Fig. 6. Marker analysis in mouse pharyngeal pouches at 9.5 dpc. (A,B) Pax1 in situ hybridisation in wild type (A) and Sox3 null (B) embryos. Note the abnormal appearance of proximal PA3 (arrow). (C,D) Coronal sections through the proximal pharyngeal region of wild-type (C) and Sox3 null (D) embryos hybridised with Pax1. The domain of expression is expanded throughout PA2 endoderm (arrow). (E,F) Bmp7 in situ hybridisation in wild-type (E) and Sox3 null (F) embryos. (G,H) Coronal sections of wild-type (G) and Sox3 null (H) embryos hybridised with Bmp7. (I,J) Fgf8 in situ hybridisation in wild type (I) in the anterior pouch margin (arrow) and Sox3 null embryo (J), where it is present across the reduced PA2 (bracket). (K,L) Coronal sections of wild-type (K) and Sox3 null (L) embryos hybridised with Fgf8. (M,N) Fgf3 in situ hybridisation in wild type (M) in the posterior pouch margin (arrow) and Sox3 null embryo (N), where it is present across the reduced PA2 (bracket). (O,P) Bmp4 in situ hybridisation in wild-type (O) and Sox3 null (P) embryos with uninterrupted expression between first and second pharyngeal clefts, arrow. All these markers of the pouch endoderm and/or ectoderm show an expansion of their expression across proximal PA2 in the mutant embryos. Scale bar: 100 µm in C for all sections.