Fig. 2. Dynamic expression of Olig1 and Olig2 in normal embryos. Cross sections from the presumptive brachial region of E8.5, and the brachial region of E10.0 to E13.25, heterozygous Olig1-Cre knockin mice were used for immunohistochemical analysis of Olig1 (Cre) (A-H) and Olig2 (I-Q) expression. Olig1 (Cre) and Olig2 are first detectable at E8.5 (A,I). They reach their expression peak in the ventricular zone at E10.0, and double staining indicates a complete overlap of the two expression patterns (B,J,K). From E10.5 to E12.0, more Olig2⁺ than Olig1⁺ (Cre⁺) cells can be detected (C-F,L-O). Both Olig1⁺ and Olig2⁺ cells start to migrate out of the ventricular zone starting from E12.5 (G,P). By E13.25, most Olig1⁺ (Cre⁺) and Olig2⁺ cells are also Pdgfr⁺ OPCs (H,Q). Scale bar: 50 µm for A,B,H,I-K,Q; 100 µm for C-G,L-P.