Combined use of chromosome painting and telomere detection to analyse radiation-induced chromosomal aberrations in mouse splenocytes.

PURPOSE

Analysis of chromosomal aberrations by fluorescence in situ hybridization using a combination of chromosome painting and telomere detection in order to get more insight into: (a) the extent of incompleteness of exchanges and (b) the frequencies of interstitial fragments.

MATERIALS AND METHODS

Isolated mouse splenocytes were exposed in vitro to X-rays at a dose of 2 Gy. Aberrations involving chromosomes 2 and 3 were analysed by FISH using simultaneous chromosome painting and telomere detection.

RESULTS

At 2 Gy, about 10% of apparently simple exchanges are incomplete. A striking observation was the high induction of interstitial fragments, with frequencies nearly as high as that of dicentrics. Assuming, that both ends of all interstitial fragments have rejoined with each other (to form acentric rings), it can be estimated that over 92% of reactive ends of detectable breakpoints have rejoined illegitimately. Overall, equal frequencies of translocation types t(Ab) and t(Ba) (according to the PAINT nomenclature) were observed. Also, the ratios between reciprocal forms of translocations and dicentrics were close to 1 for both the chromosomes studied.

CONCLUSIONS

These studies have shown that many of the frequently observed 'one-way' exchanges using painting probes, are in fact reciprocal exchanges with one participating lesion so close to the telomere that no distal signal can be detected. Frequencies of true incomplete exchanges were found to be low. Intrachanges, here detected as interstitial fragments, were observed frequently.