The striated muscle of hydrozoan medusae: Development and stability of thedifferentiated state

In phylogeny, striated muscle cells have evolved the first time in the medu sa generation of Cnidaria. Development and histology of this cell type have raised speculations whether or not Cnidaria originate from ancient triplob lats. A molecular approach for the identification and expression of genes s pecifying the mesoderm lineage in true triploblasts will help to answer thi s question. In difference to the striated muscle cells of other phyla those of medusae exhibit an unparalleled transdifferentiation potential which ev en includes organ regeneration in vitro. The extracellular matrix controls the stability of the differentiated state of the striated muscle and the in itiation of transdifferentiation follows the classical signal transduction from the cell substrate complex through protein kinase C to the nucleus. Ma ny of the typical ECM ligands known from vertebrates were identified in Hyd rozoa, however, their role in the control of gene expression needs to be id entified in this system.