TYPE-IV COLLAGEN IN SPONGES, THE MISSING LINK IN BASEMENT-MEMBRANE UBIQUITY

Basement membrane structures, or their main component, type IV collage n, have been detected in all multicellular animal species, except spon ges. We cancel this exception by the demonstration of type IV collagen ous sequences in a new marine sponge species by cDNA and genomic DNA s tudies. One of these sequences is long enough to demonstrate the speci fic characteristics of type IV collagen chains. The 12 cysteines are a t conserved positions in the carboxyl-terminal non-helical NC1 domain, as are the interruptions in the carboxyl-terminal end of the triple h elical domain. The gene organization of the region coding for the NC1 domain is similar to that of the human genes COL4A2, COL4A4 and COL4A6 . An additional, shorter sequence suggests the presence of a second ch ain. The expected tissue localization of this collagen has been confir med using polyclonal antibodies raised against a sponge recombinant pr otein. These results demonstrate that type IV collagen is representate d in all animal phyla. It is actually the only known ubiquitous collag en and it has at least two different alpha chains in all the species w here it has been characterized.