Figure 2.

Neurogenesis. (A) Neurulation. Schematic representation of the neurulation process. Neuroectoderm derived cells proliferate at different rates along the apicobasal polarity. (B) Embryonic Neurogenesis. During embryonic development the central nervous system develops in an inside-out fashion. Neuroepithelial stem cells, via asymmetrical divisions, differentiate into radial glial cells (RGCs), establishing the Ventricular Zone near the apical surface. Near the pial surface, Cajal- Retzius (CRCs) cells will make the marginal zone during embryogenesis and the cortical layer I postnatally. The other cortical layers are formed in sequential waves during neurogenesis. Later in development, neural progenitors enter a gliogenic mode, generating astrocytes and oligodendrocytes. Neuroepithelial, radial glial and intermediate progenitor cells are capable of symmetric and asymmetric divisions. (C) Postnatal Neurogenesis. In the adult brain, neural stem cells can be found in two neurogenic niches, the Subventricular Zone (SVZ) and in the Subgranular cell layer of the Dentate Gyrus (DG). In rodents (C1), after differentiating in the SVZ, immature neurons migrate along the rostral migratory stream (RMS) to the olfactory bulb (OB) where they will mature mainly into GABAergic interneurons. On the other hand, in humans (C2), immature neurons are thought to migrate along the RMS to the striatum (STR). In rodents and humans, differentiating neurons from the DG mature by making functional connections with pyramidal CA3 hippocampal neurons.