Abstract
We have used Restriction Landmark Genome Scanning method to assess mutation induction rate at GC-rich sequences in mice after exposure of spermatogonial cells. In the present study, we used a restriction enzyme AflII to expand our knowledge to AT-rich sequences. To identify the parental origin of mutations, we used F1 mice prepared by crosses of irradiated BALB/c males (spermatogonia) with JF1 females and screened 1,120 selected spots (514 paternal and 606 maternal spots). We detected five mutations in the control group (184 animals, 92,655 paternal spots) and 11 mutations (including a cluster mutation of two that arose spontaneously) in the 5-Gy-exposed group (184 F1, 92,789 paternal spots). We also found 5 mutations (including a cluster mutation of three) in the un-irradiated maternal alleles (368 F1, 218,411 spots). Most of the DNA fragments mutated were found to comprise simple tandem repeats or satellite DNA, which hindered us from characterizing the mutations except for two mutations that appeared as due to base substitutions at recognition sites of the enzymes used. There was no indication that the mutation induction rates largely differed between GC- and AT-rich sequences. Our pooled estimate of mutation induction rate, including both GC- and AT-rich sequences, was ~1 x 10-5/locus/Gy, which appeared to be substantially smaller than the mean induction rate at 7 loci of Russell (2~3 x 10-5/locus/Gy).
