Evidence for the presence of the sphingosine-1-phosphate receptor Edg-8 in human radial glial fibers.
The distribution pattern of Edg-8 immunostaining in the human developing brain has been investigated with special reference to radial glial fibers. At 24 weeks of gestation, fragments of radial glial fibers are Edg-8-positive within the cortical plate and subplate of allocortical areas. These Edg-8-positive fragments often appear enlarged as varicosities and some of them terminate at blood vessels. Between 28 and 30 weeks of gestation, all iso- and allocortical areas contain Edg-8-immunolabelled radial glial fibers revealing curvature next to sulci. After 32 weeks of gestation, radial glial fibers gradually disappear; instead Edg-8-positive transitional stages between radial glia and astrocytes were found. The findings indicate that sphingosine-1-phosphate may play a regulatory role in the transformation of radial glial cells into astrocytes and may affect proliferative activity of these cells.