Ultra Fast Contractions and Emergent Dynamics in a Living Active Solid - The Epithelium of the Primitive Animal Trichoplax adhaerens

Abstract

Apical contractions in epithelial sheets are often associated with embryogenesis. Conventionally, these contractions are slow and precisely controlled in space and time, patterning the shape and form of a developing embryo. In this work we report the discovery of ultra-fast epithelial contractions (50% cell area in 1 second, at least an order of magnitude faster) in a “simple” primitive marine invertebrate, Trichoplax adherence, lacking neurons or muscles. Using theoretical calculations, we demonstrate that this speed can still be explained by existing models of acto-myosin contractility and load reduction. We show that tissue architecture is reducing the load on the molecular motors at work. Furthermore, live imaging of the whole animal in vivo reveals emerging contraction patterns, including propagating radial and axial waves. We hypothesize a new role of cellular contractions in epithelium - keeping tissue integrity and enabling resilience to rupture via “active cohesion”. Studying this primitive epithelium highlights a novel unstudied realm in active soft matter.