Frequencies and types of exchange aberrations induced by X-rays and neutrons in Chinese hamster splenocytes detected by FISH using chromosome-specific DNA libraries

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Abstract
To estimate the frequencies of radiation- (low and high LET) induced chromosome aberrations in Chinese hamster splenocytes by two-colour fluorescence in situ hybridization using DNA painting probes specific for chromosomes 2, 3, 8, X and Y and to determine (1) the ratio of radiation-induced translocations and dicentrics; (2) the spectrum of exchange aberrations induced by X-rays and neutrons; and (3) the relative involvement of the different chromosomes in the formation of aberrations. Isolated splenocytes from the Chinese hamster were irradiated in vitro with different doses of 200 kV X-rays (0.75, 1.5, 3.0 Gy) and 1 MeV fast neutrons (0.25, 0.5, 1.0 Gy). Conventional 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-colour FISH. The results indicate that when all types of translocations are taken into account both X-rays and neutrons induce more translocations than dicentrics, the ratio between the two types of exchanges being 1.4 and 1.8 respectively. The ratio of 'apparently simple' reciprocal translocations and reciprocal complete dicentrics was close 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 and translocations than that expected on the basis of its chromosome length. The high content of interstitial telomeric sequences in chromosome 8 may be responsible for the observed sensitivity of this chromosome. The results obtained in this study indicate that: (1) more translocations are found than dicentrics; (2) heterogeneity exists among Chinese hamster chromosomes for involvement in radiation-induced exchanges; (3) the spectrum and distribution of exchange aberrations are different between X-rays and neutrons; and (4) the relative frequencies of insertions could be used as a 'fingerprint' for exposure to high LET radiation.

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