Figure 1. The Periventricular Adult Stem Cell Niche.

This illustration summarizes recent advances on our understanding of the adult VZ-SVZ niche. The apical ventricular zone is shown at top. Ependymal cells (E, in gray) are multiciliated, and the basal bodies of these cilia are oriented in the direction of cerebrospinal fluid (CSF) flow. Ependymal cells form pinwheel-like structures around the apical processes of type B1 cells (shown in blue). Type B1 cells extend a short, non-motile primary cilium into the ventricle. These cells maintain contact with the ventricle, but disassemble the primary cilium, while dividing. Type B1 cells also frequently extend a basal process with an endfoot that contacts blood vessels (Bv). Type B2 cells, in contrast, have astrocytic characteristics but do not contact the ventricle. Transit-amplifying type C cells (in green) are found close to type B cells. Dividing C cells are also often found in close proximity to blood vessels (shown at left). Type B1 cells also contact their more differentiated progeny, the chains of migrating type A neuroblasts (shown in red). Type A cells migrate tangentially in chains (shown towards right of figure) that ultimately coalesce to form the rostral migratory stream taking these young neurons to the olfactory bulb for terminal differentiation. The VZ-SVZ also includes extracellular matrix (shaded) that contacts all the cell types in this region, including blood vessels and microglia (in purple).