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Brennan KJ, Weilert M, Krueger S, Pampari A, Liu HY, Yang AWH, Morrison JA, Hughes TR, Rushlow CA, Kundaje A, Zeitlinger J. Chromatin accessibility in the Drosophila embryo is determined by transcription factor pioneering and enhancer activation. Dev Cell 2023; 58:1898-1916.e9. [PMID: 37557175 PMCID: PMC10592203 DOI: 10.1016/j.devcel.2023.07.007] [Citation(s) in RCA: 9] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/28/2022] [Revised: 05/09/2023] [Accepted: 07/13/2023] [Indexed: 08/11/2023]
Abstract
Chromatin accessibility is integral to the process by which transcription factors (TFs) read out cis-regulatory DNA sequences, but it is difficult to differentiate between TFs that drive accessibility and those that do not. Deep learning models that learn complex sequence rules provide an unprecedented opportunity to dissect this problem. Using zygotic genome activation in Drosophila as a model, we analyzed high-resolution TF binding and chromatin accessibility data with interpretable deep learning and performed genetic validation experiments. We identify a hierarchical relationship between the pioneer TF Zelda and the TFs involved in axis patterning. Zelda consistently pioneers chromatin accessibility proportional to motif affinity, whereas patterning TFs augment chromatin accessibility in sequence contexts where they mediate enhancer activation. We conclude that chromatin accessibility occurs in two tiers: one through pioneering, which makes enhancers accessible but not necessarily active, and the second when the correct combination of TFs leads to enhancer activation.
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Affiliation(s)
- Kaelan J Brennan
- Stowers Institute for Medical Research, Kansas City, MO 64110, USA
| | - Melanie Weilert
- Stowers Institute for Medical Research, Kansas City, MO 64110, USA
| | - Sabrina Krueger
- Stowers Institute for Medical Research, Kansas City, MO 64110, USA
| | - Anusri Pampari
- Department of Computer Science, Stanford University, Palo Alto, CA 94305, USA
| | - Hsiao-Yun Liu
- Department of Biology, New York University, New York, NY 10003, USA
| | - Ally W H Yang
- Donnelly Centre, University of Toronto, Toronto, ON M5S 3E1, Canada
| | - Jason A Morrison
- Stowers Institute for Medical Research, Kansas City, MO 64110, USA
| | - Timothy R Hughes
- Donnelly Centre, University of Toronto, Toronto, ON M5S 3E1, Canada
| | | | - Anshul Kundaje
- Department of Computer Science, Stanford University, Palo Alto, CA 94305, USA; Department of Genetics, Stanford University, Palo Alto, CA 94305, USA
| | - Julia Zeitlinger
- Stowers Institute for Medical Research, Kansas City, MO 64110, USA; Department of Pathology & Laboratory Medicine, The University of Kansas Medical Center, Kansas City, KS 66160, USA.
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2
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Chahda JS, Ambrosi P, Mizutani CM. The nested embryonic dorsal domains of BMP-target genes are not scaled to size during the evolution of Drosophila species. JOURNAL OF EXPERIMENTAL ZOOLOGY. PART B, MOLECULAR AND DEVELOPMENTAL EVOLUTION 2023; 340:131-142. [PMID: 35451554 PMCID: PMC9587137 DOI: 10.1002/jez.b.23137] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/07/2021] [Revised: 03/21/2022] [Accepted: 04/03/2022] [Indexed: 11/08/2022]
Abstract
Egg size is a fast-evolving trait among Drosophilids expected to change the spatial distribution of morphogens that pattern the embryonic axes. Here we asked whether the patterning of the dorsal region of the embryo by the Decapentaplegic/Bone Morphogenetic Protein-4 (DPP/BMP-4) gradient is scaled among Drosophila species with different egg sizes. This region specifies the extra-embryonic tissue amnioserosa and the ectoderm. We find that the entire dorsal region scales with embryo size, but the gene expression patterns regulated by DPP are not proportional, suggesting that the DPP gradient is differentially scaled during evolution. To further test whether the DPP gradient can scale or not in Drosophila melanogaster, we created embryos with expanded dorsal regions that mimic changes in scale seen in other species and measured the resulting domains of DPP-target genes. We find that the proportions of these domains are not maintained, suggesting that the DPP gradient is unable to scale in the embryo. These and previous findings suggest that the embryonic dorso-ventral patterning lack scaling in the ventral and dorsal sides but is robust in the lateral region where the neuroectoderm is specified and two opposing gradients, Dorsal/NFkappa-B and DPP, intersect. We propose that the lack of scaling of the DPP gradient may contribute to changes in the size of the amnioserosa and the numbers of ectodermal cells with specific cortical tensions, which are expected to generate distinct mechanical forces for gastrulating embryos of different sizes.
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Affiliation(s)
- Juan Sebastian Chahda
- Department of Biology, College of Arts and Sciences, Case Western Reserve University, Cleveland, Ohio, USA
| | - Priscilla Ambrosi
- Department of Biology, College of Arts and Sciences, Case Western Reserve University, Cleveland, Ohio, USA
| | - Claudia Mieko Mizutani
- Department of Biology, College of Arts and Sciences, Case Western Reserve University, Cleveland, Ohio, USA.,Department of Genetics and Genome Sciences, School of Medicine, Case Western Reserve University, Cleveland, Ohio, USA.,Corresponding author:
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3
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The Genetic Mechanisms Underlying the Concerted Expression of the yellow and tan Genes in Complex Patterns on the Abdomen and Wings of Drosophila guttifera. Genes (Basel) 2023; 14:genes14020304. [PMID: 36833231 PMCID: PMC9957387 DOI: 10.3390/genes14020304] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/13/2022] [Revised: 01/12/2023] [Accepted: 01/21/2023] [Indexed: 01/26/2023] Open
Abstract
How complex morphological patterns form is an intriguing question in developmental biology. However, the mechanisms that generate complex patterns remain largely unknown. Here, we sought to identify the genetic mechanisms that regulate the tan (t) gene in a multi-spotted pigmentation pattern on the abdomen and wings of Drosophila guttifera. Previously, we showed that yellow (y) gene expression completely prefigures the abdominal and wing pigment patterns of this species. In the current study, we demonstrate that the t gene is co-expressed with the y gene in nearly identical patterns, both transcripts foreshadowing the adult abdominal and wing melanin spot patterns. We identified cis-regulatory modules (CRMs) of t, one of which drives reporter expression in six longitudinal rows of spots on the developing pupal abdomen, while the second CRM activates the reporter gene in a spotted wing pattern. Comparing the abdominal spot CRMs of y and t, we found a similar composition of putative transcription factor binding sites that are thought to regulate the complex expression patterns of both terminal pigmentation genes y and t. In contrast, the y and t wing spots appear to be regulated by distinct upstream factors. Our results suggest that the D. guttifera abdominal and wing melanin spot patterns have been established through the co-regulation of y and t, shedding light on how complex morphological traits may be regulated through the parallel coordination of downstream target genes.
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4
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DeepSTARR predicts enhancer activity from DNA sequence and enables the de novo design of synthetic enhancers. Nat Genet 2022; 54:613-624. [PMID: 35551305 DOI: 10.1038/s41588-022-01048-5] [Citation(s) in RCA: 69] [Impact Index Per Article: 34.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/20/2021] [Accepted: 03/08/2022] [Indexed: 02/06/2023]
Abstract
Enhancer sequences control gene expression and comprise binding sites (motifs) for different transcription factors (TFs). Despite extensive genetic and computational studies, the relationship between DNA sequence and regulatory activity is poorly understood, and de novo enhancer design has been challenging. Here, we built a deep-learning model, DeepSTARR, to quantitatively predict the activities of thousands of developmental and housekeeping enhancers directly from DNA sequence in Drosophila melanogaster S2 cells. The model learned relevant TF motifs and higher-order syntax rules, including functionally nonequivalent instances of the same TF motif that are determined by motif-flanking sequence and intermotif distances. We validated these rules experimentally and demonstrated that they can be generalized to humans by testing more than 40,000 wildtype and mutant Drosophila and human enhancers. Finally, we designed and functionally validated synthetic enhancers with desired activities de novo.
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5
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Dibaeinia P, Sinha S. Deciphering enhancer sequence using thermodynamics-based models and convolutional neural networks. Nucleic Acids Res 2021; 49:10309-10327. [PMID: 34508359 PMCID: PMC8501998 DOI: 10.1093/nar/gkab765] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/16/2021] [Revised: 08/18/2021] [Accepted: 08/25/2021] [Indexed: 11/18/2022] Open
Abstract
Deciphering the sequence-function relationship encoded in enhancers holds the key to interpreting non-coding variants and understanding mechanisms of transcriptomic variation. Several quantitative models exist for predicting enhancer function and underlying mechanisms; however, there has been no systematic comparison of these models characterizing their relative strengths and shortcomings. Here, we interrogated a rich data set of neuroectodermal enhancers in Drosophila, representing cis- and trans- sources of expression variation, with a suite of biophysical and machine learning models. We performed rigorous comparisons of thermodynamics-based models implementing different mechanisms of activation, repression and cooperativity. Moreover, we developed a convolutional neural network (CNN) model, called CoNSEPT, that learns enhancer 'grammar' in an unbiased manner. CoNSEPT is the first general-purpose CNN tool for predicting enhancer function in varying conditions, such as different cell types and experimental conditions, and we show that such complex models can suggest interpretable mechanisms. We found model-based evidence for mechanisms previously established for the studied system, including cooperative activation and short-range repression. The data also favored one hypothesized activation mechanism over another and suggested an intriguing role for a direct, distance-independent repression mechanism. Our modeling shows that while fundamentally different models can yield similar fits to data, they vary in their utility for mechanistic inference. CoNSEPT is freely available at: https://github.com/PayamDiba/CoNSEPT.
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Affiliation(s)
- Payam Dibaeinia
- Department of Computer Science, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA
| | - Saurabh Sinha
- Department of Computer Science, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA
- Carl R. Woese Institute for Genomic Biology, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA
- Cancer Center at Illinois, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA
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6
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Jindal GA, Farley EK. Enhancer grammar in development, evolution, and disease: dependencies and interplay. Dev Cell 2021; 56:575-587. [PMID: 33689769 PMCID: PMC8462829 DOI: 10.1016/j.devcel.2021.02.016] [Citation(s) in RCA: 47] [Impact Index Per Article: 15.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/13/2020] [Revised: 02/15/2021] [Accepted: 02/16/2021] [Indexed: 12/19/2022]
Abstract
Each language has standard books describing that language's grammatical rules. Biologists have searched for similar, albeit more complex, principles relating enhancer sequence to gene expression. Here, we review the literature on enhancer grammar. We introduce dependency grammar, a model where enhancers encode information based on dependencies between enhancer features shaped by mechanistic, evolutionary, and biological constraints. Classifying enhancers based on the types of dependencies may identify unifying principles relating enhancer sequence to gene expression. Such rules would allow us to read the instructions for development within genomes and pinpoint causal enhancer variants underlying disease and evolutionary changes.
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Affiliation(s)
- Granton A Jindal
- Division of Cardiology, Department of Medicine, University of California San Diego, La Jolla, CA 92093, USA; Division of Biological Sciences, Section of Molecular Biology, University of California San Diego, La Jolla, CA 92093, USA
| | - Emma K Farley
- Division of Cardiology, Department of Medicine, University of California San Diego, La Jolla, CA 92093, USA; Division of Biological Sciences, Section of Molecular Biology, University of California San Diego, La Jolla, CA 92093, USA.
