Fig. 5. Tbx5 is upstream of Wnt and FGF signaling. Lef1 and Tcf1 expression is undetectable in the forelimb field of Tbx5^del/del embryos (arrowheads in A,C,E), but is intact elsewhere in the embryo, including the hindlimb field (yellow arrows in A). Expression of Tbx5 is intact in Lef1^-/-;Tcf1^-/- embryos (B). Fgf10 expression is initiated, but expressed at lower levels than in wild type in the forelimb field of Lef1^-/-;Tcf1^-/- embryos at E9 (D) and E9.5 (F). Tbx5 (G) and Lef1 (H) expression is unaffected in Fgfr2^IgIII/IgIII embryos. Arrowheads in B,D-H indicate the forelimb field.