Fig. 5. Late-onset cardiac defects in Blimp1 mutant embryos. (A-D) Transiently expressed Blimp1 in the splanchnic mesoderm anterior to the heart marks progenitors of the SHF. Blimp1⁺ cells contribute to the myocardium of the right ventricle, the outflow tract, and to the leaflets of the ventricular valves and walls of the aorta and pulmonary artery (D). (E-H) Outflow tract morphogenesis defects in Blimp1-deficient embryos (G,H) leads to persistent truncus arteriosus (PTA), in association with ventricular septal defects (VSD). Fgf8 (I-J') and Tbx1 (K-L') expression domains are severely downregulated, in part reflecting loss of the caudal pharyngeal arches (PA), and reduced staining in the surface epithelial and associated mesoderm. Red arrows indicate expression of Fgf8 and Tbx1 in the SHF in wild-type embryos. LV, left ventricle; RV, right ventricle; LA, left atrium; RA, right atrium; Ao, aorta; PA, pulmonary artery; VV, ventricular valves; PA, pharyngeal arch; SE, surface ectoderm; M, arch mesenchyme; PE, pharyngeal endoderm.