1
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Andreas E, Cummins B, Gedeon T. Quantifying robustness of the gap gene network. J Theor Biol 2024; 580:111720. [PMID: 38211890 DOI: 10.1016/j.jtbi.2024.111720] [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: 06/02/2023] [Revised: 12/28/2023] [Accepted: 12/30/2023] [Indexed: 01/13/2024]
Abstract
Early development of Drosophila melanogaster (fruit fly) facilitated by the gap gene network has been shown to be incredibly robust, and the same patterns emerge even when the process is seriously disrupted. We investigate this robustness using a previously developed computational framework called DSGRN (Dynamic Signatures Generated by Regulatory Networks). Our mathematical innovations include the conceptual extension of this established modeling technique to enable modeling of spatially monotone environmental effects, as well as the development of a collection of graph theoretic robustness scores for network models. This allows us to rank order the robustness of network models of cellular systems where each cell contains the same genetic network topology but operates under a parameter regime that changes continuously from cell to cell. We demonstrate the power of this method by comparing the robustness of two previously introduced network models of gap gene expression along the anterior-posterior axis of the fruit fly embryo, both to each other and to a random sample of networks with same number of nodes and edges. We observe that there is a substantial difference in robustness scores between the two models. Our biological insight is that random network topologies are in general capable of reproducing complex patterns of expression, but that using measures of robustness to rank order networks permits a large reduction in hypothesis space for highly conserved systems such as developmental networks.
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Affiliation(s)
- Elizabeth Andreas
- Department of Mathematical Sciences, Montana State University, Bozeman, 59718, MT, USA.
| | - Breschine Cummins
- Department of Mathematical Sciences, Montana State University, Bozeman, 59718, MT, USA
| | - Tomáš Gedeon
- Department of Mathematical Sciences, Montana State University, Bozeman, 59718, MT, USA
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2
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Moudgil A, Sobti RC, Kaur T. In-silico identification and comparison of transcription factor binding sites cluster in anterior-posterior patterning genes in Drosophila melanogaster and Tribolium castaneum. PLoS One 2023; 18:e0290035. [PMID: 37590227 PMCID: PMC10434971 DOI: 10.1371/journal.pone.0290035] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/16/2023] [Accepted: 07/26/2023] [Indexed: 08/19/2023] Open
Abstract
The cis-regulatory data that help in transcriptional regulation is arranged into modular pieces of a few hundred base pairs called CRMs (cis-regulatory modules) and numerous binding sites for multiple transcription factors are prominent characteristics of these cis-regulatory modules. The present study was designed to localize transcription factor binding site (TFBS) clusters on twelve Anterior-posterior (A-P) genes in Tribolium castaneum and compare them to their orthologous gene enhancers in Drosophila melanogaster. Out of the twelve A-P patterning genes, six were gap genes (Kruppel, Knirps, Tailless, Hunchback, Giant, and Caudal) and six were pair rule genes (Hairy, Runt, Even-skipped, Fushi-tarazu, Paired, and Odd-skipped). The genes along with 20 kb upstream and downstream regions were scanned for TFBS clusters using the Motif Cluster Alignment Search Tool (MCAST), a bioinformatics tool that looks for set of nucleotide sequences for statistically significant clusters of non-overlapping occurrence of a given set of motifs. The motifs used in the current study were Hunchback, Caudal, Giant, Kruppel, Knirps, and Even-skipped. The results of the MCAST analysis revealed the maximum number of TFBS for Hunchback, Knirps, Caudal, and Kruppel in both D. melanogaster and T. castaneum, while Bicoid TFBS clusters were found only in D. melanogaster. The size of all the predicted TFBS clusters was less than 1kb in both insect species. These sequences revealed more transversional sites (Tv) than transitional sites (Ti) and the average Ti/Tv ratio was 0.75.
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Affiliation(s)
- Anshika Moudgil
- Department of Zoology, DAV University, Jalandhar, Punjab, India
| | | | - Tejinder Kaur
- Department of Zoology, DAV University, Jalandhar, Punjab, India
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3
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Thermodynamic Modelling of Transcriptional Control: A Sensitivity Analysis. MATHEMATICS 2022. [DOI: 10.3390/math10132169] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
Modelling is a tool used to decipher the biochemical mechanisms involved in transcriptional control. Experimental evidence in genetics is usually supported by theoretical models in order to evaluate the effects of all the possible interactions that can occur in these complicated processes. Models derived from the thermodynamic method are critical in this labour because they are able to take into account multiple mechanisms operating simultaneously at the molecular micro-scale and relate them to transcriptional initiation at the tissular macro-scale. This work is devoted to adapting computational techniques to this context in order to theoretically evaluate the role played by several biochemical mechanisms. The interest of this theoretical analysis relies on the fact that it can be contrasted against those biological experiments where the response to perturbations in the transcriptional machinery environment is evaluated in terms of genetically activated/repressed regions. The theoretical reproduction of these experiments leads to a sensitivity analysis whose results are expressed in terms of the elasticity of a threshold function determining those activated/repressed regions. The study of this elasticity function in thermodynamic models already proposed in the literature reveals that certain modelling approaches can alter the balance between the biochemical mechanisms considered, and this can cause false/misleading outcomes. The reevaluation of classical thermodynamic models gives us a more accurate and complete picture of the interactions involved in gene regulation and transcriptional control, which enables more specific predictions. This sensitivity approach provides a definite advantage in the interpretation of a wide range of genetic experimental results.
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4
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Lee KM, Linskens AM, Doe CQ. Hunchback activates Bicoid in Pair1 neurons to regulate synapse number and locomotor circuit function. Curr Biol 2022; 32:2430-2441.e3. [PMID: 35512697 PMCID: PMC9178783 DOI: 10.1016/j.cub.2022.04.025] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/17/2022] [Revised: 04/01/2022] [Accepted: 04/08/2022] [Indexed: 12/26/2022]
Abstract
Neural circuit function underlies cognition, sensation, and behavior. Proper circuit assembly depends on the identity of the neurons in the circuit (gene expression, morphology, synapse targeting, and biophysical properties). Neuronal identity is established by spatial and temporal patterning mechanisms, but little is known about how these mechanisms drive circuit formation in postmitotic neurons. Temporal patterning involves the sequential expression of transcription factors (TFs) in neural progenitors to diversify neuronal identity, in part through the initial expression of homeodomain TF combinations. Here, we address the role of the Drosophila temporal TF Hunchback and the homeodomain TF Bicoid in the assembly of the Pair1 (SEZ_DN1) descending neuron locomotor circuit, which promotes larval pausing and head casting. We find that both Hunchback and Bicoid are expressed in larval Pair1 neurons, Hunchback activates Bicoid in Pair1 (opposite of their embryonic relationship), and the loss of Hunchback function or Bicoid function from Pair1 leads to ectopic presynapse numbers in Pair1 axons and an increase in Pair1-induced pausing behavior. These phenotypes are highly specific, as the loss of Bicoid or Hunchback has no effect on Pair1 neurotransmitter identity, dendrite morphology, or axonal morphology. Importantly, the loss of Hunchback or Bicoid in Pair1 leads to the addition of new circuit partners that may underlie the exaggerated locomotor pausing behavior. These data are the first to show a role for Bicoid outside of embryonic patterning and the first to demonstrate a cell-autonomous role for Hunchback and Bicoid in interneuron synapse targeting and locomotor behavior.
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Affiliation(s)
- Kristen M Lee
- Howard Hughes Medical Institute, Institute of Neuroscience, University of Oregon, Eugene, OR 97403, USA.
| | - Amanda M Linskens
- Howard Hughes Medical Institute, Institute of Neuroscience, University of Oregon, Eugene, OR 97403, USA
| | - Chris Q Doe
- Howard Hughes Medical Institute, Institute of Neuroscience, University of Oregon, Eugene, OR 97403, USA.
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5
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Fernandes G, Tran H, Andrieu M, Diaw Y, Perez Romero C, Fradin C, Coppey M, Walczak AM, Dostatni N. Synthetic reconstruction of the hunchback promoter specifies the role of Bicoid, Zelda and Hunchback in the dynamics of its transcription. eLife 2022; 11:74509. [PMID: 35363606 PMCID: PMC8975551 DOI: 10.7554/elife.74509] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/07/2021] [Accepted: 03/10/2022] [Indexed: 11/23/2022] Open
Abstract
For over 40 years, the Bicoid-hunchback (Bcd-hb) system in the fruit fly embryo has been used as a model to study how positional information in morphogen concentration gradients is robustly translated into step-like responses. A body of quantitative comparisons between theory and experiment have since questioned the initial paradigm that the sharp hb transcription pattern emerges solely from diffusive biochemical interactions between the Bicoid transcription factor and the gene promoter region. Several alternative mechanisms have been proposed, such as additional sources of positional information, positive feedback from Hb proteins or out-of-equilibrium transcription activation. By using the MS2-MCP RNA-tagging system and analysing in real time, the transcription dynamics of synthetic reporters for Bicoid and/or its two partners Zelda and Hunchback, we show that all the early hb expression pattern features and temporal dynamics are compatible with an equilibrium model with a short decay length Bicoid activity gradient as a sole source of positional information. Meanwhile, Bicoid’s partners speed-up the process by different means: Zelda lowers the Bicoid concentration threshold required for transcriptional activation while Hunchback reduces burstiness and increases the polymerase firing rate.
