(A–F) Immunofluorescent analysis and quantification of the cerebellar area using DAPI at E15.5 (A,B) and E17.5 (C,D) showing a significant reduction in area at E17.5 (F; Student’s t-test) but not at E15.5 (E; Student’s t-test) in Atoh1-En1/2 CKOs compared to littermate controls (n = 3/condition). A slight delay in foliation was also observed at E17.5 (* base of folds). (G–N) Immunofluorescent analysis of TDTom and TUNEL on sagittal sections from a Atoh1-TDTom (G–H, K–L) and Atoh1-TDTom-En1/2 CKO (I–J, M–N) embryo showing that apoptosis is increased in the precursors of the medial and intermediate eCN of mutants at E15.5 (I–J) and at E17.5 (G–L). (O–R) Representative images of sagittal sections at the level of the intermediate CN in (S,T) stained for MEIS2 and TDTom in Atoh1-TDTom (O,P) and Atoh-TDTom-En1/2 CKOs (Q,R). (S,T) Quantification of the average number of MEIS2+ eCN cells in every second sagittal section along the medial-lateral axis at E15.5 and E17.5 in Atoh1-TDTom compared to Atoh-TDTom-En1/2 CKOs (n = 3 for each genotype) showing reduction in the medial/intermediate eCN at E17.5. eCN counts are plotted as bins of 5% percent of the mediolateral distance (E15.5: Two-way ANOVA F(1,42)=2.182, p=0.1471, E17.5: Two-way ANOVA, F(1,42)=23.67, p<0.0001). (U,V) Quantification of PCs (FOXP2+ cells, see A-D) showing reduced PC numbers in Atoh1-En1/2 CKOs compared to controls (n = 3 each genotype) at E17.5 (V) but not at E15.5 (U) (E15.5: Student’s t-test, p=0.88). Scale bars: 100 μm.