Proliferating cell nuclear antigen: contradictory results regarding its presence in the lens.

Background: Cell division of the normal lens is believed to occur in the germinative zone of the lens epithelium only. The expression of proliferating cell nuclear antigen (PCNA) at least in its insoluble form, is restricted to cells shortly after and during DNA synthesis.

Method: To elucidate the location of the previously reported notable amounts of PCNA in lens epithelium, 6-micron sections of 10 New Zealand rabbit corneas were stained with specific antibodies.

Results: No PCNA-positive cells were detected in the lens epithelium, neither in the central-zone nor in the germinative zone.

Conclusion: As the mitotic activity of lens epithelium is physiologically low (below 0.03% in adult rabbits), the likelihood of detecting mitotic figures in histologic sections is very limited. We hence conclude that PCNA may be expressed in the epithelia of the lens but is only occasionally visible in histological sections. Our most recent studies have confirmed this. The fixation process and the use of specific antibodies are decisive factors that may, when used correctly, allow specific localization PCNA that is involved in cell replication of lens epithelium. However, it has to be pointed out that the mitotic index of lens epithelium is age- and species-related, and hence so is the expression of PCNA, which makes comparison with other studies more difficult.