Fig. 3. Fgf8 signaling pathways require low doses of Pitx2. (A,B) In situ analysis of 9.5 dpc wild-type (A) and Pitx2 abc^null embryo (B) with Fgf8 probe. (C,D) Parasagittal cryosections of 9.5 dpc Fgf8 whole-mount of wild-type (C) and Pitx2 abc^null mutant (D) embryos. (E-N) In situ of wild-type (E,G,I,K,M), Pitx2 abc^null homozygous mutant embryos (F,H,J,L,N). (O,P) Cartilage staining of 13.5 dpc wild-type (O), Pitx2 abc^null homozygous mutant (P) embryos. (Q-S) In situ of 10.5 dpc wild-type (Q), Pitx2 abc^null homozygous mutant (R) and abc^null; ab^hypoc (S) embryos with Fgf8. Arrows indicate areas of oral ectoderm expression. (T-V) In situ of 10.5 dpc wild-type (T), Pitx2 abc^null homozygous mutant (U) and abc^null; ab^hypoc (V) embryos with a Barx1 probe. Arrows denote expression in proximal mandibular mesenchyme that is absent in Pitx2 abc^null mutant. Arrowhead indicates expression in caudal mandibular arch mesenchyme that is probably induced by Fgf8 signaling from the caudal mandibular ectoderm. (W-Y) In situ of 12.0 dpc wild-type (W), Pitx2 abc^null homozygous mutant (X) and abc^null; ab^hypoc (Y) embryos with Pax9. Arrows (mandibular incisor) and arrowheads (mandibular molar) indicate areas of expression in dental mesenchyme that are reduced in abc^null homozygous mutant. md, mandibular process; mx maxillary process.