Fig. 7. Time course of TUNEL and Olig1/2 expression in the spinal cord of normal and Olig1-DTA embryos. (A-G) Few apoptotic cells detected by TUNEL staining are found in E9.0 to E12.5 control spinal cords. (H,O) Olig1-DTA-mediated cell death is first detected at E9.0. (I-L,P-S) Massive cell death continues until E11.5. (M,T) E12.0 Olig1-DTA embryos have very few TUNEL-positive cells. (N,U) From E12.5 on, dying cells are seen on the edges of the Olig gene expression domain. Olig2⁺ cells seen in controls (C-E) are always present from E9.0 to E12.5 in Olig1-DTA embryos (H-N). In particular, similar numbers of Olig2⁺ cells are found in E12.0 control and Olig1-DTA animals (F,M). Scale bars: in O, 50 µm for A,B,H,I,O,P; in U, 100 µm for C-G,J-N,Q-U.