Abstract
N-ethyl-N-nitrosourea (ENU) is an alkylating agent, which shows carcinogenic and mutagenic potentials. In order to clarify the mutagenesis mechanism of ENU in vivo, we examined mutations at the gpt gene in B6C3F1 gpt-delta mice treated with ENU. Mice at 4 weeks of age were exposed to ENU (200 ppm) in the drinking water for 4 weeks, and were sacrificed immediately (8 weeks old), four weeks (12 weeks old), or eight weeks (16 weeks old) after the termination of ENU treatment. Genomic DNA was prepared from thymus, lung and small intestine, and the mutant frequency at the gpt gene was determined by selecting bacterial colonies that were resistant to 6-thioguanine. The mutant frequencies in thymus decreased from 4 to 8 weeks after treatment, although mutant frequencies in lung and small intestine remained unchanged. Sequence analysis of the gpt gene revealed that the mutation spectrum was different among the tissues. These results indicate that there may be a tissue-specificity of ENU-induced mutations in vivo, which might reflect the difference of cell types, such as cell turnover rate and repair capacity.
