... synthesized in the Spemannorganizer, namely Follistatin, Chordin and Noggin[12]. These proteins are antagonists of BMP and othermembers of the TGF-b family, binding to and inhibit-ing these signaling ... from binding to theirreceptors in the extracellular space, thus inhibiting ven-tralizing activities. Of these proteins, Chordin has along-range effect. In Xenopus, expression of the chordingene ... secreted and bind to the type I and type II receptors on the cellsurface. These receptors are serine ⁄ threonine kinasereceptors with a single transmembrane domain. Bind-ing of the ligand to...