Winn Richard N, Majeske Audrey J, Jagoe Charles H, Glenn Travis C, Smith Michael H, Norris Michelle B
Aquatic Biotechnology and Environmental Laboratory, Warnell School of Forestry and Natural Resources, University of Georgia, Athens, Georgia.
Environ Mol Mutagen. 2008 Apr;49(3):173-84. doi: 10.1002/em.20364.
To address the need for improved approaches to study mutations transmitted to progeny from mutagen-exposed parents, we evaluated lambda transgenic medaka, a small fish that carries the cII mutation target gene, as a new model for germ cell mutagenesis. Mutations in the cII gene in progeny derived from ethyl-nitrosourea (ENU)-exposed males were readily detected. Frequencies of mutant offspring, proportions of mosaic or whole body mutant offspring, and mutational spectra differed according to germ cell stage exposed to ENU. Postmeiotic germ cells (spermatozoa/late spermatids) generated a higher frequency of mutant offspring (11%) compared to premeiotic germ cells (3.5%). Individuals with cII mutant frequencies (MF) elevated more than threefold above the spontaneous MF (3 x 10(-5)) in the range of 10(-4) to 10(-3) were mosaic mutant offspring, whereas those with MFs approaching 1 x 10(-2) were whole body mutant offspring. Mosaic mutant offspring comprised the majority of mutant offspring derived from postmeiotic germ cells, and unexpectedly, from spermatogonial stem cells. Mutational spectra comprised of two different mutations, but at identical sites were unusual and characteristic of delayed mutations, in which fixation of a second mutation was delayed following fertilization. Delayed mutations and prevalence of mosaic mutant offspring add to growing evidence that implicates germ cells in mediating processes postfertilization that contribute to genomic instability in progeny. This model provides an efficient and sensitive approach to assess germ cell mutations, expands opportunities to increase understanding of fundamental mechanisms of mutagenesis, and provides a means for improved assessment of potential genetic health risks.
为满足研究从接触诱变剂的亲代传递给子代的突变的改进方法的需求，我们评估了携带cII突变靶基因的小型鱼类——λ转基因青鳉，作为生殖细胞诱变的新模型。很容易检测到来自暴露于乙基亚硝基脲（ENU）的雄性亲代的子代中cII基因的突变。根据暴露于ENU的生殖细胞阶段不同，突变后代的频率、嵌合或全身突变后代的比例以及突变谱也有所不同。与减数分裂前的生殖细胞（3.5%）相比，减数分裂后的生殖细胞（精子/晚期精子细胞）产生的突变后代频率更高（11%）。cII突变频率（MF）比自发MF（3×10⁻⁵）升高三倍以上，范围在10⁻⁴至10⁻³之间的个体是嵌合突变后代，而MF接近1×10⁻²的个体是全身突变后代。嵌合突变后代占来自减数分裂后生殖细胞以及意外地来自精原干细胞的突变后代的大多数。由两种不同突变组成但位于相同位点的突变谱是不寻常的，且具有延迟突变的特征，即受精后第二个突变的固定延迟。延迟突变和嵌合突变后代的普遍性进一步证明了生殖细胞在介导受精后过程中对后代基因组不稳定有贡献。该模型提供了一种评估生殖细胞突变的有效且灵敏的方法，扩大了增加对诱变基本机制理解的机会，并为改进潜在遗传健康风险的评估提供了手段。
