FREQUENCIES AND TYPES OF EXCHANGE ABERRATIONS INDUCED BY X-RAYS AND NEUTRONS IN CHINESE-HAMSTER SPLENOCYTES DETECTED BY FISH USING CHROMOSOME-SPECIFIC DNA LIBRARIES

Purpose: To estimate the frequencies of radiation- (low and high LET) induced chromosome aberrations in Chinese hamster splenocytes by two-c olour fluorescence in situ hybridization using DNA painting probes spe cific for chromosomes 2, 3, 8, X and Y and to determine (1) the ratio of radiation-induced translocations and dicentrics; (2) the spectrum o f exchange aberrations induced by X-rays and neutrons; and (3) the rel ative involvement of the different chromosomes in the formation of abe rrations. Materials and methods: Isolated splenocytes from the Chinese hamster were irradiated in vitro with different doses of 200 kV X-ray s (0.75, 1.5, 3.0 Gy) and 1 MeV fast neutrons (0.25, 0.5, 1.0 Gy). Con ventional analysis of chromosome aberrations was carried out in Giemsa -stained preparations. Chromosome aberrations involving chromosomes 2, 3, 8, X and Y were analysed in first division metaphases using two-co lour FISH. Results: The results indicate that when all types of transl ocations are taken into account both X-rays and neutrons induce more t ranslocations than dicentrics, the ratio between the two types of exch anges being 1.4 and 1.8 respectively. The ratio of 'apparently simple' reciprocal translocations and reciprocal complete dicentrics was clos e to 1 for both types of radiation. The RBE of neutrons for induction of exchanges was found to be between 5 and 8. Neutron irradiation was more efficient at inducing insertions. Among the chromosomes studied, an increased involvement was observed for chromosome 8 in dicentrics a nd translocations than that expected on the basis of its chromosome le ngth. The high content of interstitial telomeric sequences in chromoso me 8 may be responsible for the observed sensitivity of this chromosom e. Conclusions: The results obtained in this study indicate that: (1) more translocations are found than dicentrics; (2) heterogeneity exist s among Chinese hamster chromosomes for involvement in radiation-induc ed exchanges; (3) the spectrum and distribution of exchange aberration s are different between X-rays and neutrons; and (4) the relative freq uencies of insertions could be used as a 'fingerprint' for exposure to high LET radiation.