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7
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Chen L, Capra JA. Learning and interpreting the gene regulatory grammar in a deep learning framework. PLoS Comput Biol 2020; 16:e1008334. [PMID: 33137083 PMCID: PMC7660921 DOI: 10.1371/journal.pcbi.1008334] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/16/2019] [Revised: 11/12/2020] [Accepted: 09/12/2020] [Indexed: 12/12/2022] Open
Abstract
Deep neural networks (DNNs) have achieved state-of-the-art performance in identifying gene regulatory sequences, but they have provided limited insight into the biology of regulatory elements due to the difficulty of interpreting the complex features they learn. Several models of how combinatorial binding of transcription factors, i.e. the regulatory grammar, drives enhancer activity have been proposed, ranging from the flexible TF billboard model to the stringent enhanceosome model. However, there is limited knowledge of the prevalence of these (or other) sequence architectures across enhancers. Here we perform several hypothesis-driven analyses to explore the ability of DNNs to learn the regulatory grammar of enhancers. We created synthetic datasets based on existing hypotheses about combinatorial transcription factor binding site (TFBS) patterns, including homotypic clusters, heterotypic clusters, and enhanceosomes, from real TF binding motifs from diverse TF families. We then trained deep residual neural networks (ResNets) to model the sequences under a range of scenarios that reflect real-world multi-label regulatory sequence prediction tasks. We developed a gradient-based unsupervised clustering method to extract the patterns learned by the ResNet models. We demonstrated that simulated regulatory grammars are best learned in the penultimate layer of the ResNets, and the proposed method can accurately retrieve the regulatory grammar even when there is heterogeneity in the enhancer categories and a large fraction of TFBS outside of the regulatory grammar. However, we also identify common scenarios where ResNets fail to learn simulated regulatory grammars. Finally, we applied the proposed method to mouse developmental enhancers and were able to identify the components of a known heterotypic TF cluster. Our results provide a framework for interpreting the regulatory rules learned by ResNets, and they demonstrate that the ability and efficiency of ResNets in learning the regulatory grammar depends on the nature of the prediction task.
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Affiliation(s)
- Ling Chen
- Department of Biological Sciences, Vanderbilt University, Nashville, TN, United States of America
| | - John A. Capra
- Department of Biological Sciences, Vanderbilt University, Nashville, TN, United States of America
- Vanderbilt Genetics Institute and Department of Biomedical Informatics, Vanderbilt University Medical Center, Nashville, TN, United States of America
- Department of Computer Science, Vanderbilt University, Nashville, TN, United States of America
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8
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Crocker J, Ilsley GR. Using synthetic biology to study gene regulatory evolution. Curr Opin Genet Dev 2017; 47:91-101. [DOI: 10.1016/j.gde.2017.09.001] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/05/2017] [Revised: 09/06/2017] [Accepted: 09/11/2017] [Indexed: 12/21/2022]
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9
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Elmas A, Wang X, Dresch JM. The folded k-spectrum kernel: A machine learning approach to detecting transcription factor binding sites with gapped nucleotide dependencies. PLoS One 2017; 12:e0185570. [PMID: 28982128 PMCID: PMC5628859 DOI: 10.1371/journal.pone.0185570] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/11/2017] [Accepted: 09/14/2017] [Indexed: 12/22/2022] Open
Abstract
Understanding the molecular machinery involved in transcriptional regulation is central to improving our knowledge of an organism's development, disease, and evolution. The building blocks of this complex molecular machinery are an organism's genomic DNA sequence and transcription factor proteins. Despite the vast amount of sequence data now available for many model organisms, predicting where transcription factors bind, often referred to as 'motif detection' is still incredibly challenging. In this study, we develop a novel bioinformatic approach to binding site prediction. We do this by extending pre-existing SVM approaches in an unbiased way to include all possible gapped k-mers, representing different combinations of complex nucleotide dependencies within binding sites. We show the advantages of this new approach when compared to existing SVM approaches, through a rigorous set of cross-validation experiments. We also demonstrate the effectiveness of our new approach by reporting on its improved performance on a set of 127 genomic regions known to regulate gene expression along the anterio-posterior axis in early Drosophila embryos.
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Affiliation(s)
- Abdulkadir Elmas
- Department of Electrical Engineering, Columbia University, New York, NY, United States of America
| | - Xiaodong Wang
- Department of Electrical Engineering, Columbia University, New York, NY, United States of America
| | - Jacqueline M. Dresch
- Department of Mathematics and Computer Science, Clark University, Worcester, MA, United States of America
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10
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Crocker J, Stern DL. Functional regulatory evolution outside of the minimal even-skipped stripe 2 enhancer. Development 2017; 144:3095-3101. [PMID: 28760812 DOI: 10.1242/dev.149427] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/19/2017] [Accepted: 07/19/2017] [Indexed: 12/27/2022]
Abstract
Transcriptional enhancers are regions of DNA that drive precise patterns of gene expression. Although many studies have elucidated how individual enhancers can evolve, most of this work has focused on what are called 'minimal' enhancers, the smallest DNA regions that drive expression that approximates an aspect of native gene expression. Here, we explore how the Drosophila erecta even-skipped (eve) locus has evolved by testing its activity in the divergent D. melanogaster genome. We found, as has been reported previously, that the D. erecta eve stripe 2 enhancer (eveS2) fails to drive appreciable expression in D. melanogaster However, we found that a large transgene carrying the entire D. erecta eve locus drives normal eve expression, including in stripe 2. We performed a functional dissection of the region upstream of the D. erecta eveS2 region and found multiple Zelda motifs that are required for normal expression. Our results illustrate how sequences outside of minimal enhancer regions can evolve functionally through mechanisms other than changes in transcription factor-binding sites that drive patterning.
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Affiliation(s)
- Justin Crocker
- Janelia Research Campus, Howard Hughes Medical Institute, 19700 Helix Drive, Ashburn, VA 20147, USA
| | - David L Stern
- Janelia Research Campus, Howard Hughes Medical Institute, 19700 Helix Drive, Ashburn, VA 20147, USA
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11
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Crocker J, Tsai A, Stern DL. A Fully Synthetic Transcriptional Platform for a Multicellular Eukaryote. Cell Rep 2017; 18:287-296. [DOI: 10.1016/j.celrep.2016.12.025] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/09/2015] [Revised: 12/14/2015] [Accepted: 12/07/2016] [Indexed: 01/12/2023] Open
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12
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Sandler JE, Stathopoulos A. Stepwise Progression of Embryonic Patterning. Trends Genet 2016; 32:432-443. [PMID: 27230753 DOI: 10.1016/j.tig.2016.04.004] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/18/2016] [Revised: 04/20/2016] [Accepted: 04/21/2016] [Indexed: 01/23/2023]
Abstract
It is long established that the graded distribution of Dorsal transcription factor influences spatial domains of gene expression along the dorsoventral (DV) axis of Drosophila melanogaster embryos. However, the more recent realization that Dorsal levels also change with time raises the question of whether these dynamics are instructive. An overview of DV axis patterning is provided, focusing on new insights identified through quantitative analysis of temporal changes in Dorsal target gene expression from one nuclear cycle to the next ('steps'). Possible roles for the stepwise progression of this patterning program are discussed including (i) tight temporal regulation of signaling pathway activation, (ii) control of gene expression cohorts, and (iii) ensuring the irreversibility of the patterning and cell fate specification process.
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Affiliation(s)
- Jeremy E Sandler
- Division of Biology and Biological Engineering, California Institute of Technology, Pasadena, CA 91125, USA
| | - Angelike Stathopoulos
- Division of Biology and Biological Engineering, California Institute of Technology, Pasadena, CA 91125, USA.
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13
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Integration of Orthogonal Signaling by the Notch and Dpp Pathways in Drosophila. Genetics 2016; 203:219-40. [PMID: 26975664 PMCID: PMC4858776 DOI: 10.1534/genetics.116.186791] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/04/2016] [Accepted: 03/08/2016] [Indexed: 11/18/2022] Open
Abstract
The transcription factor Suppressor of Hairless and its coactivator, the Notch intracellular domain, are polyglutamine (pQ)-rich factors that target enhancer elements and interact with other locally bound pQ-rich factors. To understand the functional repertoire of such enhancers, we identify conserved regulatory belts with binding sites for the pQ-rich effectors of both Notch and BMP/Dpp signaling, and the pQ-deficient tissue selectors Apterous (Ap), Scalloped (Sd), and Vestigial (Vg). We find that the densest such binding site cluster in the genome is located in the BMP-inducible nab locus, a homolog of the vertebrate transcriptional cofactors NAB1/NAB2 We report three major findings. First, we find that this nab regulatory belt is a novel enhancer driving dorsal wing margin expression in regions of peak phosphorylated Mad in wing imaginal discs. Second, we show that Ap is developmentally required to license the nab dorsal wing margin enhancer (DWME) to read out Notch and Dpp signaling in the dorsal compartment. Third, we find that the nab DWME is embedded in a complex of intronic enhancers, including a wing quadrant enhancer, a proximal wing disc enhancer, and a larval brain enhancer. This enhancer complex coordinates global nab expression via both tissue-specific activation and interenhancer silencing. We suggest that DWME integration of BMP signaling maintains nab expression in proliferating margin descendants that have divided away from Notch-Delta boundary signaling. As such, uniform expression of genes like nab and vestigial in proliferating compartments would typically require both boundary and nonboundary lineage-specific enhancers.
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14
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Quantitatively predictable control of Drosophila transcriptional enhancers in vivo with engineered transcription factors. Nat Genet 2016; 48:292-8. [DOI: 10.1038/ng.3509] [Citation(s) in RCA: 26] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/30/2015] [Accepted: 01/15/2016] [Indexed: 12/13/2022]
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15
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Dresch JM, Arnosti DN. The Wisdom of Crowds: Can Mathematical Models Crack the cis Regulatory Code? Cell Syst 2015; 1:379-80. [PMID: 27136351 DOI: 10.1016/j.cels.2015.12.006] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022]
Abstract
Genomic information includes not just a "parts list" of encoded proteins and RNAs, but also the information on regulation and function. To understand this more complex, deeper layer of biological information, recent efforts have turned to mathematical models as discovery engines of the cis regulatory code.
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Affiliation(s)
- Jacqueline M Dresch
- Mathematics and Computer Science Department, Clark University, 950 Main Street, Worcester, MA 01610, USA.
| | - David N Arnosti
- Biochemistry and Molecular Biology, Michigan State University, East Lansing, MI 48824, USA.
