Neural stem cell systems: physiological players or in vitro entities?

Neural stem cells (NSCs) can be experimentally derived or induced from different sources, and the NSC systems generated so far are promising tools for basic research and biomedical applications. However, no direct and thorough comparison of their biological and molecular properties or of their physiological relevance and possible relationship to endogenous NSCs has yet been carried out. Here we review the available information on different NSC systems and compare their properties. A better understanding of these systems will be crucial to control NSC fate and functional integration following transplantation and to make NSCs suitable for regenerative efforts following injury or disease.