AbstractThree recent reports(1–3)identify two genes,thick veins (tkv)andsaxophone (sax), which encode serine/threonine transmembrane proteins that act as receptors for mediating different aspects of theDrosophilaTGF‐β‐related signal,dpp. tkvis required for patterning the entire embryonic dorsal region, whilesaxis required for patterning only amnioserosa, the dorsalmost cell fates.dppsignaling in other developmental processes again requires bothtkvandsax, but to differing degrees.tkvandsax, encode type I receptors, which appear to directly bind ligand, unlike what has been observed for other type I rec