Cellular Proliferation in the Lens.

The lens epithelium occurs as a single sheet of epithelial cells on the anterior surface of the lens in most species studied. This sheet lies subjacent to the lens capsule which completely encloses the lens. Under normal conditions, in rabbit lens epithelium, mitotic activity is restricted to a peripheral area knoion as the germinative zone. However, under certain in vitro conditions and by injury, viitotic activity can be induced in the central region. In the case of a penetrating needle injury, this mitotic response appears to be propagated. More and more cells further away from the injury are stimulated to synthesize DNA and divide. This large mitotic response to a needle injury ceases after about 3 days. Frequently, with large injuries, a second xoave of DNA synthesis and mitosis starts at the injury site. Experiments performed with the chromosomes of lens epithelial cells indicate that some cells in the injury area divide twice in response to the injury. This information has proved useful in characterizing the cell cycle of lens epithelium from rabbit and in comparing it with the cell cycle times reported for lens epithelium from other species. Finally, the general aspects of the control of cell proliferation in the lens are discussed in the light of in vitro and in vivo experiments and pertinent findings in other cell systems.