Figure 2. Astrocytogenesis from the ventricular/subventricular zones and outer cortical layers in the mouse developing central nervous system (CNS).

( a) In the developing cortex, radial glia (RG) first give rise to glioblasts (GBs) during the late embryonic to perinatal period. Glioblasts undergo several rounds of division while migrating out along radial glia, resulting in clusters of astrocytes in the developing cortex. At the terminal stage of radial glial differentiation, radial glia detach from the ventricular zone and form unipolar transitional radial glia (tRG), which give rise to protoplasmic and fibrous astrocytes in the gray matter and white matter of the cortex, respectively. During the early postnatal period, differentiated astrocytes in the outer cortical layer undergo symmetric division and generate daughter astrocytes that exhibit astrocytic morphology and functions. ( b) In the developing spinal cord, radial glia first proliferate during embryonic day 12 (E12) to 13, giving rise to radial glial pool which differentiates into astrocytes between E14 and postnatal day 3 (P3). Alternatively, radial glial cells differentiate into intermediate astrocyte precursors (IAPs), which proliferate during E14 to P3 and undergo terminal differentiation, ultimately giving rise to astrocytes. The progression from embryonic stage to adult is shown from left to right below each panel. Straight arrows indicate differentiation or maturation from one cell type to another. Circular arrows indicate proliferation. Dashed arrows indicate migration. CP, cortical plate; fAstro, fibrous astrocyte; GM, gray matter; iAstro, immature astrocyte; P, pia mater; pAstro, protoplasmic astrocyte; SVZ, subventricular zone; VZ, ventricular zone; WM, white matter.