1
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McGehee J, Stathopoulos A. Target gene responses differ when transcription factor levels are acutely decreased by nuclear export versus degradation. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2024:2024.05.20.595009. [PMID: 38826476 PMCID: PMC11142056 DOI: 10.1101/2024.05.20.595009] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2024]
Abstract
Defining the time of action for morphogens requires tools capable of temporally controlled perturbations. To study how the transcription factor Dorsal affects patterning of the Drosophila embryonic dorsal-ventral axis, we used two light-inducible tags that result in either nuclear export or degradation of Dorsal when exposed to blue light. Nuclear export of Dorsal results in loss of expression for the high threshold, ventrally-expressed target gene snail (sna) but retention of the low threshold, laterally-expressed target gene short-gastrulation (sog). In contrast, degradation of Dorsal results in retention of sna, loss of sog, and lower nuclear levels than when Dorsal is exported from the nucleus. To elucidate how nuclear export results in loss of sna but degradation does not, we investigated Dorsal kinetics using photobleaching and found it reenters the nucleus even under conditions of blue-light when export is favored. The associated kinetics of being imported and exported continuously are likely responsible for loss of sna but, alternatively, can support sog. Collectively, our results show that this dynamic patterning process is influenced by both Dorsal concentration and nuclear retention.
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Affiliation(s)
- James McGehee
- California Institute of Technology, Division of Biology and Biological Engineering, 1200 East California Boulevard, Pasadena, CA 91125
| | - Angelike Stathopoulos
- California Institute of Technology, Division of Biology and Biological Engineering, 1200 East California Boulevard, Pasadena, CA 91125
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2
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Zhao J, Faryabi RB. Spatial promoter-enhancer hubs in cancer: organization, regulation, and function. Trends Cancer 2023; 9:1069-1084. [PMID: 37599153 PMCID: PMC10840977 DOI: 10.1016/j.trecan.2023.07.017] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/24/2023] [Revised: 07/14/2023] [Accepted: 07/27/2023] [Indexed: 08/22/2023]
Abstract
Transcriptional dysregulation is a hallmark of cancer and can be driven by altered enhancer landscapes. Recent studies in genome organization have revealed that multiple enhancers and promoters can spatially coalesce to form dynamic topological assemblies, known as promoter-enhancer hubs, which strongly correlate with elevated gene expression. In this review, we discuss the structure and complexity of promoter-enhancer hubs recently identified in multiple cancer types. We further discuss underlying mechanisms driving dysregulation of promoter-enhancer hubs and speculate on their functional role in pathogenesis. Understanding the role of promoter-enhancer hubs in transcriptional dysregulation can provide insight into new therapeutic approaches to target these complex features of genome organization.
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Affiliation(s)
- Jingru Zhao
- Department of Pathology and Laboratory Medicine, University of Pennsylvania Perelman School of Medicine, Philadelphia, PA 19104, USA; Penn Epigenetics Institute, University of Pennsylvania Perelman School of Medicine, Philadelphia, PA 19104, USA; Abramson Family Cancer Research Institute, University of Pennsylvania Perelman School of Medicine, Philadelphia, PA 19104, USA
| | - Robert B Faryabi
- Department of Pathology and Laboratory Medicine, University of Pennsylvania Perelman School of Medicine, Philadelphia, PA 19104, USA; Penn Epigenetics Institute, University of Pennsylvania Perelman School of Medicine, Philadelphia, PA 19104, USA; Abramson Family Cancer Research Institute, University of Pennsylvania Perelman School of Medicine, Philadelphia, PA 19104, USA.
