Autoradiographic study on the regenerative capability of the epithelium lining the center of the cornea after multiple debridements of its peripheral region

The epithelium lining the center of the cornea is assumed to lack stem cells.The purpose is to investigate by autoradiography the regenerative capability of the epithelium lining the central region of the rabbit cornea following seven scrapings of its peripheral lining, during several months. After marking the center of the cornea with a 6 mm-diameter trephine, the epithelium outside this area was scraped until reaching the corneoscleral zone. This procedure was repeated seven times on the same eye at intervals of 20 days. One day after the last scraping, H-3-thymidine was injected intravitreally and the corneas processed for autoradiography. At 2 days after injection, the corneal surface was entirely lined by an epithelium made up by two layers of squamous cells, most of them being labeled with the DNA precursor. A multilayered epithelium was visualized at the center with most of its basal cells also labeled. The limbal epithelium had at least two of its layers labeled with the precursor. At 9 days, the multilayered central unscraped epithelium exhibited labeled cells not only in the basal but also in its suprabasal layers. The labeling index (labeled nuclei/100 cells) for its basal stratum was very close to 100%. A similar feature was observed at 16 days, except that the mutilayered central epithelium was seen lining a larger area when compared to the precedent interval and that it exhibited evidences for vertical renewal. The epithelium lining the central region of the cornea-where it was assumed that stem cells do not exist-exhibited capability for regeneration and self-renewal in spite of seven consecutive debridements of its periphery. No evidence was found for transposition of limbal epithelial cells to the center of the cornea during the early merger of the epithelial sliding fronts.