Regulated proliferation of stem cells is required for growth, maintenance and repair of tissues. Many stem cells undergo periods of reversible cell-cycle arrest accompanied by low biosynthetic activity, termed quiescence1. Quiescence prevents stem cell exhaustion and proliferation-induced mutations. Neural stem cells (NSCs) are mostly quiescent in the adult mammalian CNS, and their (re)activation also regulates learning, memory and mood. Cancer cells too can undergo quiescence, which renders them refractory to chemo- and radiotherapies. Despite its crucial purpose, quiescence remains poorly understood at the cellular and molecular levels. We have discovered a novel, evolutionarily conserved, post-transcriptional mechanism of controlling NSC quiescence/activation.
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