Fig. 2. Deletion of distal cranial sensory ganglia in Eya1^–/– and Six1^–/– embryos. (A-C) Whole-mount hybridization with an SCG10 riboprobe of wild-type (A), Eya1^–/– (B), and Six1^–/– (C) embryos at E10.5. A lack of neuronal differentiation of VIIIth and distal VIIth, IXth and Xth precursors is observed in Eya1^–/– embryos. In Six1^–/– embryos, SCG10 staining was also missing in the regions of VIIIth and distal VIIth ganglia and slightly reduced in the regions of distal IXth and Xth ganglia. (D-F) E9.5 embryos hybridized with an Neurog2 riboprobe. Neurog2 expression in distal VII, IX and X placodes is readily visible in wild-type embryos, but its expression is completely lost in these structures in Eya1^–/– embryos. In Six1^–/– embryos, Neurog2 expression is undetectable in the VIIth placode and markedly reduced in the IXth and reduced in Xth placode. (G-O) Section in situ hybridization with the Neurog2 riboprobe of wild-type (G,J,M), Eya1^–/– H,K,N) and Six1^–/– (I,L,O) embryos at E8.5 to 9.25. Strong Neurog2 expression was observed in the distal VIIth placode (VIIp), and some migratory precursors (arrowhead) at E8.5-9.0 and in the distal IXth placode (IXp), and migratory precursors (arrowhead) at E8.75-9.25 and the Xth placode (Xp) at E9.0-9.25 in wild-type embryos, whereas its expression is completely absent in these structures of Eya1^–/– at these stages (arrow, H,K,N). In Six1^–/– embryos, its expression was reduced to background level in the VIIth precursors (arrow, I), also slightly reduced in the IXth (arrow, L) and relatively normal in the Xth precursors (arrow, O).