Studies of Somatic Mutation Frequencies and Spectra with a Sensitive and Efficient Detection Method by Using Transgenic Mice.

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We have developed a transgenic system to detect somatic mutations in vivo by using the E.coli rpsL gene as a positively selectable marker. In addition to the pML4 shuttle vector, a newly constructed pSSW was also introduced into mice. As results ; 1) the background mutant frequency was reduced to 1x10^<-5>,2) the efficiency of the detection increased 3-fold, 3) methylated shuttle vectors were rescued in E.coli, 4) the mode of mutations was the indistinguishable between two shuttle systems. Mutagens, i.e., MNU,MeIQx, AOM,AFBI and Trp-P-2 were examined so far. Effects of antimutagenicity of chlorophirin and EGCG were also studied. The mutagenicity of rpsL was extensively analyzed in the E.coli system in terms of mutators of hosts and/or hot spot sequences in the rpsL gene. The comparison was made with newly developed positive selection systems with the gpt and cII transgenic mice in addition to MutaMouse and BigBlue. The delayd radiation effects were recognized in mice as well as Drosophila, which are the candidate systems for the future research. Progenies were obtained from the mating of pML4-or pSSW-transgenic mice to the mice deficient for the XPA or MLH1 gene. The mutation spectra studies suggested the possibility to distinguish the effect of mutagenicity from the effect of cytotoxicity of an administered agent.