Fig. S1. Knockdown of OLIG2 results in decreased OPC generation. (A) Infection with RNAi virus for OLIG2, but not control virus, blocks the expression of OLIG2. (B) Quantification of OLIG2⁺ cells among GFP⁺ and GFP⁻ populations in the OLIG2 RNAi group and control infection. Scale bar: 50 m.

Fig. S2. FGF2 inhibits neurogenesis and motoneuron generation. (A-D) The presence of FGF2 in cultures with or without SHH both resulted in decreased Tuj1⁺ neurons and a lack of HB9⁺ motoneurons. (E) Quantitative analysis of the effect of FGF2 on neuronal differentiation. Scale bar: 50 m.

Fig. S3. FGF2-treated cultures do not generate motoneurons. (A) OLIG2⁺ progenitors enriched by FGF2 and purmorphamine at day 35 were cultured under conditions for motoneuron differentiation (SHH 100 ng/ml, RA 100 nM, BDGF, GDNF and IGF each at 10 ng/ml) for 14 days. (B) Large numbers of OLIG2⁺ cells, but no HB9⁺ cells, were observed. Scale bar: 50 m.

Fig. S4. Expression of markers for OPCs. (A) O4 does not overlap with PDGFRα. (B) O4 and NG2 are often expressed by typical oligodendrocytes. Scale bar: 50 m.