Sticky fingers: Hox genes and cell adhesion in vertebrate limb development

During vertebrate limb development, various genes of the Hox family, the products of which influence skeletal element identity, are expressed in specific spatiotemporal patterns in the limb bud mesenchyme. At the same time, the cells also exhibit 'self-organizing' behavior--interacting with each other via extracellular matrix and cell-cell adhesive molecules to form the arrays of mesenchymal condensations that lead to the cartilaginous skeletal primordia. A recent study by Yokouchi et al. establishes a connection between these phenomena. They misexpressed the product of the Hoxa-13 gene in chick limb buds and demonstrated both skeletal pattern perturbations and changes in cell-cell adhesivity in mesenchyme aberrantly expressing this protein.