SUMMARY Repair of DNA double-strand breaks (DSBs) by non-homologous end-joining is critical for neural development, and brain cells frequently contain somatic genomic variations that might involve DSB intermediates. We now use an unbiased, high-throughput approach to identify genomic regions harboring recurrent DSBs in primary neural stem/progenitor cells (NSPCs). We identify 27 recurrent DSB clusters (RDCs) and, remarkably, all occur within gene bodies. Most of these NSPC RDCs were detected only upon mild, aphidicolin-induced replication stress, providing a nucleotide-resolution view of replication-associated genomic fragile sites. The vast majority of RDCs occur in long, transcribed, and late-replicating genes. Moreover, almost 90% of identified RDC-containing genes are involved in synapse function and/or neural cell adhesion, with a substantial fraction also implicated in tumor suppression and/or mental disorders. Our characterization of NSPC RDCs reveals a basis of gene fragility and suggests potential impacts of DNA breaks on neurodevelopment and neural functions.

Summary NPGPx is a member of the glutathione peroxidase (GPx) family; however, it lacks GPx enzymatic activity due to the absence of a critical selenocysteine residue, rendering its function an enigma. We report that NPGPx is a novel stress sensor that transmits oxidative stress signals by transferring the disulfide bond between its Cys57 and Cys86 residues to downstream effectors. Oxidized NPGPx binds and oxidizes the chaperone glucose-regulated protein (GRP)78 in the endoplasmic reticulum through covalent bonding between Cys86 of NPGPx and Cys41/Cys420 of GRP78, and facilitates the refolding of misfolded proteins by GRP78 to alleviate stress. NPGPx-deficient cells display impaired GRP78 chaperone activity, accumulate misfolded proteins, and suffer oxidative stress. Complete loss of NPGPx in animals causes systemic oxidative stress, increases carcinogenesis, and shortens lifespan. These results, for the first time, suggest that NPGPx is essential for mediating the oxidative stress response by modulating GRP78 chaperone activity to maintain physiological homeostasis.