Fig. 6. Loss of FGF8 signaling in the SHF and pharyngeal endoderm disrupts BMP and TGFβ signaling. (A,B) Intensity maps of relative expression of members and targets of the FGF and BMP/TGFβ signaling pathways obtained from four Agilent microarrays comparing Fgf8;Isl1Cre mutant to control OFTs. Red indicates increased expression and green decreased expression in mutants. Note the reproducible direction and magnitude of the changes. In the BMP/TGFβgene list, BMP pathway members are in bold, TGFβ pathway members are in regular type and shared genes are marked with an asterisk. Fold changes are log base 2; P<0.05. (C-E) mRNA in situ hybridizations of E9.5 control and Fgf8;Isl1Cre mutants. Bmp4 expression is decreased in the OFT (arrowhead) and SHF (arrow) of (D) Fgf8;Isl1Cre and (E) Fgfr1^c/c;Fgfr2^c/+;Isl1Cre mutants that develop PTA. (F,G) Anti-phosphoSMAD1/5/8 immunohistochemistry on sagittal sections of control versus Fgf8;Isl1Cre mutant OFTs. Hoechst staining in blue, anti-pSMAD in red. pSMAD⁺ cells are abundant in control, compared with mutant, pharyngeal and subendothelial mesenchyme (arrows) and in the OFT endothelium (arrowheads). cu, proximal OFT cushion; PA, pharyngeal arch. (H-I') Anti-phosphoSMAD1/5/8 immunohistochemistry on transverse sections of control versus Spry2-GOF;Mesp1Cre mutant OFTs. Hoechst staining in blue, anti-pSMAD in red. pSMAD⁺ cells are abundant in control OFT endothelium (arrowheads) and in subendothelial mesenchymal cells (arrows). (H,I) Distal OFT cushions (cu). (H',I') Proximal OFT cushions. Bracket in H' shows large numbers of pSMAD⁺ endothelial cells in the control.