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Affiliation(s)
- Gonçalo Fernandes
- Institut Curie, Université PSL, Sorbonne Université, CNRS, Nuclear Dynamics, Paris, France
| | - Huy Tran
- Institut Curie, Université PSL, Sorbonne Université, CNRS, Nuclear Dynamics, Paris, France.,Laboratoire de Physique de l'École Normale Supérieure, CNRS, Université PSL, Sorbonne Université and Université de Paris, Paris, France
| | - Maxime Andrieu
- Institut Curie, Université PSL, Sorbonne Université, CNRS, Nuclear Dynamics, Paris, France
| | - Youssoupha Diaw
- Institut Curie, Université PSL, Sorbonne Université, CNRS, Nuclear Dynamics, Paris, France
| | - Carmina Perez Romero
- Department of Biochemistry and Biomedical Sciences, McMaster University, Hamilton, Canada
| | - Cécile Fradin
- Department of Biochemistry and Biomedical Sciences, McMaster University, Hamilton, Canada.,Department of Physics and Astronomy, McMaster University, Hamilton, Canada
| | - Mathieu Coppey
- Institut Curie, Université PSL, Sorbonne Université, CNRS UMR168, Laboratoire Physico Chimie Curie, Paris, France
| | - Aleksandra M Walczak
- Laboratoire de Physique de l'École Normale Supérieure, CNRS, Université PSL, Sorbonne Université and Université de Paris, Paris, France
| | - Nathalie Dostatni
- Institut Curie, Université PSL, Sorbonne Université, CNRS, Nuclear Dynamics, Paris, France
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6
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Onal P, Gunasinghe HI, Umezawa KY, Zheng M, Ling J, Azeez L, Dalmeus A, Tazin T, Small S. Suboptimal Intermediates Underlie Evolution of the Bicoid Homeodomain. Mol Biol Evol 2021; 38:2179-2190. [PMID: 33599280 PMCID: PMC8136501 DOI: 10.1093/molbev/msab051] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023] Open
Abstract
Changes in regulatory networks generate materials for evolution to create phenotypic diversity. For transcription networks, multiple studies have shown that alterations in binding sites of cis-regulatory elements correlate well with the gain or loss of specific features of the body plan. Less is known about alterations in the amino acid sequences of the transcription factors (TFs) that bind these elements. Here we study the evolution of Bicoid (Bcd), a homeodomain (HD) protein that is critical for anterior embryo patterning in Drosophila. The ancestor of Bcd (AncBcd) emerged after a duplication of a Zerknullt (Zen)-like ancestral protein (AncZB) in a suborder of flies. AncBcd diverged from AncZB, gaining novel transcriptional and translational activities. We focus on the evolution of the HD of AncBcd, which binds to DNA and RNA, and is comprised of four subdomains: an N-terminal arm (NT) and three helices; H1, H2, and Recognition Helix (RH). Using chimeras of subdomains and gene rescue assays in Drosophila, we show that robust patterning activity of the Bcd HD (high frequency rescue to adulthood) is achieved only when amino acid substitutions in three separate subdomains (NT, H1, and RH) are combined. Other combinations of subdomains also yield full rescue, but with lower penetrance, suggesting alternative suboptimal activities. Our results suggest a multistep pathway for the evolution of the Bcd HD that involved intermediate HD sequences with suboptimal activities, which constrained and enabled further evolutionary changes. They also demonstrate critical epistatic forces that contribute to the robust function of a DNA-binding domain.
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Affiliation(s)
- Pinar Onal
- Department of Biology, New York University, New York, NY, USA
| | | | | | - Michael Zheng
- Department of Biology, New York University, New York, NY, USA
| | - Jia Ling
- Department of Biology, New York University, New York, NY, USA
| | - Leen Azeez
- Department of Biology, New York University, New York, NY, USA
| | - Anecine Dalmeus
- Department of Biology, New York University, New York, NY, USA
| | - Tasmima Tazin
- Department of Biology, New York University, New York, NY, USA
| | - Stephen Small
- Department of Biology, New York University, New York, NY, USA
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7
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Nakao H. Early embryonic development of Bombyx. Dev Genes Evol 2021; 231:95-107. [PMID: 34296338 DOI: 10.1007/s00427-021-00679-8] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/03/2020] [Accepted: 07/09/2021] [Indexed: 11/25/2022]
Abstract
Decades have passed since the early molecular embryogenesis of Drosophila melanogaster was outlined. During this period, the molecular mechanisms underlying early embryonic development in other insects, particularly the flour beetle, Tribolium castaneum, have been described in more detail. The information clearly demonstrated that Drosophila embryogenesis is not representative of other insects and has highly distinctive characteristics. At the same time, this new data has been gradually clarifying ancestral operating mechanisms. The silk moth, Bombyx mori, is a lepidopteran insect and, as a representative of the order, has many unique characteristics found in early embryonic development that have not been identified in other insect groups. Herein, some of these characteristics are introduced and discussed in the context of recent information obtained from other insects.
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Affiliation(s)
- Hajime Nakao
- Insect Genome Research and Engineering Unit, Division of Applied Genetics, Institute of Agrobiological Sciences, National Agriculture and Food Research Organization (NARO), 1-2 Oowashi, Tsukuba, Ibaraki, 305-8634, Japan.
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8
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Profile of Claude Desplan. Proc Natl Acad Sci U S A 2021; 118:2110547118. [PMID: 34244438 DOI: 10.1073/pnas.2110547118] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
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9
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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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10
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Makashov AA, Myasnikova EM, Spirov AV. Fuzzy Linguistic Modeling of the Regulation of Drosophila Segmentation Genes. Biophysics (Nagoya-shi) 2021. [DOI: 10.1134/s0006350921010073] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022] Open
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11
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A sensitive mNeonGreen reporter system to measure transcriptional dynamics in Drosophila development. Commun Biol 2020; 3:663. [PMID: 33184447 PMCID: PMC7665215 DOI: 10.1038/s42003-020-01375-5] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/05/2019] [Accepted: 10/08/2020] [Indexed: 12/20/2022] Open
Abstract
The gene regulatory network governing anterior–posterior axis formation in Drosophila is a well-established paradigm to study transcription in developmental biology. The rapid temporal dynamics of gene expression during early stages of development, however, are difficult to track with standard techniques. We optimized the bright and fast-maturing fluorescent protein mNeonGreen as a real-time, quantitative reporter of enhancer expression. We derive enhancer activity from the reporter fluorescence dynamics with high spatial and temporal resolution, using a robust reconstruction algorithm. By comparing our results with data obtained with the established MS2-MCP system, we demonstrate the higher detection sensitivity of our reporter. We used the reporter to quantify the activity of variants of a simple synthetic enhancer, and observe increased activity upon reduction of enhancer–promoter distance or addition of binding sites for the pioneer transcription factor Zelda. Our reporter system constitutes a powerful tool to study spatio-temporal gene expression dynamics in live embryos. Ceolin et al. optimise the fluorescent protein mNeonGreen to generate a reporter to measure enhancer expression in living Drosophila embryos. They also find that reduced enhancer–promoter distance or addition of binding sites for the pioneer transcription factor Zelda increases enhancer activity.
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12
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Abstract
Key discoveries in Drosophila have shaped our understanding of cellular "enhancers." With a special focus on the fly, this chapter surveys properties of these adaptable cis-regulatory elements, whose actions are critical for the complex spatial/temporal transcriptional regulation of gene expression in metazoa. The powerful combination of genetics, molecular biology, and genomics available in Drosophila has provided an arena in which the developmental role of enhancers can be explored. Enhancers are characterized by diverse low- or high-throughput assays, which are challenging to interpret, as not all of these methods of identifying enhancers produce concordant results. As a model metazoan, the fly offers important advantages to comprehensive analysis of the central functions that enhancers play in gene expression, and their critical role in mediating the production of phenotypes from genotype and environmental inputs. A major challenge moving forward will be obtaining a quantitative understanding of how these cis-regulatory elements operate in development and disease.
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Affiliation(s)
- Stephen Small
- Department of Biology, Developmental Systems Training Program, New York University, 10003 and
| | - David N Arnosti
- Department of Biochemistry and Molecular Biology, Michigan State University, East Lansing, Michigan 48824
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13
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Tran H, Walczak AM, Dostatni N. Constraints and limitations on the transcriptional response downstream of the Bicoid morphogen gradient. Curr Top Dev Biol 2020; 137:119-142. [PMID: 32143741 DOI: 10.1016/bs.ctdb.2019.12.002] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 03/06/2023]
Abstract
The regulation of the hunchback promoter expression by the maternal Bicoid gradient has been studied as a model system in development for many years. Yet, at the level of quantitative agreement between data and theoretical models, even the first step of this regulation, transcription, continues to be challenging. This situation is slowly progressing, thanks to quantitative live-imaging techniques coupled to advanced statistical data analysis and modeling. Here, we outline the current state of our knowledge of this apparently "simple" step, highlighting the newly appreciated role of bursty transcription dynamics and its regulation.
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Affiliation(s)
- Huy Tran
- Institut Curie, PSL Research University, CNRS, Sorbonne Université, Nuclear Dynamics, Paris, France; Ecole Normale Supérieure, PSL Research University, CNRS, Sorbonne Université, Laboratoire de Physique, Paris, France
| | - Aleksandra M Walczak
- Ecole Normale Supérieure, PSL Research University, CNRS, Sorbonne Université, Laboratoire de Physique, Paris, France.
| | - Nathalie Dostatni
- Institut Curie, PSL Research University, CNRS, Sorbonne Université, Nuclear Dynamics, Paris, France.
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14
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Abstract
Spatially distributed signaling molecules, known as morphogens, provide spatial information during development. A host of different morphogens have now been identified, from subcellular gradients through to morphogens that act across a whole embryo. These gradients form over a wide-range of timescales, from seconds to hours, and their time windows for interpretation are also highly variable; the processes of morphogen gradient formation and interpretation are highly dynamic. The morphogen Bicoid (Bcd), present in the early Drosophila embryo, is essential for setting up the future Drosophila body segments. Due to its accessibility for both genetic perturbations and imaging, this system has provided key insights into how precise patterning can occur within a highly dynamic system. Here, we review the temporal scales of Bcd gradient formation and interpretation. In particular, we discuss the quantitative evidence for different models of Bcd gradient formation, outline the time windows for Bcd interpretation, and describe how Bcd temporally adapts its own ability to be interpreted. The utilization of temporal information in morphogen readout may provide crucial inputs to ensure precise spatial patterning, particularly in rapidly developing systems.
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15
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Classification-Based Inference of Dynamical Models of Gene Regulatory Networks. G3-GENES GENOMES GENETICS 2019; 9:4183-4195. [PMID: 31624138 PMCID: PMC6893186 DOI: 10.1534/g3.119.400603] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 12/05/2022]
Abstract
Cell-fate decisions during development are controlled by densely interconnected gene regulatory networks (GRNs) consisting of many genes. Inferring and predictively modeling these GRNs is crucial for understanding development and other physiological processes. Gene circuits, coupled differential equations that represent gene product synthesis with a switch-like function, provide a biologically realistic framework for modeling the time evolution of gene expression. However, their use has been limited to smaller networks due to the computational expense of inferring model parameters from gene expression data using global non-linear optimization. Here we show that the switch-like nature of gene regulation can be exploited to break the gene circuit inference problem into two simpler optimization problems that are amenable to computationally efficient supervised learning techniques. We present FIGR (Fast Inference of Gene Regulation), a novel classification-based inference approach to determining gene circuit parameters. We demonstrate FIGR’s effectiveness on synthetic data generated from random gene circuits of up to 50 genes as well as experimental data from the gap gene system of Drosophila melanogaster, a benchmark for inferring dynamical GRN models. FIGR is faster than global non-linear optimization by a factor of 600 and its computational complexity scales much better with GRN size. On a practical level, FIGR can accurately infer the biologically realistic gap gene network in under a minute on desktop-class hardware instead of requiring hours of parallel computing. We anticipate that FIGR would enable the inference of much larger biologically realistic GRNs than was possible before.
