Fibrillin in the extracellular matrix of cnidarians: An Immunohistochemical approach
S. Reber-Müller, S.-I. Ono, P. Schuchert, J. Spring and V. Schm
Monoclonal antibody 44 (mAb 44) was developed against the isolated ECM (extracellular matrix = mesogloea) of the anthomedusa Podocoryne carnea M. Sars and previously identified to be directed against a 330 - 340 kD protein of this ECM. The antigen was characterized by molecular cloning to be a homologue of the fibrillins, a group of ECM proteins until now only cloned from mammalians. Human fibrillins are important structural components of connective tissue. In the Podocoryne carnea medusa mAb 44 stains in immunohistochemical preparations radially arranged strong fibers in the outer ECM and an irregular meshwork of strong fibers and fine fibrils in the inner ECM. In the ECM of the manubrium and the tentacles the antibody stains homogeneously distributed fine fibrils. The same type of fine fibrils are seen in the ECM of the planula larva and of the polypoid stage. In the hydroid these fibrils form a very dense meshwork at the bases of the tentacles, and in the stalk additionally to the fibrils irregular patches are labelled on mAb 44 staining. The staining pattern was surveyed in various cnidarians. In the ECMs of most species belonging to the Athecatae/Anthomedusae the basic fibrillar staining pattern is similar to the one observed in Podocoryne carnea. The distribution of fibrillin additionally reflects the biomechanical requirements of come specialized body structures. No staining was observed in the Thecatae/Leptomedusae and the Trachymedusae. Siphonophora show a weak staining and some but not al1 Scyphozoa gave positive results, but showed a different distribution of the epitope compared to the anthomedusae. Most of the tested Anthozoa and the ctenophore Pleurobrachia sp. did not stain. We suggest that the distribution of the mAb 44 antigen reflects the biomechanical needs of the tissues adhering to the different types of ECMs in cnidarians.