INDUCTION OF CHROMOSOMAL INSTABILITY IN HUMAN MAMMARY CELLS BY NEUTRONS AND GAMMA-RAYS

There is now substantial evidence that ionizing radiations can induce genomic instability in the form of chromosomal aberrations that appear several cell generations after irradiation. However, questions remain concerning the influence of radiation quality on this phenomenon. In this study, progeny of either gamma- or neutron-irradiated human epith elial MCF-10A cells were examined for chromosomal aberrations between 5 and 40 population doublings postirradiation. Exposure to either type of radiation resulted in an increase in chromatid-type gaps and break s several doublings after the irradiation; no such effect was observed for chromosome-type aberrations. Neutron-irradiated cells showed cons istently elevated frequencies of aberrations compared to nonirradiated controls at all times examined. Aberration frequencies for gamma-irra diated cells were not significantly different from controls until 20 t o 35 population doublings postirradiation, where they increased 2-fold above background before returning to near control levels. To our know ledge these data represent the first evidence of chromosomal instabili ty caused by neutron exposure. Results show that while either gamma ra ys or neutrons are capable of inducing similar types of delayed aberra tions, the time course of their appearance can differ markedly. (C) 19 97 by Radiation Research Society.