Origin, maturation, and astroglial transformation of secondary radial glial cells in the developing dentate gyrus.

The dentate gyrus is a brain region where neurons are continuously born throughout life. In the adult, the role of its radial glia in neurogenesis has attracted much attention over the past years; however, little is known about the generation and differentiation of glial cells and their relationship to radial glia during the ontogenetic development of this brain structure. Here, we combine immunohistochemical phenotyping using antibodies against glial marker proteins with BrdU birthdating to characterize the development of the secondary radial glial scaffold in the dentate gyrus and its potential to differentiate into astrocytes. We demonstrate that the expression of brain lipid-binding protein, GLAST, and glial fibrillary acidic protein (GFAP) characterizes immature differentiating cells confined to an astrocytic fate in the early postnatal dentate gyrus. On the basis of our studies, we propose a model where immature astrocytes migrate radially through the granule cell layer to adopt their final positions in the molecular layer of the dentate gyrus. Time-lapse imaging of acute hippocampal slices from hGFAP-eGFP transgenic mice provides direct evidence for such a migration mode of differentiating astroglial cells in the developing dentate gyrus.