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16
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Garcia HG, Berrocal A, Kim YJ, Martini G, Zhao J. Lighting up the central dogma for predictive developmental biology. Curr Top Dev Biol 2019; 137:1-35. [PMID: 32143740 DOI: 10.1016/bs.ctdb.2019.10.010] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
Although the last 30years have witnessed the mapping of the wiring diagrams of the gene regulatory networks that dictate cell fate and animal body plans, specific understanding building on such network diagrams that shows how DNA regulatory regions control gene expression lags far behind. These networks have yet to yield the predictive power necessary to, for example, calculate how the concentration dynamics of input transcription factors and DNA regulatory sequence prescribes output patterns of gene expression that, in turn, determine body plans themselves. Here, we argue that reaching a predictive understanding of developmental decision-making calls for an interplay between theory and experiment aimed at revealing how the regulation of the processes of the central dogma dictate network connections and how network topology guides cells toward their ultimate developmental fate. To make this possible, it is crucial to break free from the snapshot-based understanding of embryonic development facilitated by fixed-tissue approaches and embrace new technologies that capture the dynamics of developmental decision-making at the single cell level, in living embryos.
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Affiliation(s)
- Hernan G Garcia
- Department of Molecular and Cell Biology, University of California at Berkeley, Berkeley, CA, United States; Department of Physics, University of California at Berkeley, Berkeley, CA, United States; Biophysics Graduate Group, University of California at Berkeley, Berkeley, CA, United States; Quantitative Biosciences-QB3, University of California at Berkeley, Berkeley, CA, United States.
| | - Augusto Berrocal
- Department of Molecular and Cell Biology, University of California at Berkeley, Berkeley, CA, United States
| | - Yang Joon Kim
- Biophysics Graduate Group, University of California at Berkeley, Berkeley, CA, United States
| | - Gabriella Martini
- Department of Molecular and Cell Biology, University of California at Berkeley, Berkeley, CA, United States
| | - Jiaxi Zhao
- Department of Physics, University of California at Berkeley, Berkeley, CA, United States
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17
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Repele A, Krueger S, Bhattacharyya T, Tuineau MY. The regulatory control of Cebpa enhancers and silencers in the myeloid and red-blood cell lineages. PLoS One 2019; 14:e0217580. [PMID: 31181110 PMCID: PMC6557489 DOI: 10.1371/journal.pone.0217580] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/18/2019] [Accepted: 05/14/2019] [Indexed: 12/31/2022] Open
Abstract
Cebpa encodes a transcription factor (TF) that plays an instructive role in the development of multiple myeloid lineages. The expression of Cebpa itself is finely modulated, as Cebpa is expressed at high and intermediate levels in neutrophils and macrophages respectively and downregulated in non-myeloid lineages. The cis-regulatory logic underlying the lineage-specific modulation of Cebpa's expression level is yet to be fully characterized. Previously, we had identified 6 new cis-regulatory modules (CRMs) in a 78kb region surrounding Cebpa. We had also inferred the TFs that regulate each CRM by fitting a sequence-based thermodynamic model to a comprehensive reporter activity dataset. Here, we report the cis-regulatory logic of Cebpa CRMs at the resolution of individual binding sites. We tested the binding sites and functional roles of inferred TFs by designing and constructing mutated CRMs and comparing theoretical predictions of their activity against empirical measurements in a myeloid cell line. The enhancers were confirmed to be activated by combinations of PU.1, C/EBP family TFs, Egr1, and Gfi1 as predicted by the model. We show that silencers repress the activity of the proximal promoter in a dominant manner in G1ME cells, which are derived from the red-blood cell lineage. Dominant repression in G1ME cells can be traced to binding sites for GATA and Myb, a motif shared by all of the silencers. Finally, we demonstrate that GATA and Myb act redundantly to silence the proximal promoter. These results indicate that dominant repression is a novel mechanism for resolving hematopoietic lineages. Furthermore, Cebpa has a fail-safe cis-regulatory architecture, featuring several functionally similar CRMs, each of which contains redundant binding sites for multiple TFs. Lastly, by experimentally demonstrating the predictive ability of our sequence-based thermodynamic model, this work highlights the utility of this computational approach for understanding mammalian gene regulation.
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Affiliation(s)
- Andrea Repele
- Department of Biology, University of North Dakota, Grand Forks, ND, United States of America
| | - Shawn Krueger
- Department of Biology, University of North Dakota, Grand Forks, ND, United States of America
| | - Tapas Bhattacharyya
- Department of Biology, University of North Dakota, Grand Forks, ND, United States of America
| | - Michelle Y Tuineau
- Department of Biology, University of North Dakota, Grand Forks, ND, United States of America
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18
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Lucas T, Tran H, Perez Romero CA, Guillou A, Fradin C, Coppey M, Walczak AM, Dostatni N. 3 minutes to precisely measure morphogen concentration. PLoS Genet 2018; 14:e1007676. [PMID: 30365533 PMCID: PMC6221364 DOI: 10.1371/journal.pgen.1007676] [Citation(s) in RCA: 24] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/26/2018] [Revised: 11/07/2018] [Accepted: 09/05/2018] [Indexed: 11/18/2022] Open
Abstract
Morphogen gradients provide concentration-dependent positional information along polarity axes. Although the dynamics of the establishment of these gradients is well described, precision and noise in the downstream activation processes remain elusive. A simple paradigm to address these questions is the Bicoid morphogen gradient that elicits a rapid step-like transcriptional response in young fruit fly embryos. Focusing on the expression of the major Bicoid target, hunchback (hb), at the onset of zygotic transcription, we used the MS2-MCP approach which combines fluorescent labeling of nascent mRNA with live imaging at high spatial and temporal resolution. Removing 36 putative Zelda binding sites unexpectedly present in the original MS2 reporter, we show that the 750 bp of the hb promoter are sufficient to recapitulate endogenous expression at the onset of zygotic transcription. After each mitosis, in the anterior, expression is turned on to rapidly reach a plateau with all nuclei expressing the reporter. Consistent with a Bicoid dose-dependent activation process, the time period required to reach the plateau increases with the distance to the anterior pole. Despite the challenge imposed by frequent mitoses and high nuclei-to-nuclei variability in transcription kinetics, it only takes 3 minutes at each interphase for the MS2 reporter loci to distinguish subtle differences in Bicoid concentration and establish a steadily positioned and steep (Hill coefficient ~ 7) expression boundary. Modeling based on the cooperativity between the 6 known Bicoid binding sites in the hb promoter region, assuming rate limiting concentrations of the Bicoid transcription factor at the boundary, is able to capture the observed dynamics of pattern establishment but not the steepness of the boundary. This suggests that a simple model based only on the cooperative binding of Bicoid is not sufficient to describe the spatiotemporal dynamics of early hb expression.
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Affiliation(s)
- Tanguy Lucas
- Institut Curie, PSL Research University, CNRS, Sorbonne Université, Nuclear Dynamics, Paris, France
| | - Huy Tran
- Institut Curie, PSL Research University, CNRS, Sorbonne Université, Nuclear Dynamics, Paris, France
- Ecole Normale Supérieure, PSL Research University, CNRS, Sorbonne Université, Physique Théorique, Paris, France
| | - Carmina Angelica Perez Romero
- Institut Curie, PSL Research University, CNRS, Sorbonne Université, Nuclear Dynamics, Paris, France
- Dept. of Physics and Astronomy, McMaster University, Hamilton, Ontario, Canada
| | - Aurélien Guillou
- Institut Curie, PSL Research University, CNRS, Sorbonne Université, Nuclear Dynamics, Paris, France
| | - Cécile Fradin
- Institut Curie, PSL Research University, CNRS, Sorbonne Université, Nuclear Dynamics, Paris, France
- Dept. of Physics and Astronomy, McMaster University, Hamilton, Ontario, Canada
| | - Mathieu Coppey
- Institut Curie, PSL Research University, CNRS, Sorbonne Université, Physico Chimie, Paris, France
| | - Aleksandra M. Walczak
- Ecole Normale Supérieure, PSL Research University, CNRS, Sorbonne Université, Physique Théorique, Paris, France
| | - Nathalie Dostatni
- Institut Curie, PSL Research University, CNRS, Sorbonne Université, Nuclear Dynamics, Paris, France
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Vincent BJ, Staller MV, Lopez-Rivera F, Bragdon MDJ, Pym ECG, Biette KM, Wunderlich Z, Harden TT, Estrada J, DePace AH. Hunchback is counter-repressed to regulate even-skipped stripe 2 expression in Drosophila embryos. PLoS Genet 2018; 14:e1007644. [PMID: 30192762 PMCID: PMC6145585 DOI: 10.1371/journal.pgen.1007644] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/06/2017] [Revised: 09/19/2018] [Accepted: 08/17/2018] [Indexed: 01/18/2023] Open
Abstract
Hunchback is a bifunctional transcription factor that can activate and repress gene expression in Drosophila development. We investigated the regulatory DNA sequence features that control Hunchback function by perturbing enhancers for one of its target genes, even-skipped (eve). While Hunchback directly represses the eve stripe 3+7 enhancer, we found that in the eve stripe 2+7 enhancer, Hunchback repression is prevented by nearby sequences-this phenomenon is called counter-repression. We also found evidence that Caudal binding sites are responsible for counter-repression, and that this interaction may be a conserved feature of eve stripe 2 enhancers. Our results alter the textbook view of eve stripe 2 regulation wherein Hb is described as a direct activator. Instead, to generate stripe 2, Hunchback repression must be counteracted. We discuss how counter-repression may influence eve stripe 2 regulation and evolution.
