Fig. 6

Fgf signaling is required for rescue of the MHB program and cerebellar differentiation but not URL specification in gbx-;otxMO. Dorsal views of 22 hpf embryos (A–H) or 4 dpf larvae (I–L) with anterior to the left. Genotypes are indicated at the top. (A–H) RNA in situ hybridizations with genes indicated on left. atoh1a expression in the URL (black arrows in A) is absent in dnFgfr (B) but is rescued in dnFgfr;otxMO (C) and gbx-;dnFgfr;otxMO embryos (D). By contrast, MHB gene expression (pax2a, E) is not rescued by otx knock-down in the absence of Fgf signaling (G and H). (I–L) Zebrin II/Aldoca (red) normally expresses in cerebellar Purkinje cells and Tg(ptf1a:EGFP) (green) marks Purkinje neuron progenitors in WT (I; 14 larvae examined), but zebrin expression is absent and Tg(ptf1a:EGFP) is only expressed in lower rhombic lip in gbx-;dnFgfr;otxMO (L; 8 larvae examined). In dnFgfr (J) larvae, zebrin expression is absent (9 out of 18 larvae) or few zebrin-expressing cells are lying laterally at the junction of the tectum and the ptf1a:EGFP-expressing lower rhombic lip (the box in J; 9 out of 18). Similar to dnFgfr larvae, zebrin expression is either in the lateral junction between the tectum and lower rhombic lip in dnFgfr;otxMO (K; 15 out of 30 larvae) or is absent (the box in K).