Attenuated sensing of SHH underlies adaptive evolution of bovine limbs

Artiodactyls display skeletal adaptations for cursorial (running) locomotion. In these animals, the distal limb skeleton is symmetric, which facilitates walking on the tips of the two central digits, while lateral digits are reduced or lost. We have identified that one primary molecular alteration during the formation of the bovine limb is that, in contrast to mouse, the posterior limb bud mesenchyme does not upregulate Ptch1 expression in response to SHH. We have tracked down this dissimilarity to a cis-regulatory SHH-responsive element that is functionally altered in bovine and established a causal link between lack of upregulation of Ptch1 and acquisition of a symmetric distal autopod. Overall design: A high resolution 4C-seq protocol involving two restriction digests was applied to viewpoint in Ptch1 promoter (mm9 chr13:63,667,995-63,669,157) in three different tissues, allowing robust detection of physical interactions between regulatory DNA elements.