THE EVOLUTION OF FIBRILLAR COLLAGENS - A SEA-PEN COLLAGEN SHARES COMMON FEATURES WITH VERTEBRATE TYPE-V COLLAGEN

The extracellular matrix of marine primitive invertebrates (sponges, p olyps and jellyfishes) contains collagen fibrils with narrow diameters . From various data, it has been hypothesized that these primitive col lagens could represent ancestral forms of the vertebrate minor collage ns, i.e. types V or XI. Recently, we have isolated a primitive collage n from the soft tissues of the sea-pen Veretillum cynomorium (31). Thi s report examines whether the sea-pen collagen shares some features wi th vertebrate type V collagen. Rotary shadowed images of acid soluble collagen molecules extracted from beta-APN treated animals, positive s taining of segment-long-spacing crystallites precipitated from pepsini zed collagen, Western blots of the pepsinized alpha 1 and alpha 2 chai ns with antibodies to vertebrate types I, III and V collagens, and in situ gold immunolabeling of ECM collagen fibrils were examined. Our re sults showed that the tissue form oi the sea-pen collagen is a 340-nm threadlike molecule, which is close to the vertebrate type V collagen with its voluminous terminal globular domain, the distribution of most of its polar amino-acid residues, and its antigenic properties.