Ultraviolet-induced mutations to asparagine independence in Jensen sarcoma cells in vitro

The effect of dose fractionation on gamma-radiation induced mutations in mammalian cells

The lethal and mutagenic effects of single and fractionated doses of gamma-radiation were studied in V79-4 Chinese hamster cells, as dose fractionation is of interest in radiation protection studies. The results show that the induction of 8-azaguanine resistant (Agr) mutants has a non-linear dose response curve following single doses of radiation. The lethal and mutagenic effects of fractionated doses were always less than if the radiation was given in a single dose. Any change in treatment which led to an increase in survival also led to a decrease in induced mutation frequency. There was a relationship between mutation and survival which was independent of the number of fractions in which the radiation was given. This could be of consequence in radiological protection.

Prospects for evaluating genetic damage in mammalian cells in culture

Starting from some general considerations on cultured mammalian cells as a biological material for the detection of genetic changes, information is given on cell lines and genetic markers that have been the subject of extensive research. The experimental variables of mutation assays are then considered, with special reference to those involved in the system resistant to 8-azaguanine. Work now in progressin the field of environmental mutagenesis is mentioned at the end of the article.

Linear dose--response relationships after prolonged expression times in V-79 Chinese hamster cells

The expression time for induced mutants resistant to 6-thioguanine, in V-79 Chinese hamster cells, was determined by respreading the cells in the selective medium, at various times after treatment. The length of the expression time for mutants induced by X-rays, ethyl methane sulphonate and ultraviolet irradiation was dose dependent. For the highest dose used this was 7 to 8 days, beyond which there was no further changes in mutant frequency. The dose-response relationship of these agents does not appear to deviate from linearity; this permits the calculation of mutation rate per unit dose. For X-rays this value was 1.35 - 10(-7) per rad per locus, for ethyl methane sulphonate, 2.2 - 10(-2) per mole per locus and for ultraviolet irradiation, 6.3 - 10(-6) per erg per mm2 per locus. The effectiveness of the 3 different mutagens for the induction of mutations was compared by calculating the increase in mutant frequency per unit of decrease in survival (Do). These increments in frequency were: 5.6 - 10(-5) for X-rays, 69.5 - 10(-5) for ethyl methane sulphonate and 16.1 - 10(-5) for ultraviolet irradiation.

Mutagenesis studies on cultured mammalian cells. The sensitivity of the asparagine-requiring phenotype to several chemical agents

The effect of several chemical agents on the mutation frequency from asparagine dependence to asparagine independence has been studied in Jensen sarcoma cells. It was found that ethylmethanesulfonate brought about a dramatic exponential increase, while nitrosoguanidine was not lighly effective as a mutagen, causing only a modest increase in mutation frequency, and quinacrine HCl was ineffective. The results presented here are compared with those obtained in other systems and with our previous work on the effects of UV on mutation induction in the asparagine system. They suggest that the basis of the asparagine requirement of mammalian cell lines resides in a specific genetic alteration in nuclear DNA which is corrected by the mutagenic action of the agents tested here.

Effect of ploidy on spontaneous mutation rate to asparagine non-requirement in cultured cells

Variations in ploidy do not affect the spontaneous mutation rate to asparagine non-requirement in Jensen rat sarcoma cells cultivated in vitro.