Fig. 5. Cerebellum formation in fgf8^-/-; OtxH embryos at 5 days post-fertilization. Transverse sections of cerebellar areas from wild-type (A,E,I), OtxH (B,F,J), fgf8^-/- (C,G,K) and fgf8^-/-; OtxH (D,H,L) embryos showing expression of pax6 and reelin in granule cells (arrowheads in A-D and E-H, respectively) and zebrin in Purkinje cells (I-L). A total number of 10, 4 and 12 fgf8^-/-; OtxH embryos were analysed for pax6, reelin and zebrin staining, respectively. All the fgf8^-/-; OtxH embryos show the rescued phenotype. The count of zebrin-positive cells on vibratome 15 µm sections shows that a very small number of Purkinje cells are sometimes present [fgf8^-/- embryos have 2.4±2.4 positive cells (n=4 embryos counted) whereas fgf8^-/-; OtxH embryos have 15±5 Purkinje cells per section (n=4)]. Cartoons represent transverse section through the cerebellum in wild type (M), OtxH (N), fgf8^-/- (O) and fgf8^-/-; OtxH (P). Zebrin-positive cells are brow; reelin and reelin+ pax6 granule cells are blue and green, respectively. Only a subset of reelin cells is positive for pax6. Granule cells are always missing in fgf8^-/- (C,G). Ventral reelin staining corresponds to glial cells of the reticular formation, whereas proliferative regions of the midline at the level of the IVth ventricule and two lateral stripes of radial glia are pax6 positive.