that overexpressing VP64 alone had no appreciable effect on the OPC differentiation (Supplementary Fig. 1d). Transcriptomic analyses revealed that genes programmed to be inhibited by OLIG2 upon differentiation were upregulated in the OLIG2-VP64 overexpressed cells (Fig. 1f). To assess the role of OLIG2 in OPC differentiation in vivo, we injected with retrovirus containing either Cre-T2A-Olig2-T2A-GFP or Cre-T2A-Olig2-VP64-T2A-GFP into the corpus callosum of Olig2Flox/Flox mice at postnatal day 5 (P5) (Supplementary Fig. 1e). Endogenous Olig2 was deleted by Cre recombinase, which was reconstituted with exogenous OLIG2 or OLIG2-VP64. We collected the GFP+ cells (infected cells) from animals at P15 for cell fate analyses. (Fig. 1g). 60% of OPCs reconstituted with OLIG2 successfully differentiate into CC1+ oligodendrocytes. In contrast, less than 10% of OPCs reconstituted with OLIG2-VP64 were CC1+ (Fig. 1h, i). Taken together, the repressive role of OLIG2 is required for myelinogenesis.
