Increased embryonic OPCs after expression of Q79R-Shp2 GOF mutation in Olig2 lineage. Embryonic OPCs labeled by Olig2 (A–F) and Pdgfrα (H–M) are increased in Q79R-Shp2-tg;Olig2cre/+ embryos (Olig2, B, E, F; Pdgfrα, I, L, M) compared with Q79R-Shp2-tg controls (Olig2, A, C, D; Pdgfrα, H, J, K). Images show the increased Olig2 (compare B, E, F with A, C, D) and Pdgfrα (compare I, L, M with H, J, K) in Q79R-Shp2-tg;Olig2cre/+ embryos compared with controls in the forming white matter tracts: medial/lateral CC and AC and VF regions. Graphical representation of Olig2 cell counts in G and Pdgfrα cell counts in N. **p < 0.005 (Student's t test). *p < 0.05 (Student's t test).