The major constituent of basement membrane is type IV collagen. It consists of two genetically distinct polypeptide chains, pro Alpha1(IV) and pro Alpha2(IV) with apparent molecular weights of 180,000 and 170,000 daltons respectively. The biosynthesis of basement membranes is an active area of research with significant implications for the maintenance of normal structure and function. In diabetes mellitus, basement membrane thickening has been observed in multiple organs. It is acute and best characterized in the retina, skin and kidney. Besides morphological changes, there is altered basement membrane function resulting in the retinal exudates and Alports Syndrome. There is very little information available regarding specific biochemical defects that underlie these diseases. Consequently, the synthesis and investigation of the regulation of type IV collagen should yield information relevant to the understanding of diabetic retinopathy. Recently, we have demonstrated that epithelial cells cultured from bovine anterior lens capsule explants synthesize and secrete procollagen type (IV) polypeptide chains Apha1(IV) and Alpha2(IV). Also, we have isolated poly (A+) RNA from these cells and translated in a cell-free system. In the present investigation, we propose to focus on the isolation of mRNA from cultured epithelial cells of bovine lens capsule enriched in type(IV) collagen mRNA and cloning a cDNA for Alpha1(IV). The availability of specific cDNA probes for type IV collagen will help in the identification of nascent, unmodified type IV polypeptide chains obtained by in vitro translation of bovine lens capsule mRNA. Eventually, the cDNA clone will prove very useful in studying the effect of chemical agents or hormones on the synthesis of type IV collagen using our model system of bovine lens capsule epithelial cell cultures.
