Fig. 3. Effects of Fgf8b misexpression. (A,B) Dorsal and lateral view of an E15.5 brain after misexpression of Fgf8b. The tectum has disappeared, and instead cerebellum has differentiated ectopically (arrow in A,B). (C) Misexpression on both sides has completely replaced the tectum with the cerebellum (cer). (D) Parasagittal section of the brain in B to show the cerebellum proper (cer) and the part that differentiated from the mesencephalic alar plate (arrow). (E,F) Higher magnification of the cerebellum proper (cer) and the cerebellum-like structure (indicated as E and F in D). The cerebellar structure in the mesencephalic region has an external granular layer (compare the cells indicated by an arrow in E and F), and the layer that is identical to the Purkinje cell layer (compare arrowheads in E and F). (G,H) Immunocytochemistry with anti-calbindin antibody. Parasagittal cryosection of the brain shown in C was stained with anti-calbindin antibody. H is a higher magnification micrograph of the area indicated in G. Anti-calbindin antibody specifically stains Purkinje cells in the cerebellum, and G and H show that Purukinje cells are differentiated in this structure. (I-L) E3.5 embryos after Fgf8b misexpression. (I) Lateral view; there is no tectal swelling (arrowhead). (J,K) Whole-mount immunohistochemistry with anti-neurofilament antibody. (L) Flat-mount specimen after immunohistochemistry with anti-islet-1 antibody. The oculomotor nerve trunk (arrowhead inK) and the nucleus (L) disappeared on the experimental side. cer: cerebellum, cont: control side, di: diencephalon, exp: experimental side, mes: mesencephalon, tect: tectum, tel: telencephalon, III: oculomotor nerve trunk or oculomotor nucleus, IV: trochlear nucleus, V: trigeminal nerve. The anteroposterior direction is indicated by the arrow on B, D and G. Scale bars, 4 mm (A-D,G), 800 µm (I), 400 µm (J,K), 200 µm (L) and 100 µm (E,F,H).