Symposium Series Physics and Medicine (6)
Pressure, density, elasticity are classical physical properties, which are required to fully describe the processes in human cell assemblies – for example, to distinguish tumours from healthy tissue or to stimulate the regrowth of nerve cells. These examples illustrate how physics can provide new stimuli for basic medical research.
Today, modern physical methods and physical thinking are being transferred towards physiological application worldwide. In order to promote the exchange between different researchers and working groups, the Max Planck Zentrum für Physik und Medizin is starting a new series of public mini-symposia, in which two to three scientists from North America, Europe or Asia will present their work virtually. The series has been started in March and will be continued on the 6th, 8th und 9th April.
To take part in the symposia, please register for MPL's scientific lectures newsletter (please ensure that you tick the "scientific lecture" checkbox). We will send the Zoom links about one hour before the symposium starts.
The schedule for Thursday, April 8th in detail:
15:00 - 15:05 Welcome
15:05 - 15:50 Ewa Paluch, University of Cambridge: "Cell morphogenesis across scales, from cytoskeleton organization to cellular mechanics"
A precise control of cell morphology is key for cell physiology, and cell shape deregulation is at the heart of many pathological disorders, including cancer. Cell morphology is intrinsically controlled by mechanical forces acting on the cell surface, to understand shape it is thus essential to investigate the regulation of cellular mechanics.
In animal cells, shape is primarily determined by the cellular cortex, a thin network of actin filaments and myosin motors underlying the plasma membrane. We investigate how the mechanical properties of the cell surface arise from the microscopic organisation of the cortex, and how changes in these properties drive cell deformation. We have developed methods to investigate cortex composition and nanoscale architecture, and are exploring how cortical network mechanics are regulated. Using a combination of cell biology experiments, quantitative imaging and physical modelling, we aim to understand the control of cell shape across scales.
— 10 min break —
16:00 - 16:45 Benoit Ladoux, Université Paris Diderot / CNRS: "Active nematic behaviors of cellular monolayers"
I will present how active nematic activity of cellular monolayers can help to understand biological processes and tissue organization. In the first part, I will show how these active behaviours and stresses govern cell extrusion. By modelling the epithelium as an active nematic liquid crystal and measuring mechanical parameters such as strain rates and stresses measurements within cellular monolayers, we show that apoptotic cell extrusion is provoked by singularities in cell alignments in the form of comet-shaped topological defects. The results highlight the importance of active nematic nature of epithelia. In the second part, I will focus on the intriguing extensile behavior of epithelial cells as a collective when single cells behave as contractile systems. Through a combination of experiments and in silico modeling, we uncover the mechanism behind this switch of behaviour of cell monolayers from extensile to contractile as the weakening of intercellular contacts. We find that this switch in active behaviour also promotes the buildup of tension at the cell-substrate interface through an increase in actin stress fibers and higher traction forces. Such differences in extensility and contractility act to sort cells, thus determining a general mechanism for mechanobiological pattern formation.
— 10 min break —
16:55 - 17:40 Nikta Fakhri, MIT: "Turing^2: mechanochemical basis of pattern formation"
Many cellular processes, such as cell division, cell motility, and tissue folding, rely on the precise positioning of proteins on the membrane. Such protein patterns emerge from a combination of protein interactions, transport, conformational state changes and chemical reactions at the molecular level. These proteins achieve robust spatiotemporal organization on the membrane during the dynamic cell shape changes involved in physiological processes. In this talk, I will discuss our efforts to reveal the physical self-organization principles that govern mechanochemical patterns in early stages of development.
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