THE PRESENCE OF DNA BREAKS AND THE FORMATION OF CHROMATID ABERRATIONSAFTER INCORPORATION OF (125)IDURD MAY BE NECESSARY BUT ARE NOT SUFFICIENT TO BLOCK CELL-CYCLE PROGRESSION IN G(2) PHASE

Cell progression into mitosis and chromatid aberration frequencies wer e compared in two Chinese hamster ovary (CHO) cell lines after incorpo ration of (125)IdUrd. Asynchronous, exponentially growing populations of CHO K1 and the DNA repair-deficient, radiation-sensitive CHO irs-20 cells were compared after a 10-min exposure to 14.8 kBq/ml (125)IdUrd . Essentially no differences were seen for either end point between th e cells of the two cell lines. As the cells in S phase at the time of labeling entered the mitotic cell selection window, the number of mito tic cells of each cell line declined to approximately 60% of the respe ctive unlabeled control. Chromosome analysis of the mitotically select ed cells indicated an I-125 decay-dependent increase in the number of chromatid aberrations in cells of both cell lines. The appearance of a berrations together with the known rates of production and rejoining o f DNA double-strand breaks show that cells are able to progress throug h G(2) phase and into mitosis in the presence of such breaks. The data suggest that DNA damage may be necessary, but is not sufficient to ca use a radiation-induced blockade of cell progression through G(2) phas e. (C) 1996 by Radiation Research Society