Fig. 4. Absence of motoneurons in Olig1-DTA embryos. Immunohistochemistry with antibodies against Isl1 and Hb9 was used to analyze cross sections of the brachial region of control and Olig1-DTA spinal cords from E10.0 to E13.0. Isl1⁺/Hb9⁺ motoneurons (A,B,E,F,I,J,M,N) are largely missing in the ventral horns of Olig1-DTA mice (C,D,G,H,K,L,O,P) from E10.0 to E13.0. Although a few Isl1⁺/Hb9⁺ motoneurons are still detectable around the ventricular zone of Olig1-DTA embryos from E11.0 to E12.0 (G,H,K,L, arrowheads), they are essentially undetectable by E13.0 (O,P). Scale bar: 100 µm.