Fig. 3. Tbx5 is upstream of FGF signaling in the forelimb bud. Wild-type embryos express Fgf10 (A,C,E), Fgf8 (B,D) and Snai1 (F) in the nascent limb buds (red arrowheads). These transcripts are absent in the forelimb field of Tbx5^del/del embryos, but expression at other sites in Tbx5^del/del embryos is intact, including intermediate mesoderm and hindlimb expression of Fgf10 (yellow and blue arrowheads, respectively, in A,C,E).