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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.