Fig. 7. Radial glial cells possess reelin receptors and require Dab1 for reelin-mediated signaling. (A) Corresponding fluorescent micrographs of cells isolated from E14 cortex cultured for 24 hours and stained with Rc2 (green) and anti-Apoer2 (red) as indicated in the panels. The lower panels show the absence of unspecific staining after omitting the primary Apoer2-antibody. Arrows indicate double-positive cells in the upper panels and single-positive (RC2-immunoreactive) cells in the lower panels. (B) The quantitative analysis of Apoer2 and Vldlr mRNA using light cycler quantitative RT-PCR with mRNA isolated from sorted radial glial cells [GFP-positive cells from E14 hGFAP-EGFP mice (Malatesta et al., 2003) and sorted neurons (EGFP-positive cells from E14 Tau::EGFP mice) (see Fig. 6A) (Heins et al., 2002)]. Note that radial glia and neurons contain comparable levels of Apoer2 mRNA, while Vldlr mRNA is found at higher levels in neurons. (C) Quantitative analysis of Blbp-immunoreactive cells among E14 cortical cells from wild-type or Dab1^-/- littermates cultured for 24 hours either in control or reelin-conditioned medium (compare Fig. 5). Note that the number of Blbp-positive cells increased upon reelin addition only in wild type but not in cells lacking Dab1, suggesting that Dab1 is required to mediate reelin signaling to radial glial cells. [Number of cells analysed: Ctrl, n(wild type or Dab1^+/-)=750, n(Dab1^-/-)=400; Rln-medium, n(wild type or Dab1^+/-)=700, n(Dab1^-/-)=300 from 12 different embryos.]