UBI seminar
 Date: August 30, 13:30 -
 Place: Room 107, BLDG 16, Univ. of Tokyo, Komaba I
 Hongo Campus, the Univ. of Tokyo,and Zoom
 Speaker:Daniel Riveline (Université de Strasbourg, CNRS, IGBMC, France)
 Title: Collective rotations in 2D and in 3D : experiments and theory

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. I will present two examples of spontaneous rotations with experiments synergized with theory. In a first study, 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. We also report that the Curie principle is verified in its symmetry rules. In a second experiment, we show 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 Vicsek model. Altogether both e xamples could set generic rules to quantify and predict generic motion of tissues and organs.