Spontaneous Bending of Hydra Tissue Fragments Driven by Supracellular Actomyosin Bundles

TL;DR

Hydra tissue fragments spontaneously bend into stable shapes driven by supracellular actomyosin bundles, with a mechanical model predicting shape based on contractility and elasticity anisotropy, and characterized by distinct time scales.

Contribution

This study introduces a mechanical model linking actomyosin bundle properties to spontaneous bending in Hydra tissue fragments, supported by experimental time scale measurements.

Findings

Bending is driven by supracellular actomyosin bundles inherited from Hydra.

The shape is determined by anisotropy in contractility and elasticity.

Two characteristic time scales are identified: ~0.01 seconds and several minutes.

Abstract

Hydra tissue fragments excised freshly from Hydra body bend spontaneously to some quasi-stable shape in several minutes. We propose that the spontaneous bending is driven mechanically by supracellular actomyosin bundles inherited from parent Hydra. An active-laminated-plate model is constructed, from which we predict that the fragment shape characterized by spontaneous curvature is determined by its anisotropy in contractility and elasticity. The inward bending to endoderm side is ensured by the presence of a soft intermediate matrix (mesoglea) layer. The bending process starts diffusively from the edges and relaxes exponentially to the final quasi-stable shape. Two characteristic time scales are identified from the dissipation due to viscous drag and interlayer frictional sliding, respectively. The former is about 0.01 seconds, but the latter is much larger, about several minutes, consistent with experiments.