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16
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The Nature, Extent, and Consequences of Genetic Variation in the opa Repeats of Notch in Drosophila. G3-GENES GENOMES GENETICS 2015; 5:2405-19. [PMID: 26362765 PMCID: PMC4632060 DOI: 10.1534/g3.115.021659] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Polyglutamine (pQ) tracts are abundant in proteins co-interacting on DNA. The lengths of these pQ tracts can modulate their interaction strengths. However, pQ tracts >40 residues are pathologically prone to amyloidogenic self-assembly. Here, we assess the extent and consequences of variation in the pQ-encoding opa repeats of Notch in Drosophila melanogaster. We use Sanger sequencing to genotype opa sequences (5′-CAX repeats), which have resisted assembly using short sequence reads. While most sampled lines carry the major allele opa31 encoding Q13HQ17 or the opa32 allele encoding Q13HQ18, many lines carry rare alleles encoding pQ tracts >32 residues: opa33a (Q14HQ18), opa33b (Q15HQ17), opa34 (Q16HQ17), opa35a1/opa35a2 (Q13HQ21), opa36 (Q13HQ22), and opa37 (Q13HQ23). Only one rare allele encodes a tract <31 residues: opa23 (Q13–Q10). This opa23 allele shortens the pQ tract while simultaneously eliminating the interrupting histidine. We introgressed these opa variant alleles into common backgrounds and measured the frequency of Notch-type phenotypes. Homozygotes for the short and long opa alleles have defects in embryonic survival and sensory bristle organ patterning, and sometimes show wing notching. Consistent with functional differences between Notch opa variants, we find that a scute inversion carrying the rare opa33b allele suppresses the bristle patterning defect caused by achaete/scute insufficiency, while an equivalent scute inversion carrying opa31 manifests the patterning defect. Our results demonstrate the existence of potent pQ variants of Notch and the need for long read genotyping of key repeat variables underlying gene regulatory networks.
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17
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Clifford J, Adami C. Discovery and information-theoretic characterization of transcription factor binding sites that act cooperatively. Phys Biol 2015; 12:056004. [PMID: 26331781 DOI: 10.1088/1478-3975/12/5/056004] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
Transcription factor binding to the surface of DNA regulatory regions is one of the primary causes of regulating gene expression levels. A probabilistic approach to model protein-DNA interactions at the sequence level is through position weight matrices (PWMs) that estimate the joint probability of a DNA binding site sequence by assuming positional independence within the DNA sequence. Here we construct conditional PWMs that depend on the motif signatures in the flanking DNA sequence, by conditioning known binding site loci on the presence or absence of additional binding sites in the flanking sequence of each site's locus. Pooling known sites with similar flanking sequence patterns allows for the estimation of the conditional distribution function over the binding site sequences. We apply our model to the Dorsal transcription factor binding sites active in patterning the Dorsal-Ventral axis of Drosophila development. We find that those binding sites that cooperate with nearby Twist sites on average contain about 0.5 bits of information about the presence of Twist transcription factor binding sites in the flanking sequence. We also find that Dorsal binding site detectors conditioned on flanking sequence information make better predictions about what is a Dorsal site relative to background DNA than detection without information about flanking sequence features.
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Affiliation(s)
- Jacob Clifford
- Department of Physics and Astronomy, Michigan State University, East Lansing, MI, USA. BEACON Center for the Study of Evolution in Action, Michigan State University, East Lansing, MI, USA
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18
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Gordon KL, Arthur RK, Ruvinsky I. Phylum-Level Conservation of Regulatory Information in Nematodes despite Extensive Non-coding Sequence Divergence. PLoS Genet 2015; 11:e1005268. [PMID: 26020930 PMCID: PMC4447282 DOI: 10.1371/journal.pgen.1005268] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/15/2014] [Accepted: 05/09/2015] [Indexed: 11/28/2022] Open
Abstract
Gene regulatory information guides development and shapes the course of evolution. To test conservation of gene regulation within the phylum Nematoda, we compared the functions of putative cis-regulatory sequences of four sets of orthologs (unc-47, unc-25, mec-3 and elt-2) from distantly-related nematode species. These species, Caenorhabditis elegans, its congeneric C. briggsae, and three parasitic species Meloidogyne hapla, Brugia malayi, and Trichinella spiralis, represent four of the five major clades in the phylum Nematoda. Despite the great phylogenetic distances sampled and the extensive sequence divergence of nematode genomes, all but one of the regulatory elements we tested are able to drive at least a subset of the expected gene expression patterns. We show that functionally conserved cis-regulatory elements have no more extended sequence similarity to their C. elegans orthologs than would be expected by chance, but they do harbor motifs that are important for proper expression of the C. elegans genes. These motifs are too short to be distinguished from the background level of sequence similarity, and while identical in sequence they are not conserved in orientation or position. Functional tests reveal that some of these motifs contribute to proper expression. Our results suggest that conserved regulatory circuitry can persist despite considerable turnover within cis elements. To explore the phylogenetic limits of conservation of cis-regulatory elements, we used transgenesis to test the functions of enhancers of four genes from several species spanning the phylum Nematoda. While we found a striking degree of functional conservation among the examined cis elements, their DNA sequences lacked apparent conservation with the C. elegans orthologs. In fact, sequence similarity between C. elegans and the distantly related nematodes was no greater than would be expected by chance. Short motifs, similar to known regulatory sequences in C. elegans, can be detected in most of the cis elements. When tested, some of these sites appear to mediate regulatory function. However, they seem to have originated through motif turnover, rather than to have been preserved from a common ancestor. Our results suggest that gene regulatory networks are broadly conserved in the phylum Nematoda, but this conservation persists despite substantial reorganization of regulatory elements and could not be detected using naïve comparisons of sequence similarity.
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Affiliation(s)
- Kacy L. Gordon
- Department of Organismal Biology and Anatomy, The University of Chicago, Chicago, Illinois, United States of America
- * E-mail: (KLG); (IR)
| | - Robert K. Arthur
- Department of Ecology and Evolution, The University of Chicago, Chicago, Illinois, United States of America
| | - Ilya Ruvinsky
- Department of Organismal Biology and Anatomy, The University of Chicago, Chicago, Illinois, United States of America
- Department of Ecology and Evolution, The University of Chicago, Chicago, Illinois, United States of America
- * E-mail: (KLG); (IR)
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19
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Camino EM, Butts JC, Ordway A, Vellky JE, Rebeiz M, Williams TM. The evolutionary origination and diversification of a dimorphic gene regulatory network through parallel innovations in cis and trans. PLoS Genet 2015; 11:e1005136. [PMID: 25835988 PMCID: PMC4383587 DOI: 10.1371/journal.pgen.1005136] [Citation(s) in RCA: 34] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/10/2014] [Accepted: 03/10/2015] [Indexed: 01/15/2023] Open
Abstract
The origination and diversification of morphological characteristics represents a key problem in understanding the evolution of development. Morphological traits result from gene regulatory networks (GRNs) that form a web of transcription factors, which regulate multiple cis-regulatory element (CRE) sequences to control the coordinated expression of differentiation genes. The formation and modification of GRNs must ultimately be understood at the level of individual regulatory linkages (i.e., transcription factor binding sites within CREs) that constitute the network. Here, we investigate how elements within a network originated and diversified to generate a broad range of abdominal pigmentation phenotypes among Sophophora fruit flies. Our data indicates that the coordinated expression of two melanin synthesis enzymes, Yellow and Tan, recently evolved through novel CRE activities that respond to the spatial patterning inputs of Hox proteins and the sex-specific input of Bric-à-brac transcription factors. Once established, it seems that these newly evolved activities were repeatedly modified by evolutionary changes in the network’s trans-regulators to generate large-scale changes in pigment pattern. By elucidating how yellow and tan are connected to the web of abdominal trans-regulators, we discovered that the yellow and tan abdominal CREs are composed of distinct regulatory inputs that exhibit contrasting responses to the same Hox proteins and Hox cofactors. These results provide an example in which CRE origination underlies a recently evolved novel trait, and highlights how coordinated expression patterns can evolve in parallel through the generation of unique regulatory linkages. The genomic content of regulatory genes such as transcription factors is surprisingly conserved between diverse animal species, raising the paradox of how new traits emerge, and are subsequently modified and lost. In this study we make a connection between the developmental basis for the formation of a fruit fly trait and the evolutionary basis for that trait’s origin, diversification, and loss. We show how the origin of a novel pigmentation trait is associated with the evolution of two regulatory sequences that control the co-expression of two key pigmentation genes. These sequences interact in unique ways with evolutionarily conserved Hox transcription factors to drive gene co-expression. Once these unique connections evolved, the alteration of this trait appears to have proceeded through changes to regulatory genes rather than regulatory sequences of the pigmentation genes. Thus, our findings support a scenario where regulatory sequence evolution provided new functions to old transcription factors, how co-expression can emerge from different utilizations of the same transcription factors, and that trait diversity was surprisingly shaped by changes in some manner to the deeply conserved regulatory genes.
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Affiliation(s)
- Eric M. Camino
- Department of Biology, University of Dayton, Dayton, Ohio, United States of America
| | - John C. Butts
- Department of Biology, University of Dayton, Dayton, Ohio, United States of America
| | - Alison Ordway
- Department of Biological Sciences, University of Pittsburgh, Pittsburgh, Pennsylvania, United States of America
| | - Jordan E. Vellky
- Department of Biology, University of Dayton, Dayton, Ohio, United States of America
| | - Mark Rebeiz
- Department of Biological Sciences, University of Pittsburgh, Pittsburgh, Pennsylvania, United States of America
| | - Thomas M. Williams
- Department of Biology, University of Dayton, Dayton, Ohio, United States of America
- Center for Tissue Regeneration and Engineering at Dayton, University of Dayton, Dayton, Ohio, United States of America
- * E-mail:
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20
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Ozdemir A, Ma L, White KP, Stathopoulos A. Su(H)-mediated repression positions gene boundaries along the dorsal-ventral axis of Drosophila embryos. Dev Cell 2015; 31:100-13. [PMID: 25313963 DOI: 10.1016/j.devcel.2014.08.005] [Citation(s) in RCA: 29] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/17/2013] [Revised: 06/10/2014] [Accepted: 08/05/2014] [Indexed: 12/22/2022]
Abstract
In Drosophila embryos, a nuclear gradient of the Dorsal (Dl) transcription factor directs differential gene expression along the dorsoventral (DV) axis, translating it into distinct domains that specify future mesodermal, neural, and ectodermal territories. However, the mechanisms used to differentially position gene expression boundaries along this axis are not fully understood. Here, using a combination of approaches, including mutant phenotype analyses and chromatin immunoprecipitation, we show that the transcription factor Suppressor of Hairless, Su(H), helps define dorsal boundaries for many genes expressed along the DV axis. Synthetic reporter constructs also provide molecular evidence that Su(H) binding sites support repression and act to counterbalance activation through Dl and the ubiquitous activator Zelda. Our study highlights a role for broadly expressed repressors, like Su(H), and organization of transcription factor binding sites within cis-regulatory modules as important elements controlling spatial domains of gene expression to facilitate flexible positioning of boundaries across the entire DV axis.
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Affiliation(s)
- Anil Ozdemir
- Division of Biology and Biological Engineering, California Institute of Technology, Pasadena, CA 91125, USA
| | - Lijia Ma
- Institute for Genomics and Systems Biology and Department of Human Genetics, University of Chicago, Chicago, IL 60637, USA
| | - Kevin P White
- Institute for Genomics and Systems Biology and Department of Human Genetics, University of Chicago, Chicago, IL 60637, USA
| | - Angelike Stathopoulos
- Division of Biology and Biological Engineering, California Institute of Technology, Pasadena, CA 91125, USA.
