RADIAL GLIAL-CELL TRANSFORMATION TO ASTROCYTES IS BIDIRECTIONAL - REGULATION BY A DIFFUSIBLE FACTOR IN EMBRYONIC FOREBRAIN

During development of mammalian cerebral cortex, two classes of glial cells are thought to underlie the establishment of cell patterning, In the embryonic period, migration of young neurons is supported by a sy stem of radial glial cells spanning the thickness of the cortical wall . In the neonatal period, neuronal function is assisted by the physiol ogical support of a second class of astroglial cell, the astrocyte. He re, we show that expression of embryonic radial glial identity require s extrinsic soluble signals present in embryonic forebrain. Moreover, astrocytes reexpress features of radial glia in vitro in the presence of the embryonic cortical signals and in vivo after transplantation in to embryonic neocortex. These findings suggest that the transformation of radial glia cells into astrocytes is regulated by availability of inducing signals rather than by changes in cell potential.