A mechano-chemical model of Hydra regeneration

Hydra is a freshwater animal with extraordinary regeneration properties making it an excellent model organism to study morphogenesis. The epithelial layer of an adult Hydra contains actin muscle fibres that are highly organized with an aster point defect positioned at the head and foot of the animal. Starting from an excised tissue fragment Hydra can fully regenerate, however, it is unclear how the fibre pattern self organizes and forms stable +1 defects. Experiments indicate that the formation of +1 defect at the head is inhibited by weakening the elasticity of the underlying tissue and is aided by the localisation of Wnt, which is a morphogen relevant for head regeneration. We propose a mechano-chemical feedback between tissue mechanics, nematic fibre pattern and morphogen dynamics, as a mechanism of Hydra regeneration. For this we have developed a vertex model of curved epithelia that incorporates the feedback mechanism and simulate the repeated contraction events observed during the regeneration process. We find that the contraction events localise the tissue strain which stabilizes the +1 aster defect through the proposed feedback loop. Thus our model is able to reproduce the observed dynamics of Hydra tissue and the nematic fibres in a robust manner.