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First published online November 10, 2005
doi: 10.1242/10.1242/dev.02086

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Tbx1 expression in pharyngeal epithelia is necessary for pharyngeal arch artery development

¹ Department of Pediatrics (Cardiology), Baylor College of Medicine, Houston, TX 77030, USA
² Program in Cardiovascular Sciences, Baylor College of Medicine, Houston, TX 77030, USA
³ Department of Biochemistry and Molecular Biology, MD Anderson Cancer Center and Program in Genes and Development, Graduate School of Biomedical Sciences, University of Texas, Houston, TX 77030, USA
⁴ Alkek Institute of Biosciences and Technology, Texas A and M System Health Science Center, Houston, TX 77030, USA
⁵ Center for Cardiovascular Development, Baylor College of Medicine, Houston, TX 77030, USA
⁶ Department of Human and Molecular Genetics, Baylor College of Medicine, Houston, TX 77030, USA
⁷ CEINGE – Biotecnologie Avanzate S.C. ar. I., via Communale Margherita, 482-80145, Naples, Italy
⁸ Division of Cardiology, Second University of Naples, Naples, Italy

View larger version (83K): [in a new window]   Fig. 1. Tbx1 expression in the pharyngeal region. (A,A') X-gal staining pattern generated by a Tbx1-lacZ knock-in allele (Tbx1+/–) at E8 (A), and in a transverse section through the pharynx of the same embryo (A'). D, dorsal; V, ventral; da, dorsal aorta; se, surface ectoderm; pe, pharyngeal endoderm; pm, pharyngeal mesoderm; p, pharynx; h, heart. (B,B') Tbx1 expression in surface ectoderm overlying the presumptive caudal arches (arrowheads) at E9. A, anterior; P, posterior; II, III, second and third pharyngeal arch. (C,C') Radioactive in situ hybridization with an Fgf8 antisense probe on coronal sections of wild-type (C) and Tbx1–/– (C') embryos at E9. There is a loss of Tbx1 expression in the pharyngeal endoderm (arrowhead) but not in the surface ectoderm (arrow) of Tbx1–/– mutants. (D,D') Fate map of Tbx1-expressing cells in the fourth pharyngeal arch: X-gal staining pattern in coronal sections of a Tbx1mcm/+;R26R embryo at E10.5. Red arrowhead in D' indicates X-gal staining in endothelial cells lining the fourth pharyngeal arch artery (PAA); no staining is observed in the surrounding vascular smooth muscle (red arrow). A, anterior; P, posterior; III, IV, third and fourth pharyngeal arch. Scale bars: 100 µm in A,A',B',C-D'; 10 µm in B.

View larger version (117K): [in a new window]   Fig. 2. Tbx1-lacZ expression and Cre-induced recombination in the pharyngeal region of embryos at E10.5. (A) Tbx1-lacZ expression in a whole-mount Tbx1+/– embryo (A), and on sagittal sections of the same embryo (Aa-Ad) showing expression in the core arch mesoderm of pharyngeal arches I and II (arrowheads in Aa), in the pharyngeal mesoderm (secondary heart field, arrow in Ab) and in the third and fourth pharyngeal pouches (red arrowheads in Ac). The absent fourth PAA (asterisk in Ad, Dd, Ed, Fd) at E10.5 is revealed by intracardiac ink injection. I-IV, pharyngeal arches I-IV; 3p, 4p, third and fourth pharyngeal pouches; da, dorsal aorta; 3, 6, third and sixth pharyngeal arch artery; A, anterior; P, posterior; D, dorsal; V, ventral. (B-F) X-gal-stained wholemounts and sagittal sections of Cre-driver; R26R embryos. (B) Nkx2.5Cre/+; R26R; (C) Mesp1Cre; R26R (D) Foxg1Cre/+; R26R; (E) TgFgf15Cre; R26R; (F) Hoxa3Cre/+; R26R. Sagittal sections in B-F are similar to those in A, and arrows and arrowheads show the same tissues and structures. In all histological sections, cranial is up and dorsal is right. In the lower panel of ink injected embryos, Ad, Bd and Dd are oriented as indicated in Ad; Cd, Ed and Fd are in the opposite orientation, as indicated in Cd. Scale bars: 100 µm.

View larger version (106K): [in a new window]   Fig. 3. Tbx1 gene expression and Cre recombination in embryos at E9. X-gal-stained wholemount embryos (A-F) and coronal sections through the pharynx of the same embryos (A'-F'). (A,A') Tbx1+/–; (B-B'') Nkx2.5Cre/+; R26R; (C,C') Mesp1Cre/+; R26R; (D,D') Foxg1Cre/+; R26R; (E,E') TgFgf15Cre; R26R (E9.5 embryo); (F,F') Hoxa3Cre/+; R26R. Position of the sections in B' and B'' are indicated in B. se, surface ectoderm; pm, pharyngeal mesoderm; pe, pharyngeal endoderm; p, pharynx; II, III, second and third pharyngeal arches. Scale bars: 200 µm.

View larger version (124K): [in a new window]   Fig. 4. Early Cre-induced recombination from Cre drivers Mesp1Cre (A,A'), Foxg1Cre (B,B'), TgFgf15Cre (C,C') and Hoxa3Cre (D-E'). A',B' and D' are transverse sections through the pharynx, D, dorsal; V, ventral. C' and E' are coronal sections. (A,A') Mesp1Cre induces recombination in all mesoderm-derived tissues, including vascular endothelia (arrowheads in A'). da, dorsal aorta; pe, pharyngeal endoderm; se, surface ectoderm; spm, splanchnic mesoderm; h, heart; oft, outflow tract. (B,B') Foxg1Cre induces patchy recombination in pharyngeal ectoderm, endoderm and mesoderm from E8.5. oft, outflow tract. (C,C') TgFgf15Cre recombination begins in pharyngeal endoderm (pe) at E9. Hoxa3Cre recombination in the pharyngeal region begins at E8.25 in surface ectoderm (D,D', arrows), and extends into pharyngeal endoderm and mesoderm by E8.5 (E,E'). Scale bars: 100 µm.