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3
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Brennan KJ, Weilert M, Krueger S, Pampari A, Liu HY, Yang AWH, Morrison JA, Hughes TR, Rushlow CA, Kundaje A, Zeitlinger J. Chromatin accessibility in the Drosophila embryo is determined by transcription factor pioneering and enhancer activation. Dev Cell 2023; 58:1898-1916.e9. [PMID: 37557175 PMCID: PMC10592203 DOI: 10.1016/j.devcel.2023.07.007] [Citation(s) in RCA: 5] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/28/2022] [Revised: 05/09/2023] [Accepted: 07/13/2023] [Indexed: 08/11/2023]
Abstract
Chromatin accessibility is integral to the process by which transcription factors (TFs) read out cis-regulatory DNA sequences, but it is difficult to differentiate between TFs that drive accessibility and those that do not. Deep learning models that learn complex sequence rules provide an unprecedented opportunity to dissect this problem. Using zygotic genome activation in Drosophila as a model, we analyzed high-resolution TF binding and chromatin accessibility data with interpretable deep learning and performed genetic validation experiments. We identify a hierarchical relationship between the pioneer TF Zelda and the TFs involved in axis patterning. Zelda consistently pioneers chromatin accessibility proportional to motif affinity, whereas patterning TFs augment chromatin accessibility in sequence contexts where they mediate enhancer activation. We conclude that chromatin accessibility occurs in two tiers: one through pioneering, which makes enhancers accessible but not necessarily active, and the second when the correct combination of TFs leads to enhancer activation.
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Affiliation(s)
- Kaelan J Brennan
- Stowers Institute for Medical Research, Kansas City, MO 64110, USA
| | - Melanie Weilert
- Stowers Institute for Medical Research, Kansas City, MO 64110, USA
| | - Sabrina Krueger
- Stowers Institute for Medical Research, Kansas City, MO 64110, USA
| | - Anusri Pampari
- Department of Computer Science, Stanford University, Palo Alto, CA 94305, USA
| | - Hsiao-Yun Liu
- Department of Biology, New York University, New York, NY 10003, USA
| | - Ally W H Yang
- Donnelly Centre, University of Toronto, Toronto, ON M5S 3E1, Canada
| | - Jason A Morrison
- Stowers Institute for Medical Research, Kansas City, MO 64110, USA
| | - Timothy R Hughes
- Donnelly Centre, University of Toronto, Toronto, ON M5S 3E1, Canada
| | | | - Anshul Kundaje
- Department of Computer Science, Stanford University, Palo Alto, CA 94305, USA; Department of Genetics, Stanford University, Palo Alto, CA 94305, USA
| | - Julia Zeitlinger
- Stowers Institute for Medical Research, Kansas City, MO 64110, USA; Department of Pathology & Laboratory Medicine, The University of Kansas Medical Center, Kansas City, KS 66160, USA.
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4
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Harrison MM, Marsh AJ, Rushlow CA. Setting the stage for development: the maternal-to-zygotic transition in Drosophila. Genetics 2023; 225:iyad142. [PMID: 37616526 PMCID: PMC10550319 DOI: 10.1093/genetics/iyad142] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/18/2023] [Accepted: 07/18/2023] [Indexed: 08/26/2023] Open
Abstract
The zygote has a daunting task ahead of itself; it must develop from a single cell (fertilized egg) into a fully functioning adult with a multitude of different cell types. In the beginning, the zygote has help from its mother, in the form of gene products deposited into the egg, but eventually, it must rely on its own resources to proceed through development. The transfer of developmental control from the mother to the embryo is called the maternal-to-zygotic transition (MZT). All animals undergo this transition, which is defined by two main processes-the degradation of maternal RNAs and the synthesis of new RNAs from the zygote's own genome. Here, we review the regulation of the MZT in Drosophila, but given the broad conservation of this essential process, much of the regulation is shared among metazoans.
