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
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.
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.
Project description:Understanding the principles governing mammalian gene regulation has been hampered by the difficulty in measuring in vivo binding dynamics of large numbers of transcription factors (TF) to DNA. Here, we develop a high-throughput Chromatin ImmunoPrecipitation (HT-ChIP) method to systematically map protein-DNA interactions. HT-ChIP was applied to define the dynamics of DNA binding by 25 TFs and 4 chromatin marks at 4 time-points following pathogen stimulus of dendritic cells. Analyzing over 180,000 TF-DNA interactions we find that TFs vary substantially in their temporal binding landscapes. This data suggests a model for transcription regulation whereby TF networks are hierarchically organized into cell differentiation factors, factors that bind targets prior to stimulus to prime them for induction, and factors that regulate specific gene programs. Overlaying HT-ChIP data on gene-expression dynamics shows that many TF-DNA interactions are established prior to the stimuli, predominantly at immediate-early genes, and identified specific TF ensembles that coordinately regulate gene-induction.
Project description:A scalable and high-throughput method to identify precise subcellular localization of endogenous proteins is essential for integrative understanding of a cell at the molecular level. Here, we developed a simple and generalizable technique to image endogenous proteins with high specificity, resolution, and contrast in single cells in mammalian brain tissue. The technique, single-cell labeling of endogenous proteins by clustered regularly interspaced short palindromic repeats (CRISPR)-Cas9-mediated homology-directed repair (SLENDR), uses in vivo genome editing to insert a sequence encoding an epitope tag or a fluorescent protein to a gene of interest by CRISPR-Cas9-mediated homology-directed repair (HDR). Single-cell, HDR-mediated genome editing was achieved by delivering the editing machinery to dividing neuronal progenitors through in utero electroporation. We demonstrate that SLENDR allows rapid determination of the localization and dynamics of many endogenous proteins in various cell types, regions, and ages in the brain. Thus, SLENDR provides a high-throughput platform to map the subcellular localization of endogenous proteins with the resolution of micro- to nanometers in the brain.
Project description:Here, we present a preselected small set of ordered structures (PSSOS) method, a first principles-based high fidelity (HF), high throughput (HT) approach, for fast screening of the large composition space of high entropy alloys (HEAs) to select the most energetically stable, single-phase HEAs. Taking quinary AlCoCrFeNi HEA as an example system, we performed PSSOS calculations on the formation energies and mass densities of 8801 compositions in both FCC and BCC lattices and selected five most stable FCC and BCC HEAs for detailed analysis. The calculation results from the PSSOS approach were compared with existing experimental and first-principles data, and the good agreement was achieved. We also compared the PSSOS with the special quasi-random structures (SQS) method, and found that with a comparable accuracy, the PSSOS significantly outperforms the SQS in efficiency, making it ideal for HF, HT calculations of HEAs.
Project description:Determining the half-life of proteins is critical for an understanding of virtually all cellular processes. Current methods for measuring in vivo protein stability, including large-scale approaches, are limited in their throughput or in their ability to discriminate among small differences in stability. We developed a new method, Stable-seq, which uses a simple genetic selection combined with high-throughput DNA sequencing to assess the in vivo stability of a large number of variants of a protein. The variants are fused to a metabolic enzyme, which here is the yeast Leu2 protein. Plasmids encoding these Leu2 fusion proteins are transformed into yeast, with the resultant fusion proteins accumulating to different levels based on their stability and leading to different doubling times when the yeast are grown in the absence of leucine. Sequencing of an input population of variants of a protein and the population of variants after leucine selection allows the stability of tens of thousands of variants to be scored in parallel. By applying the Stable-seq method to variants of the protein degradation signal Deg1 from the yeast Matα2 protein, we generated a high-resolution map that reveals the effect of ∼30,000 mutations on protein stability. We identified mutations that likely affect stability by changing the activity of the degron, by leading to translation from new start codons, or by affecting N-terminal processing. Stable-seq should be applicable to other organisms via the use of suitable reporter proteins, as well as to the analysis of complex mixtures of fusion proteins.
Project description:There are a variety of in vivo and in vitro methods to determine the genome-wide specificity of a particular trans-acting factor. However there is an inherent limitation to these candidate approaches. Most biological studies focus on the regulation of particular genes, which are bound by numerous unknown trans-acting factors. Therefore, most biological inquiries would be better addressed by a method that maps all trans-acting factors that bind particular regions rather than identifying all regions bound by a particular trans-acting factor. Here, we present a high-throughput binding assay that returns thousands of unbiased measurements of complex formation on nucleic acid. We applied this method to identify transcriptional complexes that form on DNA regions upstream of genes involved in pluripotency in embryonic stem cells (ES cells) before and after differentiation. The raw binding scores, motif analysis and expression data are used to computationally reconstruct remodeling events returning the identity of the transcription factor(s) most likely to comprise the complex. The most significant remodeling event during ES cell differentiation occurred upstream of the REST gene, a transcriptional repressor that blocks neurogenesis. We also demonstrate how this method can be used to discover RNA elements and discuss applications of screening polymorphisms for allelic differences in binding.
Project description:The interpretation of genome sequences requires reliable and standardized methods to assess protein function at high throughput. Here we describe a fast and reliable pipeline to study protein function in mammalian cells based on protein tagging in bacterial artificial chromosomes (BACs). The large size of the BAC transgenes ensures the presence of most, if not all, regulatory elements and results in expression that closely matches that of the endogenous gene. We show that BAC transgenes can be rapidly and reliably generated using 96-well-format recombineering. After stable transfection of these transgenes into human tissue culture cells or mouse embryonic stem cells, the localization, protein-protein and/or protein-DNA interactions of the tagged protein are studied using generic, tag-based assays. The same high-throughput approach will be generally applicable to other model systems.
Project description:The need for dynamic, elastomeric polymeric biomaterials remains high, with few options with tunable control of mechanical properties, and environmental responses. Yet the diversity of these types of protein polymers pursued for biomaterials-related needs remains limited. Robust high-throughput synthesis and characterization methods will address the need to expand options for protein-polymers for a range of applications. To address this need, a combinatorial library approach with high throughput screening is used to select specific examples of dynamic protein silk-elastin-like polypeptides (SELPs) with unique stimuli responsive features, including tensile strength, and adhesion. Using this approach 64 different SELPs with different sequences and molecular weights are selected out of over 2,000 recombinant E. coli colonies. New understanding of sequence-function relationships with this family of proteins is gained through this combinatorial-screening approach and can provide a guide to future library designs. Further, this approach yields new families of SELPs to match specific material functions.