<i>Gng5^−/−</i> mutants fail to form the cardiac outflow tract and right ventricle and have severely hypoplastic pharyngeal arches.

<p><b>Panels A–D</b> images of e8.5 whole mount wild type and mutant embryos. By comparing the left lateral (A, C) and ventral (B, D) views of intact wild type and <i>Gng5^−/−</i> embryos, respectively, the unlooped heart tube is clearly evident (B, D). <b>Panels E–H</b>, images of e9.5 wild type and mutant embryos. The left parasagittal section from a control embryo shows the inflow tract and left side of common atrium, endocardial cushion in the atrioventricular canal, and left ventricle (E). The red arrowheads mark the first pharyngeal arch, also labeled 1. The midline section shows the outflow tract connecting to aortic sac in the second pharyngeal arch (bracket), right ventricle, the right portion of the common atrium, and the sinus venosus in the control embryo (F). The left parasagittal section of a <i>Gng5^−/−</i> mutant shows severely hypoplastic but vascularized first pharyngeal arch (red arrowhead), dilated heart tube with atrial chamber caudal to ventricle, narrow inflow, and paucity of cells in the pharyngeal mesoderm (G). The midline section shows the unlooped, dilated heart tube and no outflow tract; cardiac chamber opens directly into dilated aortic sac (bracket) in a <i>Gng5^−/−</i> embryo (H). TB, tail bud; HF, head fold; OFT, outflow tract; RV, right ventricle; LV, left ventricle; A, atrium V, ventricle; EC, endocardial cushion; SV, sinus venosus.