Increase of radiation-induced mutation frequency by partial hepatectomy in new HITEC mice

Full text: Radiation-induced mutations were studied in vivo with a transgenic mouse strain called HITEC (Hypersensitive In vitro Test of Carcinogenicity), which carries the rpsL gene as a reporter for mutations. The wild-type rpsL gene, which confers a streptomycin-sensitive phenotype, and a gene conferring kanamycin resistance were placed in a shuttle vector plasmid, pSSW, that was subsequently transfected into E. coli by electroporation. Transfected cells were plated onto LB plates containing kanamycin (Km) or Km plus streptomycin (Sm). The rpsL mutation frequency was defined as the ratio of the colony number on Km plus Sm plates to that on Km plates. We had previously investigated the increase in mutation frequency caused by ∼3-5 Gy of gamma-rays in mouse liver. However, no obvious increase in mutation frequency was observed due to a high background mutation frequency. We therefore performed a partial hepatectomy to amplify the mutation frequency. HITEC mice were irradiated with 5 Gy of gamma rays 2 or 10 days before hepatectomy. The remaining liver was resected 2 or 10 days after hepatectomy, and the mutation frequency was then analyzed. In mice in which hepatectomy was done 2 days after whole body irradiation and the remaining liver was resected 10 days after hepatectomy, the mutation frequency was approximately two-fold higher than that of mice in which only irradiation was performed. In mice in which hepatectomy was done 10 days after whole body irradiation and the remaining liver was resected 2 or 10 days after hepatectomy, the mutation frequency was two to three times greater than that of mice in which only irradiation was done. These results indicate that partial hepatectomy increases the frequency of gamma ray-induced liver mutations in HITEC mice and that the length of the period from irradiation to hepatectomy or from hepatectomy to remaining liver excision does not influence this frequency