Recombination between homologous chromosomes does not play a dominant rolein the formation of radiation-induced chromosomal aberrations

Purpose: In mammalian cells, the relevance of homologous recombination in r adiation-induced double-strand break (DSB) repair is not yet well understoo d. In the present work, the role of recombination between homologous chromo somes and homology-directed repair of DSB were studied, using X-ray-induced chromosomal aberrations as an end-point. Materials and methods: Human-hamster hybrid cells containing one or two cop ies of human chromosome 8 were used. If recombination between homologous ch romosomes plays a dominant role in DSB repair, it is expected that X-irradi ation of cells with two copies of chromosome 8 would result in a lower Freq uency of aberrations involving this chromosome compared with cells with onl y one copy of chromosome 8. The aberrations involving human chromosome 8 we re detected by fluorescence in situ hybridization (FISH). Furthermore, a co mparison between the hamster cell line XR-C1 (defective in non-homologous r epair), CHO-9 (the wild-type cells) and the cell line XR-C1#8 (in which the defect of XR-C1 is complemented by human chromosome 8) was made to determi ne, indirectly, the involvement of homology-directed recombination in DSB r epair. Results: The observed frequencies of aberrations per human chromosome 8 wer e not significantly different between cells containing one or two copies of this chromosome. The frequency of chromatid-type aberrations was doubled i n XR-Cl cells compared with CHO-9 and XR-C1#8 cells. Conclusions: In hamster cells, recombination between homologous chromosomes appears not to have a major role in the formation of radiation-induced chr omosomal aberrations, while nonhomologous repair seems to be important in b oth the G1 and G2 phases of the cell cycle.