Figure 5.

FGF2 and Shh mediate the effects of Wnt 7a on EGFR expression and primary neurospheres. A, Explants of E10.5 cortex were exposed to FGF2 (10 ng/ml) or Shh (5μg/ml) for 2–3 d, then dissociated and cultured in a neurosphere assay. These factors induce mitotic responsiveness to EGF prematurely and increase the number of neurosphere-forming cells when FGF2 is used as the neurosphere mitogen. B, EGFR expression is reduced by FGF2-neutralizing antibodies in control infected explants and explants infected with Wnt 7a virus. For these experiments, E10.5 explants were infected, treated for 4 d with control or FGF2-neutralizing antibodies, then stained with β-gal and EGFR antibodies. C, Inhibiting signaling by endogenous Shh in explants of E11.5 cortex reduces expression of EGFRs among cells infected with control, Wnt 7a, or dnBMPR1B viruses. Explants were treated with cyclopamine (0.5–5 μm) or Shh-neutralizing antibody (5E1, 1:5 to 1:4) for 4 d after infection, and EGFR expression was assessed as in B. DMSO or PAX6 hybridoma supernatant was used for control. D, The increase in primary neurospheres associated with Wnt 7a depends on Shh but not FGF2. FGF2 (10 ng/m) was used as the neurosphere mitogen. ^*p < 0.05 relative to control treatment or control virus; ^**p < 0.005 relative to control treatment.