In Drosophila embryos, Tolloid (Tld) – an extracellular protease related to bone morphogenetic protein 1 (Bmp1) – helps to specify dorsal structures by cleaving the Bmp inhibitor Short gastrulation(Sog) to release Decapentaplegic from an inhibitory complex. On p. 2645, Serpe and colleagues report that, during posterior crossvein (PCV) formation in Drosophila wings, the embryonic role of Tld in spatially restricting Bmp signalling is recapitulated by Tolloid-related (Tlr). The researchers show that, like Tld, Tlr cleaves Sog but with slightly different kinetics and that tlr mutants lack the PCV probably through excess Sog activity reducing Bmp signalling. However, other results indicate that, as in the embryo, Sog has both negative and positive effects on Bmp signalling in the wing. Finally, because Tld and Tlr cannot substitute for each other during development, the researchers propose that their different Sog catalytic properties match them to dorsal structure and PCV specification,respectively.