Variations in radiosensitivity during the cell cycle in a marsupial cell line

Abstract

A permanent marsupial cell line, with 96% diploidy, of the male Potorous tridactylus (2n = 13) was irradiated in different stages of the cell cycle. The results for first-division postirradiation show that cells in G 2 had more chromatid deletions and more total damage than cells in late G 1 and all parts of S. The unusual length of S has enabled a more detailed examination of this stage of the cell cycle. The number on total aberrations decreased with progress through S. Contrary to other reports on animal cells, the frequency of isochromatid deletions was found to vary considerably in S and G 2. The number of isochromatid aberrations in early S was at least twice the number found in late S for 4 different series of irradiation experiments. It was also shown that isochromatid deletions respond to a fractionated dose as the accepted two-hit aberrations do. These data suggest that isochromatid deletions may, in part at least, originate from two-hit events. This finding can be interpreted as lending support to Revell's 21,22 contention that all chromatid aberrations result from incomplete exchanges and should be regarded as multi-hit phenomena.