Fig. 7. Differentiation and fate of Notch1-ablated cells in the cerebellar primordium at E15. (A,B) In situ RNA hybridization for calbindin D 28k expression on sagittal sections of E15 mutant (A; homozygous Floxed Notch1 En2-Cre) and control embryos (B; heterozygous Floxed Notch1 En2-Cre) show no differences in the expression of the Purkinje cell marker. (C,D) Cell fate analysis of mutant (C) and control animals (B) at E15 using the lineage tracer Cre-reporter transgene R26R revealed an absence of ß-galactosidase expressing cells from the cerebellum (CB) of mutant compared with control embryos, where most of the cerebellar cells had undergone R26R recombination. Some ß-galactosidase-expressing cells were detected in the isthmus (IST) and posterior midbrain (pMB) region of the E15 mutant brain. However, the control embryos also showed substantially more ß-galactosidase-expressing cells in these brain regions. (E,F) TUNEL analysis (green; arrows) for dying cells and nestin (red) for neuroepithelial progenitor cells on cross-sections of the hemi-cerebellum (midline to the right and dorsal to the top) at E15 showed no significant difference between mutant (E) and control animals (F). Scale bars: in A, 100 µm for A-D; in E, 100 µm for E,F.