Fig. 6.

Model representing the lineage relationships of neural stem cells and constitutively proliferating (CP) progenitor cells. A, Neural stem cells localized to the dorsolateral corner of the adult forebrain subependyma give rise to CP progenitor cells that proliferate to give rise to neuronal progenitor cells that are destined to migrate to the olfactory bulbs where they differentiate into mature neurons. Some cells in the dorsolateral corner also may remain localized to the dorsolateral corner of the subependyma where they continue to proliferate and subsequently undergo cell death, as do the cells in the rest of the subependyma (B). B, Neural stem cells throughout the rest of the subependyma give rise to CP progenitor cells that proliferate to give rise to one more CP cell and one cell destined to die. In both A and B the CP cells proliferate for <1 month before they are replenished by a neural stem cell division.