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21
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Crocker J, Abe N, Rinaldi L, McGregor AP, Frankel N, Wang S, Alsawadi A, Valenti P, Plaza S, Payre F, Mann RS, Stern DL. Low affinity binding site clusters confer hox specificity and regulatory robustness. Cell 2014; 160:191-203. [PMID: 25557079 DOI: 10.1016/j.cell.2014.11.041] [Citation(s) in RCA: 245] [Impact Index Per Article: 24.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/05/2014] [Revised: 09/11/2014] [Accepted: 11/13/2014] [Indexed: 11/26/2022]
Abstract
In animals, Hox transcription factors define regional identity in distinct anatomical domains. How Hox genes encode this specificity is a paradox, because different Hox proteins bind with high affinity in vitro to similar DNA sequences. Here, we demonstrate that the Hox protein Ultrabithorax (Ubx) in complex with its cofactor Extradenticle (Exd) bound specifically to clusters of very low affinity sites in enhancers of the shavenbaby gene of Drosophila. These low affinity sites conferred specificity for Ubx binding in vivo, but multiple clustered sites were required for robust expression when embryos developed in variable environments. Although most individual Ubx binding sites are not evolutionarily conserved, the overall enhancer architecture-clusters of low affinity binding sites-is maintained and required for enhancer function. Natural selection therefore works at the level of the enhancer, requiring a particular density of low affinity Ubx sites to confer both specific and robust expression.
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Affiliation(s)
- Justin Crocker
- Janelia Research Campus, Howard Hughes Medical Institute, 19700 Helix Drive, Ashburn, VA 20147, USA
| | - Namiko Abe
- Columbia University Medical Center, 701 West 168(th) Street, HHSC 1104, New York, NY 10032, USA
| | - Lucrezia Rinaldi
- Columbia University Medical Center, 701 West 168(th) Street, HHSC 1104, New York, NY 10032, USA
| | - Alistair P McGregor
- Department of Biological and Medical Sciences, Oxford Brookes University, Gipsy Lane, Oxford OX3 0BP, UK
| | - Nicolás Frankel
- Departamento de Ecología, Genética y Evolución, IEGEBA-CONICET, Facultad, de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Ciudad, Universitaria, Pabellón 2, 1428 Buenos Aires, Argentina
| | - Shu Wang
- New Jersey Neuroscience Institute, 65 James Street, Edison, NJ 08820, USA
| | - Ahmad Alsawadi
- Centre de Biologie du Développement, Université de Toulouse, UPS, 31062 Cedex 9, France; CNRS, UMR5547, Centre de Biologie du Développement, Toulouse, 31062 Cedex 9, France
| | - Philippe Valenti
- Centre de Biologie du Développement, Université de Toulouse, UPS, 31062 Cedex 9, France; CNRS, UMR5547, Centre de Biologie du Développement, Toulouse, 31062 Cedex 9, France
| | - Serge Plaza
- Centre de Biologie du Développement, Université de Toulouse, UPS, 31062 Cedex 9, France; CNRS, UMR5547, Centre de Biologie du Développement, Toulouse, 31062 Cedex 9, France
| | - François Payre
- Centre de Biologie du Développement, Université de Toulouse, UPS, 31062 Cedex 9, France; CNRS, UMR5547, Centre de Biologie du Développement, Toulouse, 31062 Cedex 9, France
| | - Richard S Mann
- Columbia University Medical Center, 701 West 168(th) Street, HHSC 1104, New York, NY 10032, USA.
| | - David L Stern
- Janelia Research Campus, Howard Hughes Medical Institute, 19700 Helix Drive, Ashburn, VA 20147, USA.
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22
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Slattery M, Zhou T, Yang L, Dantas Machado AC, Gordân R, Rohs R. Absence of a simple code: how transcription factors read the genome. Trends Biochem Sci 2014; 39:381-99. [PMID: 25129887 DOI: 10.1016/j.tibs.2014.07.002] [Citation(s) in RCA: 352] [Impact Index Per Article: 35.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/03/2014] [Revised: 07/11/2014] [Accepted: 07/15/2014] [Indexed: 12/21/2022]
Abstract
Transcription factors (TFs) influence cell fate by interpreting the regulatory DNA within a genome. TFs recognize DNA in a specific manner; the mechanisms underlying this specificity have been identified for many TFs based on 3D structures of protein-DNA complexes. More recently, structural views have been complemented with data from high-throughput in vitro and in vivo explorations of the DNA-binding preferences of many TFs. Together, these approaches have greatly expanded our understanding of TF-DNA interactions. However, the mechanisms by which TFs select in vivo binding sites and alter gene expression remain unclear. Recent work has highlighted the many variables that influence TF-DNA binding, while demonstrating that a biophysical understanding of these many factors will be central to understanding TF function.
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Affiliation(s)
- Matthew Slattery
- Department of Biomedical Sciences, University of Minnesota Medical School, Duluth, MN 55812, USA; Developmental Biology Center, University of Minnesota, Minneapolis, MN 55455, USA.
| | - Tianyin Zhou
- Molecular and Computational Biology Program, Departments of Biological Sciences, Chemistry, Physics, and Computer Science, University of Southern California, Los Angeles, CA 90089, USA
| | - Lin Yang
- Molecular and Computational Biology Program, Departments of Biological Sciences, Chemistry, Physics, and Computer Science, University of Southern California, Los Angeles, CA 90089, USA
| | - Ana Carolina Dantas Machado
- Molecular and Computational Biology Program, Departments of Biological Sciences, Chemistry, Physics, and Computer Science, University of Southern California, Los Angeles, CA 90089, USA
| | - Raluca Gordân
- Center for Genomic and Computational Biology, Departments of Biostatistics and Bioinformatics, Computer Science, and Molecular Genetics and Microbiology, Duke University, Durham, NC 27708, USA.
| | - Remo Rohs
- Molecular and Computational Biology Program, Departments of Biological Sciences, Chemistry, Physics, and Computer Science, University of Southern California, Los Angeles, CA 90089, USA.
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23
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Arnold CD, Gerlach D, Spies D, Matts JA, Sytnikova YA, Pagani M, Lau NC, Stark A. Quantitative genome-wide enhancer activity maps for five Drosophila species show functional enhancer conservation and turnover during cis-regulatory evolution. Nat Genet 2014; 46:685-92. [PMID: 24908250 PMCID: PMC4250274 DOI: 10.1038/ng.3009] [Citation(s) in RCA: 120] [Impact Index Per Article: 12.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/03/2014] [Accepted: 05/15/2014] [Indexed: 12/14/2022]
Abstract
Phenotypic differences between closely related species are thought to arise primarily from changes in gene expression due to mutations in cis-regulatory sequences (enhancers). However, it has remained unclear how frequently mutations alter enhancer activity or create functional enhancers de novo. Here we use STARR-seq, a recently developed quantitative enhancer assay, to determine genome-wide enhancer activity profiles for five Drosophila species in the constant trans-regulatory environment of Drosophila melanogaster S2 cells. We find that the functions of a large fraction of D. melanogaster enhancers are conserved for their orthologous sequences owing to selection and stabilizing turnover of transcription factor motifs. Moreover, hundreds of enhancers have been gained since the D. melanogaster-Drosophila yakuba split about 11 million years ago without apparent adaptive selection and can contribute to changes in gene expression in vivo. Our finding that enhancer activity is often deeply conserved and frequently gained provides functional insights into regulatory evolution.
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Affiliation(s)
- Cosmas D Arnold
- 1] Research Institute of Molecular Pathology (IMP), Vienna Biocenter (VBC), Vienna, Austria. [2]
| | - Daniel Gerlach
- 1] Research Institute of Molecular Pathology (IMP), Vienna Biocenter (VBC), Vienna, Austria. [2] [3]
| | - Daniel Spies
- Research Institute of Molecular Pathology (IMP), Vienna Biocenter (VBC), Vienna, Austria
| | - Jessica A Matts
- 1] Department of Biology, Brandeis University, Waltham, Massachusetts, USA. [2] Rosenstiel Basic Medical Science Research Center at Brandeis University, Waltham, Massachusetts, USA. [3]
| | - Yuliya A Sytnikova
- 1] Department of Biology, Brandeis University, Waltham, Massachusetts, USA. [2] Rosenstiel Basic Medical Science Research Center at Brandeis University, Waltham, Massachusetts, USA
| | - Michaela Pagani
- Research Institute of Molecular Pathology (IMP), Vienna Biocenter (VBC), Vienna, Austria
| | - Nelson C Lau
- 1] Department of Biology, Brandeis University, Waltham, Massachusetts, USA. [2] Rosenstiel Basic Medical Science Research Center at Brandeis University, Waltham, Massachusetts, USA
| | - Alexander Stark
- Research Institute of Molecular Pathology (IMP), Vienna Biocenter (VBC), Vienna, Austria
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24
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Brittain A, Stroebele E, Erives A. Microsatellite repeat instability fuels evolution of embryonic enhancers in Hawaiian Drosophila. PLoS One 2014; 9:e101177. [PMID: 24978198 PMCID: PMC4076327 DOI: 10.1371/journal.pone.0101177] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/02/2014] [Accepted: 06/03/2014] [Indexed: 12/16/2022] Open
Abstract
For ∼30 million years, the eggs of Hawaiian Drosophila were laid in ever-changing environments caused by high rates of island formation. The associated diversification of the size and developmental rate of the syncytial fly embryo would have altered morphogenic gradients, thus necessitating frequent evolutionary compensation of transcriptional responses. We investigate the consequences these radiations had on transcriptional enhancers patterning the embryo to see whether their pattern of molecular evolution is different from non-Hawaiian species. We identify and functionally assay in transgenic D. melanogaster the Neurogenic Ectoderm Enhancers from two different Hawaiian Drosophila groups: (i) the picture wing group, and (ii) the modified mouthparts group. We find that the binding sites in this set of well-characterized enhancers are footprinted by diverse microsatellite repeat (MSR) sequences. We further show that Hawaiian embryonic enhancers in general are enriched in MSR relative to both Hawaiian non-embryonic enhancers and non-Hawaiian embryonic enhancers. We propose embryonic enhancers are sensitive to Activator spacing because they often serve as assembly scaffolds for the aggregation of transcription factor activator complexes. Furthermore, as most indels are produced by microsatellite repeat slippage, enhancers from Hawaiian Drosophila lineages, which experience dynamic evolutionary pressures, would become grossly enriched in MSR content.
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Affiliation(s)
- Andrew Brittain
- Department of Biology, University of Iowa, Iowa City, Iowa, United States of America
| | - Elizabeth Stroebele
- Department of Biology, University of Iowa, Iowa City, Iowa, United States of America
| | - Albert Erives
- Department of Biology, University of Iowa, Iowa City, Iowa, United States of America
- * E-mail:
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25
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Barrière A, Ruvinsky I. Pervasive divergence of transcriptional gene regulation in Caenorhabditis nematodes. PLoS Genet 2014; 10:e1004435. [PMID: 24968346 PMCID: PMC4072541 DOI: 10.1371/journal.pgen.1004435] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/02/2013] [Accepted: 04/28/2014] [Indexed: 12/18/2022] Open
Abstract
Because there is considerable variation in gene expression even between closely related species, it is clear that gene regulatory mechanisms evolve relatively rapidly. Because primary sequence conservation is an unreliable proxy for functional conservation of cis-regulatory elements, their assessment must be carried out in vivo. We conducted a survey of cis-regulatory conservation between C. elegans and closely related species C. briggsae, C. remanei, C. brenneri, and C. japonica. We tested enhancers of eight genes from these species by introducing them into C. elegans and analyzing the expression patterns they drove. Our results support several notable conclusions. Most exogenous cis elements direct expression in the same cells as their C. elegans orthologs, confirming gross conservation of regulatory mechanisms. However, the majority of exogenous elements, when placed in C. elegans, also directed expression in cells outside endogenous patterns, suggesting functional divergence. Recurrent ectopic expression of different promoters in the same C. elegans cells may reflect biases in the directions in which expression patterns can evolve due to shared regulatory logic of coexpressed genes. The fact that, despite differences between individual genes, several patterns repeatedly emerged from our survey, encourages us to think that general rules governing regulatory evolution may exist and be discoverable.
