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 epithelial 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 breaks several doublings after the irradiation; no such effect was observed for chromosome-type aberrations. Neutron-irradiated cells showed consistently elevated frequencies of aberrations compared to nonirradiated controls at all times examined. Aberration frequencies for gamma-irradiated cells were not significantly different from controls until 20 to 35 population doublings postirradiation, where they increased 2-fold above background before returning to near control levels. To our knowledge these data represent the first evidence of chromosomal instability caused by neutron exposure. Results show that while either gamma rays or neutrons are capable of inducing similar types of delayed aberrations, the time course of their appearance can differ markedly.