Genetic markers for quantitative mutagenesis studies in Chinese hamster ovary cells Characteristics of some recently developed selective systems

Selection conditions have been optimized in the Chinese hamster ovary (CHO) cell system for a number of genetic markers. The genetic systems studied include resistance to the protein-synthesis inhibitors emetine (Emtr) and diphtheria toxin (Dipr), resistance to methylglyoxalbisguanylhydrazone (Mbgr) which affects polyamine transport, resistance to the nucleoside analogs toyocamycin and tubercidin (Toyr), and resistance to thioguanine (Thgr) and ouabain (OuaR). The optimal expression time following mutagenesis for various markers was between 2 and 6 days. A linear dose--response relationship between the concentration of mutagen (ethyl methanesulfonate) and mutation frequency has been observed over the range of 10--700 micrograms/ml, for all of the above markers except Toyr. The response of these markers to other mutagens such as tritium (3H) decay and ICR-191 show some specificity. Since the response of a number of genetic markers can be studied simultaneously in the CHO system, it should prove very useful for studies of quantitative mutagenesis and in assay systems for mutagen detection.