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Affiliation(s)
- Ben J. Vincent
- Department of Systems Biology, Harvard Medical School, Boston, Massachusetts, United States of America
| | - Max V. Staller
- Department of Systems Biology, Harvard Medical School, Boston, Massachusetts, United States of America
| | - Francheska Lopez-Rivera
- Department of Systems Biology, Harvard Medical School, Boston, Massachusetts, United States of America
| | - Meghan D. J. Bragdon
- Department of Systems Biology, Harvard Medical School, Boston, Massachusetts, United States of America
| | - Edward C. G. Pym
- Department of Systems Biology, Harvard Medical School, Boston, Massachusetts, United States of America
| | - Kelly M. Biette
- Department of Systems Biology, Harvard Medical School, Boston, Massachusetts, United States of America
| | - Zeba Wunderlich
- Department of Systems Biology, Harvard Medical School, Boston, Massachusetts, United States of America
| | - Timothy T. Harden
- Department of Systems Biology, Harvard Medical School, Boston, Massachusetts, United States of America
| | - Javier Estrada
- Department of Systems Biology, Harvard Medical School, Boston, Massachusetts, United States of America
| | - Angela H. DePace
- Department of Systems Biology, Harvard Medical School, Boston, Massachusetts, United States of America
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20
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Datta RR, Ling J, Kurland J, Ren X, Xu Z, Yucel G, Moore J, Shokri L, Baker I, Bishop T, Struffi P, Levina R, Bulyk ML, Johnston RJ, Small S. A feed-forward relay integrates the regulatory activities of Bicoid and Orthodenticle via sequential binding to suboptimal sites. Genes Dev 2018; 32:723-736. [PMID: 29764918 PMCID: PMC6004077 DOI: 10.1101/gad.311985.118] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/18/2018] [Accepted: 04/17/2018] [Indexed: 11/25/2022]
Abstract
Datta et al. define three major classes of enhancers that are differentially sensitive to binding and transcriptional activation by Bicoid (Bcd) and Orthodenticle (Otd). The specific activities of enhancers in each class are mediated by DNA motif variants preferentially bound by Bcd or Otd and the presence or absence of sites for cofactors that interact with these proteins. The K50 (lysine at amino acid position 50) homeodomain (HD) protein Orthodenticle (Otd) is critical for anterior patterning and brain and eye development in most metazoans. In Drosophila melanogaster, another K50HD protein, Bicoid (Bcd), has evolved to replace Otd's ancestral function in embryo patterning. Bcd is distributed as a long-range maternal gradient and activates transcription of a large number of target genes, including otd. Otd and Bcd bind similar DNA sequences in vitro, but how their transcriptional activities are integrated to pattern anterior regions of the embryo is unknown. Here we define three major classes of enhancers that are differentially sensitive to binding and transcriptional activation by Bcd and Otd. Class 1 enhancers are initially activated by Bcd, and activation is transferred to Otd via a feed-forward relay (FFR) that involves sequential binding of the two proteins to the same DNA motif. Class 2 enhancers are activated by Bcd and maintained by an Otd-independent mechanism. Class 3 enhancers are never bound by Bcd, but Otd binds and activates them in a second wave of zygotic transcription. The specific activities of enhancers in each class are mediated by DNA motif variants preferentially bound by Bcd or Otd and the presence or absence of sites for cofactors that interact with these proteins. Our results define specific patterning roles for Bcd and Otd and provide mechanisms for coordinating the precise timing of gene expression patterns during embryonic development.
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Affiliation(s)
- Rhea R Datta
- Center for Developmental Genetics, Department of Biology, New York University, New York, New York 10003, USA
| | - Jia Ling
- Center for Developmental Genetics, Department of Biology, New York University, New York, New York 10003, USA
| | - Jesse Kurland
- Division of Genetics, Department of Medicine, Brigham and Women's Hospital, Harvard Medical School, Boston, Massachusetts 02115, USA.,Department of Pathology, Brigham and Women's Hospital, Harvard Medical School, Boston, Massachusetts 02115, USA
| | - Xiaotong Ren
- Center for Developmental Genetics, Department of Biology, New York University, New York, New York 10003, USA
| | - Zhe Xu
- Center for Developmental Genetics, Department of Biology, New York University, New York, New York 10003, USA
| | - Gozde Yucel
- Center for Developmental Genetics, Department of Biology, New York University, New York, New York 10003, USA
| | - Jackie Moore
- Center for Developmental Genetics, Department of Biology, New York University, New York, New York 10003, USA
| | - Leila Shokri
- Division of Genetics, Department of Medicine, Brigham and Women's Hospital, Harvard Medical School, Boston, Massachusetts 02115, USA.,Department of Pathology, Brigham and Women's Hospital, Harvard Medical School, Boston, Massachusetts 02115, USA
| | - Isabel Baker
- Center for Developmental Genetics, Department of Biology, New York University, New York, New York 10003, USA
| | - Timothy Bishop
- Center for Developmental Genetics, Department of Biology, New York University, New York, New York 10003, USA
| | - Paolo Struffi
- Center for Developmental Genetics, Department of Biology, New York University, New York, New York 10003, USA
| | - Rimma Levina
- Center for Developmental Genetics, Department of Biology, New York University, New York, New York 10003, USA
| | - Martha L Bulyk
- Division of Genetics, Department of Medicine, Brigham and Women's Hospital, Harvard Medical School, Boston, Massachusetts 02115, USA.,Department of Pathology, Brigham and Women's Hospital, Harvard Medical School, Boston, Massachusetts 02115, USA
| | - Robert J Johnston
- Department of Biology, Johns Hopkins University, Baltimore, Maryland 21218, USA
| | - Stephen Small
- Center for Developmental Genetics, Department of Biology, New York University, New York, New York 10003, USA
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Aguilar-Hidalgo D, Werner S, Wartlick O, González-Gaitán M, Friedrich BM, Jülicher F. Critical Point in Self-Organized Tissue Growth. PHYSICAL REVIEW LETTERS 2018; 120:198102. [PMID: 29799239 DOI: 10.1103/physrevlett.120.198102] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/25/2017] [Revised: 02/20/2018] [Indexed: 06/08/2023]
Abstract
We present a theory of pattern formation in growing domains inspired by biological examples of tissue development. Gradients of signaling molecules regulate growth, while growth changes these graded chemical patterns by dilution and advection. We identify a critical point of this feedback dynamics, which is characterized by spatially homogeneous growth and proportional scaling of patterns with tissue length. We apply this theory to the biological model system of the developing wing of the fruit fly Drosophila melanogaster and quantitatively identify signatures of the critical point.
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Affiliation(s)
- Daniel Aguilar-Hidalgo
- Max Planck Institute for the Physics of Complex Systems, Nöthnitzer Straße 38, 01187 Dresden, Germany
- Department of Biochemistry, Faculty of Sciences, University of Geneva, 1205 Geneva, Switzerland
| | - Steffen Werner
- Max Planck Institute for the Physics of Complex Systems, Nöthnitzer Straße 38, 01187 Dresden, Germany
- cfaed, TU Dresden, 01062 Dresden, Germany
| | - Ortrud Wartlick
- Department of Biochemistry, Faculty of Sciences, University of Geneva, 1205 Geneva, Switzerland
| | - Marcos González-Gaitán
- Department of Biochemistry, Faculty of Sciences, University of Geneva, 1205 Geneva, Switzerland
| | - Benjamin M Friedrich
- Max Planck Institute for the Physics of Complex Systems, Nöthnitzer Straße 38, 01187 Dresden, Germany
- cfaed, TU Dresden, 01062 Dresden, Germany
| | - Frank Jülicher
- Max Planck Institute for the Physics of Complex Systems, Nöthnitzer Straße 38, 01187 Dresden, Germany
- Center for Systems Biology Dresden, Pfotenhauerstraße 108, 01307 Dresden, Germany
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22
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Fradin C. On the importance of protein diffusion in biological systems: The example of the Bicoid morphogen gradient. BIOCHIMICA ET BIOPHYSICA ACTA-PROTEINS AND PROTEOMICS 2017; 1865:1676-1686. [PMID: 28919007 DOI: 10.1016/j.bbapap.2017.09.002] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/29/2017] [Revised: 08/16/2017] [Accepted: 09/05/2017] [Indexed: 10/18/2022]
Abstract
Morphogens are proteins that form concentration gradients in embryos and developing tissues, where they act as postal codes, providing cells with positional information and allowing them to behave accordingly. Bicoid was the first discovered morphogen, and remains one of the most studied. It regulates segmentation in flies, forming a striking exponential gradient along the anterior-posterior axis of early Drosophila embryos, and activating the transcription of multiple target genes in a concentration-dependent manner. In this review, the work done by us and by others to characterize the mobility of Bicoid in D. melanogaster embryos is presented. The central role played by the diffusion of Bicoid in both the establishment of the gradient and the activation of target genes is discussed, and placed in the context of the need for these processes to be all at once rapid, precise and robust. The Bicoid system, and morphogen gradients in general, remain amongst the most amazing examples of the coexistence, often observed in living systems, of small-scale disorder and large-scale spatial order. This article is part of a Special Issue entitled: Biophysics in Canada, edited by Lewis Kay, John Baenziger, Albert Berghuis and Peter Tieleman.
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Affiliation(s)
- Cécile Fradin
- Dept. of Physics and Astronomy, McMaster University, 1280 Main St W., Hamilton, ON L8S 4M1, Canada
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Maintenance of Heterochromatin by the Large Subunit of the CAF-1 Replication-Coupled Histone Chaperone Requires Its Interaction with HP1a Through a Conserved Motif. Genetics 2016; 205:125-137. [PMID: 27838630 DOI: 10.1534/genetics.116.190785] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/22/2016] [Accepted: 10/30/2016] [Indexed: 11/18/2022] Open
Abstract
In eukaryotic cells, the organization of genomic DNA into chromatin regulates many biological processes, from the control of gene expression to the regulation of chromosome segregation. The proper maintenance of this structure upon cell division is therefore of prime importance during development for the maintenance of cell identity and genome stability. The chromatin assembly factor 1 (CAF-1) is involved in the assembly of H3-H4 histone dimers on newly synthesized DNA and in the maintenance of a higher order structure, the heterochromatin, through an interaction of its large subunit with the heterochromatin protein HP1a. We identify here a conserved domain in the large subunit of the CAF-1 complex required for its interaction with HP1a in the Drosophila fruit fly. Functional analysis reveals that this domain is dispensable for viability but participates in two processes involving heterochromatin: position-effect variegation and long range chromosomal interactions during meiotic prophase. Importantly, the identification in the large subunit of CAF-1 of a domain required for its interaction with HP1 allows the separation of its functions in heterochromatin-related processes from its function in the assembly of H3-H4 dimers onto newly synthesized DNA.
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24
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Hoermann A, Cicin-Sain D, Jaeger J. A quantitative validated model reveals two phases of transcriptional regulation for the gap gene giant in Drosophila. Dev Biol 2016; 411:325-338. [DOI: 10.1016/j.ydbio.2016.01.005] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/24/2015] [Revised: 12/22/2015] [Accepted: 01/08/2016] [Indexed: 01/05/2023]
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Abstract
The Drosophila blastoderm and the vertebrate neural tube are archetypal examples of morphogen-patterned tissues that create precise spatial patterns of different cell types. In both tissues, pattern formation is dependent on molecular gradients that emanate from opposite poles. Despite distinct evolutionary origins and differences in time scales, cell biology and molecular players, both tissues exhibit striking similarities in the regulatory systems that establish gene expression patterns that foreshadow the arrangement of cell types. First, signaling gradients establish initial conditions that polarize the tissue, but there is no strict correspondence between specific morphogen thresholds and boundary positions. Second, gradients initiate transcriptional networks that integrate broadly distributed activators and localized repressors to generate patterns of gene expression. Third, the correct positioning of boundaries depends on the temporal and spatial dynamics of the transcriptional networks. These similarities reveal design principles that are likely to be broadly applicable to morphogen-patterned tissues.
