(a) Start:Finish Venus::HES5 intensity ratio in E10.5 Venus::HES5 heterozygous spinal cord slices treated with control (DMSO) and Notch inhibitor DBZ (2 μM) observed over 16h; bars indicate mean and standard deviation of DMS0 (n=3 experiments) and DBZ (n=4 experiments); 2-tailed t-test ****p=0.0001. 