Fig. 4. FGFR-dependent ERK signaling in extra-embryonic ectoderm (exe), heart primordia (h), frontal nasal process (fnp), midbrain-hindbrain boundary (mhb), eye primordia (ey), branchial arches (ba) and limb buds (lb) at 6.5, 8.0 and 10.5 dpc. Prior to dp-ERK staining, embryos were cultured in the absence (A-C) or presence (D-F) of the FGFR inhibitor (40 µM SU5402) for 30-90 minutes. Note that culturing embryos alters dp-ERK patterns somewhat causing more diffuse boundaries of dp-ERK, some ectopic regions of dp-ERK and a loss of dp-ERK staining in some weaker regions of signaling. Dp-ERK staining in the ectoplacental cone (epc) and left heart ventricle (hv) were unaffected by the FGFR inhibitor. Scale bars: 50 µm in A,D; 100 µm in B,E; 700 µm in C,F.