Decreased mutant frequency in embryonic brain of DNA polymerase β null mice
Decreased mutant frequency in embryonic brain of DNA polymerase β null mice
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DOI：
10.1093/mutage/gei074
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发表时间：
2006-01-01
期刊：
影响因子：
2.7
通讯作者：
Koyama, H
中科院分区：
文献类型：
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作者：
Niimi, N;Sugo, N;Koyama, H
DNA聚合酶β (Pol β)敲除小鼠胚胎在有丝分裂后神经元细胞中表现出广泛的凋亡，并在出生后立即死亡。相比之下，在突变胚胎的其他组织和肝脏中未观察到细胞凋亡。为了研究发育和神经发生过程中Pol β缺乏与突变的关系，我们利用pSSW穿梭载体与大肠杆菌rpsL报告基因组成的转基因突变检测系统，检测了Pol β零型（Pol β(-/-)）和野生型（Pol β(+/+)）小鼠胚胎的自发突变。出乎意料的是，我们发现与野生型对照（3.12 +/- 0.83 x 10(-5)）相比，Pol β(-/-)脑突变频率显著降低（1.63 +/- 0.67 x 10(-5)） （P < 0.001）。相比之下，Pol β (-/-) （0.92 +/- 0.38 × 10(-5)）和野生型（0.71 +/- 0.31 × 10(-5)）胚胎的肝脏没有这种差异。突变谱分析显示，这两种基因型在大脑中的突变几乎完全是单碱基缺失，这些位点位于2-6个相同碱基和rpsL序列中两个碱基重复的序列中，而相应肝脏中的突变包含碱基替换和单碱基缺失。结合与Pol β缺乏相关的广泛的神经元凋亡，我们认为在Pol β(-/-)胚胎脑中观察到的较低突变频率可能是由于细胞凋亡消除了具有未修复DNA损伤的神经元细胞。
DNA polymerase beta (Pol beta) knockout mouse embryos exhibit extensive apoptosis in postmitotic neuronal cells and die immediately after birth. In contrast, no apoptosis has been observed in other tissues as well as liver in the mutant embryos. To study the relationship of Pol beta deficiency and mutagenesis during development and neurogenesis, we examined spontaneous mutations in Pol beta null (Pol beta(-/-)) and wild-type (Pol beta(+/+)) mouse embryos, by using the transgenic mutation detection system consisting of a pSSW shuttle vector with the Escherichia coli rpsL reporter gene. Unexpectedly, we found a significant decrease in the mutant frequency of Pol beta(-/-) brain (1.63 +/- 0.67 x 10(-5)) compared with wild-type controls (3.12 +/- 0.83 x 10(-5)) (P < 0.001). In contrast, no such difference was found between livers from Pol beta(-/-) (0.92 +/- 0.38 x 10(-5)) and wild-type (0.71 +/- 0.31 x 10(-5)) embryos. Analysis of mutation spectra revealed that mutations in brains from the two genotypes were almost exclusively single-base deletions and that these sites fell within runs of 2-6 identical bases and a two base repeat in the rpsL sequence, while mutations in the corresponding livers contained base substitutions as well as single-base deletions. Taken together with the extensive neuronal apoptosis associated with Pol beta deficiency, we suggest that the lower mutant frequency observed in Pol beta(-/-) embryonic brain may be caused by the elimination of neuronal cells with unrepaired DNA damage through apoptosis.