The expression of paraxial protocadherin. (A) Expression of paraxial protocadherin during late gastrulation shows the distinct down-regulation in the notochord and the absence of expression in the head region. (B) Double-stained cross section through a late Xenopus gastrula shows the separation of notochord (brown staining for chordin) and the paraxial mesoderm (blue staining for paraxial protocadherin). (Photographs courtesy of E. M. De Robertis.)