Secretion of collagen by corneal epithelium. II. Effect of the underlying substratum on secretion and polymerization of epithelial products

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Abstract
Corneal epithelium isolated with EDTA from 5–11 day old chick embryos was grown on a variety of substrata in organ culture to judge the effect of the substratum on the ability of the epithelium to produce a corneal stroma. When grown on the capsule of either living or frozen‐killed lens, the corneal epithelium synthesized and secreted a proline‐rich product (as judged by autoradiography) which was shown by electron microscopy to accumulate under and within the epithelium in the form of striated collagen fibrils, many of which were 250 Å in diameter and arranged at right angles to one another as in the normal corneal stroma. Basal lamina formed, but was not continuous under the epithelium. On EDTA‐treated frozen‐killed corneal stroma, new basal lamina formation was difficult to detect because of the persistence of the old basal lamina on the stroma. When this old basal lamina was digested by trypsin, the remaining corneal stroma failed to promote new basal lamina formation by the epithelium unless the stroma contained living fibroblasts. When grown on rat tendon collagen gels, epithelia produced a proline‐rich product which seemed to polymerize in the gel instead of forming a cornea‐like stroma. Millipore filter failed to elicit any basal lamina or collagen fibril formation. The data presented in this paper are consistent with the hypothesis that juxtaepithelial extracellular matrix may provide cell surface‐stabilizing factors which promote corneal epithelial differentiation.