Genome stability is essential for brain development and function, as de novo mutations during neuronal development cause psychiatric disorders. However, the contribution of DNA repair to genome stability in neurons remains elusive. Here, we demonstrate that the base excision repair protein DNA polymerase β (Polβ) is involved in hippocampal pyramidal neuron differentiation via a TET-mediated active DNA demethylation during early postnatal stages using Nex-Cre/Polβ^fl/fl mice of either sex, in which forebrain postmitotic excitatory neurons lack Polβ expression. Polβ deficiency induced extensive DNA double-strand breaks (DSBs) in hippocampal pyramidal neurons, but not dentate gyrus granule cells, and to a lesser extent in neocortical neurons, during a period in which decreased levels of 5-methylcytosine and 5-hydroxymethylcytosine were observed in genomic DNA. Inhibition of the hydroxylation of 5-methylcytosine by expression of microRNAs miR-29a/b-1 diminished DSB formation. Conversely, its induction by TET1 catalytic domain overexpression increased DSBs in neocortical neurons. Furthermore, the damaged hippocampal neurons exhibited aberrant neuronal gene expression profiles and dendrite formation, but not apoptosis. Comprehensive behavioral analyses revealed impaired spatial reference memory and contextual fear memory in adulthood. Thus, Polβ maintains genome stability in the active DNA demethylation that occurs during early postnatal neuronal development, thereby contributing to differentiation and subsequent learning and memory.

SIGNIFICANCE STATEMENT Increasing evidence suggests that de novo mutations during neuronal development cause psychiatric disorders. However, strikingly little is known about how DNA repair is involved in neuronal differentiation. We found that Polβ, a component of base excision repair, is required for differentiation of hippocampal pyramidal neurons in mice. Polβ deficiency transiently led to increased DNA double-strand breaks, but not apoptosis, in early postnatal hippocampal pyramidal neurons. This aberrant double-strand break formation was attributed to active DNA demethylation as an epigenetic regulation. Furthermore, the damaged neurons exhibited aberrant gene expression profiles and dendrite formation, resulting in impaired learning and memory in adulthood. Thus, these findings provide new insight into the contribution of DNA repair to the neuronal genome in early brain development.

基因组稳定性对于大脑发育和功能至关重要，因为神经元发育过程中的从头突变会引起精神疾病。但是，DNA修复对神经元基因组稳定性的贡献仍然难以捉摸。在这里，我们证明了碱基切除修复蛋白DNA聚合酶β（Polβ）参与海马锥体神经元分化通过在早期产后阶段使用TET介导的活性DNA去甲基化NEX-的Cre / POL β ^{FL / FL}前脑有丝分裂后兴奋性神经元缺乏Polβ表达的任何性别的小鼠。在观察到5-甲基胞嘧啶和5-羟甲基胞嘧啶水平降低的时期，Polβ缺乏症在海马锥体神经元中引起广泛的DNA双链断裂（DSB），但在齿状回颗粒细胞中没有，而在新皮层神经元中引起程度较小在基因组DNA中。通过表达microRNA miR-29a / b-1抑制5-甲基胞嘧啶的羟基化可减少DSB的形成。相反，TET1催化结构域过表达诱导它增加了新皮层神经元的DSBs。此外，受损的海马神经元表现出异常的神经元基因表达谱和树突形成，但没有凋亡。全面的行为分析表明，成年后空间参考记忆和上下文恐惧记忆受损。因此，Polβ维持了在出生后早期神经元发育过程中发生的活性DNA去甲基化过程中的基因组稳定性，从而有助于分化以及随后的学习和记忆。

意义声明越来越多的证据表明，从头开始神经元发育过程中的突变会导致精神疾病。然而，关于DNA修复如何参与神经元分化的知之甚少。我们发现，Polβ是基础切除修复的一个组成部分，是小鼠海马锥体神经元分化所必需的。Polβ缺乏症在出生后的早期海马锥体神经元中暂时导致DNA双链断裂增加，但未导致凋亡。这种异常的双链断裂的形成归因于作为表观遗传调控的活跃的DNA去甲基化。此外，受损的神经元表现出异常的基因表达谱和树突形成，导致成年学习和记忆受损。因此，这些发现为早期大脑发育中DNA修复对神经元基因组的贡献提供了新的见解。