Fate specification in the adult brain lessons for eliciting neurogenesis from glial cells

In the adult mammalian brain, neurogenesis is restricted to few regions, while gliogenesis continues in a wide-spread manner. Here we discuss our knowledge of extrinsic and intrinsic factors regulating neuro- and gliogenesis in the adult brain and propose a model of fate specification identifying the states of easiest transition between glio- and neurogenesis, highlighting the unique mechanisms stabilising the neural stem cell state. The model also encompasses the fate alterations achieved by direct reprogramming, and hence addresses a novel avenue for repair, namely eliciting neurogenesis from glial cells outside the neurogenic niches.