Identity crisis for adult periventricular neural stem cells: subventricular zone astrocytes, ependymal cells or both?

The existence of neural stem cells (NSCs) in the walls of the lateral ventricle is well known, yet debate about the precise identity of these cells continues. Weiss and colleagues describe tools used to study NSCs and consider the controversies in the field. A population of neural stem cells (NSCs) resides adjacent to the lateral ventricles in the adult mammalian brain. Despite knowledge of their existence since the early 1990s, their identity remains controversial, with evidence suggesting that they may be ependymal cells, glial fibrillary acidic protein (GFAP)-expressing subventricular zone (SVZ) cells or several distinct NSC populations. This issue has major implications for the therapeutic use of NSCs as well as for the study and treatment of brain cancers. Recent studies have both shed light on the issue and added to the controversy.