Fig. 6. FGFR2 interacts with Wnt/β-catenin signaling to maintain the AER. (A-D) Reduction of Wnt/β-catenin signaling in Fgfr2^AER-KO forelimb buds. (A,B) lacZ expression in BAT-Gal transgenic limb buds. Broken black lines mark the basement membrane. Arrow in B denotes ectopic Wnt signaling in the distal-dorsal mesenchyme. (C,D) Lef1 expression was moderately reduced in mutant limb buds. (E-T) β-Catenin^GOF prevented premature AER loss and restored the autopod of Fgfr2^AER-KO embryos. (E-H) β-Catenin expression immunofluorescence. Stabilized β-catenin was present in the ventral ectoderm. (I-L) Fgf8 expression on vibratome sections. Ectopic Fgf8-expression in the ventral ectoderm (white arrowheads). Black arrowheads indicate the endogenous AER (K,L). (M,N) Cell death as detected by TUNEL. Dying cells in the ventral ectoderm, which were prominent in Fgfr2^AER-KO limb buds, were absent in Fgfr2^AER-KO;β-cat^GOF limb buds at this stage (Fig. 3D). Broken white lines indicate the basement-membrane. (O,P) Hoxa13 expression (white arrow) was initiated in β-cat^GOF limb buds at 32 s. (Q-T) Sox9 expression and skeletal preparations at the stages indicated. Note that the autopod was restored in Fgfr2^AER-KO;β-cat^GOF embryos (R,T). Asterisk indicates skeletal fusions between digits (syndactyly) in β-cat^GOF (S) and Fgfr2^AER-KO;β-cat^GOF limbs (T). VI' indicates a post-axial extra digit (S). E10.5 is equivalent to 35 s stage and E11.75 is equivalent to 48 s stage. Scale bars: red, 50 µm; black, 200 µm. Abbreviations: an, anterior; di, distal; do, dorsal; pr, proximal; po, posterior; ve, ventral; s, somite.