Adult neural stem cells and their niche: a dynamic duo during homeostasis, regeneration, and aging.

Stem cells persist in specialized niches in the adult mammalian brain. Emerging findings highlight the complexity and heterogeneity of different compartments in the niche, as well as the presence of local signaling microdomains. Stem cell quiescence and activation are regulated not only by anchorage to the niche and diffusible signals, but also by biophysical properties, including fluid dynamics. Importantly, the adult neural stem cell niche integrates both local and systemic changes, reflecting the physiological state of the organism. Moreover niche signaling is bidirectional, with stem cells and their progeny and niche cells dynamically interacting with each other during homeostasis, regeneration and aging.