Correlation of chromosomal aberrations and sister chromatid exchanges in individual CHO cells pre-labelled with BrdU and treated with DNaseI or X-rays.

PURPOSE: To analyse the correlation between chromosomal aberrations and sister-chromatid exchanges (SCE) in cells treated in G1 phase with X-rays or DNaseI. MATERIALS AND METHODS: Chinese hamster ovary (CHO) cells were labelled with 5'-bromodeoxyuridine (BrdU) for one round of replication and irradiated in G1 phase with 1.2, 2.4, 3.6 and 4.8 Gy X-rays or treated by electroporation with 1000, 2000, 3000 and 4000 units DNaseI per 800 microl electroporation buffer. Using a computer-aided metaphase relocation system first post-treatment mitoses were analysed for SCE and chromosomal aberrations allowing a precise investigation of correlation between both phenomena. RESULTS: A better correlation between aberrations and SCE was observed for DNaseI than for X-rays. X-rays induced more SCE than expected on the basis of aberrations, whereas the frequencies of SCE induced by DNaseI can mainly be accounted for by chromosomal aberrations. DISCUSSION: The results obtained with X-rays support an earlier observation that radiation induces both "true" SCE that are not related to chromosomal aberrations and result from radiation damage to BrdU, and "false" SCE that result from exchange-type aberrations. The high frequency of aberrations observed in cells treated with DNaseI and the good correlation between aberrations and SCE suggests that the endonuclease induces mainly "false" SCE.