DNA polymerase θ contributes to the generation of C/G mutations during somatic hypermutation of Ig genes
DNA polymerase θ contributes to the generation of C/G mutations during somatic hypermutation of Ig genes
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DOI：
10.1073/pnas.0505636102
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发表时间：
2005-09-27
影响因子：
11.1
通讯作者：
O-Wang, JY
中科院分区：
文献类型：
--
作者：
Masuda, K;Ouchida, R;O-Wang, JY
IG可变区基因的体细胞超突变由激活诱导的胞苷脱氨酶启动;然而，需要多种DNA聚合酶的活性来最终引入突变。DNA聚合酶eta（Pol eta）与A/T突变有关，但与C/G突变有关的聚合酶尚未确定。我们已经产生了突变小鼠表达DNA聚合酶（波罗），特别是缺乏聚合酶活性。与WT小鼠相比，Polq失活（Polq，编码Pol theta的基因）小鼠表现出血清IgM和IgG 1水平降低。突变小鼠安装相对正常的初级和二级免疫反应的T依赖性抗原，但生产的高亲和力特异性抗体部分受损。对J（H）4内含子序列的分析显示，Polq失活小鼠的总体突变频率略有降低。值得注意的是，虽然A/T突变不受影响，但C/G突变显著减少，表明波罗活性的重要作用，尽管不是唯一的作用。C/G突变的减少特别集中在内在体细胞高突变热点上，转换和颠换都类似地减少。这些发现，加上最近的观察，波罗有效地催化无碱基位点的旁路，使我们提出，Pol θ通过复制尿嘧啶-DNA糖基化酶产生的无碱基位点在C/G引入突变。
Somatic hypermutation of Ig variable region genes is initiated by activation-induced cyticline deaminase; however, the activity of multiple DNA polymerases is required to ultimately introduce mutations. DNA polymerase eta (Pol eta) has been implicated in mutations at A/T, but polymerases involved in C/G mutations have not been identified. We have generated mutant mice expressing DNA polymerase (Polo) specifically devoid of polymerase activity. Compared with WT mice, Polq-inactive (Polq, the gene encoding Pol theta) mice exhibited a reduced level of serum lgM and IgG1. The mutant mice mounted relatively normal primary and secondary immune responses to a T-dependent antigen, but the production of high-affinity specific antibodies was partially impaired. Analysis of the J(H)4 intronic sequences revealed a slight reduction in the overall mutation frequency in Polq-inactive mice. Remarkably, although mutations at A/T were unaffected, mutations at C/G were significantly decreased, indicating an important, albeit not exclusive, role for Polo activity. The reduction of C/G mutations was particularly focused on the intrinsic somatic hypermutation hotspots and both transitions and transversions were similarly reduced. These findings, together with the recent observation that Polo efficiently catalyzes the bypass of abasic sites, lead us to propose that Pol theta introduces mutations at C/G by replicating over abasic sites generated via uracil-DNA glycosylase.