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Affiliation(s)
- Melissa M Harrison
- Department of Biomolecular Chemistry, University of Wisconsin-Madison, Madison, WI 53706USA
| | - Audrey J Marsh
- Department of Biomolecular Chemistry, University of Wisconsin-Madison, Madison, WI 53706USA
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5
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Fletcher A, Wunderlich Z, Enciso G. Shadow enhancers mediate trade-offs between transcriptional noise and fidelity. PLoS Comput Biol 2023; 19:e1011071. [PMID: 37205714 DOI: 10.1371/journal.pcbi.1011071] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/04/2022] [Accepted: 04/03/2023] [Indexed: 05/21/2023] Open
Abstract
Enhancers are stretches of regulatory DNA that bind transcription factors (TFs) and regulate the expression of a target gene. Shadow enhancers are two or more enhancers that regulate the same target gene in space and time and are associated with most animal developmental genes. These multi-enhancer systems can drive more consistent transcription than single enhancer systems. Nevertheless, it remains unclear why shadow enhancer TF binding sites are distributed across multiple enhancers rather than within a single large enhancer. Here, we use a computational approach to study systems with varying numbers of TF binding sites and enhancers. We employ chemical reaction networks with stochastic dynamics to determine the trends in transcriptional noise and fidelity, two key performance objectives of enhancers. This reveals that while additive shadow enhancers do not differ in noise and fidelity from their single enhancer counterparts, sub- and superadditive shadow enhancers have noise and fidelity trade-offs not available to single enhancers. We also use our computational approach to compare the duplication and splitting of a single enhancer as mechanisms for the generation of shadow enhancers and find that the duplication of enhancers can decrease noise and increase fidelity, although at the metabolic cost of increased RNA production. A saturation mechanism for enhancer interactions similarly improves on both of these metrics. Taken together, this work highlights that shadow enhancer systems may exist for several reasons: genetic drift or the tuning of key functions of enhancers, including transcription fidelity, noise and output.
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Affiliation(s)
- Alvaro Fletcher
- Mathematical, Computational, and Systems Biology, University of California, Irvine, Irvine, CA, United States of America
| | - Zeba Wunderlich
- Department of Biology, Boston University, Boston, MA, United States of America
- Biological Design Center, Boston University, Boston, MA, United States of America
| | - German Enciso
- Department of Mathematics, University of California, Irvine, Irvine, CA, United States of America
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6
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Whitney PH, Shrestha B, Xiong J, Zhang T, Rushlow CA. Shadow enhancers modulate distinct transcriptional parameters that differentially effect downstream patterning events. Development 2022; 149:dev200940. [PMID: 36264246 PMCID: PMC9687063 DOI: 10.1242/dev.200940] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/12/2022] [Accepted: 10/06/2022] [Indexed: 11/07/2022]
Abstract
Transcription in the early Drosophila blastoderm is coordinated by the collective action of hundreds of enhancers. Many genes are controlled by so-called 'shadow enhancers', which provide resilience to environment or genetic insult, allowing the embryo to robustly generate a precise transcriptional pattern. Emerging evidence suggests that many shadow enhancer pairs do not drive identical expression patterns, but the biological significance of this remains unclear. In this study, we characterize the shadow enhancer pair controlling the gene short gastrulation (sog). We removed either the intronic proximal enhancer or the upstream distal enhancer and monitored sog transcriptional kinetics. Notably, each enhancer differs in sog spatial expression, timing of activation and RNA Polymerase II loading rates. In addition, modeling of individual enhancer activities demonstrates that these enhancers integrate activation and repression signals differently. Whereas activation is due to the sum of the two enhancer activities, repression appears to depend on synergistic effects between enhancers. Finally, we examined the downstream signaling consequences resulting from the loss of either enhancer, and found changes in tissue patterning that can be explained by the differences in transcriptional kinetics measured.
