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Yang W, Cui J, Chen Y, Wang C, Yin Y, Zhang W, Liu S, Sun C, Li H, Duan Y, Song F, Cai W, Hines HM, Tian L. Genetic Modification of a Hox Locus Drives Mimetic Color Pattern Variation in a Highly Polymorphic Bumble Bee. Mol Biol Evol 2023; 40:msad261. [PMID: 38039153 PMCID: PMC10724181 DOI: 10.1093/molbev/msad261] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/01/2023] [Revised: 11/11/2023] [Accepted: 11/27/2023] [Indexed: 12/03/2023] Open
Abstract
Müllerian mimicry provides natural replicates ideal for exploring mechanisms underlying adaptive phenotypic divergence and convergence, yet the genetic mechanisms underlying mimetic variation remain largely unknown. The current study investigates the genetic basis of mimetic color pattern variation in a highly polymorphic bumble bee, Bombus breviceps (Hymenoptera, Apidae). In South Asia, this species and multiple comimetic species converge onto local Müllerian mimicry patterns by shifting the abdominal setal color from orange to black. Genetic crossing between the orange and black phenotypes suggested the color dimorphism being controlled by a single Mendelian locus, with the orange allele being dominant over black. Genome-wide association suggests that a locus at the intergenic region between 2 abdominal fate-determining Hox genes, abd-A and Abd-B, is associated with the color change. This locus is therefore in the same intergenic region but not the same exact locus as found to drive red black midabdominal variation in a distantly related bumble bee species, Bombus melanopygus. Gene expression analysis and RNA interferences suggest that differential expression of an intergenic long noncoding RNA between abd-A and Abd-B at the onset setal color differentiation may drive the orange black color variation by causing a homeotic shift late in development. Analysis of this same color locus in comimetic species reveals no sequence association with the same color shift, suggesting that mimetic convergence is achieved through distinct genetic routes. Our study establishes Hox regions as genomic hotspots for color pattern evolution in bumble bees and demonstrates how pleiotropic developmental loci can drive adaptive radiations in nature.
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Affiliation(s)
- Wanhu Yang
- Department of Entomology and MOA Key Lab of Pest Monitoring and Green Management, College of Plant Protection, China Agricultural University, Beijing 100193, China
| | - Jixiang Cui
- Department of Entomology and MOA Key Lab of Pest Monitoring and Green Management, College of Plant Protection, China Agricultural University, Beijing 100193, China
| | - Yuxin Chen
- Department of Entomology and MOA Key Lab of Pest Monitoring and Green Management, College of Plant Protection, China Agricultural University, Beijing 100193, China
| | - Chao Wang
- Department of Entomology and MOA Key Lab of Pest Monitoring and Green Management, College of Plant Protection, China Agricultural University, Beijing 100193, China
| | - Yuanzhi Yin
- Department of Entomology and MOA Key Lab of Pest Monitoring and Green Management, College of Plant Protection, China Agricultural University, Beijing 100193, China
| | - Wei Zhang
- State Key Laboratory of Protein and Plant Gene Research, School of Life Sciences, Peking University, Beijing 100871, China
| | - Shanlin Liu
- Department of Entomology and MOA Key Lab of Pest Monitoring and Green Management, College of Plant Protection, China Agricultural University, Beijing 100193, China
| | - Cheng Sun
- College of Life Sciences, Capital Normal University, Beijing 100048, China
| | - Hu Li
- Department of Entomology and MOA Key Lab of Pest Monitoring and Green Management, College of Plant Protection, China Agricultural University, Beijing 100193, China
| | - Yuange Duan
- Department of Entomology and MOA Key Lab of Pest Monitoring and Green Management, College of Plant Protection, China Agricultural University, Beijing 100193, China
| | - Fan Song
- Department of Entomology and MOA Key Lab of Pest Monitoring and Green Management, College of Plant Protection, China Agricultural University, Beijing 100193, China
| | - Wanzhi Cai
- Department of Entomology and MOA Key Lab of Pest Monitoring and Green Management, College of Plant Protection, China Agricultural University, Beijing 100193, China
| | - Heather M Hines
- Department of Biology, The Pennsylvania State University, University Park, PA 16802, USA
| | - Li Tian
- Department of Entomology and MOA Key Lab of Pest Monitoring and Green Management, College of Plant Protection, China Agricultural University, Beijing 100193, China
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Different transcriptional responses by the CRISPRa system in distinct types of heterochromatin in Drosophila melanogaster. Sci Rep 2022; 12:11702. [PMID: 35810197 PMCID: PMC9271074 DOI: 10.1038/s41598-022-15944-7] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/03/2022] [Accepted: 07/01/2022] [Indexed: 11/09/2022] Open
Abstract
Transcription factors (TFs) activate gene expression by binding to elements close to promoters or enhancers. Some TFs can bind to heterochromatic regions to initiate gene activation, suggesting that if a TF is able to bind to any type of heterochromatin, it can activate transcription. To investigate this possibility, we used the CRISPRa system based on dCas9-VPR as an artificial TF in Drosophila. dCas9-VPR was targeted to the TAHRE telomeric element, an example of constitutive heterochromatin, and to promoters and enhancers of the HOX Ultrabithorax (Ubx) and Sex Combs Reduced (Scr) genes in the context of facultative heterochromatin. dCas9-VPR robustly activated TAHRE transcription, showing that although this element is heterochromatic, dCas9-VPR was sufficient to activate its expression. In the case of HOX gene promoters, although Polycomb complexes epigenetically silence these genes, both were ectopically activated. When the artificial TF was directed to enhancers, we found that the expression pattern was different compared to the effect on the promoters. In the case of the Scr upstream enhancer, dCas9-VPR activated the gene ectopically but with less expressivity; however, ectopic activation also occurred in different cells. In the case of the bxI enhancer located in the third intron of Ubx, the presence of dCas9-VPR is capable of increasing transcription initiation while simultaneously blocking transcription elongation, generating a lack of functional phenotype. Our results show that CRISPRa system is able to activate transcription in any type of heterochromatin; nevertheless, its effect on transcription is subject to the intrinsic characteristics of each gene or regulatory element.
