Fig. 7. Morphology of proximal PA2 in Sox3 null mouse embryos. (A,B,D,E,G-I) Confocal sections of phalloidin-stained 9.5 dpc wild-type (A) and Sox3 null (D) embryos. PP1 and PP2 appear connected in the mutant. (B,E) Higher magnification and deeper sections of a wild-type (B) and Sox3 null (E) embryos with a `stem' connecting distal PA2 (arrow). (C,F) Confocal sections of phalloidin and anti-CRABPI double-stained 9.5 dpc wild-type embryo (C) and Sox3 null mutant (F), where ncc migrate through the `stem'. (G-I) High magnification of PP1 posterior margin in wild type (G) and of the `stem' in mutant embryos (H,I). Superficial section (H), where margin-like cells form a `stem' but show a disruption of apical actin accumulation. Deeper section (I), where two margins flank what is left of PA2. Actin polarisation is also disrupted. (J-M) Anti-N-cadherin immunofluorescence on 9.5 dpc embryos. (J) 3D reconstruction of a wild-type embryo sagittal half, inside view. Expression is seen in the neural tube and pharyngeal endoderm. (K) High magnification of a confocal section (region boxed in H) with apical accumulation of N-cadherin in the pouch margin. (L) 3D reconstruction of a mutant embryo sagittal half, inside view. (M) High magnification of confocal section (region boxed in J) with a disruption of apical N-cadherin accumulation. (N) Anti-GFP immunohistochemistry of a 17 ss Sox3 null embryo (transverse section, PA2 level). The close apposition between ectoderm and endoderm on one side (arrow) interrupts PA2. (O,P) Spry-1 in situ hybridisation on 8/9 ss wild-type (O) and 7/8 ss Sox2^+/-; Sox3^Y/- (P) embryos sectioned at pharyngeal level, posterior to PA1; the gene is expressed in pharyngeal epithelia and mesenchyme. No significant difference is observed between wild type and double mutant. Scale bar: 100 µm in A for A,D; 50 µm for B,E and O,P; 25 µm for C,F; 10 µm for G,H,I,K,M. ov, otic vesicle.