Fig. 3. Tbx1 is required early for aortic arch patterning and later for cardiac outflow tract (OFT) morphogenesis. (A) Aortic arch patterning defects in an E18.5 TgCAGG-CreER^TM;Tbx1^flox/+ embryo exposed to TM at E7.5. The arrowhead indicates aberrant origin of the right subclavian artery; the arrow indicates interruption of the aortic arch, compared with normal arrangement in a Tbx1^flox/+ control littermate (B). (C,D) Persistent truncus arteriosus (T) in an E18.5 TgCAGG-CreER^TM;Tbx1^flox/- embryo exposed to TM at E8.5 (C), compared with normal anatomy in a TgCAGG-CreER^TM;Tbx1^flox/+ littermate (D). (E-G) Intracardiac ink injection of E10.5 TgCAGG-CreER^TM;Tbx1^flox/+ embryos exposed to TM at E7.5 (E), E8.5 (F) and E9.5 (G). Numbers indicate the pharyngeal arch arteries (PAAs). The 4th PAA is absent in embryos exposed to TM at E7.5 (E) and exhibits very mild hypoplasia in embryos exposed to TM at E8.5 (F); normal morphology is present in the embryo exposed at E9.5 (G). (H-J) Timed fate mapping of Tbx1 expressing cells in E10.5 Tbx1^mcm/+;R26R embryos exposed to TM at E7.5 (H), E8.5 (I) and E9.5 (J) stained with X-gal; coronal sections, cranial is upwards. Arrowheads indicate labeling of surface ectoderm, arrows indicate labeling of endothelial cells of the 4th PAA. (K-M,K'-M') Timed fate mapping of Tbx1-expressing cells in E12.5 Tbx1^mcm/+;R26R embryos exposed to TM at E7.5 (K,K'), E8.5 (L,L'), and E9.5 (M,M') stained with X-gal; whole-mount preparation of the heart (K-M) and coronal section through the OFT (K'-M') at the truncal-conal transition. RSA and LSA, right and left subclavian arteries; BT, brachiocephalic trunk; Ao, aorta; PT, pulmonary trunk; RCA and LCA, right and left common carotid arteries; PA, pulmonary arteries; RV and LV, right and left ventricles. Scale bars: 0.5 mm in B,D,M; 0.2 mm in G; 50 µm in J; 100 µm in M'.