Spatiotemporal Regulation ofDe Novoand Salvage Purine Synthesis during Brain Development

Abstract

The levels of purines, essential molecules to sustain eukaryotic cell homeostasis, are regulated by the coordination of thede novoand salvage synthesis pathways. In the embryonic central nervous system (CNS), thede novopathway is considered crucial to meet the requirements for the active proliferation of neural stem/progenitor cells (NSPCs). However, how these two pathways are balanced or separately used during CNS development remains poorly understood. In this study, we showed a dynamic shift in pathway utilization, with greater reliance on thede novopathway during embryonic stages and on the salvage pathway in postnatal–adult mouse brain. The pharmacological effects of various purine synthesis inhibitorsin vitroand the expression profile of purine synthesis enzymes indicated that NSPCs in the embryonic cerebrum mainly use thede novopathway. Simultaneously, NSPCs in the cerebellum require both thede novoand the salvage pathways.In vivoadministration ofde novoinhibitors resulted in severe hypoplasia of the forebrain cortical region, indicating a gradient of purine demand along the anteroposterior axis of the embryonic brain, with cortical areas of the dorsal forebrain having higher purine requirements than ventral or posterior areas such as the striatum and thalamus. This histologic defect of the neocortex was accompanied by strong downregulation of the mechanistic target of rapamycin complex 1 (mTORC1)/ribosomal protein S6 kinase (S6K)/S6 signaling cascade, a crucial pathway for cell metabolism, growth, and survival. These findings indicate the importance of the spatiotemporal regulation of both purine pathways for mTORC1 signaling and proper brain development.