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Affiliation(s)
- James Briscoe
- The Francis Crick Institute, Mill Hill Laboratory, The Ridgeway, Mill Hill, London NW7 1AA, UK
| | - Stephen Small
- Department of Biology, New York University, 100 Washington Square East, New York, NY 10003, USA
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Wotton KR, Jiménez-Guri E, Jaeger J. Maternal co-ordinate gene regulation and axis polarity in the scuttle fly Megaselia abdita. PLoS Genet 2015; 11:e1005042. [PMID: 25757102 PMCID: PMC4355411 DOI: 10.1371/journal.pgen.1005042] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/20/2014] [Accepted: 01/30/2015] [Indexed: 02/01/2023] Open
Abstract
Axis specification and segment determination in dipteran insects are an excellent model system for comparative analyses of gene network evolution. Antero-posterior polarity of the embryo is established through systems of maternal morphogen gradients. In Drosophila melanogaster, the anterior system acts through opposing gradients of Bicoid (Bcd) and Caudal (Cad), while the posterior system involves Nanos (Nos) and Hunchback (Hb) protein. These systems act redundantly. Both Bcd and Hb need to be eliminated to cause a complete loss of polarity resulting in mirror-duplicated abdomens, so-called bicaudal phenotypes. In contrast, knock-down of bcd alone is sufficient to induce double abdomens in non-drosophilid cyclorrhaphan dipterans such as the hoverfly Episyrphus balteatus or the scuttle fly Megaselia abdita. We investigate conserved and divergent aspects of axis specification in the cyclorrhaphan lineage through a detailed study of the establishment and regulatory effect of maternal gradients in M. abdita. Our results show that the function of the anterior maternal system is highly conserved in this species, despite the loss of maternal cad expression. In contrast, hb does not activate gap genes in this species. The absence of this activatory role provides a precise genetic explanation for the loss of polarity upon bcd knock-down in M. abdita, and suggests a general scenario in which the posterior maternal system is increasingly replaced by the anterior one during the evolution of the cyclorrhaphan dipteran lineage. The basic head-to-tail polarity of an animal is established very early in development. In dipteran insects (flies, midges, and mosquitoes), polarity is established with the help of so-called morphogen gradients. Morphogens are regulatory proteins that are distributed as a concentration gradient, often involving diffusion from a localised source. This graded distribution then leads to the concentration-dependent activation of different target genes along the embryo’s axis. We examine this process, which differs to a surprising extent between dipteran species, in the scuttle fly Megaselia abdita, and compare our results to the model organism Drosophila melanogaster. In this way, we not only gain insights into how the mechanisms that establish polarity function differently in different species, but also how the system has evolved since these two flies shared a common ancestor. Specifically, we pin down the main difference between Drosophila and Megaselia in the altered function of the maternal Hunchback morphogen gradient, which activates target genes in the former, but not the latter species, where it has been completely replaced by the Bicoid morphogen during evolution.
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Affiliation(s)
- Karl R. Wotton
- EMBL/CRG Research Unit in Systems Biology, Centre for Genomic Regulation (CRG), Barcelona, Spain
- Universitat Pompeu Fabra (UPF), Barcelona, Spain
- * E-mail: (KW); (JJ)
| | - Eva Jiménez-Guri
- EMBL/CRG Research Unit in Systems Biology, Centre for Genomic Regulation (CRG), Barcelona, Spain
- Universitat Pompeu Fabra (UPF), Barcelona, Spain
| | - Johannes Jaeger
- EMBL/CRG Research Unit in Systems Biology, Centre for Genomic Regulation (CRG), Barcelona, Spain
- Universitat Pompeu Fabra (UPF), Barcelona, Spain
- * E-mail: (KW); (JJ)
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Shadow enhancers enable Hunchback bifunctionality in the Drosophila embryo. Proc Natl Acad Sci U S A 2015; 112:785-90. [PMID: 25564665 DOI: 10.1073/pnas.1413877112] [Citation(s) in RCA: 41] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
Abstract
Hunchback (Hb) is a bifunctional transcription factor that activates and represses distinct enhancers. Here, we investigate the hypothesis that Hb can activate and repress the same enhancer. Computational models predicted that Hb bifunctionally regulates the even-skipped (eve) stripe 3+7 enhancer (eve3+7) in Drosophila blastoderm embryos. We measured and modeled eve expression at cellular resolution under multiple genetic perturbations and found that the eve3+7 enhancer could not explain endogenous eve stripe 7 behavior. Instead, we found that eve stripe 7 is controlled by two enhancers: the canonical eve3+7 and a sequence encompassing the minimal eve stripe 2 enhancer (eve2+7). Hb bifunctionally regulates eve stripe 7, but it executes these two activities on different pieces of regulatory DNA--it activates the eve2+7 enhancer and represses the eve3+7 enhancer. These two "shadow enhancers" use different regulatory logic to create the same pattern.
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Abstract
BACKGROUND The detailed analysis of transcriptional regulation is crucially important for understanding biological processes. The gap gene network in Drosophila attracts large interest among researches studying mechanisms of transcriptional regulation. It implements the most upstream regulatory layer of the segmentation gene network. The knowledge of molecular mechanisms involved in gap gene regulation is far less complete than that of genetics of the system. Mathematical modeling goes beyond insights gained by genetics and molecular approaches. It allows us to reconstruct wild-type gene expression patterns in silico, infer underlying regulatory mechanism and prove its sufficiency. RESULTS We developed a new model that provides a dynamical description of gap gene regulatory systems, using detailed DNA-based information, as well as spatial transcription factor concentration data at varying time points. We showed that this model correctly reproduces gap gene expression patterns in wild type embryos and is able to predict gap expression patterns in Kr mutants and four reporter constructs. We used four-fold cross validation test and fitting to random dataset to validate the model and proof its sufficiency in data description. The identifiability analysis showed that most model parameters are well identifiable. We reconstructed the gap gene network topology and studied the impact of individual transcription factor binding sites on the model output. We measured this impact by calculating the site regulatory weight as a normalized difference between the residual sum of squares error for the set of all annotated sites and for the set with the site of interest excluded. CONCLUSIONS The reconstructed topology of the gap gene network is in agreement with previous modeling results and data from literature. We showed that 1) the regulatory weights of transcription factor binding sites show very weak correlation with their PWM score; 2) sites with low regulatory weight are important for the model output; 3) functional important sites are not exclusively located in cis-regulatory elements, but are rather dispersed through regulatory region. It is of importance that some of the sites with high functional impact in hb, Kr and kni regulatory regions coincide with strong sites annotated and verified in Dnase I footprint assays.
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Affiliation(s)
- Konstantin Kozlov
- St.Petersburg State Polytechnical University, Polytekhnicheskaya 29, 195251 St.Petersburg, Russia
| | - Vitaly Gursky
- Ioffe Physical-Technical Institute, RAS, Polytekhnicheskaya 26, 194021 St.Petersburg, Russia
| | - Ivan Kulakovskiy
- Engelhardt Institute of Molecular Biology, RAS, Vavilov 32, 119991 Moscow, Russia
| | - Maria Samsonova
- St.Petersburg State Polytechnical University, Polytekhnicheskaya 29, 195251 St.Petersburg, Russia
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Duncan EJ, Johnson TK, Whisstock JC, Warr CG, Dearden PK. Capturing embryonic development from metamorphosis: how did the terminal patterning signalling pathway of Drosophila evolve? CURRENT OPINION IN INSECT SCIENCE 2014; 1:45-51. [PMID: 32846729 DOI: 10.1016/j.cois.2014.04.007] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/02/2014] [Revised: 04/29/2014] [Accepted: 04/29/2014] [Indexed: 06/11/2023]
Abstract
The Torso receptor tyrosine kinase has two crucial roles in Drosophila melanogaster development. One is in the control of insect moulting, which is regulated by the neuropeptide hormone PTTH (prothoracicotropic hormone). PTTH activates ERK signalling via Torso in the prothoracic gland to stimulate ecdysone secretion. Torso also has a role in control of one of the earliest events in embryogenesis in Drosophila; patterning of the embryonic termini. Here Torso is activated by a different, but related, peptide called Trunk. During terminal patterning another protein, Torso-like, has a key role in mediating activation of Torso by Trunk. Torso-like is also expressed in the prothoracic gland and null-mutants have defective developmental timing in Drosophila. This function, however, has been recently shown to be independent of Torso and PTTH. We refer to these proteins, Trunk, PTTH, Torso and Torso-like, as the Torso-activation module. Outside Drosophila we see that the genes encoding the Torso-activation module have a complex phylogenetic history, with different origins and multiple losses of components of this signalling pathway during arthropod evolution. This, together with expression and functional data in a range of insects, leads us to propose that the terminal patterning pathway in Drosophila and Tribolium arose through co-option of PTTH/Trunk and Torso, which has a role in developmental timing, into a new context, and that Torso-like was recruited specifically in the ovary to modulate the specificity of this pathway.
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Affiliation(s)
- Elizabeth J Duncan
- Genetics Otago, University of Otago, P.O. Box 56, Dunedin, Aotearoa, New Zealand; Gravida; The National Centre for Growth and Development, University of Otago, P.O. Box 56, Dunedin, Aotearoa, New Zealand
| | - Travis K Johnson
- School of Biological Sciences, Monash University, Clayton, VIC 3800, Australia; Department of Biochemistry and Molecular Biology, Monash University, Clayton, VIC 3800, Australia
| | - James C Whisstock
- Department of Biochemistry and Molecular Biology, Monash University, Clayton, VIC 3800, Australia; Australian Research Council Centre of Excellence in Advanced Molecular Imaging, Monash University, Clayton, VIC 3800, Australia
| | - Coral G Warr
- School of Biological Sciences, Monash University, Clayton, VIC 3800, Australia
| | - Peter K Dearden
- Genetics Otago, University of Otago, P.O. Box 56, Dunedin, Aotearoa, New Zealand; Gravida; The National Centre for Growth and Development, University of Otago, P.O. Box 56, Dunedin, Aotearoa, New Zealand.
