Fig. 4. Notch1a^ac increases the number of ventral spinal cord cells that express olig2. Transverse sections, dorsal to top, labeled by olig2 RNA hybridization. (A) Wild-type control embryo revealing normal distribution of olig2⁺ cells at 26 hpf. (B) 26 hpf transgenic embryo in which Notch1a^ac was induced at 8 and 24 hpf expressed olig2 similarly to wild type in spinal cord (sc) but expressed olig2 ectopically in somites (so). (C) Wild-type control embryo revealing normal distribution of olig2⁺ cells at 36 hpf. (D) Excess spinal cord cells expressed olig2 at 36 hpf in transgenic embryo that was heat shocked at 8 and 24 hpf. (E) Quantification of olig2⁺ cells at 24 and 36 hpf in wild-type (wt) and Notch1a^ac-expressing embryos. Bars indicate the average number of olig2⁺ cells per transverse section. Data were obtained from 20 sections from each of five control and five heat-shocked transgenic embryos for each time point. P<0.00000001 by Student's t test. Scale bar: 20 µm.