The effects of x-rays on the cell cycle and differentiation in the lens epithelium

It has been shown that the initial effect of radiation leading to the development of cataracts occurs in the lens epithelial cell population. Historically, it was recognized that early perturbations of the cell cycle follow exposure of the lens to X-rays. These are typified by a mitotic delay followed by an overshoot in the number of dividing cells. The authors' studies confirm these early observations and furthermore demonstrate that the overshoot, at least in the initial stages, is the result of cells entering mitosis after having accumulated in G2. Thus, the mitotic delay is due to a G2 block. A decrease in DNA synthesis indicates, also, the existence of a G1 - S block. This ostensibly contributes to the mitotic overshoot period some time after its beginning. Cells irradiated during the 3 phase typically disappear from the population during or soon after completion of the following cell division. In addition to mitotic death, a subpopulation of cells undergoes interphase death. While the role of cell death in cataractogenesis is problematic, the observed interphase death is associated with an early but transient loss of architecture in the meridional rows (area of early lens fiber cell differentiation). These observations are detailed and their implications in understanding the cataractogenic process are discussed