Syndactyly phenotype of the Smad1/5 mutants is not caused by changes in mesenchymal BMP signaling of the developing autopod. Whole mount in situ hybridization of E12.5 controls (A, C, E, G, I and K) and mutants (B, D, F, H, J and L) forelimb buds using the probes as indicated. All are dorsal views. Arrowheads indicated ectopic expression of the genes indicated in the distal ectoderm. Arrows indicate the major axes: A, anterior; P, posterior; Di, distal; Pr, proximal. Scale bars = 500 µm.