Fig. 1. Four astrocyte sources in the postnatal cerebral cortex.

There are four astrocyte sources in the cerebral cortex: radial glia, SVZ-derived progenitors, locally proliferating glia, and NG2 glia. (a) Radial glia translocate from the VZ to the cortex and become immature astrocytes by retracting their long leading processes. (b) Astrocytes derived from the SVZ migrate into the cerebral cortex likely along radial glial shafts. Most radial glia in rodents start to disappear during late embryonic stages, and few remain after postnatal week 2. (c) NG2 glia produce a portion of astrocytes in the ventral cortex of the forebrain. (d) Locally proliferating astrocytes in the cortex undergo symmetric division to generate additional astrocytes. These locally produced astrocytes are a major astrocyte source in the postnatal cortex. Note: locally proliferating astrocytes are originally produced from progenitors in the SVZ and radial glia.