Ultra-Fast Contractions and Emergent Dynamics in a Living Active Matter - the Epithelium of the Primitive Animal Trichoplax adherence

Non-muscle cellular contractions are a common way for animal cells/tissues to apply forces on their surroundings and/or shape themselves. In early evolution of multicellularity, epithelial contractions played a crucial role in keeping animal integrity and coordination, opposing and then replacing ciliary power. In most animals today epithelial contractions are associated with embryogenesis, where slow and precisely controlled contraction patterns are shaping the embryo. In this work we report the discovery of ultra-fast epithelial contractions (50% cell area in 1 second, an order of magnitude faster) in the early diverging, “simple" animal Trichoplax adherence, that lacks neurons or muscles. Using theoretical calculations, we demonstrate that the observed speeds can be explained by actin-myosin contractility with bundle geometry and minimal load. We show that the unique tissue architecture is indeed reducing the load on the molecular motors. Live imaging of the whole animal in vivo reveals emerging contraction patterns, including propagating waves. We hypothesize a new role of cellular contractions in epithelium - enabling resilience to rupture via "active cohesion". Studying this early epithelium highlights a novel unstudied realm in cell cytoskeleton as active soft matter