Mapping gene regulatory networks in Drosophila eye development by large-scale transcriptome perturbations and motif inference [ChIP-Seq]
Ontology highlight
ABSTRACT: Genome control is operated by transcription factors (TF) controlling their target genes by binding to promoters and enhancers. Conceptually, the interactions between TFs, their binding sites, and their functional targets are represented by gene regulatory networks (GRN). Deciphering in vivo GRNs underlying organ development in an unbiased genome-wide setting involves identifying both functional TF-gene interactions and physical TF-DNA interactions. To reverse-engineer the GRN of eye development in Drosophila, we performed RNA-seq across 72 genetic perturbations and sorted cell types, and inferred a co-expression network. Next, we derived direct TF-DNA interactions using computational motif inference, ultimately connecting 241 TFs to 5632 direct target genes through 24926 enhancers. Using this network we found network motifs, cis-regulatory codes, and new regulators of eye development. We validate the predicted target regions of Grainyhead by ChIP-seq and identify this factor as a general co-factor in the eye network, being bound to thousands of nucleosome-free regions.
Project description:Genome control is operated by transcription factors (TF) controlling their target genes by binding to promoters and enhancers. Conceptually, the interactions between TFs, their binding sites, and their functional targets are represented by gene regulatory networks (GRN). Deciphering in vivo GRNs underlying organ development in an unbiased genome-wide setting involves identifying both functional TF-gene interactions and physical TF-DNA interactions. To reverse-engineer the GRN of eye development in Drosophila, we performed RNA-seq across 72 genetic perturbations and sorted cell types, and inferred a co-expression network. Next, we derived direct TF-DNA interactions using computational motif inference, ultimately connecting 241 TFs to 5632 direct target genes through 24926 enhancers. Using this network we found network motifs, cis-regulatory codes, and new regulators of eye development. We validate the predicted target regions of Grainyhead by ChIP-seq and identify this factor as a general co-factor in the eye network, being bound to thousands of nucleosome-free regions.
Project description:Glucocorticoid receptor (GR) is an essential transcription factor (TF), controlling metabolism, development and immune responses. SUMOylation regulates chromatin occupancy and target gene expression of GR in a locus-selective manner, but the mechanism of regulation has remained elusive. Here, we show using selective isolation of chromatin-associated proteins that the protein network around chromatin-bound GR is affected by SUMOylation, with several nuclear receptor coregulators and chromatin modifiers being more avidly associated with SUMOylation-deficient than SUMOylation competent GR. This difference is reflected in our chromatin accessibility and gene expression data, showing that the SUMOylation-deficient GR is more potent in opening chromatin at glucocorticoid-regulated enhancers and inducing expression of their target loci. Our results thus show that SUMOylation determines GR specificity by regulating the chromatin protein network and accessibility at GR-driven enhancers. We speculate that a similar mechanism is utilized by many other SUMOylated TFs.
Project description:Understanding the regulatory genome remains a significant challenge. Annotation of regulatory elements and identification of the transcription factors (TFs) targeting these elements are key steps in understanding how a given cell interprets its genetic blueprint. One goal of the modENCODE (model organism Encyclopedia of DNA Elements) project is to survey a diverse sampling of TFs, both DNA-binding and non-DNA binding factors, to provide a framework for the subsequent study of the mechanisms by which transcriptional regulators target the genome. Here we provide an updated map of the Drosophila melanogaster regulatory genome based on the location of 84 TFs at various stages of development. This regulatory map reveals a variety of genomic targeting patterns, including factors with strong preferences toward proximal promoter binding, factors that target intergenic and intronic DNA, and factors with distinct chromatin state preferences. The data also suggest the existence of a partially self-contained Polycomb regulatory network, and highlight the importance of Trithorax-like (Trl) in maintaining hotspots of DNA binding throughout development. Furthermore, the data identify over 5,800 instances in which TFs target DNA regions with demonstrated enhancer activity. Regions of high TF co-occupancy are more likely to be associated with open enhancers used across cell types, while lower TF occupancy regions are associated with complex enhancers that are also regulated at the epigenetic level. A putative regulatory network generated based on these 84 regulators reveals hundreds of co-binding events, thousands of potential regulatory interactions, and distinct regulatory strategies at developmental and housekeeping genes. These data serve as a resource for the research community in the continued effort to dissect transcriptional regulatory mechanisms directing Drosophila development. For data usage terms and conditions, please refer to http://www.genome.gov/27528022 and http://www.genome.gov/Pages/Research/ENCODE/ENCODEDataReleasePolicyFinal2008.pdf This is a dataset generated by the Drosophila Regulatory Elements modENCODE Project led by Kevin P. White at the University of Chicago.
Project description:Cell fate transitions are accompanied by global transcriptional, epigenetic and topological changes driven by transcription factors (TFs), as is strikingly exemplified by reprogramming somatic cells to pluripotent stem cells (PSCs) via expression of OCT4, KLF4, SOX2 and cMYC. How TFs orchestrate the complex molecular changes around their target gene loci in a temporal manner remains incompletely understood. Here, using KLF4 as a paradigm, we provide the first TF-centric view of chromatin reorganization and its association to 3D enhancer rewiring and transcriptional changes of linked genes during reprogramming of mouse embryonic fibroblasts (MEFs) to PSCs. Inducible depletion of KLF factors in PSCs caused a genome-wide decrease in the connectivity of enhancers, while disruption of individual KLF4 binding sites from PSC-specific enhancers was sufficient to impair enhancer-promoter contacts and reduce expression of associated genes. Our study provides an integrative view of the complex activities of a lineage-specifying TF during a controlled cell fate transition and offers novel insights into the order and nature of molecular events that follow TF binding.
