Patterns of cellular organization and cell division in the epithelium of the cultured lens

Abstract

Crystalline lenses (rabbit) were cultured for periods ranging from 1 hr to 46 days. A dialysis system which facilitates the culture of large numbers of lenses under virtually identical conditions was used. The lens was enclosed in a dialysis bag containing 2–3 ml of synthetic culture medium (inside medium), and immersed in a 125 ml flask containing 50 ml of the same medium (outside medium). Several lenses were incubated in one flask and the outside medium was changed at regular intervals of 1–3 days. Some lenses were injured after 8 days of culture and incubated for 2 further days. In most cases, tritiated thymidine was introduced into the medium just prior to termination of culture. Whole-mount preparations and autoradiographs of the epithelia were examined and the general and nuclear morphology, number of mitotic figures and number of radioactive nuclei noted. Lenses remained clear and refractile as long as 30 days. Except for small areas probably related to injuries accidentally inflicted during isolation of the lens, the epithelia of these lens showed little morphological alteration. These preparations indicated that cell density in the germinative zone approaches that of the central area as culture continues, and that the epithelium tends to extend on to the posterior capsule. Cell division in the epithelium of such lenses does not cease during culture, but the distribution of labeled nuclei and mitotic figures is altered; this alteration appears to follow a well defined sequence. The lenses injured during culture showed a great burst of cell division around the site of injury 48 hr later. Lenses that became cataractous did so after the appearance of microbial infection in the outside culture medium. The epithelia of these lenses showed great alterations in general morphology, very extensive nuclear labeling, and nearly complete population of the posterior capsule by epithelial cells. The various patterns of cell proliferation observed in the epithelia of cultured lenses, and comparison of these with that found in vivo, seem to indicate that physical forces exerted on the lens (such as those due to the varying tension of the suspensory ligaments) and the resulting wear and tear on the epithelium may be causally related to the rate of cell proliferation and the distribution of dividing cells in this tissue. This hypothesis, as opposed to that involving diffusible chemical inhibitors or stimulators, is discussed.