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31
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Lynch JA. Diversity of molecules and mechanisms in establishing insect anterior-posterior polarity. CURRENT OPINION IN INSECT SCIENCE 2014; 1:39-44. [PMID: 32846728 DOI: 10.1016/j.cois.2014.05.003] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/04/2014] [Revised: 04/27/2014] [Accepted: 05/02/2014] [Indexed: 06/11/2023]
Abstract
Anterior-posterior (AP) patterning is an essential process that requires the generation of large amounts of positional information to properly specify many distinct cell fates along the long axis of the insect embryo. While the general molecular basis of this process has long been known in the fly Drosophila, detailed understanding of this process is still emerging in other insect species. What is now clear is that this process in extremely labile, and distinct AP patterning programs can exist even within a single species. This review presents recent progress on this topic in an attempt to synthesize the disparate data and provide an outlook on the future of the field.
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Affiliation(s)
- Jeremy A Lynch
- University of Illinois at Chicago, 4020 MBRB, 900 Ashland Ave., Chicago, IL 60607, USA.
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32
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Expression pattern of empty-spiracles, a conserved head-patterning gene, in honeybee (Apis mellifera) embryos. Gene Expr Patterns 2014; 15:142-8. [PMID: 24999162 DOI: 10.1016/j.gep.2014.06.003] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/09/2014] [Revised: 06/19/2014] [Accepted: 06/20/2014] [Indexed: 11/21/2022]
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Xu Z, Chen H, Ling J, Yu D, Struffi P, Small S. Impacts of the ubiquitous factor Zelda on Bicoid-dependent DNA binding and transcription in Drosophila. Genes Dev 2014; 28:608-21. [PMID: 24637116 PMCID: PMC3967049 DOI: 10.1101/gad.234534.113] [Citation(s) in RCA: 70] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
The Drosophila transcription factor Bicoid (Bcd) binds thousands of genomic sites during early embryogenesis, but it is unclear how many of these binding events are functionally important. Here, Small and colleagues test the role of the maternal factor Zelda (Zld) in Bcd-mediated binding and transcription. Embryos lacking Zld show enhanced Bcd binding to a subset of genomic locations, causing early activation of target genes normally silent until later stages. This study demonstrates a critical role for Zld in controlling Bcd binding and target gene activation in the early embryo. In vivo cross-linking studies suggest that the Drosophila transcription factor Bicoid (Bcd) binds to several thousand sites during early embryogenesis, but it is not clear how many of these binding events are functionally important. In contrast, reporter gene studies have identified >60 Bcd-dependent enhancers, all of which contain clusters of the consensus binding sequence TAATCC. These studies also identified clusters of TAATCC motifs (inactive fragments) that failed to drive Bcd-dependent activation. In general, active fragments showed higher levels of Bcd binding in vivo and were enriched in predicted binding sites for the ubiquitous maternal protein Zelda (Zld). Here we tested the role of Zld in Bcd-mediated binding and transcription. Removal of Zld function and mutations in Zld sites caused significant reductions in Bcd binding to known enhancers and variable effects on the activation and spatial positioning of Bcd-dependent expression patterns. Also, insertion of Zld sites converted one of six inactive fragments into a Bcd-responsive enhancer. Genome-wide binding experiments in zld mutants showed variable effects on Bcd-binding peaks, ranging from strong reductions to significantly enhanced levels of binding. Increases in Bcd binding caused the precocious Bcd-dependent activation of genes that are normally not expressed in early embryos, suggesting that Zld controls the genome-wide binding profile of Bcd at the qualitative level and is critical for selecting target genes for activation in the early embryo. These results underscore the importance of combinatorial binding in enhancer function and provide data that will help predict regulatory activities based on DNA sequence.
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Affiliation(s)
- Zhe Xu
- Department of Biology, New York University, New York, New York 10003, USA
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34
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Martinez C, Rest JS, Kim AR, Ludwig M, Kreitman M, White K, Reinitz J. Ancestral resurrection of the Drosophila S2E enhancer reveals accessible evolutionary paths through compensatory change. Mol Biol Evol 2014; 31:903-16. [PMID: 24408913 DOI: 10.1093/molbev/msu042] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
Upstream regulatory sequences that control gene expression evolve rapidly, yet the expression patterns and functions of most genes are typically conserved. To address this paradox, we have reconstructed computationally and resurrected in vivo the cis-regulatory regions of the ancestral Drosophila eve stripe 2 element and evaluated its evolution using a mathematical model of promoter function. Our feed-forward transcriptional model predicts gene expression patterns directly from enhancer sequence. We used this functional model along with phylogenetics to generate a set of possible ancestral eve stripe 2 sequences for the common ancestors of 1) D. simulans and D. sechellia; 2) D. melanogaster, D. simulans, and D. sechellia; and 3) D. erecta and D. yakuba. These ancestral sequences were synthesized and resurrected in vivo. Using a combination of quantitative and computational analysis, we find clear support for functional compensation between the binding sites for Bicoid, Giant, and Krüppel over the course of 40-60 My of Drosophila evolution. We show that this compensation is driven by a coupling interaction between Bicoid activation and repression at the anterior and posterior border necessary for proper placement of the anterior stripe 2 border. A multiplicity of mechanisms for binding site turnover exemplified by Bicoid, Giant, and Krüppel sites, explains how rapid sequence change may occur while maintaining the function of the cis-regulatory element.
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Affiliation(s)
- Carlos Martinez
- Institute for Genomics and Systems Biology, University of Chicago
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35
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Erceg J, Saunders TE, Girardot C, Devos DP, Hufnagel L, Furlong EEM. Subtle changes in motif positioning cause tissue-specific effects on robustness of an enhancer's activity. PLoS Genet 2014; 10:e1004060. [PMID: 24391522 PMCID: PMC3879207 DOI: 10.1371/journal.pgen.1004060] [Citation(s) in RCA: 42] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/19/2013] [Accepted: 11/11/2013] [Indexed: 12/14/2022] Open
Abstract
Deciphering the specific contribution of individual motifs within cis-regulatory modules (CRMs) is crucial to understanding how gene expression is regulated and how this process is affected by sequence variation. But despite vast improvements in the ability to identify where transcription factors (TFs) bind throughout the genome, we are limited in our ability to relate information on motif occupancy to function from sequence alone. Here, we engineered 63 synthetic CRMs to systematically assess the relationship between variation in the content and spacing of motifs within CRMs to CRM activity during development using Drosophila transgenic embryos. In over half the cases, very simple elements containing only one or two types of TF binding motifs were capable of driving specific spatio-temporal patterns during development. Different motif organizations provide different degrees of robustness to enhancer activity, ranging from binary on-off responses to more subtle effects including embryo-to-embryo and within-embryo variation. By quantifying the effects of subtle changes in motif organization, we were able to model biophysical rules that explain CRM behavior and may contribute to the spatial positioning of CRM activity in vivo. For the same enhancer, the effects of small differences in motif positions varied in developmentally related tissues, suggesting that gene expression may be more susceptible to sequence variation in one tissue compared to another. This result has important implications for human eQTL studies in which many associated mutations are found in cis-regulatory regions, though the mechanism for how they affect tissue-specific gene expression is often not understood.
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Affiliation(s)
- Jelena Erceg
- Genome Biology Unit, European Molecular Biology Laboratory (EMBL), Heidelberg, Germany
| | - Timothy E. Saunders
- Genome Biology Unit, European Molecular Biology Laboratory (EMBL), Heidelberg, Germany
- Cell Biology and Biophysics Unit, European Molecular Biology Laboratory (EMBL), Heidelberg, Germany
| | - Charles Girardot
- Genome Biology Unit, European Molecular Biology Laboratory (EMBL), Heidelberg, Germany
| | - Damien P. Devos
- Genome Biology Unit, European Molecular Biology Laboratory (EMBL), Heidelberg, Germany
| | - Lars Hufnagel
- Cell Biology and Biophysics Unit, European Molecular Biology Laboratory (EMBL), Heidelberg, Germany
| | - Eileen E. M. Furlong
- Genome Biology Unit, European Molecular Biology Laboratory (EMBL), Heidelberg, Germany
- * E-mail:
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36
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Mao J, Liu C, Zeng F. Hunchback is required for abdominal identity suppression and germband growth in the parthenogenetic embryogenesis of the pea aphid, Acyrthosiphon pisum. ARCHIVES OF INSECT BIOCHEMISTRY AND PHYSIOLOGY 2013; 84:209-221. [PMID: 24222010 DOI: 10.1002/arch.21137] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/02/2023]
Abstract
Aphid, a short germband insect, displays an embryogenesis different from that of long germband insect species. Furthermore, the development of its parthenogenetic and viviparous embryo is different from that of the embryo resulting from sexual reproduction. To better understand the genetic regulation of this type of embryogenesis, the functions of hunchback in asexual Acyrthosiphon pisum were investigated by parental RNAi. Microinjection of Aphb double-stranded RNA yielded several defective phenotypes. Quantitative real-time PCR analysis revealed that these defects resulted from reduction of Aphb mRNA level in injected aphids. All these results suggested that the hb gene in parthenogenetic and viviparous Acyrthosiphon pisum was involved in abdominal identity suppression and germband growth as its homologue does in sexual insects.
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Affiliation(s)
- Jianjun Mao
- Key Laboratory of Integrated Pest Management in Crops, Ministry of Agriculture, Institute of Plant Protection, Chinese Academy of Agricultural Sciences, Beijing, People's Republic of China
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37
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Cheung D, Miles C, Kreitman M, Ma J. Adaptation of the length scale and amplitude of the Bicoid gradient profile to achieve robust patterning in abnormally large Drosophila melanogaster embryos. Development 2013; 141:124-35. [PMID: 24284208 DOI: 10.1242/dev.098640] [Citation(s) in RCA: 37] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
The formation of patterns that are proportional to the size of the embryo is an intriguing but poorly understood feature of development. Molecular mechanisms controlling such proportionality, or scaling, can be probed through quantitative interrogations of the properties of morphogen gradients that instruct patterning. Recent studies of the Drosophila morphogen gradient Bicoid (Bcd), which is required for anterior-posterior (AP) patterning in the early embryo, have uncovered two distinct ways of scaling. Whereas between-species scaling is achieved by adjusting the exponential shape characteristic of the Bcd gradient profile, namely, its length scale or length constant (λ), within-species scaling is achieved through adjusting the profile's amplitude, namely, the Bcd concentration at the anterior (B0). Here, we report a case in which Drosophila melanogaster embryos exhibit Bcd gradient properties uncharacteristic of their size. The embryos under investigation were from a pair of inbred lines that had been artificially selected for egg size extremes. We show that B0 in the large embryos is uncharacteristically low but λ is abnormally extended. Although the large embryos have more total bcd mRNA than their smaller counterparts, as expected, its distribution is unusually broad. We show that the large and small embryos develop gene expression patterns exhibiting boundaries that are proportional to their respective lengths. Our results suggest that the large-egg inbred line has acquired compensating properties that counteract the extreme length of the embryos to maintain Bcd gradient properties necessary for robust patterning. Our study documents, for the first time to our knowledge, a case of within-species Bcd scaling achieved through adjusting the gradient profile's exponential shape characteristic, illustrating at a molecular level how a developmental system can follow distinct operational paths towards the goal of robust and scaled patterning.
