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Neuronal target-derived gene activation mediated by widespread use of a BMP-activation element

ABSTRACT: In Drosophila, efferent neurons gain access to a target-derived BMP signal in the periphery that is required for differentiation and/or synaptic growth and neurotransmission. This requires transcriptional activity of the BMP-activated Smad transcription factors, but the Smad-bound enhancers and BMP-regulated effector genes they control remain unidentified. In the absence of insight into how BMP signaling controls these fundamental aspects of neuronal development and function, here we test whether Smads act directly at widely-deployed archetypal Smad-binding motifs to directly co-regulate batteries of BMP-responsive genes. To target these motifs for analysis, we employed a bioinformatics approach to identify candidate motifs conforming to the consensus 15bp BMP-Activation Element (BMP-AE). After filtering for high conservation and proximity to neuronally-expressed genes, we prioritized 62 BMP-AEs for analysis. Testing the in vivo enhancer activity of 58 genomic fragments containing these BMP-AEs in transgenic reporters, we show that 61% are functional BMP enhancers in diverse motoneuron and neuropeptidergic neuronal populations, and that the BMP-AE motif itself is required for activity. Moreover, 60% of these functional BMP-AEs were located within 20kb of at least one BMP activated gene, as identified by RNAseq analysis. Finally, we show that the BMP-AE motif plays a conserved activator function in the vertebrate nervous system, by electroporation in the developing chick neural tube. Our results provide evidence that BMP signaling controls neuronal development and function by directly coordinating networks of genes through widespread deployment of conserved, consensus Smad-binding motifs.

ORGANISM(S): Drosophila melanogaster

PROVIDER: GSE106650 | GEO | 2018/10/25

REPOSITORIES: GEO

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Project description:Recent genome-scale ChIP-chip studies of transcription factors have shown that a low percentage of experimentally determined binding sites contain the consensus motif for the immunoprecipitated factor. In most cases, differences between in vivo target sites that contain or lack a consensus motif have not been explored. We have previously shown that most sites to which E2F family members are bound in vivo do not contain E2F consensus motifs. The main purpose of this study was to develop an understanding of how E2F binding specificity is achieved in vivo. In particular, we have addressed how E2F family members are recruited to core promoter regions that lack a consensus motif and are excluded from other regions that contain a consensus motif. Using promoter and ENCODE arrays, we have shown that the predominant factors specifying whether E2F is recruited to an in vivo binding site are a) the site must be in a core promoter and b) the promoter region must be utilized as a promoter by the transcriptional machinery in that particular cell type. We have tested three models for recruitment of E2F to core promoters lacking a consensus site, including a) indirect recruitment, b) looping to the core promoter mediated by an E2F bound to a distal consensus motif, and c) assisted binding of E2F to a site that weakly resembles an E2F consensus motif within the core promoter. To test these models, we developed a new in vivo assay, termed eChIP, which allows analysis of transcription factor binding to isolated promoter fragments. Our findings suggest that in vivo a) the presence of a consensus motif is not sufficient to recruit E2Fs, b) E2Fs can bind to isolated regions that lack a consensus motif, and c) binding can require regions other than the best match to the E2F PWM in the core promoter. Keywords: E2F, ChIP-chip, transcription factor binding, consensus motifs 37 ChIP-chip arrays (of these, 14 array sets are biological duplicates). 22 samples are included in this series, the rest can be found in supplementary info to the following papers: Xu 2007, Jin 2006, Komashko 2008

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Neuronal target-derived gene activation mediated by widespread use of a BMP-activation element

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