Fig. 6. Evidence that Fgf10 plays a role in foregut patterning. (A,C) Wholemount and section of foregut of E10.5 FGF10^lacZ embryo after staining for ß-galactosidase. (A) Ventral view after dissection of the heart. Section in C shows strong Fgf10 expression in ventral mesenchyme. (B) Ventral epithelium (black arrowhead) and mesenchyme (white arrowhead) are positive for phosphorylated ERK1/2 staining. (E-G) Fluorescence microscopy of foreguts from 32-somite stage Sox2^EGFP/+ embryo before (E) and after culture for 36 hours without (F) or with (G) 50 ng/ml Fgf10 in the culture medium. White arrowhead marks the junction of the esophagus with the foregut and the white line marks the undivided proximal foregut. The anterior limit was determined from phase microscopy. Note that in samples incubated with Fgf10 the region of undivided foregut is longer than in control incubated without Fgf. (H-O) Section through the esophagus of samples similar to those shown in F,G, stained with antibodies to Sox2 (H,L), p63 (I,M), merged (J,N) and haematoxlyin and eosin (K,O). (H-K) Cultured without Fgf10, (L-O) cultured with Fgf10. The dotted line in K-O outlines the esophageal epithelial layer. Note the difference in length of the scale bars. (D) RT-PCR of transcript levels in isolated esophagi from E11 embryos cultured with and without Fgf10. Primers for p63 were for the transactivating isoform. Scale bars: 100 µm in E-G; 50 µm in H-O.