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 relations 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).