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Affiliation(s)
- Antoine Barrière
- Department of Ecology and Evolution and Institute for Genomics and Systems Biology, The University of Chicago, Chicago, Illinois, United States of America
- * E-mail: (AB); (IR)
| | - Ilya Ruvinsky
- Department of Ecology and Evolution and Institute for Genomics and Systems Biology, The University of Chicago, Chicago, Illinois, United States of America
- Department of Organismal Biology and Anatomy, The University of Chicago, Chicago, Illinois, United States of America
- * E-mail: (AB); (IR)
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26
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Abstract
Instructions for when, where and to what level each gene should be expressed are encoded within regulatory sequences. The importance of motifs recognized by DNA-binding regulators has long been known, but their extensive characterization afforded by recent technologies only partly accounts for how regulatory instructions are encoded in the genome. Here, we review recent advances in our understanding of regulatory sequences that influence transcription and go beyond the description of motifs. We discuss how understanding different aspects of the sequence-encoded regulation can help to unravel the genotype-phenotype relationship, which would lead to a more accurate and mechanistic interpretation of personal genome sequences.
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Affiliation(s)
- Michal Levo
- Department of Molecular Cell Biology, and Department of Computer Science and Applied Mathematics, Weizmann Institute of Science, Rehovot 76100, Israel
| | - Eran Segal
- Department of Molecular Cell Biology, and Department of Computer Science and Applied Mathematics, Weizmann Institute of Science, Rehovot 76100, Israel
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27
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Foo SM, Sun Y, Lim B, Ziukaite R, O'Brien K, Nien CY, Kirov N, Shvartsman SY, Rushlow CA. Zelda potentiates morphogen activity by increasing chromatin accessibility. Curr Biol 2014; 24:1341-1346. [PMID: 24909324 DOI: 10.1016/j.cub.2014.04.032] [Citation(s) in RCA: 90] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/14/2014] [Revised: 03/18/2014] [Accepted: 04/15/2014] [Indexed: 11/20/2022]
Abstract
Zygotic genome activation (ZGA) is a major genome programming event whereby the cells of the embryo begin to adopt specified fates. Experiments in Drosophila and zebrafish have revealed that ZGA depends on transcription factors that provide large-scale control of gene expression by direct and specific binding to gene regulatory sequences. Zelda (Zld) plays such a role in the Drosophila embryo, where it has been shown to control the action of patterning signals; however, the mechanisms underlying this effect remain largely unclear. A recent model proposed that Zld binding sites act as quantitative regulators of the spatiotemporal expression of genes activated by Dorsal (Dl), the morphogen that patterns the dorsoventral axis. Here we tested this model experimentally, using enhancers of brinker (brk) and short gastrulation (sog), both of which are directly activated by Dl, but at different concentration thresholds. In agreement with the model, we show that there is a clear positive correlation between the number of Zld binding sites and the spatial domain of enhancer activity. Likewise, the timing of expression could be advanced or delayed. We present evidence that Zld facilitates binding of Dl to regulatory DNA, and that this is associated with increased chromatin accessibility. Importantly, the change in chromatin accessibility is strongly correlated with the change in Zld binding, but not Dl. We propose that the ability of genome activators to facilitate readout of transcriptional input is key to widespread transcriptional induction during ZGA.
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Affiliation(s)
- Sun Melody Foo
- Department of Biology, New York University, New York, NY 10003, USA
| | - Yujia Sun
- Department of Biology, New York University, New York, NY 10003, USA
| | - Bomyi Lim
- Department of Chemical and Biological Engineering and Lewis-Sigler Institute for Integrative Genomics, Princeton University, Princeton, NJ 08544, USA
| | - Ruta Ziukaite
- Department of Biology, New York University, New York, NY 10003, USA
| | - Kevin O'Brien
- Department of Biology, New York University, New York, NY 10003, USA
| | - Chung-Yi Nien
- Department of Biology, New York University, New York, NY 10003, USA
| | - Nikolai Kirov
- Department of Biology, New York University, New York, NY 10003, USA
| | - Stanislav Y Shvartsman
- Department of Chemical and Biological Engineering and Lewis-Sigler Institute for Integrative Genomics, Princeton University, Princeton, NJ 08544, USA
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28
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Naturally occurring deletions of hunchback binding sites in the even-skipped stripe 3+7 enhancer. PLoS One 2014; 9:e91924. [PMID: 24786295 PMCID: PMC4006794 DOI: 10.1371/journal.pone.0091924] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/19/2013] [Accepted: 02/18/2014] [Indexed: 11/23/2022] Open
Abstract
Changes in regulatory DNA contribute to phenotypic differences within and between taxa. Comparative studies show that many transcription factor binding sites (TFBS) are conserved between species whereas functional studies reveal that some mutations segregating within species alter TFBS function. Consistently, in this analysis of 13 regulatory elements in Drosophila melanogaster populations, single base and insertion/deletion polymorphism are rare in characterized regulatory elements. Experimentally defined TFBS are nearly devoid of segregating mutations and, as has been shown before, are quite conserved. For instance 8 of 11 Hunchback binding sites in the stripe 3+7 enhancer of even-skipped are conserved between D. melanogaster and Drosophila virilis. Oddly, we found a 72 bp deletion that removes one of these binding sites (Hb8), segregating within D. melanogaster. Furthermore, a 45 bp deletion polymorphism in the spacer between the stripe 3+7 and stripe 2 enhancers, removes another predicted Hunchback site. These two deletions are separated by ∼250 bp, sit on distinct haplotypes, and segregate at appreciable frequency. The Hb8Δ is at 5 to 35% frequency in the new world, but also shows cosmopolitan distribution. There is depletion of sequence variation on the Hb8Δ-carrying haplotype. Quantitative genetic tests indicate that Hb8Δ affects developmental time, but not viability of offspring. The Eve expression pattern differs between inbred lines, but the stripe 3 and 7 boundaries seem unaffected by Hb8Δ. The data reveal segregating variation in regulatory elements, which may reflect evolutionary turnover of characterized TFBS due to drift or co-evolution.
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29
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Abstract
Many organisms and their constituent tissues and organs vary substantially in size but differ little in morphology; they appear to be scaled versions of a common template or pattern. Such scaling involves adjusting the intrinsic scale of spatial patterns of gene expression that are set up during development to the size of the system. Identifying the mechanisms that regulate scaling of patterns at the tissue, organ and organism level during development is a longstanding challenge in biology, but recent molecular-level data and mathematical modeling have shed light on scaling mechanisms in several systems, including Drosophila and Xenopus. Here, we investigate the underlying principles needed for understanding the mechanisms that can produce scale invariance in spatial pattern formation and discuss examples of systems that scale during development.
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Affiliation(s)
- David M Umulis
- Agricultural and Biological Engineering, Weldon School of Biomedical Engineering, Purdue University, West Lafayette, IN 47907, USA
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30
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Mousavi K, Zare H, Koulnis M, Sartorelli V. The emerging roles of eRNAs in transcriptional regulatory networks. RNA Biol 2014; 11:106-10. [PMID: 24525859 DOI: 10.4161/rna.27950] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022] Open
Abstract
Following reports by ENCyclopedia Of DNA Elements (ENCODE; GENCODE) Consortium and others, it is now fairly evident that the majority (70-80%) of the mammalian genome has the potential to be transcribed into non-protein-coding RNAs (ncRNAs). Critical to our understanding of genetic processes is the mechanism by which ncRNAs exert their roles. Accordingly, ncRNAs are shown to regulate the expression of protein-coding loci (i.e., genes) at the transcriptional as well as post-transcriptional stages. We recently reported on a widespread transcription at the DNA enhancer elements in myogenic cells. In our study, we found certain enhancer RNAs (eRNAs) regulate chromatin accessibility of the transcriptional machinery at loci encoding master regulators of myogenesis (i.e., MyoD/MyoG), thus suggesting their significance and site-specific impact in cellular programming. Here, we examine recent discoveries pertinent to the proposed role(s) of eRNAs in regulating gene expression. We will highlight consistencies, discuss confounding observations, and consider a lack of critical information in a way to prioritize future objectives.
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Affiliation(s)
| | - Hossein Zare
- Laboratory of Muscle Stem Cells and Gene Regulation; National Institute of Arthritis, Musculoskeletal, and Skin Diseases; National Institutes of Health; Bethesda, MD USA
| | - Miroslav Koulnis
- Laboratory of Muscle Stem Cells and Gene Regulation; National Institute of Arthritis, Musculoskeletal, and Skin Diseases; National Institutes of Health; Bethesda, MD USA
| | - Vittorio Sartorelli
- Laboratory of Muscle Stem Cells and Gene Regulation; National Institute of Arthritis, Musculoskeletal, and Skin Diseases; National Institutes of Health; Bethesda, MD USA
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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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Chang J, Zhou Y, Hu X, Lam L, Henry C, Green EM, Kita R, Kobor MS, Fraser HB. The molecular mechanism of a cis-regulatory adaptation in yeast. PLoS Genet 2013; 9:e1003813. [PMID: 24068973 PMCID: PMC3778017 DOI: 10.1371/journal.pgen.1003813] [Citation(s) in RCA: 34] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/10/2013] [Accepted: 07/17/2013] [Indexed: 11/23/2022] Open
Abstract
Despite recent advances in our ability to detect adaptive evolution involving the cis-regulation of gene expression, our knowledge of the molecular mechanisms underlying these adaptations has lagged far behind. Across all model organisms, the causal mutations have been discovered for only a handful of gene expression adaptations, and even for these, mechanistic details (e.g. the trans-regulatory factors involved) have not been determined. We previously reported a polygenic gene expression adaptation involving down-regulation of the ergosterol biosynthesis pathway in the budding yeast Saccharomyces cerevisiae. Here we investigate the molecular mechanism of a cis-acting mutation affecting a member of this pathway, ERG28. We show that the causal mutation is a two-base deletion in the promoter of ERG28 that strongly reduces the binding of two transcription factors, Sok2 and Mot3, thus abolishing their regulation of ERG28. This down-regulation increases resistance to a widely used antifungal drug targeting ergosterol, similar to mutations disrupting this pathway in clinical yeast isolates. The identification of the causal genetic variant revealed that the selection likely occurred after the deletion was already present at high frequency in the population, rather than when it was a new mutation. These results provide a detailed view of the molecular mechanism of a cis-regulatory adaptation, and underscore the importance of this view to our understanding of evolution at the molecular level. Evolutionary adaptation is the process that has given rise to the ubiquitous, yet remarkable, fit between all living organisms and their environments. The molecular mechanisms of these adaptations have been a subject of great interest, but we still know very little about their mechanisms, particularly in the case of regulatory adaptations. In this work, we investigate the molecular mechanism of a regulatory adaptation that we previously identified in ERG28, a component of the ergosterol biosynthesis pathway in budding yeast. Ergosterol is an abundant lipid component of the fungal plasma membrane, and is of major biomedical importance, being targeted by numerous antifungal drugs. We identified the causal mutation underlying the ERG28 adaptation, a two-base deletion in its promoter which leads to lower abundance of its mRNA. This deletion acts via disrupting the binding of at least two transcription factors, Mot3 and Sok2, to the promoter. The deletion increases resistance to a widely used antifungal drug, Amphotericin B, which targets ergosterol. This effect is reminiscent of misregulation of the ergosterol pathway observed in clinical yeast isolates that have evolved resistance to Amphotericin B. Our results may therefore have medical implications, while also advancing our basic understanding of evolutionary mechanisms.
