Genome stability by DNA polymerase β in neural progenitors contributes to neuronal differentiation in cortical development

Abstract

DNA repair is crucial for genome stability in the developing cortex, as somatic de novo mutations cause neurological disorders. However, how DNA repair contributes to neuronal development is largely unknown. To address this issue, we studied the spatiotemporal roles of DNA polymerase β (Polβ), a key enzyme in DNA base excision repair pathway, in the developing cortex using distinct forebrain-specific conditional knock-out mice, Emx1-Cre/Polβfl/fl and Nex-Cre/Polβfl/fl mice. Polβ expression was absent in both neural progenitors and postmitotic neurons in Emx1-Cre/Polβfl/fl mice, whereas only postmitotic neurons lacked Polβ expression in Nex-Cre/Polβfl/fl mice. We found that DNA double-strand breaks (DSBs) were frequently detected during replication in cortical progenitors of Emx1-Cre/Polβfl/fl mice. Increased DSBs remained in postmitotic cells, which resulted in p53-mediated neuronal apoptosis. This neuronal apoptosis caused thinning of the cortical plate, although laminar structure was normal. In addition, accumulated DSBs also affected growth of corticofugal axons but not commissural axons. These phenotypes were not observed in Nex-Cre/Polβfl/fl mice. Moreover, cultured Polβ-deficient neural progenitors exhibited higher sensitivity to the base-damaging agent methylmethanesulfonate, resulting in enhanced DSB formation. Similar damage was found by vitamin C treatment, which induces TET1-mediated DNA demethylation via 5-hydroxymethylcytosine. Together, genome stability mediated by Polβ-dependent base excision repair is crucial for the competence of neural progenitors, thereby contributing to neuronal differentiation in cortical development.