BMP-dependent gene repression cascade in Drosophila eggshell patterning.

Bone Morphogenetic Proteins (BMPs) signal by activating Smad transcription factors to control a number of decisions during animal development. In Drosophila , signaling by the BMP ligand Decapentaplegic (Dpp) involves the activity of brinker ( brk ) which, in most contexts, is repressed by Dpp. Brk encodes a transcription factor which represses BMP signaling output by antagonizing Smad-dependent target gene activation. Here, we study BMP-dependent gene regulation during Drosophila oogenesis by following the signal transmission from Dpp to its target broad ( br ), a gene with a crucial function in eggshell patterning. We identify regulatory sequences that account for expression of both brk and br , and connect these to the transcription factors of the pathway. We show that Dpp directly regulates brk transcription through Smad- and Schnurri (Shn)-dependent repression. Brk is epistatic to Dpp in br expression and activates br indirectly, through removal of a repressor, which is yet to be identified. Our work provides first cis -regulatory insights into transcriptional interpretation of BMP signaling in eggshell morphogenesis and defines a transcriptional cascade that connects Dpp to target gene regulation. [ABSTRACT FROM AUTHOR]