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Affiliation(s)
- Peter H. Whitney
- Department of Biology, New York University, New York, NY 10003, USA
| | - Bikhyat Shrestha
- Department of Biology, New York University, New York, NY 10003, USA
| | - Jiahan Xiong
- Department of Biology, New York University, New York, NY 10003, USA
| | - Tom Zhang
- Department of Biology, New York University, New York, NY 10003, USA
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7
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Cao Y, Xia Y, Balowski JJ, Ou J, Song L, Safi A, Curtis T, Crawford GE, Poss KD, Cao J. Identification of enhancer regulatory elements that direct epicardial gene expression during zebrafish heart regeneration. Development 2022; 149:274414. [PMID: 35179181 PMCID: PMC8918790 DOI: 10.1242/dev.200133] [Citation(s) in RCA: 12] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/23/2021] [Accepted: 01/11/2022] [Indexed: 12/17/2022]
Abstract
The epicardium is a mesothelial tissue layer that envelops the heart. Cardiac injury activates dynamic gene expression programs in epicardial tissue, which in zebrafish enables subsequent regeneration through paracrine and vascularizing effects. To identify tissue regeneration enhancer elements (TREEs) that control injury-induced epicardial gene expression during heart regeneration, we profiled transcriptomes and chromatin accessibility in epicardial cells purified from regenerating zebrafish hearts. We identified hundreds of candidate TREEs, which are defined by increased chromatin accessibility of non-coding elements near genes with increased expression during regeneration. Several of these candidate TREEs were incorporated into stable transgenic lines, with five out of six elements directing injury-induced epicardial expression but not ontogenetic epicardial expression in larval hearts. Whereas two independent TREEs linked to the gene gnai3 showed similar functional features of gene regulation in transgenic lines, two independent ncam1a-linked TREEs directed distinct spatiotemporal domains of epicardial gene expression. Thus, multiple TREEs linked to a regeneration gene can possess either matching or complementary regulatory controls. Our study provides a new resource and principles for understanding the regulation of epicardial genetic programs during heart regeneration. This article has an associated 'The people behind the papers' interview.
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Affiliation(s)
- Yingxi Cao
- Cardiovascular Research Institute, Weill Cornell Medicine, 1300 York Avenue, New York, NY 10021, USA,Department of Cell and Developmental Biology, Weill Cornell Medicine, 1300 York Avenue, New York, NY 10021, USA
| | - Yu Xia
- Cardiovascular Research Institute, Weill Cornell Medicine, 1300 York Avenue, New York, NY 10021, USA,Department of Cell and Developmental Biology, Weill Cornell Medicine, 1300 York Avenue, New York, NY 10021, USA
| | - Joseph J. Balowski
- Department of Cell Biology, Duke University Medical Center, Durham, NC 27710, USA,Duke Regeneration Center, Duke University, Durham, NC 27710, USA
| | - Jianhong Ou
- Department of Cell Biology, Duke University Medical Center, Durham, NC 27710, USA,Duke Regeneration Center, Duke University, Durham, NC 27710, USA
| | - Lingyun Song
- Center for Genomic and Computational Biology, Duke University Medical Center, Durham, NC 27710, USA,Department of Pediatrics, Division of Medical Genetics, Duke University Medical Center, Durham, NC 27710, USA
| | - Alexias Safi
- Center for Genomic and Computational Biology, Duke University Medical Center, Durham, NC 27710, USA,Department of Pediatrics, Division of Medical Genetics, Duke University Medical Center, Durham, NC 27710, USA
| | - Timothy Curtis
- Department of Cell Biology, Duke University Medical Center, Durham, NC 27710, USA,Duke Regeneration Center, Duke University, Durham, NC 27710, USA
| | - Gregory E. Crawford
- Center for Genomic and Computational Biology, Duke University Medical Center, Durham, NC 27710, USA,Department of Pediatrics, Division of Medical Genetics, Duke University Medical Center, Durham, NC 27710, USA
| | - Kenneth D. Poss
- Department of Cell Biology, Duke University Medical Center, Durham, NC 27710, USA,Duke Regeneration Center, Duke University, Durham, NC 27710, USA,Authors for correspondence (; )
| | - Jingli Cao
- Cardiovascular Research Institute, Weill Cornell Medicine, 1300 York Avenue, New York, NY 10021, USA,Department of Cell and Developmental Biology, Weill Cornell Medicine, 1300 York Avenue, New York, NY 10021, USA,Authors for correspondence (; )
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8
