Fig. 4. Expression of Fgf3 and Fgf10 during inner ear formation. (A-C) Expression of Fgf3 was detected at the stages indicated by whole-mount in situ hybridization. The position of the prospective rhombomeres and rhombomeres are indicated. The arrow in B indicates the level of the transversal section shown in C, where expression in the hindbrain and otic placode can be observed. (D-N) Expression of Fgf10 was detected by whole-mount RNA in situ hybridisation at the stages of development indicated. (D-F) Expression of Fgf10 is observed in the anterior mesenchyme (m). The arrow in D indicates the level of the transversal section shown in E. A transverse section at this level in a four-somite stage embryo shows that Fgf10 expression is localized to ventral anterior mesenchyme (F). (G-N) Expression of Fgf10 in the hindbrain. To facilitate the localisation of Fgf10 expression relative to the position of rhombomeres 5 and 6, a probe for the Mafb gene was used in G-K. (L-N) Transverse sections at the levels indicated by arrows in H,I,K, respectively, show expression of Fgf10 restricted to the ventral part of the hindbrain. The broken line in I indicates the position the otic placode. In K and N, Fgf10 expression is also detected in the anterior part of the otic cup. Scale bars: in A, 200 µm for A; in B, 200 µm for B; in D, 50 µm for D; in G, 200 µm for G; in H, 200 µm for H; in I, 200 µm for I; in J, 200 µm for J; in K, 200 µm for K.