Lecturer:  Daniel Riveline, Université de Strasbourg, CNRS, IGBMC, France

Abstract:
Cells, tissues and organs can rotate spontaneously in vivo and in vitro. These motions
are remarkable for their robustness and for their potential functions. However, physical
mechanisms coordinating these dynamics are poorly understood. Active matter
formalisms are required to understand these out-of-equilibrium phenomena with
quantitative comparisons between theory and experiments.
I will present two examples of spontaneous rotation with experiments synergized with
theory (1,2). In a first study (1), we report that rings of epithelial cells can undergo
spontaneous rotation below a threshold perimeter. We demonstrate that the tug-of-war
between cell polarities together with the ring boundaries determine the onset to
coherent motion. The principal features of these dynamics are recapitulated with a
numerical simulation (Vicsek model). In a second study (2), we show that cell doublets
rotate in a 3D matrix and we identify mesoscopic structures leading the movement. Our
theoretical framework integrates consistently cell polarity, cell motion, and interface
deformation with equations capturing the physics of cortical cell layers. We also report
that the Curie principle is verified in these cellular doublets with its symmetry rules
between causes and effects. Altogether both examples could set generic rules to
quantify and predict generic motion of tissues and organs as well as active synthetic
materials.
1- S. Lo Vecchio et al. Nature Physics 20:322–331(2024).
2- L. Lu et al. Nature Physics 20:1194–1203 (2024).