Mutation spectrum in UVB-exposed skin epidermis of Xpa-knockout mice:: Frequent recovery of triplet mutations
Mutation spectrum in UVB-exposed skin epidermis of Xpa-knockout mice:: Frequent recovery of triplet mutations
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DOI：
10.1002/em.20262
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发表时间：
2007-01-01
影响因子：
2.8
通讯作者：
Ono, Tetsuya
中科院分区：
文献类型：
--
作者：
Ikehata, Hironobu;Yanase, Fumitaka;Ono, Tetsuya
Xpa 基因的两个等位基因的敲除突变导致哺乳动物细胞中核苷酸切除修复（NER）完全缺陷。我们使用携带基于 lambda 噬菌体的 lacZ 突变报告基因的转基因小鼠来研究 Xpa 无效突变 (Xpa(-/-)) 对 UVB 照射后小鼠皮肤表皮损伤诱导、修复和诱变的影响。 UVB在Xpa(-/-)和野生型小鼠的小鼠皮肤表皮中诱导等量的环丁烷嘧啶二聚体(CPD)和嘧啶(64)嘧啶酮光产物(64PP)。照射后 12 小时，Xpa(-/-) 表皮中的光损伤均未去除，而在野生型小鼠的表皮中观察到 64PP 的去除。 200和300 J/m(2) UVB照射增加了Xpa(-/-)小鼠表皮中lacZ突变频率，但诱导的突变频率与之前测定的野生型小鼠没有显着差异。对从暴露于 UVB 的 Xpa(-/-) 小鼠表皮中分离出的 100 个 lacZ 突变体进行了分析，并与之前为受辐射的野生型小鼠确定的突变体序列进行了比较。 Xpa(-/-) 和野生型小鼠的突变体中，沿着 lacZ 转基因的突变分布和 UV 特异性突变的首选二嘧啶背景是相似的。两种基因型的突变谱均具有高度 UV 特异性，并且在二嘧啶位点的 C -> T 转变的优势方面相似；然而，Xpa(-/-)小鼠比野生型小鼠有更高的二碱基串联取代频率，包括CC→TT突变、三碱基串联突变和三碱基序列中由一个未改变碱基分隔的双碱基取代（交替突变）。这些串联/交替突变包括大量的三联体突变，这是最近报道的一种新型UV特异性突变，其特征是含有二嘧啶的三核苷酸序列内的多个碱基取代或移码。我们得出的结论是，三联体突变是一种 UV 特异性突变，最好发生在 NER 缺陷的遗传背景中。
Knockout mutations in both alleles of the Xpa gene give rise to a complete deficiency in nucleotide excision repair (NER) in mammalian cells. We used transgenic mice harboring the lambda-phage-based lacZ mutational reporter gene to study the effect of Xpa null mutation (Xpa(-/-)) on damage induction, repair, and mutagenesis in mouse skin epidermis after UVB irradiation. UVB induced equal amounts of cyclobutane pyrimidine dimers (CPDs) and pyrimidine(64)pyrimidone photoproducts (64PPs) in mouse skin epidermis of Xpa(-/-) and wild-type mice. Neither photolesion was removed in the Xpa(-/-) epidermis by 12 hr after irradiation whereas removal of 64PPs was observed in the epidermis of wild-type mice. Irradiation with 200 and 300 J/m(2) UVB increased the lacZ mutant frequency in the epidermis of Xpa(-/-) mice, but the induced mutant frequencies were not significantly different from those previously determined for wild-type mice. One-hundred lacZ mutants isolated from the UVB-exposed epidermis of Xpa(-/-) mice were analyzed and compared with mutant sequences previously determined for irradiated wild-type mice. The distribution of the mutations along the lacZ transgene and the preferred dipyrimidine context of the UV-specific mutations were similar in mutants from the Xpa(-/-) and wild-type mice. The spectra of the mutations in the two genotypes were both highly UV-specific and similar in a dominance of C -> T transitions at dipyrimidine sites; however, Xpa(-/-) mice had a higher frequency than wild-type mice of two-base tandem substitutions, including CC -> TT mutations, three-base tandem mutations and double base substitutions that were separated by one unchanged base in a three-base sequence (alternating mutations). These tandem/alternating mutations included a remarkably large number of triplet mutations, a recently reported, novel type of UV-specific mutation, characterized by multiple base substitutions or frameshifts within a three-nucleotide sequence containing a dipyrimidine. We conclude that the triplet mutation is a UV-specific mutation that preferably occurs in NER-deficient genetic backgrounds.