology in collaboration with Dr. A. Chizhik (Third Inst. Of Physics, U. Göttingen). For this, cells are seeded on a gold film and imaged by scanning a focused laser beam. Fluorescence lifetimes are detected with a single photon counting device. With MIET microscopy providing access to the cleft between cell and substrate, we are in the position to understand the spatiotemporal dynamics of cells in response to the formation of gaps as a function of ECM composition, substrate stiffness and chemistry, gap size and curvature as well as the origin of void formation.
An important, yet still unanswered question is how static and dynamic mechanical stresses influence epithelial tissues and the mechanical properties of cell-cell contacts. Our group has designed a system for strain application employing a motorized stretcher made from polydimethylsiloxane (PDMS) for optimal compatibility with a theoretical maximum strain of 75%, allowing to apply biological relevant strains for epithelial tissues. The mechanical properties of the cells during strain are probed with an atomic force microscope to determine the influence of strain on the mechanical response of cell collectives.
