Fig. 4. Abnormal cardiac morphogenesis in E10.5 embryos with compound mutations in Hand1 and Hand2. (A-F) E10.5 embryos stained for lacZ activity expressed from the Hand1^lacZ allele. Left lateral view (A-C); frontal view (D-F). (G-I) Nuclear Fast Red counterstained transverse sections of the hearts of embryos in A-F. Genotypes of embryos are shown above each set of panels. There is severe reduction in Hand1-expressing cells in the LV and the hypoplastic ventricular chambers in H and I, and an absence of the interventricular groove and ventricular septation in I. lv, left ventricle; rv, right ventricle.