Heterogeneity of quiescent and active neural stem cells in the postnatal brain.

In the postnatal mammalian brain, neurogenic activity is retained in anatomically restricted areas, driven by pools of Neural Stem Cells (NSCs). These cells and their progeny have been studied intensively as potential targets for regenerative treatments, aiming either to their in situmanipulation, or to their use as sources of cells for transplantation-based strategies. Although their full identity, heterogeneity and differentiation potential remain elusive, due to the absence of specific cell-type markers, our knowledge on their properties is constantly expanding. Here, we focus on the NSC niche that is located at the Subependymal Zone (SEZ/ also known as Subventricular Zone) of the lateral ventricles of the brain. We review, summarize and explain the different faces of the NSC, as they have been described using a wide range of experimental approaches in a time-frame of three decades: the primitive, definitive, quiescent or activated NSC. We also review the accumulating evidence on the existence of latent NSCs outside of niches, in the brain parenchyma, that constitute new promising therapeutic targets, complemented by the novel technologies of in vivocell reprogramming.