Fig. 2. SHH-knockout mice have latent in vitro oligodendrocyte potential. (A) Whole E12.5 SHH-null spinal cords were examined for O4 or GC expression before (primary) or after (expanded) exposure to FGF2. Primary cultures contain no O4⁺ or GC⁺ cells, but following FGF2 stimulation there are significant numbers of oligodendrocyte lineage cells (^*=P<0.01, ^**=P<0.05). (B) Immunofluorescent micrograph showing representative labelling of Hoechst⁺, O4⁺ and GC⁺ cells in E12.5 null spinal cord cultures after (expanded) exposure to FGF2. O4⁺ cells (red), and O4 and GC co-labelled cell (yellow; arrow) are shown. (C) Immunomicrograph showing O4⁺ oligodendrocyte derived from SHH null cultures following treatment with FGF2 in the presence of cyclopamine (1 µM). (D) Clonal analysis of SHH null cultures. Immunomicrograph showing monoclonal derivation of tripotential and bipotential clones containing ß-tubulin⁺ neurones (green), O4⁺ oligodendrocytes (red) and GFAP⁺ astrocytes (blue) from E12.5 SHH null-derived FGF2-treated single cell cultures.