X-Ray-Induced Prophase Delay and Reversion of Selected Cells in Certain Avian and Mammalian Tissues in Culture

Effects of x-ray exposures ranging from 32 to 1024 R on mitosis in chick, mouse, and rat fibroblasts, mouse mammary carcinoma (LH5), Walker rat carcinoma-sarcoma 256, and human carcinomas of the larynx (H. Ep. No. 2) and cervix (HeLa) were determined by repeated observations of selected prophase cells at short intervals after irradiation. Prophase reversion was detected in all cell types except HeLa. It was preceded by a postirradiation inertia during which the cell continued its forward progress for a few minutes. Duration of inertia was inversely related to dose. Cells whose inertia carried them into terminal-middle prophase might revert, but not if it carried them into late prophase. There was a positive correlation between the percentage of cells x-irradiated at middle prophase that reverted and the normal duration of middle prophase in that tissue. The percentage of cells that reverted when treated at early prophase tended to be smaller for cell types with shorter early + middle prophase duration. The percentage of middle prophase cells that reverted was small compared with the percentage of early prophase cells for each type of tissue. Reversion of cells exposed at interphase occurs but is detectable only if postirradiation inertia carries the cell into prophase. The relation of morphologically defined mitotic stages to the DNA synthetic cycle of the acridian neuroblast, chick fibroblast, and mouse mammary carcinoma cell is described.