Dpp signaling thresholds in the dorsal ectoderm of the Drosophila embryo

The dorsal ectoderm of the Drosophila embryo is subdivided into different c ell types by an activity gradient of two TGF beta signaling molecules, Deca pentaplegic (Dpp) and Screw (Scw), Patterning responses to this gradient de pend on a secreted inhibitor, Short gastrulation (Sog) and a newly identifi ed transcriptional repressor, Brinker (Brk), which are expressed in neuroge nic regions that abut the dorsal ectoderm, Here we examine the expression o f a number of Dpp target genes in transgenic embryos that contain ectopic s tripes of Dpp, Sog and Brk expression. These studies suggest that the Dpp/S cw activity gradient directly specifies at least three distinct thresholds of gene expression in the dorsal ectoderm of gastrulating embryos. Brk was found to repress two target genes, tailup and pannier, that exhibit differe nt limits of expression within the dorsal ectoderm, These results suggest t hat the Sog inhibitor and Brk repressor work in concert to establish sharp dorsolateral limits of gene expression. We also present evidence that the a ctivation of Dpp/Scw target genes depends on the Drosophila homolog of the CBP histone acetyltransferase.