Mediator and RNA polymerase II clusters associate in transcription-dependent condensates
27 Jul 2018-Science (American Association for the Advancement of Science (AAAS))-Vol. 361, Iss: 6400, pp 412-415
TL;DR: This work used live-cell superresolution and light-sheet imaging to study the organization and dynamics of the Mediator coactivator and RNA polymerase II (Pol II) directly and suggests that large clusters of Mediator, recruited by transcription factors at large or clustered enhancer elements, interact with large Pol II clusters in transcriptional condensates in vivo.
Abstract: Models of gene control have emerged from genetic and biochemical studies, with limited consideration of the spatial organization and dynamics of key components in living cells. We used live-cell superresolution and light-sheet imaging to study the organization and dynamics of the Mediator coactivator and RNA polymerase II (Pol II) directly. Mediator and Pol II each form small transient and large stable clusters in living embryonic stem cells. Mediator and Pol II are colocalized in the stable clusters, which associate with chromatin, have properties of phase-separated condensates, and are sensitive to transcriptional inhibitors. We suggest that large clusters of Mediator, recruited by transcription factors at large or clustered enhancer elements, interact with large Pol II clusters in transcriptional condensates in vivo.
Citations
More filters
TL;DR: It is postulated that super-enhancers are phase-separated multimolecular assemblies, also known as biomolecular condensates, which provide a means to compartmentalize and concentrate biochemical reactions within cells.
Abstract: Super-enhancers (SEs) are clusters of enhancers that cooperatively assemble a high density of transcriptional apparatus to drive robust expression of genes with prominent roles in cell identity. Here, we demonstrate that the SE-enriched transcriptional coactivators BRD4 and MED1 form nuclear puncta at SEs that exhibit properties of liquid-like condensates and are disrupted by chemicals that perturb condensates. The intrinsically disordered regions (IDRs) of BRD4 and MED1 can form phase-separated droplets and MED1-IDR droplets can compartmentalize and concentrate transcription apparatus from nuclear extracts. These results support the idea that coactivators form phase-separated condensates at SEs that compartmentalize and concentrate the transcription apparatus, suggest a role for coactivator IDRs in this process, and offer insights into mechanisms involved in control of key cell identity genes.
1,506 citations
TL;DR: The latest understanding of long-range enhancer–promoter crosstalk is discussed, including target-gene specificity, interaction dynamics, protein and RNA architects of interactions, roles of 3D genome organization and the pathological consequences of regulatory rewiring.
Abstract: Spatiotemporal gene expression programmes are orchestrated by transcriptional enhancers, which are key regulatory DNA elements that engage in physical contacts with their target-gene promoters, often bridging considerable genomic distances. Recent progress in genomics, genome editing and microscopy methodologies have enabled the genome-wide mapping of enhancer-promoter contacts and their functional dissection. In this Review, we discuss novel concepts on how enhancer-promoter interactions are established and maintained, how the 3D architecture of mammalian genomes both facilitates and constrains enhancer-promoter contacts, and the role they play in gene expression control during normal development and disease.
646 citations
TL;DR: It is demonstrated that reconstituted chromatin undergoes histone tail-driven liquid-liquid phase separation (LLPS) in physiologic salt and when microinjected into cell nuclei, producing dense and dynamic droplets.
610 citations
TL;DR: CasDrop is used, a novel CRISPR-Cas9-based optogenetic technology, to show that various IDPs phase separate into liquid condensates that mechanically exclude chromatin as they grow and preferentially form in low-density, largely euchromatic regions.
490 citations
Cites background from "Mediator and RNA polymerase II clus..."
...Phase separation has also been recently implicated in driving gene activation through nanoscale transcriptional condensates assembled at enhancer-rich gene clusters (Cho et al., 2018; Chong et al., 2018; Sabari et al., 2018)....
[...]
...…in which transcriptionally active condensates such as the nucleolus (Berry et al., 2015; Feric et al., 2016) and super-enhancer clusters (Cho et al., 2018; Sabari et al., 2018) play bifunctional roles, serving to both filter out non-specific elements of the genome, while pulling…...
[...]
...…has also been recently implicated in driving gene activation through nanoscale transcriptional condensates assembled at enhancer-rich gene clusters (Cho et al., 2018; Chong et al., 2018; Sabari et al., 2018). ell 175, 1481–1491, November 29, 2018 ª 2018 Elsevier Inc. 1481 Despite the growing…...
