Fig. 7. Cell signaling analysis in Nkx2.5^Cre/+; Fgf8^flox/- mutants. Immunohistochemistry analysis demonstrates pErk is localized in the SM, but not the PE (A,A'). Nkx2.5^Cre elimination of Fgf8 results in loss of pErk from the SM (B,B'). RNA in situ hybridization demonstrates that Pea3 is expressed in the developing arches as well as SM and PE (C,C'). Loss of Fgf8 results in continued arch ectoderm expression (D, black arrowhead) but loss of SM and PE expression (D'). Ptch1^lacZ ß-gal activity (E-F') and Shh expression (G,H) demonstrate that the SM and PE are still capable of Ptch1 expression, and that Fgf8 does not regulate this pathway in these tissues. Bmp4 is downregulated within the SM (I,J), suggesting a requirement for FGF8 signaling. OT, outflow tract; SM, splanchnic mesoderm; PE, pharyngeal endoderm; Nt, neural tube/notochord.