Radical fringe positions the apical ectodermal ridge at the dorsoventral boundary of the vertebrate limb

The radical fringe gene (R-fng) in vertebrates, which encodes a protein called fringe, plays an essential role in vertebrate limb outgrowth. The gene directs the formation and positioning of the apical ectodermal ridge at the dorsoventral limb boundary. This was concluded following the cloning of the chick gene, which is homologous to the Drosophila fringe protein gene. It was also examined whether R-fng expression regulates or is regulated by the genese Wnt-7a and En-1 that establish the dorsoventral boundary of the vertebrate limb. Findings indicate that correct R-fng expression requires the prior establishment of the boundary, but does not influence it.