We further showed that the anterior limb mesenchymal cells in the Wls<sup>Shh-Cre</sup> served as a source of Wnt5a to reorientate the adjacent Wls-lacking Shh lineage cells to move anteriorly and subsequently led to syndactyly, suggesting that aberrant mesenchymal cell movement/condensation may underlie the pathogenesis of syndactyly.