Fig. 3. Effect of the expression of a wild-type or two dominant-negative forms of p53 transgenes on OPC differentiation. Purified P7 rat OPCs were cultured for 2 days in PDGF without TH and RA. They were then infected for 3 hours with either the pBird control vector encoding GFP alone or a vector encoding GFP and either wild-type (pBird-p53) or a dominant-negative p53 (pBird-DNp53 or pBird-DDp53). After a further day in PDGF alone, the cells were either left in PDGF alone or switched to PDGF and TH, PDGF and RA, or medium without PDGF for a further 3 days to induce differentiation. The percentage of GFP⁺ cells that had acquired the characteristic morphology of oligodendrocytes was scored in an inverted fluorescence microscope. Similar results were obtained when oligodendrocytes were identified by staining with anti-GC antibody (not shown). In this and the following three Figures, the results are shown as mean±s.d. of at least three experiments.