Fig. 4. Differentiation state of cells within the cerebellar primordium. Immunofluorescent analysis of cross-sections through the neural tube at E10, dorsal to the left and ventral to the right, shows a reduction in the expression of the intermediate filament protein nestin in the medial aspect of the mutant cerebellar primordium (arrow, A) compared with control littermates (B). Examination of neuronal differentiation genes, such as those encoding ß-tubulinIII (TuJ1) (C,D), and neurofilament 160 (E,F), failed to reveal ectopic formation of differentiated neurons in the cerebellar primordium between E10 mutant and control animals. Calbindin D 28k expression could not be detected in E10 mutant animals at the protein (G) or RNA (H) levels, indicating the absence of precociously differentiated postmitotic Purkinje cells. Bars in A for A,B and in C for C-H are 100 µm.