Fig. 7.

MEK and PLCγ inhibitors disrupt development of the SHF. (A) Inhibition of Ras/Erk signaling with the Mek inhibitor caused premature myocardial differentiation in the SHF. A HH16 embryo, sagittally sectioned through outflow tract and SHF, was immunostained for MF20 (red) to mark myocardium and Hoechst to label the nuclei. The MF20 was ectopically expressed in the SHF mesoderm (arrows) that is continuous with the myocardial rim (asterisk) of the outflow tract. (B) Graph showing the number of proliferating cells in the SHF of embryos treated with the PLCγ and MEK inhibitors compared with control embryos. Only inhibition of the PLCγ pathway significantly decreased SHF proliferation (*P=0.03). (C,D) Mek inhibitor treatment disrupted development of the coronary stems. Cross-section through the base of aorta at the left coronary stem insertion from a control embryo (C) and an embryo treated with the MEK inhibitor (D) and stained with SM22. Arrow in C shows normal single coronary stem. Arrows in D show the abnormal and multiple small vessels traversing the aortic wall.