Project description:Though the in vitro structural and in vivo spatial characteristics of transcription factor (TF) binding are well defined, TF interactions with chromatin and other companion TFs during development are poorly understood. To analyze such interactions in vivo, we profiled several TFs across a time course of human embryonic stem cell differentiation via CUT&RUN epigenome profiling, and studied their interactions with nucleosomes and co-occurring TFs by Enhanced Chromatin Occupancy (EChO), a computational strategy for classifying TF binding characteristics across time and space. EChO shows that at different enhancer targets, the same TF can employ either direct DNA binding, or “pioneer” nucleosome binding to access them. Pioneer binding is correlated with local binding of other TFs and enhancer motif character, including degeneracy at key bases in the pioneer factor target motif. Our strategy reveals a dynamic exchange of TFs at enhancers across developmental time that is aided by pioneer nucleosome binding.
Project description:We found that G4 structures assist to shape the nucleosome positioning and nucleosome depleted regions on enhancers. Moreover, many transcription factor (TF) clusters tend to co-target G4 on enhancers, leading to widespread enhancer transcriptional signals. These TFs further influenced the chromatin interactions between G4 enhancers and their target genes. Additionally, G4 enhancers harbored significantly higher enrichment of expression quantitative trait locus than typical enhancers, suggesting G4 enhancers displayed more enhancer regulatory activity.
Project description:Naïve pluripotency is sustained by a self-reinforcing gene regulatory network (GRN) comprising core and naïve pluripotency-specific transcription factors (TFs). Upon exiting naïve pluripotency, ES cells transition through a formative post-implantation-like pluripotent state. However, the mechanisms underlying disengagement from the naïve GRN and initiation of the formative GRN remain unclear. Here, we demonstrate that phosphorylated AKT acts as a gatekeeper that prevents nuclear localization of FoxO TFs in naïve ESCs. PTEN-mediated reduction of AKT activity allows nuclear entry by FoxO TFs, enforcing a cell fate transition by binding and activating formative pluripotency-specific enhancers. Indeed, FoxO TFs are necessary and sufficient for transition from the naïve to the formative pluripotent state. Our work uncovers a pivotal role for FoxO TFs and AKT signalling in mechanisms underlying the exit from naïve pluripotency, a critical early embryonic cell fate transition.
Project description:Naïve pluripotency is sustained by a self-reinforcing gene regulatory network (GRN) comprising core and naïve pluripotency-specific transcription factors (TFs). Upon exiting naïve pluripotency, ES cells transition through a formative post-implantation-like pluripotent state. However, the mechanisms underlying disengagement from the naïve GRN and initiation of the formative GRN remain unclear. Here, we demonstrate that phosphorylated AKT acts as a gatekeeper that prevents nuclear localization of FoxO TFs in naïve ESCs. PTEN-mediated reduction of AKT activity allows nuclear entry by FoxO TFs, enforcing a cell fate transition by binding and activating formative pluripotency-specific enhancers. Indeed, FoxO TFs are necessary and sufficient for transition from the naïve to the formative pluripotent state. Our work uncovers a pivotal role for FoxO TFs and AKT signalling in mechanisms underlying the exit from naïve pluripotency, a critical early embryonic cell fate transition.
Project description:Naïve pluripotency is sustained by a self-reinforcing gene regulatory network (GRN) comprising core and naïve pluripotency-specific transcription factors (TFs). Upon exiting naïve pluripotency, ES cells transition through a formative post-implantation-like pluripotent state. However, the mechanisms underlying disengagement from the naïve GRN and initiation of the formative GRN remain unclear. Here, we demonstrate that phosphorylated AKT acts as a gatekeeper that prevents nuclear localization of FoxO TFs in naïve ESCs. PTEN-mediated reduction of AKT activity allows nuclear entry by FoxO TFs, enforcing a cell fate transition by binding and activating formative pluripotency-specific enhancers. Indeed, FoxO TFs are necessary and sufficient for transition from the naïve to the formative pluripotent state. Our work uncovers a pivotal role for FoxO TFs and AKT signalling in mechanisms underlying the exit from naïve pluripotency, a critical early embryonic cell fate transition.
Project description:Dynamic binding of transcription factors to DNA elements specifies gene expression and cell fate, in both normal physiology and disease. To date, our understanding of mammalian gene regulation has been hampered by the difficulty of directly measuring in vivo binding of large numbers of transcription factors to DNA. Here, we develop a high-throughput indexed Chromatin ImmunoPrecipitation (iChIP) method coupled to massively parallel sequencing to systematically map protein-DNA interactions. We apply iChIP to reconstruct the physical regulatory landscape of a mammalian cell, by building genome-wide binding maps for 29 transcription factors (TFs) and chromatin marks at four time points following stimulation of primary dendritic cells (DCs) with pathogen components. Using over 180,000 TF-DNA interactions in these maps, we derive an initial dynamic physical model of a mammalian cell regulatory network. Our data demonstrates that transcription factors vary substantially in their binding dynamics, genomic localization, number of binding events, and degree of interaction with other factors. Further, many of the TF-DNA interactions at stimulus-activated genes are established during differentiation and maintained in a poised state. Functionally, the TFs are organized in a hierarchy of different types: Cell differentiation factors bind most of the genes and remain largely unchanged during the stimulation. A second set of TFs bind already in the un-stimulated and preferentially target induced genes. A third set consists of TF that bind mainly after the stimuli and target specific gene functions. Together these factors determine the magnitude and timing of stimulus induced gene expression. Our method, which allowed us to map routinely temporal binding profiles of dozens of TFs, provides a foundation for future understanding of the mammalian regulatory code. A study of dynamic binding of transcription factors in an immune cell following pathogen stimulation