Fig. 3. SEM and marker analysis of embryos with activated Wnt/ß-catenin signaling in the limb mesenchyme. (A,A') Whole-mount in situ hybridizations showing Fgf8 expression in wild-type (A) and ß-cat^ex3Prx1/+ (A', n=5) forelimbs at E11.5; note ectopic expression in the distal region (red arrow), as well as the loss from the posterior AER (white arrow). (B-B'') Fgf8 expression at E12.5 in wild-type (B) and ß-cat^ex3Prx1/+ (B',B'') embryos; note expression is lost from the posterior AER in the hindlimb (B') and is almost completely lost in the forelimb (B''). (C) Comparative quantification of the Fgf8-expressing regions (approximating the AER) in fore- and hindlimbs of wild-type and ß-cat^ex3Prx1/+ embryos at E10.5 (WT, n=6; ß-cat^ex3Prx1/+, n=12; ^*not significant) and E11.5 (WT, n=12; ß-cat^ex3Prx1/+, n=6; ^**significant: forelimb, P=0.01, hindlimb, P=0.02). (D-F') SEM images of wild-type (D-F) and ß-cat^ex3Prx1/+ (D'-F') forelimbs at E10.75 and E11.5. Brackets in D',E' indicate the flattened region of the AER; arrowhead in E indicates the necrotic region in the wild-type limb; arrowheads in F' indicate AP extension of the AER. (G,G') Wild-type Fgf4 expression in the posterior AER (G), which is downregulated in ß-cat^ex3Prx1/+ forelimbs (G'). (H,H') Wild-type Fgf9 expression in the AER (H), which is lost in ß-cat^ex3Prx1/+ forelimbs (H'). (I,I') Wild-type Fgf10 expression in the mesenchyme (I), which is lost in ß-cat^ex3Prx1/+ forelimbs (I'). (J,J') Wild-type Shh expression in the ZPA (J), which is absent in ß-cat^ex3Prx1/+ forelimbs (J'). (K,K') Wild-type Ptc1 expression (K), which is reduced in ß-cat^ex3Prx1/+ forelimbs (K'). Embryos are orientated anterior to the right. P, posterior; A, anterior. Scale bars: 100 µm in D-F'.