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 Tuesday, April 6th in detail:

15:00 - 15:05  Welcome

15:05 - 15:50  Virgile Viasnoff, MBI Singapore: "Understanding the tubulogenesis of bile canaliculi one cell at a time in regenerating or developing livers"

Abstract:

Lumenogenesis is a common mechanism in plant and animals that consists in creating, gaps, and lumens between cells to allow the formation of ducts. The creation of tubes occurs following several scenarios that are worth comparing. I will present our understanding of how small canaliculi are formed between hepatocytes during liver development and regeneration. Bile salts are secreted in canaliculi and partially drive their their morphogenesis. However the link between intraluminal osmotic pressure build up, apico basal polarity development and maturation of tight junctions is poorly understood. In particular how these mechanisms coordinate to expand micron size canaliculi to mm long tube is not even described. Deficient formation of canaliculi network leads to defects in bile flows and consequently diseases (cholestasis). We adopted a constructivist approach to understand how an osmotically driven growth of canaliculi can anisotropically lead to the development of a tube.

I will show how single hepatocytes (the main cellular constituents of the liver) can be induced to form spherical hemi-lumen by contact with an inert material, demonstrating that lumenogenesis initiation does not require the concomitant development of lumen in the neighbouring cells. I will then show how the spatial geometry of extracellular matrix provides a guidance tool to favour the development of tubulogenesis in the direction of lowest intra-cellular tension. Lastly, I will show the existence of special protrusions crossing the lumen cavity, bridging, suturing, the developing lumen to putatively minimize its extension in the lateral direction, and consequently favouring its extension along the tubular axis.

— 10 min break —

16:00 - 16:45  Yanlan Mao, University College London: "Coping with Mechanical Stress: Tissue dynamics in development and repair"

Abstract:

During growth and development, tissue dynamics, such as tissue folding, cell intercalations and oriented cell divisions, are critical for shaping tissues and organs. However, less is known about how tissues regulate their dynamics during tissue homeostasis and repair, to maintain their shape after development. In this talk, we will discuss how differential growth rates can generate precise folds in tissues. We will also discuss how tissues respond to mechanical perturbations, such as stretching or wounding, by altering their actomyosin contractile structures, to change tissue dynamics, and thus preserve tissue shape and patterning. We combine genetics, biophysics and computational modelling to study these processes.

— 10 min break —

16:55 - 17:40  Pere Roca-Cusachs, IBEC Barcelona: "Transducing - and shielding - mechanical signals from integrins to the nucleus"

Abstract:

Cell proliferation and differentiation, as well as key processes in development, tumorigenesis, and wound healing, are strongly determined by the properties of the extracellular matrix (ECM), including its mechanical rigidity and its composition. In this talk, I will discuss how mechanical force is transmitted from the ECM to the nucleus, and how this affects proteins in general, and transcription factors in particular, by controlling their shuttling between the cytoplasm and nucleus. Further, I will discuss how different matrix, integrin, and cytoskeletal proteins control whether the nucleus is exposed to, or shielded from, force transmission. Finally, I will address the implications of this regulation in biomedical applications.