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Hildebrandt K, Kolb D, Klöppel C, Kaspar P, Wittling F, Hartwig O, Federspiel J, Findji I, Walldorf U. Regulatory modules mediating the complex neural expression patterns of the homeobrain gene during Drosophila brain development. Hereditas 2022; 159:2. [PMID: 34983686 PMCID: PMC8728971 DOI: 10.1186/s41065-021-00218-5] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/11/2021] [Accepted: 12/10/2021] [Indexed: 12/02/2022] Open
Abstract
BACKGROUND The homeobox gene homeobrain (hbn) is located in the 57B region together with two other homeobox genes, Drosophila Retinal homeobox (DRx) and orthopedia (otp). All three genes encode transcription factors with important functions in brain development. Hbn mutants are embryonic lethal and characterized by a reduction in the anterior protocerebrum, including the mushroom bodies, and a loss of the supraoesophageal brain commissure. RESULTS In this study we conducted a detailed expression analysis of Hbn in later developmental stages. In the larval brain, Hbn is expressed in all type II lineages and the optic lobes, including the medulla and lobula plug. The gene is expressed in the cortex of the medulla and the lobula rim in the adult brain. We generated a new hbnKOGal4 enhancer trap strain by reintegrating Gal4 in the hbn locus through gene targeting, which reflects the complete hbn expression during development. Eight different enhancer-Gal4 strains covering 12 kb upstream of hbn, the two large introns and 5 kb downstream of the gene, were established and hbn expression was investigated. We characterized several enhancers that drive expression in specific areas of the brain throughout development, from embryo to the adulthood. Finally, we generated deletions of four of these enhancer regions through gene targeting and analysed their effects on the expression and function of hbn. CONCLUSION The complex expression of Hbn in the developing brain is regulated by several specific enhancers within the hbn locus. Each enhancer fragment drives hbn expression in several specific cell lineages, and with largely overlapping patterns, suggesting the presence of shadow enhancers and enhancer redundancy. Specific enhancer deletion strains generated by gene targeting display developmental defects in the brain. This analysis opens an avenue for a deeper analysis of hbn regulatory elements in the future.
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Affiliation(s)
- Kirsten Hildebrandt
- Developmental Biology, Saarland University, Building 61, 66421, Homburg/Saar, Germany
| | - Dieter Kolb
- Developmental Biology, Saarland University, Building 61, 66421, Homburg/Saar, Germany
| | - Christine Klöppel
- Developmental Biology, Saarland University, Building 61, 66421, Homburg/Saar, Germany
| | - Petra Kaspar
- Developmental Biology, Saarland University, Building 61, 66421, Homburg/Saar, Germany
- Present address: COS Heidelberg, University of Heidelberg, Im Neuenheimer Feld 230, 69120, Heidelberg, Germany
| | - Fabienne Wittling
- Developmental Biology, Saarland University, Building 61, 66421, Homburg/Saar, Germany
- Present address: Hemholtz Institute for Pharmaceutical Research Saarland (HIPS), Saarland University, Building E8.1, 66123, Saarbrücken, Germany
| | - Olga Hartwig
- Developmental Biology, Saarland University, Building 61, 66421, Homburg/Saar, Germany
- Present address: Hemholtz Institute for Pharmaceutical Research Saarland (HIPS), Saarland University, Building E8.1, 66123, Saarbrücken, Germany
| | - Jannic Federspiel
- Developmental Biology, Saarland University, Building 61, 66421, Homburg/Saar, Germany
| | - India Findji
- Developmental Biology, Saarland University, Building 61, 66421, Homburg/Saar, Germany
| | - Uwe Walldorf
- Developmental Biology, Saarland University, Building 61, 66421, Homburg/Saar, Germany.
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9
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Abstract
Shadow enhancers are seemingly redundant transcriptional cis-regulatory elements that regulate the same gene and drive overlapping expression patterns. Recent studies have shown that shadow enhancers are remarkably abundant and control most developmental gene expression in both invertebrates and vertebrates, including mammals. Shadow enhancers might provide an important mechanism for buffering gene expression against mutations in non-coding regulatory regions of genes implicated in human disease. Technological advances in genome editing and live imaging have shed light on how shadow enhancers establish precise gene expression patterns and confer phenotypic robustness. Shadow enhancers can interact in complex ways and may also help to drive the formation of transcriptional hubs within the nucleus. Despite their apparent redundancy, the prevalence and evolutionary conservation of shadow enhancers underscore their key role in emerging metazoan gene regulatory networks.
