Studies on Somatic Cell Mutations

Abstract

It is very importantto establish the sensitive assay systems for the mutations using mammalian cells in vitro for detecting various potential mutagens present in the human environment.These systems are also useful for studying the mechanisms of somatic mutation (involving the problems of phenotypic expression, repair of premutational damage, specific stage in the cell cycle and so on) in cultured mammalian cells. We found in the previous study (Ban et al. 1976) that the forward mutation system using prototrophic CH-hai C123 cells isolated from an original Chinese hamster hai cell line is much more sensitive than the reverse mutation system using auxotrophic CH-hai Cl 3 cells for detecting the mutations induced by radiations and chemical carcinogens or mutagens.In the present study, as a series of these experiments, we examined the frequencies of the forward and reverse mutations induced by X-rays and UV, using 8-azaguanine (8AG)-sensitive cells (the prototrophic CH-hai C123 cells) and 8AG-resistan cells which are isolated from them, and compared the sensitivities as a mutation assay system with those of the nutritionally forward and reverse mutations used previously (Ban et al. 1976) . Contrary to expectation, the results obtained in this study were rather negative as far as mutation induction are concerned. MATERIALS AND METHODSCells and medium. The origin, culture procedures and properties of the Chinese hamster hai cell line used in the present study have been described previously (Suzuki and Horikawa 1973). Alanine-, asparagine-, proline-, aspartic acid-, hypoxanthine-, and glutamic acid-prototrophic CH-hai Cl 23 cells (Suzuki and Horikawa 1975;Ban et al. 1976) isolated from the cultures of Chinese hamster hai cells by a replica plating method were used as 8AG-sensitive cells. In this study, however, CH-hai C123 cells were cultured in a medium composed of 90% Eagle's MEM+N17 medium (which lacked 1) Present address: