Fig. 6. Increased levels of Rho GDI interfered with cardiac looping morphogenesis and ventricular maturation. (A-F) Whole-mount in situ hybridization of E9.5 nontransgenic embryos (A,C,E) and F₁ heterozygotes of the H2 founder (B,D,F) with a cardiac -actin probe. (A,B) Right side, (C,D) frontal and (E,F) left side views of the hearts. The transgenic hearts did not show rightward looping and there was no evidence for the demarcation of future right and left ventricles. (G-H) Transverse sections of whole-mount in situ hybridized E9.5 nontransgenic and F₁ heterozygous embryos of the H2 founder showing cardiac -actin expression, visualized by phase-contrast microscopy. Transgenic embryos had thin ventricular wall, absence of trabeculation, and lack of chamber demarcation. (I-J) Enlargement of the boxed areas in G and H. (K-L) Sections of E10.5 nontransgenic and heterozygous hearts of the M2 line. No morphological defect was detected in the M2 heterozygous embryos. A, atrium; V, ventricle; LV, left ventricle; RV, right ventricle.