Fig. 6. Cell survival and fate analysis in the mutant cerebellum. TUNEL analysis (green) for dying cells and nestin (red) for neuroepithelial progenitor cells in the cerebellum failed to show a difference between mutant (A) and control animals (B) at E10. However, at E12.5, mutant animals (C) contained a greatly increased number of TUNEL-positive cells (green; arrow) within the medial aspect of the cerebellar primordium compared to control animals (D). These TUNEL-positive cells were in a position analogous to differentiating neuroblasts and had downregulated expression of nestin. (E,F) The lineage tracing Cre-reporter transgene R26R revealed an extensive number of ß-galactosidase-expressing cells in the midbrain-hindbrain region of control animals carrying heterozygous Floxed Notch1, En2-Cre and R26R transgenes (E). A substantial reduction in the number of ß-galactosidase-expressing cells was observed in the E12.5 mutant embryos (F; homozygous Floxed Notch1, En2-Cre and R26R), compared with control embryos. Scale bars: in A, 100 µm for A,B; in C, 50 µm for C,D.