DNA damage response pathways rely extensively on nuclease activity to process DNA intermediates. Exonuclease 1 (EXO1) is a pleiotropic evolutionary conserved DNA exonuclease involved in various DNA repair pathways, replication, antibody diversification, and meiosis. But, whether EXO1 facilitates these DNA metabolic processes through its enzymatic or scaffolding functions remains unclear. Here, we dissect the contribution of EXO1 enzymatic versus scaffolding activity by comparing Exo1DA/DA mice expressing a proven nuclease-dead mutant form of EXO1 to entirely EXO1-deficient Exo1−/− and EXO1 wild type Exo1+/+ mice. We show that Exo1DA/DA and Exo1–/– mice are compromised in canonical DNA repair processing, suggesting that the EXO1 enzymatic role is important for error-free DNA mismatch and double-strand break repair pathways. However, in non-canonical repair pathways, EXO1 appears to have a more nuanced function. Next-generation sequencing of heavy chain V region in B cells showed the mutation spectra of Exo1DA/DA mice to be intermediate between Exo1+/+ and Exo1–/– mice, suggesting that both catalytic and scaffolding roles of EXO1 are important for somatic hypermutation. Similarly, while overall class switch recombination in Exo1DA/DA and Exo1–/– mice was comparably defective, switch junction analysis suggests that EXO1 might fulfill an additional scaffolding function downstream of class switching. In contrast to Exo1−/− mice that are infertile, meiosis progressed normally in Exo1DA/DA and Exo1+/+ cohorts, indicating that a structural but not the nuclease function of EXO1 is critical for meiosis. However, both Exo1DA/DA and Exo1–/– mice displayed similar mortality and cancer predisposition profiles. Taken together, these data demonstrate that EXO1 has both scaffolding and enzymatic functions in distinct DNA repair processes and suggest a more composite and intricate role for EXO1 in DNA metabolic processes and disease.

中文翻译：

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EXO1 核酸酶活性在 Exo1D173A 小鼠基因组维护、免疫反应和肿瘤抑制中的作用


DNA 损伤反应途径广泛依赖核酸酶活性来处理 DNA 中间体。核酸外切酶 1 (EXO1) 是一种多效性进化保守 DNA 核酸外切酶，参与各种 DNA 修复途径、复制、抗体多样化和减数分裂。但是，EXO1 是否通过其酶促或支架功能促进这些 DNA 代谢过程仍不清楚。在这里，我们通过比较表达已证实的 EXO1 核酸酶死亡突变体形式的 Exo1DA/DA 小鼠与完全 EXO1 缺陷的 Exo1−/− 和 EXO1 野生型 Exo1+/+ 小鼠，剖析了 EXO1 酶活性与支架活性的贡献。我们发现 Exo1DA/DA 和 Exo1–/– 小鼠在典型的 DNA 修复过程中受到损害，这表明 EXO1 酶促作用对于无错误的 DNA 错配和双链断裂修复途径非常重要。然而，在非规范修复途径中，EXO1 似乎具有更微妙的功能。 B 细胞重链 V 区的新一代测序显示 Exo1DA/DA 小鼠的突变谱介于 Exo1+/+ 和 Exo1–/– 小鼠之间，表明 EXO1 的催化和支架作用对于体细胞超突变都很重要。同样，虽然 Exo1DA/DA 和 Exo1–/– 小鼠的总体类别转换重组相对有缺陷，但转换连接分析表明 EXO1 可能在类别转换下游履行额外的支架功能。与不育的 Exo1−/− 小鼠相比，Exo1DA/DA 和 Exo1+/+ 组中的减数分裂正常进行，表明 EXO1 的结构功能而非核酸酶功能对于减数分裂至关重要。然而，Exo1DA/DA 和 Exo1–/– 小鼠均表现出相似的死亡率和癌症易感性。 总而言之，这些数据表明 EXO1 在不同的 DNA 修复过程中同时具有支架和酶功能，并表明 EXO1 在 DNA 代谢过程和疾病中具有更加复合和复杂的作用。