Shima A, Shimada A
Zoological Institute, Faculty of Science, University of Tokyo, Japan.
Mutat Res. 1988 Mar;198(1):93-8. doi: 10.1016/0027-5107(88)90044-9.
We have studied frequencies of mutations induced at the b locus of the fish, Medaka Oryzias latipes, after gamma-irradiation. Homozygotes for the b locus have colorless melanophores whose phenotypic expression can be distinguished from that of the wild type. An advantage of the use of oviparous fish for detection of skin color mutations is that the mutant phenotype can be confirmed as early as 1.5 days after fertilization because of the transparent egg membrane of the embryo. Wild-type (B/B) male fish were exposed to 4.75 or 9.5 Gy of 137Cs gamma-rays at a dose rate of 0.95 Gy/min and then mated with the female testers (b/b). A total of 77,761 F1 offspring were examined for mutation and other abnormalities. In the control, we had 1 mutant among 22,068 offspring, resulting in a mutation rate of 4.53 X 10(-5)/locus/gamete. However, this mutant embryo died before hatching. Therefore, in an attempt to present specific-locus mutation frequencies in the fish, the frequencies of color mutants that survived more than 4 days after hatching were used as frequencies of viable mutants; (number of viable color mutants)/(number of hatched fry that survived more than 4 days after hatching). In the 4.75 Gy-irradiated group the viable mutant frequencies were 45.0 X 10(-5), 69.7 X 10(-5) and 0/locus/gamete, while exposure to 9.5 Gy resulted in mutation rates of 217 X 10(-5), 130 X 10(-5) and 8.06 X 10(-5), respectively, for sperm, spermatids and spermatogonia. In comparison with viable color mutant frequencies those of the total color mutants, which include such mutants as ones that died before hatching (defined as number of total color mutants/number of fertilized eggs minus number of early deaths), were considerably higher. For sperm, spermatids, and spermatogonia after exposure to 4.75 Gy, the frequencies were 1180 X 10(-5), 629 X 10(-5) and 9.90 X 10(-5)/locus/gamete, respectively, and in 9.5-Gy-irradiated fish, the frequencies were 1940 X 10(-5), 953 X 10(-5) and 55.5 X 10(-5). Although our data are incomplete, the present results were compared with mutation induction in mice. We concluded that the frequencies of viable color mutants in the fish can be compared with those in mice.
我们研究了伽马射线照射后，青鳉（Oryzias latipes）b位点诱导突变的频率。b位点的纯合子具有无色的黑素细胞，其表型表达可与野生型相区分。利用卵生鱼类检测皮肤颜色突变的一个优势在于，由于胚胎的卵膜是透明的，因此在受精后1.5天就可以确认突变表型。将野生型（B/B）雄鱼以0.95 Gy/分钟的剂量率暴露于4.75或9.5 Gy的137Cs伽马射线下，然后与雌性测试鱼（b/b）交配。总共检查了77,761只F1代后代的突变和其他异常情况。在对照组中，22,068只后代中有1只突变体，突变率为4.53×10^(-5)/位点/配子。然而，这个突变胚胎在孵化前死亡。因此，为了呈现鱼类中的特定位点突变频率，将孵化后存活超过4天的颜色突变体频率用作存活突变体的频率；（存活颜色突变体的数量）/（孵化后存活超过4天的鱼苗数量）。在4.75 Gy照射组中，存活突变体频率分别为45.0×10^(-5)、69.7×10^(-5)和0/位点/配子，而暴露于9.5 Gy时，精子、精细胞和精原细胞的突变率分别为217×10^(-5)、130×10^(-5)和8.06×10^(-5)。与存活颜色突变体频率相比，包括孵化前死亡的突变体在内的总颜色突变体频率（定义为总颜色突变体数量/受精卵数量减去早期死亡数量）要高得多。对于暴露于4.75 Gy后的精子、精细胞和精原细胞，频率分别为1180×10^(-5)、629×10^(-5)和9.90×10^(-5)/位点/配子，在9.5 Gy照射的鱼中，频率分别为1940×10^(-5)、953×10^(-5)和55.5×10^(-5)。尽管我们的数据不完整，但将目前的结果与小鼠中的突变诱导情况进行了比较。我们得出结论，鱼类中存活颜色突变体的频率可以与小鼠中的频率进行比较。