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Affiliation(s)
- Jessica Chang
- Department of Biology, Stanford University, Stanford , California, United States of America
| | - Yiqi Zhou
- Department of Biology, Stanford University, Stanford , California, United States of America
| | - Xiaoli Hu
- Department of Biology, Stanford University, Stanford , California, United States of America
| | - Lucia Lam
- Department of Medical Genetics, University of British Columbia, Vancouver, British Columbia, Canada
- Centre for Molecular Medicine and Therapeutics, Child and Family Research Institute, Vancouver, British Columbia, Canada
| | - Cameron Henry
- Department of Biology, Stanford University, Stanford , California, United States of America
| | - Erin M. Green
- Department of Biology, Stanford University, Stanford , California, United States of America
| | - Ryosuke Kita
- Department of Biology, Stanford University, Stanford , California, United States of America
| | - Michael S. Kobor
- Department of Medical Genetics, University of British Columbia, Vancouver, British Columbia, Canada
- Centre for Molecular Medicine and Therapeutics, Child and Family Research Institute, Vancouver, British Columbia, Canada
| | - Hunter B. Fraser
- Department of Biology, Stanford University, Stanford , California, United States of America
- * E-mail:
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33
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Paris M, Kaplan T, Li XY, Villalta JE, Lott SE, Eisen MB. Extensive divergence of transcription factor binding in Drosophila embryos with highly conserved gene expression. PLoS Genet 2013; 9:e1003748. [PMID: 24068946 PMCID: PMC3772039 DOI: 10.1371/journal.pgen.1003748] [Citation(s) in RCA: 72] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/04/2013] [Accepted: 07/10/2013] [Indexed: 11/19/2022] Open
Abstract
To better characterize how variation in regulatory sequences drives divergence in gene expression, we undertook a systematic study of transcription factor binding and gene expression in blastoderm embryos of four species, which sample much of the diversity in the 40 million-year old genus Drosophila: D. melanogaster, D. yakuba, D. pseudoobscura and D. virilis. We compared gene expression, measured by mRNA-seq, to the genome-wide binding, measured by ChIP-seq, of four transcription factors involved in early anterior-posterior patterning. We found that mRNA levels are much better conserved than individual transcription factor binding events, and that changes in a gene's expression were poorly explained by changes in adjacent transcription factor binding. However, highly bound sites, sites in regions bound by multiple factors and sites near genes are conserved more frequently than other binding, suggesting that a considerable amount of transcription factor binding is weakly or non-functional and not subject to purifying selection.
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Affiliation(s)
- Mathilde Paris
- Department of Molecular and Cell Biology, University of California Berkeley, Berkeley, California, United States of America
| | - Tommy Kaplan
- Department of Molecular and Cell Biology, University of California Berkeley, Berkeley, California, United States of America
- School of Computer Science and Engineering, The Hebrew University, Jerusalem, Israel
| | - Xiao Yong Li
- Department of Molecular and Cell Biology, University of California Berkeley, Berkeley, California, United States of America
- Howard Hughes Medical Institute, University of California Berkeley, Berkeley, California, United States of America
| | | | - Susan E. Lott
- Department of Molecular and Cell Biology, University of California Berkeley, Berkeley, California, United States of America
- Department of Evolution and Ecology, University of California, Davis, California, United States of America
| | - Michael B. Eisen
- Department of Molecular and Cell Biology, University of California Berkeley, Berkeley, California, United States of America
- School of Computer Science and Engineering, The Hebrew University, Jerusalem, Israel
- Howard Hughes Medical Institute, University of California Berkeley, Berkeley, California, United States of America
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Rogers WA, Salomone JR, Tacy DJ, Camino EM, Davis KA, Rebeiz M, Williams TM. Recurrent modification of a conserved cis-regulatory element underlies fruit fly pigmentation diversity. PLoS Genet 2013; 9:e1003740. [PMID: 24009528 PMCID: PMC3757066 DOI: 10.1371/journal.pgen.1003740] [Citation(s) in RCA: 50] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/16/2013] [Accepted: 07/09/2013] [Indexed: 11/18/2022] Open
Abstract
The development of morphological traits occurs through the collective action of networks of genes connected at the level of gene expression. As any node in a network may be a target of evolutionary change, the recurrent targeting of the same node would indicate that the path of evolution is biased for the relevant trait and network. Although examples of parallel evolution have implicated recurrent modification of the same gene and cis-regulatory element (CRE), little is known about the mutational and molecular paths of parallel CRE evolution. In Drosophila melanogaster fruit flies, the Bric-à-brac (Bab) transcription factors control the development of a suite of sexually dimorphic traits on the posterior abdomen. Female-specific Bab expression is regulated by the dimorphic element, a CRE that possesses direct inputs from body plan (ABD-B) and sex-determination (DSX) transcription factors. Here, we find that the recurrent evolutionary modification of this CRE underlies both intraspecific and interspecific variation in female pigmentation in the melanogaster species group. By reconstructing the sequence and regulatory activity of the ancestral Drosophila melanogaster dimorphic element, we demonstrate that a handful of mutations were sufficient to create independent CRE alleles with differing activities. Moreover, intraspecific and interspecific dimorphic element evolution proceeded with little to no alterations to the known body plan and sex-determination regulatory linkages. Collectively, our findings represent an example where the paths of evolution appear biased to a specific CRE, and drastic changes in function were accompanied by deep conservation of key regulatory linkages.
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Affiliation(s)
- William A. Rogers
- Department of Biology, University of Dayton, Dayton, Ohio, United States of America
| | - Joseph R. Salomone
- Department of Biology, University of Dayton, Dayton, Ohio, United States of America
| | - David J. Tacy
- Department of Biology, University of Dayton, Dayton, Ohio, United States of America
| | - Eric M. Camino
- Department of Biology, University of Dayton, Dayton, Ohio, United States of America
| | - Kristen A. Davis
- Department of Biology, University of Dayton, Dayton, Ohio, United States of America
| | - Mark Rebeiz
- Department of Biological Sciences, University of Pittsburgh, Pittsburgh, Pennsylvania, United States of America
| | - Thomas M. Williams
- Department of Biology, University of Dayton, Dayton, Ohio, United States of America
- Center for Tissue Regeneration and Engineering at Dayton, University of Dayton, Dayton, Ohio, United States of America
- * E-mail:
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35
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Menoret D, Santolini M, Fernandes I, Spokony R, Zanet J, Gonzalez I, Latapie Y, Ferrer P, Rouault H, White KP, Besse P, Hakim V, Aerts S, Payre F, Plaza S. Genome-wide analyses of Shavenbaby target genes reveals distinct features of enhancer organization. Genome Biol 2013; 14:R86. [PMID: 23972280 PMCID: PMC4053989 DOI: 10.1186/gb-2013-14-8-r86] [Citation(s) in RCA: 36] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/07/2013] [Accepted: 08/23/2013] [Indexed: 12/17/2022] Open
Abstract
Background Developmental programs are implemented by regulatory interactions between Transcription Factors (TFs) and their target genes, which remain poorly understood. While recent studies have focused on regulatory cascades of TFs that govern early development, little is known about how the ultimate effectors of cell differentiation are selected and controlled. We addressed this question during late Drosophila embryogenesis, when the finely tuned expression of the TF Ovo/Shavenbaby (Svb) triggers the morphological differentiation of epidermal trichomes. Results We defined a sizeable set of genes downstream of Svb and used in vivo assays to delineate 14 enhancers driving their specific expression in trichome cells. Coupling computational modeling to functional dissection, we investigated the regulatory logic of these enhancers. Extending the repertoire of epidermal effectors using genome-wide approaches showed that the regulatory models learned from this first sample are representative of the whole set of trichome enhancers. These enhancers harbor remarkable features with respect to their functional architectures, including a weak or non-existent clustering of Svb binding sites. The in vivo function of each site relies on its intimate context, notably the flanking nucleotides. Two additional cis-regulatory motifs, present in a broad diversity of composition and positioning among trichome enhancers, critically contribute to enhancer activity. Conclusions Our results show that Svb directly regulates a large set of terminal effectors of the remodeling of epidermal cells. Further, these data reveal that trichome formation is underpinned by unexpectedly diverse modes of regulation, providing fresh insights into the functional architecture of enhancers governing a terminal differentiation program.
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36
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Kazemian M, Pham H, Wolfe SA, Brodsky MH, Sinha S. Widespread evidence of cooperative DNA binding by transcription factors in Drosophila development. Nucleic Acids Res 2013; 41:8237-52. [PMID: 23847101 PMCID: PMC3783179 DOI: 10.1093/nar/gkt598] [Citation(s) in RCA: 65] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023] Open
Abstract
Regulation of eukaryotic gene transcription is often combinatorial in nature, with multiple transcription factors (TFs) regulating common target genes, often through direct or indirect mutual interactions. Many individual examples of cooperative binding by directly interacting TFs have been identified, but it remains unclear how pervasive this mechanism is during animal development. Cooperative TF binding should be manifest in genomic sequences as biased arrangements of TF-binding sites. Here, we explore the extent and diversity of such arrangements related to gene regulation during Drosophila embryogenesis. We used the DNA-binding specificities of 322 TFs along with chromatin accessibility information to identify enriched spacing and orientation patterns of TF-binding site pairs. We developed a new statistical approach for this task, specifically designed to accurately assess inter-site spacing biases while accounting for the phenomenon of homotypic site clustering commonly observed in developmental regulatory regions. We observed a large number of short-range distance preferences between TF-binding site pairs, including examples where the preference depends on the relative orientation of the binding sites. To test whether these binding site patterns reflect physical interactions between the corresponding TFs, we analyzed 27 TF pairs whose binding sites exhibited short distance preferences. In vitro protein–protein binding experiments revealed that >65% of these TF pairs can directly interact with each other. For five pairs, we further demonstrate that they bind cooperatively to DNA if both sites are present with the preferred spacing. This study demonstrates how DNA-binding motifs can be used to produce a comprehensive map of sequence signatures for different mechanisms of combinatorial TF action.
