Schy W E, Plewa M J
Institute for Environmental Studies, University of Illinois, Urbana-Champaign 61801.
Mutat Res. 1989 Apr;211(2):231-41. doi: 10.1016/0027-5107(89)90006-7.
The yg2 assay in Zea mays detects forward mutation in somatic cells within leaf primordia of embryos and it was used in an analysis of the molecular dosimetry of ethyl methanesulfonate (EMS). Parallel genetic and molecular dosimetry experiments were conducted in which the frequency of forward mutation and the level of covalently bound ethyl DNA adducts were determined. Prepared kernels were treated for 8 h at 20 degrees C with 1-10 mM EMS. EMS induced a direct concentration-dependent increase in mutation induction proportional to the exposure concentration (slope = 0.93). The kinetics of mutation induction demonstrated in the intact maize system were consistent with the kinetics observed earlier in in vitro model systems using cultured mammalian cells, and contrasted with the exponential increase in mutation induction characteristic of microbial species. Parallel molecular dosimetry experiments were conducted using [3H]EMS. DNA was extracted and purified from embryonic tissues containing the leaf primordia, the target tissue of the yg2 assay. A linear increase in the molecular dose was observed as a function of EMS concentration. Using concentration as a common parameter between the parallel genetic and dosimetry studies, mutation induction appeared to increase nearly in a direct proportion to the molecular dose. However, studies in other genetic systems indicate that the levels of specific DNA adducts, such as O6-ethylguanine (O6-EtGua) show a better correlation with mutation induction kinetics than molecular dose. Neither molecular dose, nor O6-EtGua levels account for differences in the absolute frequencies of mutation induction observed in different genetic systems. Therefore, reliable assessment of health risks posed to humans by chemical mutagens appears to require consideration of other factors in addition to DNA dose or adduct formation, including differences in repair capabilities and in the size of the genetic targets in humans relative to the model genetic systems under study.
玉米中的yg2检测法可检测胚胎叶原基中体细胞的正向突变，该方法被用于甲磺酸乙酯（EMS）的分子剂量测定分析。开展了平行的遗传学和分子剂量测定实验，测定正向突变频率和共价结合的乙基DNA加合物水平。将制备好的玉米粒在20℃下用1 - 10 mM的EMS处理8小时。EMS诱导的突变呈直接的浓度依赖性增加，与暴露浓度成正比（斜率 = 0.93）。在完整玉米系统中观察到的突变诱导动力学与早期在使用培养哺乳动物细胞的体外模型系统中观察到的动力学一致，与微生物物种突变诱导的指数增加形成对比。使用[3H]EMS进行了平行的分子剂量测定实验。从含有叶原基（yg2检测法的靶组织）的胚胎组织中提取并纯化DNA。观察到分子剂量随EMS浓度呈线性增加。以浓度作为平行遗传学和剂量测定研究之间的共同参数，突变诱导似乎几乎与分子剂量成正比增加。然而，其他遗传系统的研究表明，特定DNA加合物的水平，如O6 - 乙基鸟嘌呤（O6 - EtGua）与突变诱导动力学的相关性比分子剂量更好。分子剂量和O6 - EtGua水平都不能解释在不同遗传系统中观察到的突变诱导绝对频率的差异。因此，要可靠评估化学诱变剂对人类构成的健康风险，除了DNA剂量或加合物形成外，似乎还需要考虑其他因素，包括人类与所研究的模型遗传系统相比在修复能力和遗传靶标大小方面的差异。