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10
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Exelby K, Herrera-Delgado E, Perez LG, Perez-Carrasco R, Sagner A, Metzis V, Sollich P, Briscoe J. Precision of tissue patterning is controlled by dynamical properties of gene regulatory networks. Development 2021; 148:dev197566. [PMID: 33547135 PMCID: PMC7929933 DOI: 10.1242/dev.197566] [Citation(s) in RCA: 22] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/06/2020] [Accepted: 01/14/2021] [Indexed: 12/31/2022]
Abstract
During development, gene regulatory networks allocate cell fates by partitioning tissues into spatially organised domains of gene expression. How the sharp boundaries that delineate these gene expression patterns arise, despite the stochasticity associated with gene regulation, is poorly understood. We show, in the vertebrate neural tube, using perturbations of coding and regulatory regions, that the structure of the regulatory network contributes to boundary precision. This is achieved, not by reducing noise in individual genes, but by the configuration of the network modulating the ability of stochastic fluctuations to initiate gene expression changes. We use a computational screen to identify network properties that influence boundary precision, revealing two dynamical mechanisms by which small gene circuits attenuate the effect of noise in order to increase patterning precision. These results highlight design principles of gene regulatory networks that produce precise patterns of gene expression.
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Affiliation(s)
- Katherine Exelby
- Developmental Dynamics Laboratory, The Francis Crick Institute, 1 Midland Road, London NW1 1AT, UK
| | - Edgar Herrera-Delgado
- Developmental Dynamics Laboratory, The Francis Crick Institute, 1 Midland Road, London NW1 1AT, UK
- Department of Mathematics, King's College London, Strand, London WC2R 2LS, UK
- Genetics and Developmental Biology Unit, Institut Curie, 26 Rue d'Ulm, Paris 75005, France
| | - Lorena Garcia Perez
- Developmental Dynamics Laboratory, The Francis Crick Institute, 1 Midland Road, London NW1 1AT, UK
| | | | - Andreas Sagner
- Developmental Dynamics Laboratory, The Francis Crick Institute, 1 Midland Road, London NW1 1AT, UK
- School of Medical Sciences, Faculty of Biology, Medicine and Health, University of Manchester, Manchester M13 9PL, United Kingdom
| | - Vicki Metzis
- Developmental Dynamics Laboratory, The Francis Crick Institute, 1 Midland Road, London NW1 1AT, UK
- Faculty of Medicine, Institute of Clinical Sciences, Institute of Clinical Sciences, Imperial College London, London W12 0NN, UK
| | - Peter Sollich
- Department of Mathematics, King's College London, Strand, London WC2R 2LS, UK
- Faculty of Physics, Institute for Theoretical Physics, Georg-August-University Göttingen, Friedrich-Hund-Platz 1, 37077 Göttingen, Germany
| | - James Briscoe
- Developmental Dynamics Laboratory, The Francis Crick Institute, 1 Midland Road, London NW1 1AT, UK
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11
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Irizarry J, Stathopoulos A. Dynamic patterning by morphogens illuminated by cis-regulatory studies. Development 2021; 148:148/2/dev196113. [PMID: 33472851 DOI: 10.1242/dev.196113] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
Morphogen concentration changes in space as well as over time during development. However, how these dynamics are interpreted by cells to specify fate is not well understood. Here, we focus on two morphogens: the maternal transcription factors Bicoid and Dorsal, which directly regulate target genes to pattern Drosophila embryos. The actions of these factors at enhancers has been thoroughly dissected and provides a rich platform for understanding direct input by morphogens and their changing roles over time. Importantly, Bicoid and Dorsal do not work alone; we also discuss additional inputs that work with morphogens to control spatiotemporal gene expression in embryos.
