Vertebrate-conserved Schnurri zinc fingers restrain Drosophila vein patterning

The Drosophila Smad-interacting co-factor, Schnurri (Shn) confers transcriptional repression in response to Decapentaplegic (Dpp) signaling. Shn zinc fingers 6-8 mediate this Smad interaction but are lacking in vertebrate Shn homologs. In contrast, the vertebrate-conserved zinc finger 1,2 and 4,5 pairs have been reported to engage in Smad-mediated transcriptional activation in fly and vertebrate systems, and to contribute to Dpp-dependent tissue repair in the fly retina. We report that mutation of zinc coordination residues within vertebrate-conserved Shn zinc finger pairs 1,2 and 4,5 results in ectopic venation that is sensitive to Dpp signaling.