Shima A, Shimada A
Laboratory of Radiation Biology, Faculty of Science, University of Tokyo, Japan.
Proc Natl Acad Sci U S A. 1991 Mar 15;88(6):2545-9. doi: 10.1073/pnas.88.6.2545.
To develop a specific-locus test (SLT) system for environmental mutagenesis using vertebrate species other than the mouse, we first established a tester stock of the fish medaka (Oryzias latipes) that is homozygous recessive at three loci. The phenotypic expression of these loci can be easily recognized early in embryonic development by observation through the transparent egg membrane. We irradiated wild-type males with 137Cs gamma-rays to determine the dose-response relationships for dominant lethal and specific-locus mutations induced in sperm, spermatids, and spermatogonia. Through observation of 322,666 loci in control offspring and 374,026 loci in offspring obtained from 0.64-, 4.75-, or 9.50-Gy-irradiated gametes, specific-locus mutations were phenotypically detected during early development. These putative mutations, designated "total mutation," can be recognized only in embryos of oviparous animals. The developmental fate of these mutant embryos was precisely followed. During subsequent embryonic development, a large fraction died and thus was unavailable for test-crossing, which was used to identify "viable mutations." Our medaka SLT system demonstrates that the vast majority of total mutations is associated with dominant lethal mutations. Thus far only one spontaneous viable mutation has been observed, so that all doubling calculations involving this endpoint carry a large error. With these reservations, however, we conclude that the quantitative data so far obtained from the medaka SLT are quite comparable to those from the mouse SLT and, hence, indicate the validity of the medaka SLT as a possible nonmammalian test system.
为了开发一种使用小鼠以外的脊椎动物物种进行环境诱变的特定基因座测试（SLT）系统，我们首先建立了一种青鳉鱼（Oryzias latipes）的测试品系，该品系在三个基因座上是纯合隐性的。通过透明的卵膜观察，可以在胚胎发育早期轻松识别这些基因座的表型表达。我们用137Csγ射线照射野生型雄性，以确定精子、精细胞和精原细胞中诱导的显性致死和特定基因座突变的剂量反应关系。通过观察对照后代中的322,666个基因座以及从0.64、4.75或9.50 Gy照射的配子获得的后代中的374,026个基因座，在早期发育过程中从表型上检测到了特定基因座突变。这些假定的突变被称为“总突变”，只能在卵生动物的胚胎中识别。精确跟踪了这些突变胚胎的发育命运。在随后的胚胎发育过程中，很大一部分死亡，因此无法用于测交，测交用于识别“可行突变”。我们的青鳉鱼SLT系统表明，绝大多数总突变与显性致死突变有关。到目前为止，只观察到一个自发的可行突变，因此所有涉及这个终点的加倍计算都有很大误差。然而，尽管有这些保留意见，我们得出结论，到目前为止从青鳉鱼SLT获得的定量数据与从小鼠SLT获得的数据相当，因此表明青鳉鱼SLT作为一种可能的非哺乳动物测试系统的有效性。
