TI - Results Reelin treatment in vitro induces a radial glial phenotype similar to Notch-1 activation . AB - Reelin addition in vitro has been recently shown to promote the process extension of the radial glial cells and to rescue the defects in the length of these processes in the reeler mutant radial glia [8] . To test if Reelin signaling acts on Notch-1 activation to promote the radial glial phenotype , we first compared the induced radial glial phenotype obtained after Reelin treatment and Notch-1 activation . NICD overexpression was used to mimic Notch-1 activation . It has been reported that FGF and EGF signaling can also promote the radial glial phenotype [29,30] . In order to characterize only the effects of Reelin treatment or Notch-1 activation on HNPCs , we deprived the cells from these growth factors for 24 hours before Reelin addition or NICD over expression ( Figure 1A ) . The deprivation of these growth factors reduced the radial glial phenotype , which was characterized by the retraction of the processes in the GFAP positive cells ( data not shown ) . The cells were then treated with partially purified Reelin (Figure 1B) or transfected with NICD for 24 hours before fixation . As a result , Reelin treatment was observed to induce a radial glial phenotype , which was characterized by increased process extension in the GFAP positive cells (Figure 1Ad) , similar to that obtained by Notch-1 activation (Figure 1Ab) . To confirm that Reelin treatment activates Reelin signaling in HNPCs , we measured the PHOSphorylation level of the tyrosine residue 198 of Dab-1 after treating the cells with Reelin for 15 minutes , 30 minutes and 1 hour . Dab-1 PHOSphorylation increased after Reelin treatment , whereas it remained constant with the control treatment ( Figure 1C ) , indicating that these cells are responsive to Reelin .