Active laminated-plate model for spontaneous bending of Hydra tissue fragments driven by supracellular actomyosin bundles

Abstract

Abstract The outstanding regeneration of Hydra’s excised tissue fragments occurs via initial spontaneous bending to some quasi-stable shape in several minutes. However, the underlying mechanism and dynamics of such initial spontaneous bending are still debated. Here, we propose that the spontaneous bending is driven mechanically by supracellular actomyosin bundles inherited from parent Hydra. Our active laminated-plate (ALP) model predicts that the equilibrium fragment shape is determined by anisotropy in contractility and elasticity. We construct a minimal dynamic ALP model including three dissipation mechanisms. By variational analysis and bead-spring simulations, we find that the bending process starts diffusively from the edges and relaxes exponentially to the equilibrium shape. The different dissipation mechanisms take place at distinct timescales: the viscous drag occurs in 0.001 seconds, while the interlayer frictional sliding and cellular dissipation take place in minutes. The ALP model could be adapted to study multi-layered viscoelastic tissues with nematic cytoskeletal structures and provides a useful framework for tissue morphogenesis and regeneration.