Schnurri mediates Dpp-dependent repression of brinker transcription.

Signalling by Decapentaplegic (Dpp), a member of the TGFb superfamily of signalling molecules, controls many aspects ofDrosophila development by activating and repressing target genes. Several essential components of the Dpp signalling pathway have been identified, including the Dpp receptors Punt and Thick veins (Tkv) as well as the cytoplasmic mediators Mad and Medea. For target genes to be activated, Dpp signalling must suppress transcription of a repressor encoded by thebrinker (brk) gene. Here we show that Schnurri (Shn), a large zinc-finger protein, is essential for Dpp-mediated repression ofbrktranscription; in contrast, Shn is not required for target-gene activation. Thus, the Dpp signalling pathway bifurcates, downstream of the signal-mediating SMAD proteins, into a Shn-dependent pathway leading tobrk repression and a Shn-independent pathway leading to gene activation. The existence of several Shn-like proteins in vertebrates and the observation that Brk functions in BMP signalling inXenopus indicates that a similar regulatory cascade may be conserved in higher organisms. [ABSTRACT FROM AUTHOR]