Biologjia Online

A morphogen gradient patterns the dorsal surface of the Drosophila embryo. Decapentaplegic (Dpp) and Screw (Scw), two BMP-type ligands, are known to be involved, with Dpp thought to play the primary role. Shimmi et al. show that morphogen activity is actually composed of two separate components, Dpp homodimers and Dpp/Scw heterodimers. These two activities are sorted along the embryonic dorsoventral axis by differential binding to two transporter proteins, Tsg and Sog. Using a computational approach, the authors show that heterodimers can buffer biological systems against changes in gene dose, thereby providing a selective advantage for using heterodimers as morphogens.