Analysis of tissue-specific mutations induced by radiation in HITEC mice

人们认为突变会导致各种疾病，包括畸形和癌症。然而，体内突变和疾病之间的关系很难从体外实验中找到，因此，我们使用转基因小鼠研究了辐射诱导的体内突变。本研究利用转rpsL基因小鼠，即HITEC（HypersensitiveInVivoTestofCarcinogenisity），研究了睾丸、脾、肝、脑和胸腺中突变频率的差异。转基因小鼠系统对于研究辐射诱导的小鼠各种器官的体内体细胞突变非常有用。我们使用HITEC和p53（-/-）-HITEC小鼠研究了辐射诱变在突变频率和突变诱导动力学方面的组织特异性差异。将小鼠暴露于全身剂量为5戈伊的~ 13 Cs <137>γ射线，并在30、60、120和180天后处死动物。然后取出每只小鼠的脑、胸腺、肝、脾、睾丸，有趣的是，不同器官在辐射后突变频率随时间的变化模式各不相同。HITEC小鼠睾丸、脑、脾和肝的自发突变频率分别为5×10^<-5>、8×10^<-5>、1.5×10^<-4>和6×10^<-5>。当在照射后30至60天测量时，脑的突变频率比对照水平高2至3倍，然后转向自发率。睾丸的自发突变和辐射诱发突变频率明显低于其他器官。在p53（-/-）-HITEC小鼠中，没有发现任何器官中的突变积累，因此，rpsL转基因突变检测系统的灵敏度较低，但可用于检测照射后雄性生殖细胞中的基因突变。

It is thought that mutations cause various disorders including malformations and cancers. However, relation between mutations and disorders in vivo is difficult to find from in vitro experiments.Therefore, we have studied mutations induced in vivo by radiation with use of a transgenic mouse. We investigated difference in mutation frequencies in the testis, spleen, liver, brain and thymus using the rpsL transgenic mice so called HITEC (Hypersensitive In Vivo Test of Carcinogenisity). Transgenic mouse systems are very useful for the study of in vivo somatic mutations induced by radiations in various mouse organs. We investigated tissue-specific differences of radiation-induced mutagenesis in the mutant frequencies and the kinetics of mutant induction by using the HITEC and p53 (-/-)-HITEC mice. The mice were exposed to a whole-body dose of 5 Gy of ^<137>Cs Gamma-rays, and animals were killed 30, 60, 120 and 180 days later. Then the brain, thymus, liver, spleen, testes of each mouse were removed.Intriguingly, the pattern of change in the mutation frequency with time after irradiation varied for the different organs. In HITEC mice, spontaneous mutation frequencies observed were 5×10^<-5> for testis, 8×10^<-5> for brain, 1.5×10^<-4> for spleen and 6×10^<-5> for liver. When measured 30 to 60 days after irradiation, the mutation frequencies were 2 to 3-fold higher than the control level for the brain and then turned to the spontaneous rate. The frequencies of spontaneous and radiation-induced mutation in the testis were significantly lower than that in other organs. In p53(-/-)-HITEC mice, there were no findings that the accumulation of mutations in any organs.Therefore, the mutation assay system with the rpsL transgene is low in sensitivity but useful for detection of gene mutations in male germ cells after irradiation.