Assembly of chick and bovine lens-capsule collagen

Basement-membrane stromal relationships: interactions between collagen fibrils and the lamina densa

Collagens, the most abundant molecules in the extracellular space, predominantly form either fibrillar or sheet-like structures-the two major supramolecular conformations that maintain tissue integrity. In connective tissues, other than cartilage, collagen fibrils are mainly composed of collagens I, III, and V at different molecular ratios, exhibiting a D-periodic banding pattern, with diameters ranging from 30 to 150 nm, that can form a coarse network in the extracellular matrix in comparison with a fine meshwork of lamina densa. The lamina densa represents a stable sheet-like meshwork composed of collagen IV, laminin, nidogen, and perlecan compartmentalizing tissue from one another. We hypothesize that the interactions between collagen fibrils and the lamina densa are crucial for maintaining tissue-tissue interactions. A detailed analysis of these interactions forms the basis of this review article. Here, we demonstrate that there is a direct connection between collagen fibrils and the lamina densa and propose that collagen V may play a crucial role in this connection. Collagen V might also be involved in regulation of collagen fibril diameter and anchoring of epithelia to underlying connective tissues.

The biosynthesis of extracellular-matrix components by bovine retinal endothelial cells displaying distinctive morphological phenotypes

Previous studies have indicated that the morphology and behaviour of bovine retinal microvessel endothelial cells are influenced by culture conditions in vitro. Data are presented here concerning the biosynthesis of matrix macromolecules by bovine retinal endothelial cells cultured under conditions in which the cells display either the 'cobblestone' or the 'sprouting' phenotype. Newly synthesized matrix proteins were identified by their characteristic electrophoretic mobilities, immunoprecipitation with specific antibodies, susceptibilities to enzymic digestions and chromatographic behaviour. Type IV procollagen was the major collagenous species synthesized by early-passage cells forming a 'cobblestone' monolayer. In contrast, cells displaying the 'sprouting' morphology switched to the predominant synthesis of interstitial fibrillar collagens (types I and III). Fibronectin was synthesized by retinal endothelial cells under all the experimental conditions studied. A non-collagenous glycoprotein of Mr approx. 47,000 was also a major biosynthetic product of these cells. The synthesis of thrombospondin was very much dependent on the nature of the substratum on which the cells were cultured. This glycoprotein was synthesized in large amounts by 'cobblestone' endothelial cells cultured on gelatin-coated dishes, whereas its synthesis was markedly decreased by culturing the cells on collagen gels, and the protein appeared to be absent when the cells were plated within collagen gels ('sprouting' cells). Late-passage retinal cells synthesized predominantly type I procollagen, variable amounts of type III procollagen and only traces of type IV procollagen, irrespective of whether the cells displayed a 'cobblestone' or 'sprouting' morphology.

Identification of noncollagenous components of calf lens capsule: evaluation of their adhesion-promoting activity

Extraction of calf anterior and posterior lens capsules with 5 M guanidine HCI resulted in the solubilization of protein (12% of total) with a noncollagenous amino acid composition leaving behind the collagen matrix. Polyacrylamide gel electrophoresis of the solubilized material revealed a number of components, all of which were susceptible to trypsin but resistant to collagenase digestion. Fractionation of the extracted proteins by Sepharose CL-6B filtration as well as by affinity chromatography was undertaken, and laminin, fibronectin, entactin, and beta-crystallin were identified by electrophoresis and solid-phase radioimmunoassays in both anterior and posterior capsules. An entactin (Mr = 150,000), which constituted the most prominent component on electrophoresis, was purified after Sepharose CL-6B filtration by a two-step lectin affinity chromatography procedure, which was based on the failure of this protein to bind to Bandeiraea simplicifolia I but its positive reactivity with wheat germ lectin. Neither the mixture of proteins extracted from lens capsules by guanidine nor fractions prepared therefrom were able to enhance lens epithelial cell attachment to type I or type IV collagen-coated surfaces or to guanidine-prepared lens capsules; adhesion-stimulating activity could not be demonstrated even when cycloheximide-treated cells were employed. Furthermore, the cells were observed to attach as effectively to guanidine-extracted as to native capsules. These observations indicate that noncollagenous proteins are not essential for the in vitro attachment of epithelial cells to lens capsule; it appears that the collagen component itself provides an optimal surface for cell-basement membrane interaction.