Asakawa Jun-Ichi, Kodaira Mieko, Miura Akiko, Tsuji Takahiro, Nakamoto Yoshiko, Imanaka Masaaki, Kitamura Jun, Cullings Harry, Nishimura Mayumi, Shimada Yoshiya, Nakamura Nori
Department of aGenetics, Radiation Effects Research Foundation, 5-2 Hijiyama Park, Minami-ku, Hiroshima 732-0815, Japan.
b Department of Statistics, Radiation Effects Research Foundation, 5-2 Hijiyama Park, Minami-ku, Hiroshima 732-0815, Japan.
Radiat Res. 2016 Dec;186(6):568-576. doi: 10.1667/RR14402.1. Epub 2016 Nov 21.
Until the end of the 20th century, mouse germ cell data on induced mutation rates, which were collected using classical genetic methods at preselected specific loci, provided the principal basis for estimates of genetic risks from radiation in humans. The work reported on here is an extension of earlier efforts in this area using molecular methods. It focuses on validating the use of array comparative genomic hybridization (array CGH) methods for identifying radiation-induced copy number variants (CNVs) and specifically for DNA deletions. The emphasis on deletions stems from the view that it constitutes the predominant type of radiation-induced genetic damage, which is relevant for estimating genetic risks in humans. In the current study, deletion mutations were screened in the genomes of F1 mice born to unirradiated or 4 Gy irradiated sires at the spermatogonia stage (100 offspring each). The array CGH analysis was performed using a "2M array" with over 2 million probes with a mean interprobe distance of approximately 1 kb. The results provide evidence of five molecularly-confirmed paternally-derived deletions in the irradiated group (5/100) and one in the controls (1/100). These data support a calculation, which estimates that the mutation rate is 1 × 10/Gy per genome for induced deletions; this is much lower than would be expected if one assumes that the specific locus rate of 1 × 10/locus per Gy (at 34 loci) is applicable to other genes in the genome. The low observed rate of induced deletions suggests that the effective number of genes/genomic regions at which recoverable deletions could be induced would be only approximately 1,000. This estimate is far lower than expected from the size of the mouse genome (>20,000 genes). Such a discrepancy between observation and expectation can occur if the genome contains numerous genes that are far less sensitive to radiation-induced deletions, if many deletion-bearing offspring are not viable or if the current method is substandard for detecting small deletions.
直到20世纪末，利用经典遗传学方法在预先选定的特定基因座上收集的小鼠生殖细胞诱导突变率数据，为估计人类辐射遗传风险提供了主要依据。本文报道的工作是该领域早期利用分子方法所做努力的延伸。它着重于验证使用阵列比较基因组杂交（array CGH）方法来识别辐射诱导的拷贝数变异（CNV），特别是用于DNA缺失的鉴定。对缺失的关注源于这样一种观点，即它构成了辐射诱导的遗传损伤的主要类型，这对于估计人类的遗传风险具有重要意义。在当前研究中，对精原细胞阶段未受辐射或受4 Gy辐射的雄性小鼠所生的F1代小鼠（每组100只后代）的基因组进行了缺失突变筛选。使用具有超过200万个探针且平均探针间距约为1 kb的“2M阵列”进行阵列CGH分析。结果表明，在受辐射组中有5个经分子确认的父源缺失（5/100），对照组中有1个（1/100）。这些数据支持一项计算，该计算估计诱导缺失的突变率为每基因组1×10⁻²/Gy；如果假设每Gy（在34个基因座处）1×10⁻⁵/基因座的特定基因座率适用于基因组中的其他基因，那么这个数字要比预期的低得多。观察到的诱导缺失率较低表明，可诱导出可恢复缺失的基因/基因组区域的有效数量仅约为1000个。这一估计远低于从小鼠基因组大小（>20000个基因）所预期的数量。如果基因组中包含许多对辐射诱导的缺失敏感性远较低的基因、如果许多携带缺失的后代无法存活或者如果当前方法在检测小缺失方面不合格，那么观察结果与预期之间就可能出现这种差异。
