A conserved activation element in BMP signaling during Drosophila development

Abstract

The transforming growth factor beta (TGF-beta) family member Decapentaplegic (Dpp) is a key regulator of patterning and growth in Drosophila development. Previous studies have identified a short DNA motif called the silencer element (SE), which recruits a trimeric Smad complex and the repressor Schnurri to downregulate target enhancers upon Dpp signaling. We have now isolated the minimal enhancer of the dad gene and discovered a short motif we termed the activating element (AE). The AE is similar to the SE and recruits the Smad proteins via a conserved mechanism. However, the AE and SE differ at important nucleotide positions. As a consequence, the AE does not recruit Schnurri but rather integrates repressive input by the default repressor Brinker and activating input by the Smad signal transducers Mothers against Dpp (Mad) and Medea via competitive DNA binding. The AE allows the identification of hitherto unknown direct Dpp targets and is functionally conserved in vertebrates.

Inverse regulation of target genes at the brink of the BMP morphogen activity gradient

“…To distinguish between these two possibilities it was necessary to decipher how Brk actually regulates transcription of sal. To analyse this, we employed a Brk-VP16 chimeric fusion protein, in which the repression domain of the Brk repressor is replaced with the activation domain of the herpes simplex virus protein VP16 (Weiss et al, 2010 Previous studies have identified several independent regulatory regions which are responsible for distinct spatial aspects of sal expression in the wing disc (de Celis et al, 1999). Characterisation of the medial enhancer that appears to control sal expression domain only in the centre of the wing pouch (Barrio and de Celis, 2004) (Fig.…”

“…Brk is known to repress lateral expression of classic BMP responsive genes such as omb and dad through direct binding to specific sequences within their enhancers (Sivasankaran et al, 2000;Weiss et al, 2010), indicating that it is highly active in lateral regions. Since the medial enhancer of sal also contains two Brk consensus-binding sequences (Barrio and de Celis, 2004), this raises the question as to why the medial enhancer does not function to repress sal in the lateral zone?…”

A cellular process that includes asymmetric cytokinesis remodels the dorsal tracheal branches in Drosophila larvae

“…We investigated the activity of the Dpp pathway, a known regulator of DB fate in the embryo (Ribeiro et al, 2004), in staged larvae using dad-GFP and brk-Gal4,UAS-mCherry as reporters. High levels of Dad and low levels of Brk result from increased Dpp signaling, and dad-GFP was shown to be an effective Dpp signaling readout (Ninov et al, 2010;Weiss et al, 2010). By 3 h into L3, the Dpp pathway was found to be activated within the spiracular branches of all tracheomeres (supplementary material Fig.…”

Transcriptional Control by the SMADs

“…1B) (Pyrowolakis et al 2004). In Drosophila, Schnurri is predominantly found to be a repressor, and, importantly, it was shown that the other class of SMAD1/5-SMAD4-binding sites GGCGCC-AN 4 -GNCV cannot bind Schnurri and, hence, function as activating sites (Weiss et al 2010). The bestknown target of the Schnurri -SMAD complex is the gene encoding the transcriptional repressor Brinker (Pyrowolakis et al 2004;Affolter et al 2008).…”

“…SMAD1/5 -SMAD4 complexes, in contrast, bind distinct sites in vivo, defined as GRCGNC-N 5 -GTCT or GGCGCC-AN 4 -GNCV where N is any base, R is A or G, and V is A, C, or G (Pyrowolakis et al 2004;Gao et al 2005;Weiss et al 2010). The GRCGNC sequence binds two SMAD1/5 MH1 domains, while the GTCT or GNCV binds the SMAD4 MH1 domain (Fig.…”