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Affiliation(s)
- Majid Kazemian
- Department of Computer Science, University of Illinois at Urbana-Champaign, Urbana, IL, USA, Laboratory of Molecular Immunology and Immunology Center, National Heart Lung and Blood Institute, National Institutes of Health, MD, USA, Program in Gene Function and Expression, University of Massachusetts Medical School, MA, USA, Department of Biochemistry and Molecular Pharmacology University of Massachusetts Medical School, MA, USA, Department of Molecular Medicine, University of Massachusetts Medical School, MA, USA and Institute of Genomic Biology, University of Illinois at Urbana-Champaign, Urbana, IL, USA
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37
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Van Otterloo E, Cornell RA, Medeiros DM, Garnett AT. Gene regulatory evolution and the origin of macroevolutionary novelties: insights from the neural crest. Genesis 2013; 51:457-70. [PMID: 23712931 DOI: 10.1002/dvg.22403] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/22/2013] [Revised: 05/10/2013] [Accepted: 05/14/2013] [Indexed: 11/07/2022]
Abstract
The appearance of novel anatomic structures during evolution is driven by changes to the networks of transcription factors, signaling pathways, and downstream effector genes controlling development. The nature of the changes to these developmental gene regulatory networks (GRNs) is poorly understood. A striking test case is the evolution of the GRN controlling development of the neural crest (NC). NC cells emerge from the neural plate border (NPB) and contribute to multiple adult structures. While all chordates have a NPB, only in vertebrates do NPB cells express all the genes constituting the neural crest GRN (NC-GRN). Interestingly, invertebrate chordates express orthologs of NC-GRN components in other tissues, revealing that during vertebrate evolution new regulatory connections emerged between transcription factors primitively expressed in the NPB and genes primitively expressed in other tissues. Such interactions could have evolved by two mechanisms. First, transcription factors primitively expressed in the NPB may have evolved new DNA and/or cofactor binding properties (protein neofunctionalization). Alternately, cis-regulatory elements driving NPB expression may have evolved near genes primitively expressed in other tissues (cis-regulatory neofunctionalization). Here we discuss how gene duplication can, in principle, promote either form of neofunctionalization. We review recent published examples of interspecies gene-swap, or regulatory-element-swap, experiments that test both models. Such experiments have yielded little evidence to support the importance of protein neofunctionalization in the emergence of the NC-GRN, but do support the importance of novel cis-regulatory elements in this process. The NC-GRN is an excellent model for the study of gene regulatory and macroevolutionary innovation.
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Affiliation(s)
- Eric Van Otterloo
- Department of Anatomy and Cell Biology, University of Iowa, Iowa City, IA, USA
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38
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Kenigsberg E, Tanay A. Drosophila functional elements are embedded in structurally constrained sequences. PLoS Genet 2013; 9:e1003512. [PMID: 23750124 PMCID: PMC3671938 DOI: 10.1371/journal.pgen.1003512] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/31/2012] [Accepted: 03/04/2013] [Indexed: 12/22/2022] Open
Abstract
Modern functional genomics uncovered numerous functional elements in metazoan genomes. Nevertheless, only a small fraction of the typical non-exonic genome contains elements that code for function directly. On the other hand, a much larger fraction of the genome is associated with significant evolutionary constraints, suggesting that much of the non-exonic genome is weakly functional. Here we show that in flies, local (30–70 bp) conserved sequence elements that are associated with multiple regulatory functions serve as focal points to a pattern of punctuated regional increase in G/C nucleotide frequencies. We show that this pattern, which covers a region tenfold larger than the conserved elements themselves, is an evolutionary consequence of a shift in the balance between gain and loss of G/C nucleotides and that it is correlated with nucleosome occupancy across multiple classes of epigenetic state. Evidence for compensatory evolution and analysis of SNP allele frequencies show that the evolutionary regime underlying this balance shift is likely to be non-neutral. These data suggest that current gaps in our understanding of genome function and evolutionary dynamics are explicable by a model of sparse sequence elements directly encoding for function, embedded into structural sequences that help to define the local and global epigenomic context of such functional elements. A key challenge in functional genomics is to predict evolutionary dynamics from functional annotation of the genome and vice versa. Modern epigenomic studies helped assign function to numerous new sequence elements, but left most of the genome essentially uncharacterized. Evolutionary genomics, on the other hand, consistently suggests that a much larger fraction of the un-annotated genome evolves under selective pressure. We hypothesize that this function-selection gap can be attributed to sequences that facilitate the physical organization of functional elements, such as transcription factor binding sites, within chromosomes. We exemplify this by studying in detail the sequences embedding small conserved elements (CEs) in Drosophila. We show that, while CEs have typically high AT content, high GC content levels around them are maintained by a non-neutral evolutionary balance between gain and loss of GC nucleotides. This non-uniform pattern is highly correlated with nucleosome organization around CEs, potentially imposing an evolutionary constraint on as much as one quarter of the genome. We suggest this can at least partly explain the above function-selection gap. Weak evolutionary constraints on “structural” sequences (at scales ranging from one nucleosome to recently described multi-megabase topological domains) may affect genome evolution just like structural motifs shape protein evolution.
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Affiliation(s)
- Ephraim Kenigsberg
- Department of Computer Science and Applied Mathematics and Department of Biological Regulation, Weizmann Institute, Rehovot, Israel
| | - Amos Tanay
- Department of Computer Science and Applied Mathematics and Department of Biological Regulation, Weizmann Institute, Rehovot, Israel
- * E-mail:
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39
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Chahda JS, Sousa-Neves R, Mizutani CM. Variation in the dorsal gradient distribution is a source for modified scaling of germ layers in Drosophila. Curr Biol 2013; 23:710-6. [PMID: 23583556 DOI: 10.1016/j.cub.2013.03.031] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/20/2012] [Revised: 02/22/2013] [Accepted: 03/11/2013] [Indexed: 01/30/2023]
Abstract
Specification of germ layers along the dorsoventral axis by morphogenetic gradients is an ideal model to study scaling properties of gradients and cell fate changes during evolution. Classical anatomical studies in divergent insects (e.g., flies and grasshoppers) revealed that the neuroectodermal size is conserved and originates similar numbers of neuroblasts of homologous identity. In contrast, mesodermal domains vary significantly in closely related Drosophila species. To further investigate the underlying mechanisms of scaling of germ layers across Drosophila species, we quantified the Dorsal (Dl)/NF-κB gradient, the main morphogenetic gradient that initiates separation of the mesoderm, neuroectoderm, and ectoderm. We discovered a variable range of Toll activation across species and found that Dl activates mesodermal genes at the same threshold levels in melanogaster sibling species. We also show that the Dl gradient distribution can be modulated by nuclear size and packing densities. We propose that variation in mesodermal size occurs at a fast evolutionary rate and is an important mechanism to define the ventral boundary of the neuroectoderm.
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40
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Crocker J, Erives A. A Schnurri/Mad/Medea complex attenuates the dorsal-twist gradient readout at vnd. Dev Biol 2013; 378:64-72. [PMID: 23499655 DOI: 10.1016/j.ydbio.2013.03.002] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/24/2012] [Revised: 02/13/2013] [Accepted: 03/04/2013] [Indexed: 12/28/2022]
Abstract
Morphogen gradients are used in developing embryos, where they subdivide a field of cells into territories characterized by distinct cell fate potentials. Such systems require both a spatially-graded distribution of the morphogen, and an ability to encode different responses at different target genes. However, the potential for different temporal responses is also present because morphogen gradients typically provide temporal cues, which may be a potential source of conflict. Thus, a low threshold response adapted for an early temporal onset may be inappropriate when the desired spatial response is a spatially-limited, high-threshold expression pattern. Here, we identify such a case with the Drosophila vnd locus, which is a target of the dorsal (dl) nuclear concentration gradient that patterns the dorsal/ventral (D/V) axis of the embryo. The vnd gene plays a critical role in the "ventral dominance" hierarchy of vnd, ind, and msh, which individually specify distinct D/V neural columnar fates in increasingly dorsal ectodermal compartments. The role of vnd in this regulatory hierarchy requires early temporal expression, which is characteristic of low-threshold responses, but its specification of ventral neurogenic ectoderm demands a relatively high-threshold response to dl. We show that the Neurogenic Ectoderm Enhancer (NEE) at vnd takes additional input from the complementary Dpp gradient via a conserved Schnurri/Mad/Medea silencer element (SSE) unlike NEEs at brk, sog, rho, and vn. These results show how requirements for conflicting temporal and spatial responses to the same gradient can be solved by additional inputs from complementary gradients.
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Affiliation(s)
- Justin Crocker
- Janelia Farm Research Campus, Howard Hughes Medical Institute, 19700 Helix Drive, Ashburn, VA 20147, USA
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41
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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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42
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Frankel N. Multiple layers of complexity incis-regulatory regions of developmental genes. Dev Dyn 2012; 241:1857-66. [DOI: 10.1002/dvdy.23871] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 09/06/2012] [Indexed: 12/19/2022] Open
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43
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Spivakov M, Akhtar J, Kheradpour P, Beal K, Girardot C, Koscielny G, Herrero J, Kellis M, Furlong EEM, Birney E. Analysis of variation at transcription factor binding sites in Drosophila and humans. Genome Biol 2012; 13:R49. [PMID: 22950968 PMCID: PMC3491393 DOI: 10.1186/gb-2012-13-9-r49] [Citation(s) in RCA: 77] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/28/2012] [Revised: 05/23/2012] [Accepted: 06/08/2012] [Indexed: 12/31/2022] Open
Abstract
BACKGROUND Advances in sequencing technology have boosted population genomics and made it possible to map the positions of transcription factor binding sites (TFBSs) with high precision. Here we investigate TFBS variability by combining transcription factor binding maps generated by ENCODE, modENCODE, our previously published data and other sources with genomic variation data for human individuals and Drosophila isogenic lines. RESULTS We introduce a metric of TFBS variability that takes into account changes in motif match associated with mutation and makes it possible to investigate TFBS functional constraints instance-by-instance as well as in sets that share common biological properties. We also take advantage of the emerging per-individual transcription factor binding data to show evidence that TFBS mutations, particularly at evolutionarily conserved sites, can be efficiently buffered to ensure coherent levels of transcription factor binding. CONCLUSIONS Our analyses provide insights into the relationship between individual and interspecies variation and show evidence for the functional buffering of TFBS mutations in both humans and flies. In a broad perspective, these results demonstrate the potential of combining functional genomics and population genetics approaches for understanding gene regulation.
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Affiliation(s)
- Mikhail Spivakov
- European Bioinformatics Institute, Wellcome Trust Genome Campus, Hinxton, Cambridgeshire, CB10 1SD, UK.
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44
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Coevolution within and between regulatory loci can preserve promoter function despite evolutionary rate acceleration. PLoS Genet 2012; 8:e1002961. [PMID: 23028368 PMCID: PMC3447958 DOI: 10.1371/journal.pgen.1002961] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/13/2012] [Accepted: 08/06/2012] [Indexed: 11/19/2022] Open
Abstract
Phenotypes that appear to be conserved could be maintained not only by strong purifying selection on the underlying genetic systems, but also by stabilizing selection acting via compensatory mutations with balanced effects. Such coevolution has been invoked to explain experimental results, but has rarely been the focus of study. Conserved expression driven by the unc-47 promoters of Caenorhabditis elegans and C. briggsae persists despite divergence within a cis-regulatory element and between this element and the trans-regulatory environment. Compensatory changes in cis and trans are revealed when these promoters are used to drive expression in the other species. Functional changes in the C. briggsae promoter, which has experienced accelerated sequence evolution, did not lead to alteration of gene expression in its endogenous environment. Coevolution among promoter elements suggests that complex epistatic interactions within cis-regulatory elements may facilitate their divergence. Our results offer a detailed picture of regulatory evolution in which subtle, lineage-specific, and compensatory modifications of interacting cis and trans regulators together maintain conserved gene expression patterns. Some phenotypes, including gene expression patterns, are conserved between distantly related species. However, the molecular bases of those phenotypes are not necessarily conserved. Instead, regulatory DNA sequences and the proteins with which they interact can change over time with balanced effects, preserving expression patterns and concealing regulatory divergence. Coevolution between interacting molecules makes gene regulation highly species-specific, and it can be detected when the cis-regulatory DNA of one species is used to drive expression in another species. In this way, we identified regions of the C. elegans and C. briggsae unc-47 promoters that have coevolved with the lineage-specific trans-regulatory environments of these organisms. The C. briggsae promoter experienced accelerated sequence change relative to related species. All of this evolution occurred without changing the expression pattern driven by the promoter in its endogenous environment.
