Fig. 3. Alteration of Neurog1, Neurod, Math3 and Nscl1 expression in Eya1^–/– and Six1^–/– epibranchial neuronal precursors. (A-F) Transverse section hybridization showing Neurog1 expression in the otic vesicle (ov) and in the VIIIth ganglion region and epibranchial (VII, IX) neuronal precursors in wild-type embryos (A,D), no expression in Eya1^–/– epibranchial neuronal precursors (arrow in B,E) and reduced expression in Six1^–/– epibranchial neurons (arrow in C,F). Note that Neurog1 expression was observed in the VIIIth precursors (open arrow in B,C). (G-L) Transverse section hybridization showing Neurod expression in the VIIIth and epibranchial neuronal precursors in wild-type embryos (G,J), no expression in epibranchial precursors in Eya1^–/– embryos (arrow in H,K) and no expression (arrow in I) or reduced expression in Six1^–/– epibranchial neurons (arrow in L). Note that Neurod expression was detected in the VIIIth neuroblast precursors (open arrow in H,I). (M-O) Whole-mount hybridization showing Math3 expression in epibranchial neurons in wild-type embryos (M), only a few Math3-positive cells in Eya1^–/– Xth neurons (open arrow in N), and reduced expression in Six1^–/– IXth and Xth neurons (O). (P-R) Whole-mount hybridization showing Nscl1 expression in cranial sensory ganglia in wild-type embryos (P). In Eya1^–/– embryos, while Nscl1 expression appeared relatively normal in the Vth ganglion, it expression is absent in VIIIth, VIIth and IXth ganglia and very few Nscl1-positive cells were detected in Eya1^–/– Xth neurons (open arrow in Q). (R) Nscl1 expression is also absent in Six1^–/– VIIIth ganglion and markedly reduced in Six1^–/– VIIth (arrowhead) and IXth (arrow) ganglia.