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Affiliation(s)
- David Cheung
- Division of Biomedical Informatics, Cincinnati Children's Research Foundation, 3333 Burnet Avenue, Cincinnati, OH 45229, USA
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38
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Ilsley GR, Fisher J, Apweiler R, DePace AH, Luscombe NM. Cellular resolution models for even skipped regulation in the entire Drosophila embryo. eLife 2013; 2:e00522. [PMID: 23930223 PMCID: PMC3736529 DOI: 10.7554/elife.00522] [Citation(s) in RCA: 42] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/07/2013] [Accepted: 06/17/2013] [Indexed: 12/14/2022] Open
Abstract
Transcriptional control ensures genes are expressed in the right amounts at the correct times and locations. Understanding quantitatively how regulatory systems convert input signals to appropriate outputs remains a challenge. For the first time, we successfully model even skipped (eve) stripes 2 and 3+7 across the entire fly embryo at cellular resolution. A straightforward statistical relationship explains how transcription factor (TF) concentrations define eve's complex spatial expression, without the need for pairwise interactions or cross-regulatory dynamics. Simulating thousands of TF combinations, we recover known regulators and suggest new candidates. Finally, we accurately predict the intricate effects of perturbations including TF mutations and misexpression. Our approach imposes minimal assumptions about regulatory function; instead we infer underlying mechanisms from models that best fit the data, like the lack of TF-specific thresholds and the positional value of homotypic interactions. Our study provides a general and quantitative method for elucidating the regulation of diverse biological systems. DOI:http://dx.doi.org/10.7554/eLife.00522.001.
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Affiliation(s)
- Garth R Ilsley
- European Molecular Biology Laboratory, European Bioinformatics Institute, Wellcome Trust Genome Campus, Cambridge, United Kingdom
- Okinawa Institute of Science and Technology Graduate University, Okinawa, Japan
| | - Jasmin Fisher
- Microsoft Research Cambridge, Cambridge, United Kingdom
- Department of Biochemistry, University of Cambridge, Cambridge, United Kingdom
| | - Rolf Apweiler
- European Molecular Biology Laboratory, European Bioinformatics Institute, Wellcome Trust Genome Campus, Cambridge, United Kingdom
| | - Angela H DePace
- Department of Systems Biology, Harvard Medical School, Boston, United States
| | - Nicholas M Luscombe
- European Molecular Biology Laboratory, European Bioinformatics Institute, Wellcome Trust Genome Campus, Cambridge, United Kingdom
- Okinawa Institute of Science and Technology Graduate University, Okinawa, Japan
- UCL Genetics Institute, Department of Genetics, Evolution, and Environment, University College London, London, United Kingdom
- London Research Institute, Cancer Research UK, London, United Kingdom
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39
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Kim AR, Martinez C, Ionides J, Ramos AF, Ludwig MZ, Ogawa N, Sharp DH, Reinitz J. Rearrangements of 2.5 kilobases of noncoding DNA from the Drosophila even-skipped locus define predictive rules of genomic cis-regulatory logic. PLoS Genet 2013; 9:e1003243. [PMID: 23468638 PMCID: PMC3585115 DOI: 10.1371/journal.pgen.1003243] [Citation(s) in RCA: 48] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/15/2012] [Accepted: 11/30/2012] [Indexed: 01/19/2023] Open
Abstract
Rearrangements of about 2.5 kilobases of regulatory DNA located 5′ of the transcription start site of the Drosophila even-skipped locus generate large-scale changes in the expression of even-skipped stripes 2, 3, and 7. The most radical effects are generated by juxtaposing the minimal stripe enhancers MSE2 and MSE3 for stripes 2 and 3 with and without small “spacer” segments less than 360 bp in length. We placed these fusion constructs in a targeted transformation site and obtained quantitative expression data for these transformants together with their controlling transcription factors at cellular resolution. These data demonstrated that the rearrangements can alter expression levels in stripe 2 and the 2–3 interstripe by a factor of more than 10. We reasoned that this behavior would place tight constraints on possible rules of genomic cis-regulatory logic. To find these constraints, we confronted our new expression data together with previously obtained data on other constructs with a computational model. The model contained representations of thermodynamic protein–DNA interactions including steric interference and cooperative binding, short-range repression, direct repression, activation, and coactivation. The model was highly constrained by the training data, which it described within the limits of experimental error. The model, so constrained, was able to correctly predict expression patterns driven by enhancers for other Drosophila genes; even-skipped enhancers not included in the training set; stripe 2, 3, and 7 enhancers from various Drosophilid and Sepsid species; and long segments of even-skipped regulatory DNA that contain multiple enhancers. The model further demonstrated that elevated expression driven by a fusion of MSE2 and MSE3 was a consequence of the recruitment of a portion of MSE3 to become a functional component of MSE2, demonstrating that cis-regulatory “elements” are not elementary objects. Metazoan genes, including those of humans, contain large noncoding regions that are required for viability. Sequence variations in these regions are statistically associated with human disease, but the mechanisms underlying these associations are not well understood. These regions regulate transcription and are frequently larger than the gene's transcript by an order of magnitude. In this paper we attempt to elucidate the regulatory code of these noncoding segments of DNA by means of quantitative spatially resolved gene expression data and a computational model. The expression data comes from the early embryo of the fruit fly Drosophila melanogaster. We chose a family of DNA constructs to analyze that drive very different patterns of expression when very small changes in DNA sequence are made, reasoning that this sensitivity would reveal important properties of the regulatory code. The model reproduced the training data with precision greater than the expected accuracy of the training data itself. It was able to correctly predict from DNA sequence the expression of 44 segments of DNA from many genes and species.
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Affiliation(s)
- Ah-Ram Kim
- Department of Ecology and Evolution, Chicago Center for Systems Biology, University of Chicago, Chicago, Illinois, United States of America
- Department of Biochemistry and Cell Biology, Stony Brook University, Stony Brook, New York, United States of America
| | - Carlos Martinez
- Department of Ecology and Evolution, Chicago Center for Systems Biology, University of Chicago, Chicago, Illinois, United States of America
| | - John Ionides
- Department of Biochemistry, University of Cambridge, Cambridge, United Kingdom
| | - Alexandre F. Ramos
- Escola de Artes, Ciências e Humanidades, Universidade de São Paulo, São Paulo, Brazil
| | - Michael Z. Ludwig
- Department of Ecology and Evolution, Chicago Center for Systems Biology, University of Chicago, Chicago, Illinois, United States of America
| | - Nobuo Ogawa
- Genomics Division, Lawrence Berkeley National Laboratory, Berkeley, California, United States of America
| | - David H. Sharp
- Theoretical Division, Los Alamos National Laboratory, Los Alamos, New Mexico, United States of America
| | - John Reinitz
- Department of Ecology and Evolution, Chicago Center for Systems Biology, University of Chicago, Chicago, Illinois, United States of America
- Department of Statistics, Department of Molecular Genetics and Cell Biology, and Institute of Genomics and Systems Biology, University of Chicago, Chicago, Illinois, United States of America
- * E-mail:
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40
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Wunderlich Z, Bragdon MD, Eckenrode KB, Lydiard-Martin T, Pearl-Waserman S, DePace AH. Dissecting sources of quantitative gene expression pattern divergence between Drosophila species. Mol Syst Biol 2013; 8:604. [PMID: 22893002 PMCID: PMC3435502 DOI: 10.1038/msb.2012.35] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/27/2012] [Accepted: 07/12/2012] [Indexed: 12/21/2022] Open
Abstract
Gene expression patterns can diverge between species due to changes in a gene's regulatory DNA or changes in the proteins, e.g., transcription factors (TFs), that regulate the gene. We developed a modeling framework to uncover the sources of expression differences in blastoderm embryos of three Drosophila species, focusing on the regulatory circuit controlling expression of the hunchback (hb) posterior stripe. Using this framework and cellular-resolution expression measurements of hb and its regulating TFs, we found that changes in the expression patterns of hb's TFs account for much of the expression divergence. We confirmed our predictions using transgenic D. melanogaster lines, which demonstrate that this set of orthologous cis-regulatory elements (CREs) direct similar, but not identical, expression patterns. We related expression pattern differences to sequence changes in the CRE using a calculation of the CRE's TF binding site content. By applying this calculation in both the transgenic and endogenous contexts, we found that changes in binding site content affect sensitivity to regulating TFs and that compensatory evolution may occur in circuit components other than the CRE.
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Affiliation(s)
- Zeba Wunderlich
- Department of Systems Biology, Harvard Medical School, Boston, MA 02115, USA
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41
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Liu J, Ma J. Dampened regulates the activating potency of Bicoid and the embryonic patterning outcome in Drosophila. Nat Commun 2013; 4:2968. [PMID: 24336107 PMCID: PMC3902774 DOI: 10.1038/ncomms3968] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/21/2013] [Accepted: 11/18/2013] [Indexed: 01/26/2023] Open
Abstract
The Drosophila morphogen gradient of Bicoid (Bcd) initiates anterior-posterior (AP) patterning; however, it is poorly understood how its ability to activate a target gene may have an impact on this process. Here we report an F-box protein, Dampened (Dmpd) as a nuclear cofactor of Bcd that can enhance its activating potency. We establish a quantitative platform to specifically investigate two parameters of a Bcd target gene response, expression amplitude and boundary position. We show that embryos lacking Dmpd have a reduced amplitude of Bcd-activated hunchback (hb) expression at a critical time of development. This is because of a reduced Bcd-dependent transcribing probability. This defect is faithfully propagated further downstream of the AP-patterning network to alter the spatial characteristics of even-skipped (eve) stripes. Thus, unlike another Bcd-interacting F-box protein Fate-shifted (Fsd), which controls AP patterning through regulating the Bcd gradient profile, Dmpd achieves its patterning role through regulating the activating potency of Bcd.
