Fig. 12. Characters and functions of neural stem cells. (A) Embryonic neural stem cells change their characters in the following order: Hes-independent neuroepithelial cells, transitory Hes-dependent neuroepithelial cells, and Hes-dependent radial glial cells. Based on the expression patterns, transitory Hes-dependent neuroepithelial cells seem to depend on Hes1 and Hes3, while Hes-dependent radial glial cells mostly depend on Hes1 and Hes5. (B) Roles of radial glia in the inner and outer barrier formation. (a) Radial glia form the tight and adherens junctions at the apical side and contribute to the basal lamina formation at the basal side. (b) Radial glia establish the framework of the neural tube by forming the inner and outer barriers. In the absence of radial glia (Hes1^–/–;Hes5^–/–), neurons escape from the wall of the neural tube, thereby destroying the structural integrity.