Extracellular proteases in developing chick neural retina.

During retinal histogenesis, cells and their extensions migrate within the tissue to final positions. In order for the cells to move through the matrix of tissue, space must be made available. We report evidence that extracellular proteolytic activity might be associated with this process. (1) When embryonic chick neural retinal cells are seeded onto a substrate of rhodamine conjugated fluorescent gelatin, the tips of growing neurites remove the fluorescence from the substrate. (2) Latent gelatinolytic activity can be identified with soluble assays of homogenates of embryonic chick neural retina. (3) Zymogram analysis demonstrates the presence of high molecular weight bands of proteolytic activity. The activity is inhibited by 1.10 phenanthroline, suggesting that it is due to a metalloproteinase. Activity can be detected in supernatants of retinal cells grown in vitro. Gelatinolysis is not the only proteolytic activity detected in the retina. Addition of plasminogen to zymograms results in an additional band of activity.