Non-random chromosomal involvement in radiation-induced translocations in mouse spermatogonial stem cells

X-ray induced chromosomal translocations were studied in mouse spermatogonial stem cells by meiotic analysis at the spermatocyte stage many cell generations after induction. Using a composite DNA probe for mouse chromosomes 1, 11 and 13, in combination with fluorescence in situ hybridization, the involvement of these three chromosomes in translocation formation was recorded. The obtained results at various sampling times ranging from 75 to 320 days after irradiation show no significant differences in the participation pattern of the painted chromosomes in multivalent formation with increasing sampling time. Pooling of the data at the different dose levels of 5 and 7 Gy indicated significant overrepresentation of the specifically stained bivalents in translocation formation. This suggests that clonal proliferation cannot be held responsible for the observed non-randomness. Experiments with the DNA-repair inhibitor 3-aminobenzamide showed no change in the recorded overrepresentation, indicating that it is probably not the repair of lesions that is causing this phenomenon but rather non-random induction.