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45
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Romero IG, Ruvinsky I, Gilad Y. Comparative studies of gene expression and the evolution of gene regulation. Nat Rev Genet 2012; 13:505-16. [PMID: 22705669 DOI: 10.1038/nrg3229] [Citation(s) in RCA: 305] [Impact Index Per Article: 25.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
The hypothesis that differences in gene regulation have an important role in speciation and adaptation is more than 40 years old. With the advent of new sequencing technologies, we are able to characterize and study gene expression levels and associated regulatory mechanisms in a large number of individuals and species at an unprecedented resolution and scale. We have thus gained new insights into the evolutionary pressures that shape gene expression levels and have developed an appreciation for the relative importance of evolutionary changes in different regulatory genetic and epigenetic mechanisms. The current challenge is to link gene regulatory changes to adaptive evolution of complex phenotypes. Here we mainly focus on comparative studies in primates and how they are complemented by studies in model organisms.
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Affiliation(s)
- Irene Gallego Romero
- Department of Human Genetics, University of Chicago, Chicago, Illinois 60637, USA
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Pan N, Kopecky B, Jahan I, Fritzsch B. Understanding the evolution and development of neurosensory transcription factors of the ear to enhance therapeutic translation. Cell Tissue Res 2012; 349:415-32. [PMID: 22688958 DOI: 10.1007/s00441-012-1454-0] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/15/2012] [Accepted: 05/18/2012] [Indexed: 01/08/2023]
Abstract
Reconstructing a functional organ of Corti is the ultimate target towards curing hearing loss. Despite the impressive technical gains made over the last few years, many complications remain ahead for the two main restoration avenues: in vitro transformation of pluripotent cells into hair cell-like cells and adenovirus-mediated gene therapy. Most notably, both approaches require a more complete understanding of the molecular networks that ensure specific cell types form in the correct places to allow proper function of the restored organ of Corti. Important to this understanding are the basic helix-loop-helix (bHLH) transcription factors (TFs) that are highly diverse and serve to increase functional complexity but their evolutionary implementation in the inner ear neurosensory development is less conspicuous. To this end, we review the evolutionary and developmentally dynamic interactions of the three bHLH TFs that have been identified as the main players in neurosensory evolution and development, Neurog1, Neurod1 and Atoh1. These three TFs belong to the neurogenin/atonal family and evolved from a molecular precursor that likely regulated single sensory cell development in the ectoderm of metazoan ancestors but are now also expressed in other parts of the body, including the brain. They interact extensively via intracellular and intercellular cross-regulation to establish the two main neurosensory cell types of the ear, the hair cells and sensory neurons. Furthermore, the level and duration of their expression affect the specification of hair cell subtypes (inner hair cells vs. outer hair cells). We propose that appropriate manipulation of these TFs through their characterized binding sites may offer a solution by itself, or in conjunction with the two other approaches currently pursued by others, to restore the organ of Corti.
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Affiliation(s)
- Ning Pan
- Department of Biology, University of Iowa, College of Liberal Arts and Sciences, Iowa City, IA 52242, USA
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47
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Busser BW, Taher L, Kim Y, Tansey T, Bloom MJ, Ovcharenko I, Michelson AM. A machine learning approach for identifying novel cell type-specific transcriptional regulators of myogenesis. PLoS Genet 2012; 8:e1002531. [PMID: 22412381 PMCID: PMC3297574 DOI: 10.1371/journal.pgen.1002531] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/30/2011] [Accepted: 12/23/2011] [Indexed: 12/22/2022] Open
Abstract
Transcriptional enhancers integrate the contributions of multiple classes of transcription factors (TFs) to orchestrate the myriad spatio-temporal gene expression programs that occur during development. A molecular understanding of enhancers with similar activities requires the identification of both their unique and their shared sequence features. To address this problem, we combined phylogenetic profiling with a DNA-based enhancer sequence classifier that analyzes the TF binding sites (TFBSs) governing the transcription of a co-expressed gene set. We first assembled a small number of enhancers that are active in Drosophila melanogaster muscle founder cells (FCs) and other mesodermal cell types. Using phylogenetic profiling, we increased the number of enhancers by incorporating orthologous but divergent sequences from other Drosophila species. Functional assays revealed that the diverged enhancer orthologs were active in largely similar patterns as their D. melanogaster counterparts, although there was extensive evolutionary shuffling of known TFBSs. We then built and trained a classifier using this enhancer set and identified additional related enhancers based on the presence or absence of known and putative TFBSs. Predicted FC enhancers were over-represented in proximity to known FC genes; and many of the TFBSs learned by the classifier were found to be critical for enhancer activity, including POU homeodomain, Myb, Ets, Forkhead, and T-box motifs. Empirical testing also revealed that the T-box TF encoded by org-1 is a previously uncharacterized regulator of muscle cell identity. Finally, we found extensive diversity in the composition of TFBSs within known FC enhancers, suggesting that motif combinatorics plays an essential role in the cellular specificity exhibited by such enhancers. In summary, machine learning combined with evolutionary sequence analysis is useful for recognizing novel TFBSs and for facilitating the identification of cognate TFs that coordinate cell type-specific developmental gene expression patterns.
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Affiliation(s)
- Brian W. Busser
- Laboratory of Developmental Systems Biology, National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, Maryland, United States of America
| | - Leila Taher
- Computational Biology Branch, National Center for Biotechnology Information, National Library of Medicine, National Institutes of Health, Bethesda, Maryland, United States of America
| | - Yongsok Kim
- Laboratory of Developmental Systems Biology, National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, Maryland, United States of America
| | - Terese Tansey
- Laboratory of Developmental Systems Biology, National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, Maryland, United States of America
| | - Molly J. Bloom
- Laboratory of Developmental Systems Biology, National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, Maryland, United States of America
| | - Ivan Ovcharenko
- Computational Biology Branch, National Center for Biotechnology Information, National Library of Medicine, National Institutes of Health, Bethesda, Maryland, United States of America
- * E-mail: (IO); (AMM)
| | - Alan M. Michelson
- Laboratory of Developmental Systems Biology, National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, Maryland, United States of America
- * E-mail: (IO); (AMM)
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Abstract
Perennial questions of evolutionary biology can be applied to gene regulatory systems using the abundance of experimental data addressing gene regulation in a comparative context. What is the tempo (frequency, rate) and mode (way, mechanism) of transcriptional regulatory evolution? Here we synthesize the results of 230 experiments performed on insects and nematodes in which regulatory DNA from one species was used to drive gene expression in another species. General principles of regulatory evolution emerge. Gene regulatory evolution is widespread and accumulates with genetic divergence in both insects and nematodes. Divergence in cis is more common than divergence in trans. Coevolution between cis and trans shows a particular increase over greater evolutionary timespans, especially in sex-specific gene regulation. Despite these generalities, the evolution of gene regulation is gene- and taxon-specific. The congruence of these conclusions with evidence from other types of experiments suggests that general principles are discoverable, and a unified view of the tempo and mode of regulatory evolution may be achievable.
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Nelson MD, Fitch DHA. Overlap extension PCR: an efficient method for transgene construction. Methods Mol Biol 2012; 772:459-70. [PMID: 22065455 DOI: 10.1007/978-1-61779-228-1_27] [Citation(s) in RCA: 57] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
Combining genes or regulatory elements to make hybrid genes is a widely used methodology throughout the biological sciences. Here, we describe an optimized approach for hybrid gene construction called overlap extension PCR. In this method, the polymerase chain reaction (PCR) is employed for efficient and reliable construction of hybrid genes. A PCR-based approach does not rely on available restriction sites or other specific sequences, an advantage over more conventional cloning or recombineering methods. With the use of high-fidelity DNA polymerase, this method can be used for making even very large constructs (>20 kb) with minimal unwanted mutations. Finally, overlap extension-PCR can be used as a means for site-directed mutagenesis, introducing desired mutations to the final hybrid gene.
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A conserved developmental patterning network produces quantitatively different output in multiple species of Drosophila. PLoS Genet 2011; 7:e1002346. [PMID: 22046143 PMCID: PMC3203197 DOI: 10.1371/journal.pgen.1002346] [Citation(s) in RCA: 45] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/04/2011] [Accepted: 08/27/2011] [Indexed: 11/18/2022] Open
Abstract
Differences in the level, timing, or location of gene expression can contribute to alternative phenotypes at the molecular and organismal level. Understanding the origins of expression differences is complicated by the fact that organismal morphology and gene regulatory networks could potentially vary even between closely related species. To assess the scope of such changes, we used high-resolution imaging methods to measure mRNA expression in blastoderm embryos of Drosophila yakuba and Drosophila pseudoobscura and assembled these data into cellular resolution atlases, where expression levels for 13 genes in the segmentation network are averaged into species-specific, cellular resolution morphological frameworks. We demonstrate that the blastoderm embryos of these species differ in their morphology in terms of size, shape, and number of nuclei. We present an approach to compare cellular gene expression patterns between species, while accounting for varying embryo morphology, and apply it to our data and an equivalent dataset for Drosophila melanogaster. Our analysis reveals that all individual genes differ quantitatively in their spatio-temporal expression patterns between these species, primarily in terms of their relative position and dynamics. Despite many small quantitative differences, cellular gene expression profiles for the whole set of genes examined are largely similar. This suggests that cell types at this stage of development are conserved, though they can differ in their relative position by up to 3–4 cell widths and in their relative proportion between species by as much as 5-fold. Quantitative differences in the dynamics and relative level of a subset of genes between corresponding cell types may reflect altered regulatory functions between species. Our results emphasize that transcriptional networks can diverge over short evolutionary timescales and that even small changes can lead to distinct output in terms of the placement and number of equivalent cells. For a gene to function properly, it must be active in the right place, at the right time, and in the right amount. Changes in any of these features can lead to observable differences between individuals and species and in some cases can lead to disease. We do not currently understand how the position, timing, and amount of gene expression is encoded in DNA sequence. One approach to this problem is to compare how gene expression differs between species and to try to relate changes in DNA sequence to changes in gene expression. Here, we take the first step by comparing gene expression patterns at high spatial and temporal resolution between embryos of three species of fruit flies. We develop methods for comparing gene expression in individual cells, which allow us to control for variation in the size, shape, and number of nuclei between embryos. We find measurable quantitative differences in the patterns for all individual genes that we have examined. However, by considering all genes in our dataset at once, we show that many genes are changing together, leading to largely equivalent types of cells in these three species.
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