Fig. 5. Notch1a^ac promotes OPC specification. Transverse sections, dorsal to top, labeled by sox10 RNA hybridization. (A) 26 hpf wild-type embryo. Spinal cord (sc), somite (so) and notochord (nc) cells did not express sox10. (B) Transgenic embryo in which Notch1a^ac was induced at 8 and 24 hpf. Somite cells expressed sox10 but spinal cord and notochord cells did not. (C) 52 hpf wild-type embryo hybridized with sox10 probe. sox10⁺ cells had mostly dispersed from ventral spinal cord (bracket). Neural crest-derived cells on the medial migratory pathway also expressed sox10 (arrow). (D) Transgenic embryo in which Notch1a^ac was induced at 8, 24 and 36 hpf. Excess ventral spinal cord cells expressed sox10 (bracket) as did presumptive neural crest cells (arrows). (E) Quantification of sox10⁺ cells at 52 hpf in wild-type (wt) and Notch1a^ac-expressing embryos. Bars indicate the average number of sox10⁺ cells per transverse section. Data were obtained from 20 sections from each of 5 control and 5 heat-shocked transgenic embryos. P<0.00000001 by Student's t test. Scale bar: 20 µm.