The tension of hydra extracellular matrix: its maintenance, regeneration and function

Hydra extracellular matrix (ECM), mesoglea, is sandwiched in between two layers of epithelia, the ectoderm and the endoderm. The mesoglea contains a number of major ECM molecules such as laminin, Type IV collagen, and fibrillar collagens (type I through VI). When hydra polyps are decapitated or injured on the body column, significant mesoglea retraction from the cutting edge is observed indicating a tension regularly maintained within the mesoglea. Using antibodies for each mesoglea component and with different cutting methods we have observed the differences of each ECM molecule during mesoglea retraction. When hydra polyps are treated with Colchicine or Cytochalasin D, the mesoglea structure is disrupted and mesoglea retraction is affected indicating a relationship between the epithelial cells and the maintenance of a normal mesoglea structure and tension. The mesoglea retraction, together with epithelial cell migration towards the tissue opening, result in the absence of ECM at the area of wound healing. Our data provides evidences showing that the re‐synthesis and assembly of mesoglea at the wound healing site is necessary for continued tissue regeneration in the area. The ECM tension, retraction, and re‐synthesis/re‐assembly during tissue regeneration are not only observed in hydra but also in human. Our study on hydra ECM may help to understand wound healing and tissue repairing in medicine. (Supported by NIH P01‐DK065123).