Involved in dorsal-ventral patterning. Required for specification of a narrow strip of dorsal midline cells that will give rise to the amnioserosa, but not for specification of dorsal ectoderm cells. Inhibits BMP signaling; enhances the binding of sog to dpp, thus enhancing the antagonistic activity of sog. Component of a complex composed of dpp, sog and tsg. First appears in stage 4 embryos, expressed in two domains: a broad mid-dorsal saddle and an anterior cap, expression between the domains is continuous across the dorsal midline. At stage 5, expression is refined into 4 graded stripes in the mid-dorsal region and a paired domain in the anterior region. During stages 7 and 8, anterior expression fades and the mid dorsal stripes are located between the anterior and posterior transverse furrow (ATF and PTF). Expressing cells become incorporated into the deepening PTF. Gastrulating embryo. Belongs to the twisted gastrulation protein family.