Figure 1.

Neurogenesis in human fetal and adult SVZ. In the fetal brain, the neurogenic niche is organized into different strata: the ventricular zone (VZ), the subventricular zone (SVZ), the intermediate zone (IZ), and the marginal zone (MZ). Apical radial glial cells of the SVZ remain in contact with the ependymal cells and with the meninges and blood vessels, while the basal radial glial cells, which constitute the region of the SVZ called outer SVZ (oSVZ), lose contact with ventricles leading to a discontinuous scaffold of radial glial cells (RGCs). Apical and basal RGCs generate neurons through two mechanisms: either directly or indirectly through intermediate progenitor cells, which also originate astrocytes and oligodendrocytes. In the adult brain, the SVZ consists of four distinct stratified areas: layer I formed by ependymal cells in contact with the lumen of ventricles; the hypocellular gap (layer II), mainly formed by displaced ependymal cells and DCX+ astrocyte processes; layer III constituted by type B astrocytic cells; a transitional region to the brain parenchyma (layer IV) formed by mature neurons and oligodendrocytes.