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Affiliation(s)
- Jihyun Irizarry
- California Institute of Technology, Division of Biology and Biological Engineering, 1200 East California Blvd., Pasadena, CA 91125, USA
| | - Angelike Stathopoulos
- California Institute of Technology, Division of Biology and Biological Engineering, 1200 East California Blvd., Pasadena, CA 91125, USA
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12
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Waymack R, Fletcher A, Enciso G, Wunderlich Z. Shadow enhancers can suppress input transcription factor noise through distinct regulatory logic. eLife 2020; 9:59351. [PMID: 32804082 PMCID: PMC7556877 DOI: 10.7554/elife.59351] [Citation(s) in RCA: 24] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/27/2020] [Accepted: 08/14/2020] [Indexed: 12/26/2022] Open
Abstract
Shadow enhancers, groups of seemingly redundant enhancers, are found in a wide range of organisms and are critical for robust developmental patterning. However, their mechanism of action is unknown. We hypothesized that shadow enhancers drive consistent expression levels by buffering upstream noise through a separation of transcription factor (TF) inputs at the individual enhancers. By measuring the transcriptional dynamics of several Kruppel shadow enhancer configurations in live Drosophila embryos, we showed that individual member enhancers act largely independently. We found that TF fluctuations are an appreciable source of noise that the shadow enhancer pair can better buffer than duplicated enhancers. The shadow enhancer pair is also uniquely able to maintain low levels of expression noise across a wide range of temperatures. A stochastic model demonstrated the separation of TF inputs is sufficient to explain these findings. Our results suggest the widespread use of shadow enhancers is partially due to their noise suppressing ability. In all higher organisms, life begins with a single cell. During the early stages of development, this single cell grows and divides multiple times to develop into the many different kinds of cells that make up an organism. This is a highly regulated process during which cells receive instructions telling them what kind of cell to become. These instructions are relayed via genes, and a particular combination of activated genes determines the cell’s fate. Specific pieces of DNA, known as enhancers, act as switches that control when and where genes are active, while so-called shadow enhancers are found in groups and work together to turn on the same gene in a similar way. Shadow enhancers are often active during the early stages of life to direct the formation of specialized cells in different parts of the body. But so far, it has been unclear why it is beneficial to the divide the role of activating genes across several shadow enhancers rather than a single one. Here, Waymack et al. examined shadow enhancers around a gene called Kruppel in embryos of the fruit fly Drosophila melanogaster. Manipulating the shadow enhancers showed that they help to make gene activity more resistant to changes. Factors such as fluctuations in temperature have different effects on each shadow enhancer. Having several shadow enhancers working together ensures that, whatever happens, the right genes still get activated. For genes like Kruppel, which are key for healthy development, the ability to withstand unexpected changes is a valuable evolutionary benefit. The study of Waymack et al. reveals why shadow enhancers are involved in the regulation of many genes, which may help to better understand developmental defects. Many conditions caused by such defects are influenced by both genetics and the environment. Genetic illnesses can vary in severity, which may be related to the roles of shadow enhancers. As such, studying shadow enhancers could lead to new approaches for treating genetic diseases.
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Affiliation(s)
- Rachel Waymack
- Department of Developmental and Cell Biology, University of California, Irvine, Irvine, United States
| | - Alvaro Fletcher
- Mathematical, Computational, and Systems Biology Graduate Program, University of California, Irvine, Irvine, United States
| | - German Enciso
- Department of Developmental and Cell Biology, University of California, Irvine, Irvine, United States.,Department of Mathematics, University of California, Irvine, Irvine, United States
| | - Zeba Wunderlich
- Department of Developmental and Cell Biology, University of California, Irvine, Irvine, United States
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13
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Kuroiwa A. Enhancers, development, and evolution. Dev Growth Differ 2020; 62:265-268. [DOI: 10.1111/dgd.12683] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/28/2020] [Revised: 05/24/2020] [Accepted: 05/24/2020] [Indexed: 12/25/2022]
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