Neuronal-glial interactions in central nervous system neurogenesis: the neural stem cell perspective

Essentially, three neuroectoderinal-derived cell types "take tip the coniplex architecture of the adult CNS: neurons, astrocyles and oligodendrocytes. These elernents arc endowed with rernarkable inorphological, niolecular and functional heterogeneity that reaches its maxiinal expression during devclopnient when stenilpi-qgenitor cells undergo progressive changes that drive theni to a fully differentiated state. During this period the transient expression of niolecular niarkers harnpers precise identification of cell categories, even in neuronal and glial domains. These issues of alcvelopnicirtal biology arc recapitulated partially during the neurogenic processes that persist in discrete regions of the adult brain. The recent hypothesis that adult neural stein cells (NSCs) show a glial identify and derive directly front radial glia raises questions concerning the neuronalglial relationships during pre- arid post-riatal brain developnient. The fact that NSCs isolated in vitro differentiate inainly into astrocytcs, whereas in vivo they produce inainly neurons hii hlights the iniportance of epigcnetic signals in the ncurogcnic niches, where glial cells and "curous exert inutual influences. Unravelling the inechanisnis that underlie NSC plasticity in vivo and in vitro is crucial to understanding adult neurogenesis arid exploiting this physiological process for brain repair. In this review we address the issues of ncuronallglial cell identify and ncuronal-glial interactions in the context of NSC biology and NSC-driven neurogenesis during developine"t and adulthood in vivo, focusing inainly on the CNS. We also discuss the peculiarities of neuronal-glial relationships for NSCs and their progeny III the context of in vitro systents.