NONRANDOM CHROMOSOMAL INVOLVEMENT IN RADIATION-INDUCED TRANSLOCATIONSIN MOUSE SPERMATOGONIAL STEM-CELLS

X-ray-induced chromosomal translocations were studied in mouse spermat ogonial stem cells by meiotic analysis at the spermatocyte stage many cell generations after induction, Using a composite DNA probe for mous e chromosomes 1, 11 and 13, in combination with fluorescence in situ h ybridization, the involvement of these three chromosomes in translocat ion formation was recorded, The obtained results at various sampling t imes ranging from 75 to 320 days after irradiation show no significant differences in the participation pattern of the painted chromosomes i n 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 translocat ion 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 ove rrepresentation, indicating that it is probably not the repair of lesi ons that is causing this phenomenon but rather non-random induction.