ABSTRACT
Collagens are major, predominantly structural, components of the extracellular matrices (ECMs) in multicellular animals. These matrices are either organized into thin sheet-like layers, basement membranes (151) that underlie all epithelia and endothelia including those of the eye, or in interstitial matrices in forms such as cartilage, tendon, ligament, and including the sclera, cornea, and vitreous. It is noteworthy that the principal collagenous components of both basement membrane-like matrices (called collagen type IV in vertebrates) and interstitial matrices (fibril-forming or fibrillar collagens) are a
characteristic of multicellular animals and are found in both the simplest sponges and the most complex vertebrates (19). For detailed reviews of collagen structures and disease associations, see Refs. (65,94).
