Negative Smad Expression and Regulation in the Developing Chick Limb

The inhibitory or negative Smads, Smad6 and Smad7, block TGF beta superfamily signals of both the BMP and TGF beta classes by antagonizing the intracellular signal transduction machinery. We report the cloning of one Smad6 and two Smad7 (Smad7a and Smad7b) chick homologs and their expression and regulation in the developing limb. Smad6 and Smad7a are expressed in dynamic patterns reflecting the domains of BMP gene expression in the limb. Activation and inhibition of the BMP signaling pathway in limb mesenchyme indicates that negative Smad gene expression is regulated, at least in part, by BMP family signals.