Subventricular zone astrocytes are neural stem cells in the adult mammalian brain

Neural stem cells reside in the subventricular zone (SVZ) of the adult mamm alian brain. This germinal region, which continually generates new neurons destined for the olfactory bulb, is composed of four cell types: migrating neuroblasts, immature precursors, astrocytes, and ependymal cells. Here we show that SVZ astrocytes, and not ependymal cells, remain labeled with prol iferation markers after long survivals in adult mice. After elimination of immature precursors and neuroblasts by an antimitotic treatment, SVZ astroc ytes divide to generate immature precursors and neuroblasts. Furthermore, i n untreated mice, SVZ astrocytes specifically infected with a retrovirus gi ve rise to new neurons in the olfactory bulb. Finally, we show that SVZ ast rocytes give rise to cells that grow into multipotent neurospheres in vitro . We conclude that SVZ astrocytes act as neural stem cells in both the norm al and regenerating brain.