A system for mutation measurement in mammalian cells: application to gamma-irradiation.

Monitoring of mutagenesis by environmental agents for the purpose of preventing genetic disease including cancer must include quantitation of cell killing, sensitive measurement of mutation production by appropriate doses of each agent, and assessment of mutation repair effects in mammalian cells. A four-step procedure, in the presence and absence of a repair suppressor, is proposed: (i) determination of the survival curve; (ii) measurement of the mitotic index in cells collected after treatment with colcemid; (iii) construction of a mutagenesis yield curve in the presence and absence of a repair suppressor, like caffeine; and (iv) assessment of the effect of test agents on the repair of mutations produced by other mutagens. The procedure is quantitative, reproducible, and reasonably rapid. It involves measurement of mutations causing visible chromosomal aberrations. Numerical parameters are proposed defining quantitatively mutation, cell killing, and mutation repair capacity. The procedure is applied to gamma-irradiation and can detect the effects of doses as low as 2-5 cGy. Theoretical analysis of the underlying processes is presented, using the concept of D(0)E, the effective dose of mutagen after repair mechanisms and neutralizing agents have acted. Microscopically visible chromosome aberrations are due to mutations that distort the process of mitotic chromosome condensation, with or without actual chromosome breakage.