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Fig. 1. Nkx2.5Cre/+; Shhflox/-
specifically ablates pharyngeal endodermal SHH and results in a failure of OFT
septation. (A) Shh is detected by in situ hybridization in
the pharyngeal endoderm (arrowheads) at E10.5. (B)
Nkx2.5Cre expression, as detected by R26R,
demonstrates overlap with Shh expression in the pharyngeal endoderm
alone (arrowheads). (C,D) Conditional ablation of Shh
in E10.5 Nkx2.5Cre/+; Shhflox/- embryos results
in the specific loss of pharyngeal endodermal Shh (arrow, C versus
D), but not of notochord and floorplate Shh expression, as expected
(arrowheads, C,D). (E-F') Ptch1lacZ
expression at E10.5 demonstrates a specific loss of Hh activity in the
pharyngeal endoderm and overlying mesoderm and mesenchyme (arrows, F,F')
while maintaining other domains of expression, such as in the floorplate of
the neural tube (arrowheads, E-F'). (G-H') Wild-type and
Nkx2.5Cre/+; Shhflox/- E18.5 ink injections
(G,H) demonstrate a single OFT vessel in mutants (arrow in H), whereas section
analysis (G',H') reveals a complete atrioventricular canal defect
(arrows in H'). In all panels, arrows and arrowheads mark abnormal and
normal findings, respectively, in mutants as compared with control embryos. B;
brachiocephalic artery; LCC, left common carotid; LSub, left subclavian; OFT,
outflow tract; RCC, right common carotid; RSub, right subclavian.