MITOTIC METAPHASE CELLS FROM DIFFERENT CELL-LINES CAUSE DIFFERENT LEVELS OF EXPRESSION OF THE ALPHA-FORM OF INTERPHASE CHROMOSOME BREAKS INIRRADIATED CHO CELLS

We previously showed that HeLa mitotic metaphase cells, when used as i nducers of premature chromosome condensation (PCC), uncover two times more chromosome breaks in irradiated interphase cells than CHO mitotic metaphase cells, and have at the same time a 2.5-fold higher mitosis promoting factor (MPF) activity. In a different set of experiments, we provided evidence that ionizing radiation induces two forms of interp hase chromosome breaks, the alpha- and the beta-form, that can be disc riminated from each other based on their kinetics of rejoining, their sensitivities to postirradiation treatments, and the genetic requireme nts of their repair. Here we demonstrate that HeLa mitotic metaphase c ells increase the radiation yield of interphase chromosome breaks by s pecifically uncovering interphase chromosome damage of the alpha-form. Using xrs-5 cells that constitutively express chromosome breaks of th e beta-form, we also show that the choice of metaphase cells does not affect the expression of the beta-form of interphase chromosome breaks . These observations add yet another qualitative and quantitative diff erence between alpha- and beta-forms of interphase chromosome breaks, and suggest that separation of radiation damage into two components wi ll be helpful in the description of radiation action in living cells. The finding that different types of mitotic inducer cells give widely different yields of interphase chromosome breaks indicates that a quan titative comparison of the results obtained by different investigators should be made with caution and should consider the type of mitotic c ells used.