Fibronectin Lacking the ED-B Domain Is a Major Structural Component of Tracheal Cartilage

Fibronectin is a highly conserved dimeric glycoprotein found in high concentrations in plasma and widely distributed in low concentrations in the extracellular matrix of tissues. The protein is the product of a single gene, but multiple splicing variants are expressed that show tissue specificity. Three exons (IIIA, IIIB, and V) can be alternatively spliced to produce different fibronectin isoforms. We report here that fibronectin is a remarkably abundant component of the extracellular matrix of bovine tracheal cartilage, increasing with age to more than 20% of the tissue, dry weight. This matrix form of fibronectin is inextractable by 4 M guanidine HCl, indicating that it is a covalently cross-linked structural component. By protein sequence analysis, the main molecular form of fibronectin in bovine tracheal cartilage was shown to lack the ED-B domain encoded by exon IIIB.