THE DROSOPHILA DECAPENTAPLEGIC AND SHORT GASTRULATION GENES FUNCTION ANTAGONISTICALLY DURING ADULT WING VEIN DEVELOPMENT

TGF-beta-related signaling pathways play diverse roles during vertebra te and invertebrate development, A common mechanism for regulating the activity of TGF-beta family members is inhibition by extracellular an tagonists. Recently, the Drosophila short gastrulation (sog) gene was shown to encode a predicted diffusible factor which antagonizes signal ing mediated by the TGF-beta-like Decapentaplegic (Dpp) pathway in the early blastoderm embryo, sog and dpp, which are among the earliest zy gotic genes to be activated, are expressed in complementary dorsal-ven tral domains, The opposing actions of sog and dpp in the early embryo have been highly conserved during evolution as their vertebrate counte rparts, chordin and BMP-4, function homologously to define neural vers us non-neural ectoderm in Xenopus. Here we exploit the genetically sen sitive adult wing vein pattern to investigate the generality of the an tagonistic relationship between sog and dpp, We show that dpp is expre ssed in vein primordia during pupal wing development and functions to promote vein formation, In contrast, sog is expressed in complementary intervein cells and suppresses vein formation, sog and dpp function d uring the same phenocritical periods (i.e. 16-28 hours after pupariati on) to influence the vein versus intervein cell fate choice, The confl icting activities of dpp and sog are also revealed by antagonistic dos age-sensitive interactions between these two genes during vein develop ment, Analysis of vein and intervein marker expression in dpp and sog mutant wings suggests that dpp promotes vein fates indirectly by activ ating the vein gene rhomboid (rho), and that sog functions by blocking an autoactivating Dpp feedback loop. These data support the view that Sog is a dedicated Dpp antagonist.