Lineage and Development

Most of the information on development and lineage has been obtained from rodent brain developmental studies, with some confirmation using human fetal brain tissue. Astrocytes are derived from the neuroectodermal tissue of the neural crest. In the brain, the ventricular zone consists of a column of cells lining the ventricle that possesses the highly proliferative multipotential CNS stem cells. These stem cells give rise to progenitor cells of glial and neuronal lineage. Astro-cytes are thought to originate from cells in the ventricular zone that migrate to the subventricular zone before traveling to the final destination in the brain. The process by which astrocytic progenitor cells migrate to specific brain regions is poorly understood. Radial glial cells, however, are recognized as the first glial subtype to appear in the brain. They express GFAP and nestin, an intermediate filament characteristic of immature cells. Radial and Bergman glia extend processes from the subventricular zone to the meninges at the outer surface of the brain and serve as the scaffold on which precursor cells migrate to their final location. The production and release of adhesion molecules and chemokines by astrocytes is also

Figure 2 Immunofluorescent staining for GFAP in cultured human astrocytes. Note the filamentous ultrastructure of the cytoplasm. Magnification, x 200.

thought to contribute to the migratory process of progenitor cells during brain development. Additionally, astrocytes are known to produce a variety of trophic factors that assist in the maturation of other neural cells. Studies in rodent brain suggest that radial glia give rise to some astrocytes found in the gray and white matter. Little is known about the lineage progression of astrocyte progenitors and the factors responsible for directing the differentiation of the various astrocyte cell subtypes.

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