Is Chordin a morphogen?

Models employing gradients of diffusible morphogens are often invoked to explain regional specification in the early embryo. In these models, a concentration gradient of a secreted factor generates distinct cell fates, based on the differential response of cells to local concentrations of this morphogen. In recent years, there has been a great deal of focus on the factors involved in the dorsoventral patterning of the vertebrate mesoderm and ectoderm. Dorsoventral specification during amphibian gastrulation is regulated by the antagonistic actions of the Bone Morphogenetic Proteins (BMPs) and a number of dorsally expressed inhibitors, including the secreted factor, Chordin. In a recent paper, Blitz and colleagues explore the possibility that Chordin acts as a long-range factor in the amphibian gastrula embryo, to establish a functional gradient of BMP activity.