 Gradient formation depends on the BMP inhibitors Short gastrulation (Sog) and Twisted gastrulation (Tsg), and other extracellular proteins such as Tolloid (Tld), and Screw (Scw).Sog is produced in the ventral-lateral region of the embryo (perpendicular to the Dpp gradient) and forms a BMP-inhibiting gradient that prevents Dpp from binding to its receptor.Sog and Tsg form a complex with Dpp and are actively transported toward the dorsal midline (middle of the embryo), following the Sog concentration gradient.