Fig. 3. AER formation is altered by gain of BMP function. (A-I) Whole-mount RNA in situ hybridization for Fgf8 expression in the AER. (A) Uninfected stage 27 hindlimb. (B) Constitutively activated BmpRIB-infected stage 27 hindlimb. In B, the limbs are severely truncated, owing to the absence of the AER and Fgf8 expression. (C) Constitutively activated BmpRIB-infected stage 17 hindlimb. Fgf8 expression is normal in the left hindlimb but is almost absent in the right hindlimb. (D,E,H) Uninfected stage 18 embryo and (F,G,I) constitutively activated BmpRIB-infected stage 18 embryo; right and left forelimbs (RFL and LFL) viewed from the dorsal (D-G) and lateral (H,I) side. Note ectopic Fgf8 expression is limited to dorsal ectoderm (arrows in F,G) and not ventral ectoderm (I; same limb as shown in F). Alternate sections of constitutively activated BmpRIB-infected stage 19 forelimb (J-M) and stage 18 hindlimb (N,O). Fgf8 is ectopically expressed in the dorsal ectoderm (asterisks in J,N), where is correlates with viral GAG expression (K) and Msx2 (L). In another sample, ectopic Fgf8 expression is not observed in regions of high EN1 expression (line in N,O).