[...]
..., 2016) and super-enhancer clusters (Cho et al., 2018; Sabari et al., 2018) play bifunctional roles, serving to both filter out non-specific elements of the genome, while pulling together targeted regions to which they are bound (Figure 7)....
[...]
TL;DR: An overview of the molecular underpinnings of the formation and regulation of these membraneless organelles are provided and new light on neurodegenerative diseases is shone on.
463 citations
References
More filters
TL;DR: Fiji is a distribution of the popular open-source software ImageJ focused on biological-image analysis that facilitates the transformation of new algorithms into ImageJ plugins that can be shared with end users through an integrated update system.
Abstract: Fiji is a distribution of the popular open-source software ImageJ focused on biological-image analysis. Fiji uses modern software engineering practices to combine powerful software libraries with a broad range of scripting languages to enable rapid prototyping of image-processing algorithms. Fiji facilitates the transformation of new algorithms into ImageJ plugins that can be shared with end users through an integrated update system. We propose Fiji as a platform for productive collaboration between computer science and biology research communities.
43,540 citations
TL;DR: This work introduced a method for optically imaging intracellular proteins at nanometer spatial resolution and used this method to image specific target proteins in thin sections of lysosomes and mitochondria and in fixed whole cells to image retroviral protein Gag at the plasma membrane.
Abstract: We introduce a method for optically imaging intracellular proteins at nanometer spatial resolution. Numerous sparse subsets of photoactivatable fluorescent protein molecules were activated, localized (to approximately 2 to 25 nanometers), and then bleached. The aggregate position information from all subsets was then assembled into a superresolution image. We used this method--termed photoactivated localization microscopy--to image specific target proteins in thin sections of lysosomes and mitochondria; in fixed whole cells, we imaged vinculin at focal adhesions, actin within a lamellipodium, and the distribution of the retroviral protein Gag at the plasma membrane.
7,924 citations
TL;DR: A high-resolution fluorescence microscopy method based on high-accuracy localization of photoswitchable fluorophores that can, in principle, reach molecular-scale resolution is developed.
Abstract: We have developed a high-resolution fluorescence microscopy method based on high-accuracy localization of photoswitchable fluorophores. In each imaging cycle, only a fraction of the fluorophores were turned on, allowing their positions to be determined with nanometer accuracy. The fluorophore positions obtained from a series of imaging cycles were used to reconstruct the overall image. We demonstrated an imaging resolution of 20 nm. This technique can, in principle, reach molecular-scale resolution.
7,213 citations
TL;DR: A cell-permeable small molecule (JQ1) that binds competitively to acetyl-lysine recognition motifs, or bromodomains is reported, establishing proof-of-concept for targeting protein–protein interactions of epigenetic ‘readers’, and providing a versatile chemical scaffold for the development of chemical probes more broadly throughout the b romodomain family.
Abstract: Epigenetic proteins are intently pursued targets in ligand discovery. So far, successful efforts have been limited to chromatin modifying enzymes, or so-called epigenetic 'writers' and 'erasers'. Potent inhibitors of histone binding modules have not yet been described. Here we report a cell-permeable small molecule (JQ1) that binds competitively to acetyl-lysine recognition motifs, or bromodomains. High potency and specificity towards a subset of human bromodomains is explained by co-crystal structures with bromodomain and extra-terminal (BET) family member BRD4, revealing excellent shape complementarity with the acetyl-lysine binding cavity. Recurrent translocation of BRD4 is observed in a genetically-defined, incurable subtype of human squamous carcinoma. Competitive binding by JQ1 displaces the BRD4 fusion oncoprotein from chromatin, prompting squamous differentiation and specific antiproliferative effects in BRD4-dependent cell lines and patient-derived xenograft models. These data establish proof-of-concept for targeting protein-protein interactions of epigenetic 'readers', and provide a versatile chemical scaffold for the development of chemical probes more broadly throughout the bromodomain family.
3,489 citations
TL;DR: A new method for fluorescence imaging has been developed that can obtain spatial distributions of large numbers of fluorescent molecules on length scales shorter than the classical diffraction limit, and suggests a means to address a significant number of biological questions that had previously been limited by microscope resolution.
3,437 citations