Fig. 7. Requirement of Delta-Notch signaling for NPC maintenance by STAT3. (A) NPC cultures prepared from the neocortex of E12.5 mice were infected with a retroviral vector for DLL1 siRNA or a control siRNA. After culture for 3 days, cell lysates were subjected to immunoblot analysis with antibodies to DLL1 and GAPDH. (B) Neuroepithelial cells prepared from the neocortex of E12.5 mice were infected with a retrovirus for DLL1 siRNA or a control siRNA. They were also separately infected with a retrovirus for STAT3-C or a control retrovirus. The cells were then assayed for the formation of secondary neurospheres. ^*P<0.01. (C) Neuroepithelial cells prepared as in B were infected with a retrovirus encoding STAT3-C (STAT3-C) or a control retrovirus (pMX-GFP) and cultured to allow the formation of primary neurospheres for 2 days. The primary neurospheres were then incubated in the presence of the -secretase inhibitor L685,458 or of vehicle (dimethyl sulfoxide, DMSO) for 1 day. They were then dissociated and cultured to allow the formation of secondary neurospheres in the presence of FGF2 (20 ng/ml) and EGF (20 ng/ml) and in the absence of the inhibitor. ^*P<0.01.