Recombination between homologous chromosomes does not play a dominant role in the formation of radiation-induced chromosomal aberrations.
OBJECTIVE
In mammalian cells, the relevance of homologous recombination in radiation-induced double-strand break (DSB) repair is not yet well understood. In the present work, the role of recombination between homologous chromosomes and homology-directed repair of DSB were studied, using X-ray-induced chromosomal aberrations as an end-point.


METHODS
Human-hamster hybrid cells containing one or two copies of human chromosome 8 were used. If recombination between homologous chromosomes plays a dominant role in DSB repair, it is expected that X-irradiation of cells with two copies of chromosome 8 would result in a lower frequency of aberrations involving this chromosome compared with cells with only one copy of chromosome 8. The aberrations involving human chromosome 8 were detected by fluorescence in situ hybridization (FISH). Furthermore, a comparison between the hamster cell line XR-C1 (defective in non-homologous repair), 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 determine, indirectly, the involvement of homology-directed recombination in DSB repair.


RESULTS
The observed frequencies of aberrations per human chromosome 8 were not significantly different between cells containing one or two copies of this chromosome. The frequency of chromatid-type aberrations was doubled in XR-C1 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 chromosomal aberrations, while nonhomologous repair seems to be important in both the G and G2 phases of the cell cycle.
Marcon
F
F
Laboratory of Comparative Toxicology and Ecotoxicology, Istituto Superiore di Sanità, Rome, Italy. Marcon@iss.it
Boei
J J
JJ
Natarajan
A T
AT
D000818:Animals; D016466:CHO Cells; D002869:Chromosome Aberrations; D006224:Cricetinae; D004249:DNA Damage; D004260:DNA Repair; D016195:G2 Phase; D011995:Recombination, Genetic; D014965:X-Rays