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Affiliation(s)
- Junbo Liu
- Division of Biomedical Informatics Cincinnati Children's Research Foundation 3333 Burnet Avenue Cincinnati, Ohio United States of America
| | - Jun Ma
- Division of Biomedical Informatics Cincinnati Children's Research Foundation 3333 Burnet Avenue Cincinnati, Ohio United States of America
- Division of Developmental Biology Cincinnati Children's Research Foundation 3333 Burnet Avenue Cincinnati, Ohio United States of America
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42
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Jaeger J, Manu, Reinitz J. Drosophila blastoderm patterning. Curr Opin Genet Dev 2012; 22:533-41. [DOI: 10.1016/j.gde.2012.10.005] [Citation(s) in RCA: 52] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/12/2012] [Revised: 10/16/2012] [Accepted: 10/24/2012] [Indexed: 12/29/2022]
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43
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Nakao H. Anterior and posterior centers jointly regulate Bombyx embryo body segmentation. Dev Biol 2012; 371:293-301. [DOI: 10.1016/j.ydbio.2012.08.029] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/09/2012] [Accepted: 08/28/2012] [Indexed: 11/29/2022]
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44
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Depleting gene activities in early Drosophila embryos with the "maternal-Gal4-shRNA" system. Genetics 2012; 193:51-61. [PMID: 23105012 DOI: 10.1534/genetics.112.144915] [Citation(s) in RCA: 83] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
In a developing Drosophila melanogaster embryo, mRNAs have a maternal origin, a zygotic origin, or both. During the maternal-zygotic transition, maternal products are degraded and gene expression comes under the control of the zygotic genome. To interrogate the function of mRNAs that are both maternally and zygotically expressed, it is common to examine the embryonic phenotypes derived from female germline mosaics. Recently, the development of RNAi vectors based on short hairpin RNAs (shRNAs) effective during oogenesis has provided an alternative to producing germline clones. Here, we evaluate the efficacies of: (1) maternally loaded shRNAs to knockdown zygotic transcripts and (2) maternally loaded Gal4 protein to drive zygotic shRNA expression. We show that, while Gal4-driven shRNAs in the female germline very effectively generate phenotypes for genes expressed maternally, maternally loaded shRNAs are not very effective at generating phenotypes for early zygotic genes. However, maternally loaded Gal4 protein is very efficient at generating phenotypes for zygotic genes expressed during mid-embryogenesis. We apply this powerful and simple method to unravel the embryonic functions of a number of pleiotropic genes.
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45
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Riccione KA, Smith RP, Lee AJ, You L. A synthetic biology approach to understanding cellular information processing. ACS Synth Biol 2012; 1:389-402. [PMID: 23411668 PMCID: PMC3568971 DOI: 10.1021/sb300044r] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
The survival of cells and organisms requires proper responses to environmental signals. These responses are governed by cellular networks, which serve to process diverse environmental cues. Biological networks often contain recurring network topologies called "motifs". It has been recognized that the study of such motifs allows one to predict the response of a biological network and thus cellular behavior. However, studying a single motif in complete isolation of all other network motifs in a natural setting is difficult. Synthetic biology has emerged as a powerful approach to understanding the dynamic properties of network motifs. In addition to testing existing theoretical predictions, construction and analysis of synthetic gene circuits has led to the discovery of novel motif dynamics, such as how the combination of simple motifs can lead to autonomous dynamics or how noise in transcription and translation can affect the dynamics of a motif. Here, we review developments in synthetic biology as they pertain to increasing our understanding of cellular information processing. We highlight several types of dynamic behaviors that diverse motifs can generate, including the control of input/output responses, the generation of autonomous spatial and temporal dynamics, as well as the influence of noise in motif dynamics and cellular behavior.
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Affiliation(s)
| | - Robert P Smith
- Department of Biomedical Engineering, Duke University, Durham, NC 27708, USA
| | - Anna J Lee
- Department of Biomedical Engineering, Duke University, Durham, NC 27708, USA
| | - Lingchong You
- Department of Biomedical Engineering, Duke University, Durham, NC 27708, USA
- Institute for Genome Sciences and Policy, Duke University, Durham, NC 27710, USA
- Center for Systems Biology, Duke University, Durham, NC 27708, USA
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46
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Sokolowski TR, Erdmann T, ten Wolde PR. Mutual repression enhances the steepness and precision of gene expression boundaries. PLoS Comput Biol 2012; 8:e1002654. [PMID: 22956897 PMCID: PMC3431325 DOI: 10.1371/journal.pcbi.1002654] [Citation(s) in RCA: 44] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/25/2011] [Accepted: 07/07/2012] [Indexed: 11/18/2022] Open
Abstract
Embryonic development is driven by spatial patterns of gene expression that determine the fate of each cell in the embryo. While gene expression is often highly erratic, embryonic development is usually exceedingly precise. In particular, gene expression boundaries are robust not only against intra-embryonic fluctuations such as noise in gene expression and protein diffusion, but also against embryo-to-embryo variations in the morphogen gradients, which provide positional information to the differentiating cells. How development is robust against intra- and inter-embryonic variations is not understood. A common motif in the gene regulation networks that control embryonic development is mutual repression between pairs of genes. To assess the role of mutual repression in the robust formation of gene expression patterns, we have performed large-scale stochastic simulations of a minimal model of two mutually repressing gap genes in Drosophila, hunchback (hb) and knirps (kni). Our model includes not only mutual repression between hb and kni, but also the stochastic and cooperative activation of hb by the anterior morphogen Bicoid (Bcd) and of kni by the posterior morphogen Caudal (Cad), as well as the diffusion of Hb and Kni between neighboring nuclei. Our analysis reveals that mutual repression can markedly increase the steepness and precision of the gap gene expression boundaries. In contrast to other mechanisms such as spatial averaging and cooperative gene activation, mutual repression thus allows for gene-expression boundaries that are both steep and precise. Moreover, mutual repression dramatically enhances their robustness against embryo-to-embryo variations in the morphogen levels. Finally, our simulations reveal that diffusion of the gap proteins plays a critical role not only in reducing the width of the gap gene expression boundaries via the mechanism of spatial averaging, but also in repairing patterning errors that could arise because of the bistability induced by mutual repression.
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Affiliation(s)
| | - Thorsten Erdmann
- University of Heidelberg, Institute for Theoretical Physics, Heidelberg, Germany
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47
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Kang HW, Zheng L, Othmer HG. The effect of the signalling scheme on the robustness of pattern formation in development. Interface Focus 2012; 2:465-86. [PMID: 22649582 PMCID: PMC3363034 DOI: 10.1098/rsfs.2011.0116] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/16/2011] [Accepted: 02/21/2012] [Indexed: 11/12/2022] Open
Abstract
Pattern formation in development is a complex process which involves spatially distributed signals called morphogens that influence gene expression and thus the phenotypic identity of cells. Usually different cell types are spatially segregated, and the boundary between them may be determined by a threshold value of some state variable. The question arises as to how sensitive the location of such a boundary is to variations in properties, such as parameter values, that characterize the system. Here, we analyse both deterministic and stochastic reaction-diffusion models of pattern formation with a view towards understanding how the signalling scheme used for patterning affects the variability of boundary determination between cell types in a developing tissue.
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48
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Lopes FJP, Spirov AV, Bisch PM. The role of Bicoid cooperative binding in the patterning of sharp borders in Drosophila melanogaster. Dev Biol 2012; 370:165-72. [PMID: 22841642 DOI: 10.1016/j.ydbio.2012.07.020] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/24/2012] [Revised: 07/06/2012] [Accepted: 07/16/2012] [Indexed: 10/28/2022]
Abstract
In Drosophila embryonic development, the Bicoid (Bcd) protein establishes positional information of downstream developmental genes like hunchback (hb), which has a strong anterior expression and a sharp on-off boundary in the mid-embryo. The role of Bcd cooperative binding in the positioning of the Hb pattern has been previously demonstrated. However, there are discrepancies in the reported results about the role of this mechanism in the sharp Hb border. Here, we determined the Hill coefficient (nH) required for Bcd to generate the sharp border of Hb in wild-type (WT) embryos. We found that an n(H) of approximately 6.3 (s.d. 1.4) and 10.8 (s.d. 4.0) is required to account for Hb sharpness at early and late cycle 14A, respectively. Additional mechanisms are possibly required because the high nH is likely unachievable for Bcd binding to the hb promoter. To test this idea, we determined the nH required to pattern the Hb profile of 15 embryos expressing an hb14F allele that is defective in self-activation and found nH to be 3.0 (s.d. 1.0). This result indicates that in WT embryos, the hb self-activation is important for Hb sharpness. Corroborating our results, we also found a progressive increase in the required value of n(H) spanning from 4.0 to 9.2 by determining this coefficient from averaged profiles of eight temporal classes at cycle 14A (T1 to T8). Our results indicate that there is a transition in the mechanisms responsible for the sharp Hb border during cycle 14A: in early stages of this cycle, Bcd cooperative binding is primarily responsible for Hb sharpness; in late cycle 14A, hb self-activation becomes the dominant mechanism.
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Affiliation(s)
- Francisco J P Lopes
- Laboratório de Física-Biológica, Instituto de Biofúsica Carlos Chagas Filho, Universidade Federal do Rio de Janeiro, Rio de Janeiro, Brazil.
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Hardway H. Gene network models robust to spatial scaling and noisy input. Math Biosci 2012; 237:1-16. [DOI: 10.1016/j.mbs.2012.03.004] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/10/2011] [Revised: 01/12/2012] [Accepted: 03/01/2012] [Indexed: 10/28/2022]
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Kimelman D, Martin BL. Anterior-posterior patterning in early development: three strategies. WILEY INTERDISCIPLINARY REVIEWS-DEVELOPMENTAL BIOLOGY 2011; 1:253-66. [PMID: 23801439 DOI: 10.1002/wdev.25] [Citation(s) in RCA: 47] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Abstract
The anterior-posterior (AP) axis is the most ancient of the embryonic axes and exists in most metazoans. Different animals use a wide variety of mechanisms to create this axis in the early embryo. In this study, we focus on three animals, including two insects (Drosophila and Tribolium) and a vertebrate (zebrafish) to examine different strategies used to form the AP axis. While Drosophila forms the entire axis within a syncytial blastoderm using transcription factors as morphogens, zebrafish uses signaling factors in a cellularized embryo, progressively forming the AP axis over the course of a day. Tribolium uses an intermediate strategy that has commonalities with both Drosophila and zebrafish. We discuss the specific molecular mechanisms used to create the AP axis and identify conserved features.
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Affiliation(s)
- David Kimelman
- Department of Biochemistry, University of Washington, Seattle, WA, USA.
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