Studies on Synchronized Cells: Radiation-Induced Division Delay in the Flagellate Astasia Ionga

Abstract

Loss of viability, most often expressed as a failure of irradiated cells to divide indefinitely, has been the major criterion in evaluating radiation damage at the cellular level. In terms of the cell cycle, the ultimate aim is to find radiation-sensitive phases in the cell cycle, especially if they are intimately associated with cell division (1-8). A variety of approaches have been devised to single out the response of those individual cells that were irradiated at a given stage in the cell cycle. Cells have been labeled with radioactive precursors of nucleic acids, irradiated, and followed for several generations (1-3). Puck and Steffen (9) have developed a system of mathematical analysis based on the kinetics of cellular proliferation that follows the introduction of a metabolic or radiological block of cell division. This approach permits the localization of radiation lesions in the cell cycle of cells whose pattern of division fits the mathematically derived formulations. Terasima and Tolmach (10) have developed a technique for isolating mitotic HeLa cells from exponentially growing cultures. These cells then divide synchronously for a limited number of generations. They can then be used to study radiation sensitivity throughout the cell cycle. Such a method, essentially representing a technique for synchronization of cell division, has been subsequently modified so that large populations of HeLa cells can be isolated and employed in biochemical studies (11). The technique has also been extended to other cell types (12, 13). Other methods of synchronization of mammalian cells have included the use of nucleic acid precursors or analogs (14, 15) and tem-