Fig. 6. FGF-8 (A-D) and BMP-2 (E-I) expression at stages 14 and 18. (A) FGF-8 expression in the lateral pharynx. Moderate expression in arches 1 and 2 with pronounced expression in arches 3-6. FGF-8 expression persists in the pharyngeal pouch/grooves after expression in the arches has diminished. (B) Sectioned whole-mount embryo showing that FGF-8 expression in arch 3 is in the ectoderm covering the pharyngeal arches and in the endoderm where it meets the ectoderm in the pharyngeal pouches. (C) FGF-8 expression at stage 18 is diminished in the caudal pharyngeal arches and completely absent in arches 1 and 2. Expression remains in the interval between the maxillary and mandibular prominences and the second pouch/groove. (D) Sectioned stage 18 whole-mount showing the greatly diminished FGF-8 expression in arches 2 and 3. (E) BMP-2 expression in the caudal outflow tract and splanchnic mesoderm that is continuous with the outflow tract at stage 14. (F) BMP-2 expression at stage 14 stops abruptly caudal to the outflow tract in an oblique section. (G) The splanchnic mesoderm between the inflow and outflow at stage 14 is devoid of BMP-2 expression. (H) BMP-2 expression can be seen in the inflow myocardium and dorsal mesocardium at stage 14. (I) By stage 18, BMP-2 is no longer expressed by the splanchnic mesoderm or myocardium but can now be seen in the endocardium. All scale bars are 100 µm.