Fig. 4. Expression of a stabilized form of ß-catenin instructively promotes neuronal differentiation. NPCs were infected with a retrovirus encoding either GFP alone (control) or both GFP and S33Y ß-catenin at a low titer and subjected to clonal analysis. After incubation for 3 days in the presence of Fgf2, cells in each clone were stained with TuJ1 antibody and the clones were classified as containing either only TuJ1⁺ cells (neuron-only clone), both TuJ1⁺ and TuJ1^- cells (neuron-containing clone), or only TuJ1^- cells (precursor-only clone) (A). The cell number for each clone was determined (B). The results are representatives of three independent experiments. (C) NPCs were infected with a retrovirus encoding either GFP alone (control) or GFP together with Wnt7a, S33Y ß-catenin or wild-type (WT) ß-catenin. They were then plated at a density of 1000 cells/well in 96-well plates that had been coated with poly-HEME and incubated for 9 days in suspension culture in the presence of Fgf2, after which the number of GFP⁺ primary neurospheres per 1000 founding cells/well was determined. Data are the mean±s.e.m. of values from 12 samples, and are representatives of three independent experiments. ^*P<10^-5 versus control.