Mechanochemical interactions between striated muscle cells of jellyfish and grafted extracellular matrix can induce and inhibit DNA replication and transdifferentiation in vitro.

Striated muscle tissue of jellyfish was isolated with its adhering extracellular matrix (ECM) and cultured. Without further treatment the cultured muscle cells maintain their differentiated state. If, however, the isolated tissues are combined with cell-free ECM from the jellyfish or its polyp, DNA replication and proteolytic activity are induced followed by transdifferentiation into RF-amide-positive nerve cells. Changes in the mechanochemical interactions between the cells and the grafted ECM seem to induce the signals which lead to transdifferentiation. If the isolates are combined with small floating pieces of ECM most cells will leave their own ECM and overgrow the ECM graft. All cells in the combinations will then transdifferentiate. If the isolates are grafted onto large pieces of ECM kept permanently stretched on glass, a majority of cells will migrate onto the grafted ECM where they form a flat monolayer. In this case, however, DNA replication and transdifferentiation occurs mainly in those cells which have remained on or near their own ECM. Labeling experiments with [3H]-thymidine demonstrate that initiation of DNA replication occurs first in those cells which bridge from the native ECM to the grafted ECM. On the other hand inhibition of DNA replication and transdifferentiation is generally suppressed whenever tissues are allowed to form a monolayer of well-stretched cells. From these observations we conclude that mechanochemical interactions between the muscle cells and their substrate are responsible for both activation and inhibition of DNA replication and transdifferentiation.