Induction of minisatellite mutations in the mouse germline by low-dose chronic exposure to gamma-radiation and fission neutrons

Germline mutation induction at mouse minisatellite loci by patemallow-dose (0.125-1 Gy) exposure to chronic (1.66 x 10(-4) Gy min(-1)) low-linear ener gy transfer (low-LET) gamma -irradiation and high-LET fission neutrons (0.0 03 Gy min(-1)) was studied at pre-meiotic stages of spermatogenesis. Both t ypes of radiation produced Linear dose-response curves for mutation of the paternal allele. In contrast to previous results using higher doses, the pa ttern of induction of minisatellite mutation after chronic gamma -irradiati on was similar to acute (0.5 Gy min(-1)) exposure to X-rays, indicating tha t the elevated mutation rate was independent of the ability of the cell to repair damage induced immediately or over a period of up to 100 h. Chronic exposure to fission neutrons was more effective than acute or chronic low-L ET exposure (relative biological effectiveness, RBE=3.36). The data also pr ovide strong support for the previous conclusion that increases in minisate llite mutation rate are not caused by radiation-induced DNA damage at minis atellite loci themselves, but rather from damage induced by ionising radiat ion elsewhere in the genome/cell. (C) 2000 Elsevier Science B.V. All rights reserved.