Quiescence of Adult Mammalian Neural Stem Cells: A Highly Regulated Rest

Neural stem cells in the adult mammalian brain are the source of new neurons that contribute to complex sensory and cognitive functions. Most adult neural stem cells are maintained in a state of reversible cell cycle arrest, also called quiescence. Quiescent neural stem cells present a low rate of metabolic activity and a high sensitivity to their local signaling environment, and they can be activated by diverse physiological stimuli. The balance between stem cell quiescence and activity determines not only the rate of neurogenesis but also the long-term maintenance of the stem cell pool and the neurogenic capacity of the aging brain. In recent years, significant progress has been made in characterizing quiescent stem cells thanks to the introduction of new genomic and imaging techniques. We discuss in this review our current understanding of neural stem cell quiescence and its regulation by intrinsic and systemic factors.