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Jaramillo ML, Ammar D, Quispe RL, Bonatto Paese CL, Gruendling AP, Müller YM, Nazari EM. Identification of Hox genes and their expression profiles during embryonic development of the emerging model organism, Macrobrachium olfersii. JOURNAL OF EXPERIMENTAL ZOOLOGY. PART B, MOLECULAR AND DEVELOPMENTAL EVOLUTION 2022; 338:292-300. [PMID: 35037742 DOI: 10.1002/jez.b.23118] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/07/2021] [Revised: 12/13/2021] [Accepted: 12/19/2021] [Indexed: 06/14/2023]
Abstract
Hox genes encode transcription factors that specify the body segment identity during development, including crustaceans, such as amphipods and decapods, that possess a remarkable diversity of segments and specialized appendages. In amphipods, alterations of specialized appendages have been obtained using knockout experiment of Hox genes, which suggests that these genes are involved in the evolution of morphology within crustaceans. However, studies of Hox genes in crustaceans have been limited to a few species. Here, we identified the homeodomain of nine Hox genes: labial (lab), proboscipedia (pb), Deformed (Dfd), Sex combs reduced (Scr), fushi tarazu (ftz), Antennapedia (Antp), Ultrabithorax (Ubx), abdominal-A (abdA), and Abdominal-B (AbdB), and evaluated their expression by RT-qPCR and RT-PCR in the ovary, during embryonic development, and at the first larval stage (Zoea I) of the decapod Macrobrachium olfersii. The transcript levels of lab, Dfd, and ftz decreased and transcripts of pb, Scr, Antp, Ubx, abdA, and AbdB increased during embryonic development. Hox genes were expressed in mature ovaries and Zoea I larval stages, except Scr and ftz, respectively. In addition, isoforms of Dfd, Scr, Ubx, and abdA, which have been scarcely reported in crustaceans, were described. New partial sequences of 87 Hox genes from other crustaceans were identified from the GenBank database. Our results are interesting for future studies to determine the specific function of Hox genes and their isoforms in the freshwater prawn M. olfersii and to contribute to the understanding of the diversity and evolution of body plans and appendages in Crustaceans.
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Affiliation(s)
- Michael L Jaramillo
- Departamento de Biologia Celular, Embriologia e Genética, Universidade Federal de Santa Catarina, Florianópolis, Santa Catarina, Brazil
| | - Dib Ammar
- Departamento de Biologia Celular, Embriologia e Genética, Universidade Federal de Santa Catarina, Florianópolis, Santa Catarina, Brazil
| | - Ruth L Quispe
- Departamento de Bioquímica, Campus Universitário, Universidade Federal de Santa Catarina, Florianópolis, SC, Brazil
| | - Christian L Bonatto Paese
- Departamento de Biologia Celular, Embriologia e Genética, Universidade Federal de Santa Catarina, Florianópolis, Santa Catarina, Brazil
| | - Ana P Gruendling
- Departamento de Microbiologia, Imunologia e Parasitologia, Universidade Federal de Santa Catarina, Florianópolis, Brazil
| | - Yara M Müller
- Departamento de Biologia Celular, Embriologia e Genética, Universidade Federal de Santa Catarina, Florianópolis, Santa Catarina, Brazil
| | - Evelise M Nazari
- Departamento de Biologia Celular, Embriologia e Genética, Universidade Federal de Santa Catarina, Florianópolis, Santa Catarina, Brazil
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Feng S, Rastogi C, Loker R, Glassford WJ, Tomas Rube H, Bussemaker HJ, Mann RS. Transcription factor paralogs orchestrate alternative gene regulatory networks by context-dependent cooperation with multiple cofactors. Nat Commun 2022; 13:3808. [PMID: 35778382 PMCID: PMC9249852 DOI: 10.1038/s41467-022-31501-2] [Citation(s) in RCA: 18] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/03/2021] [Accepted: 06/20/2022] [Indexed: 12/23/2022] Open
Abstract
In eukaryotes, members of transcription factor families often exhibit similar DNA binding properties in vitro, yet orchestrate paralog-specific gene regulatory networks in vivo. The serially homologous first (T1) and third (T3) thoracic legs of Drosophila, which are specified by the Hox proteins Scr and Ubx, respectively, offer a unique opportunity to address this paradox in vivo. Genome-wide analyses using epitope-tagged alleles of both Hox loci in the T1 and T3 leg imaginal discs, the precursors to the adult legs and ventral body regions, show that ~8% of Hox binding is paralog-specific. Binding specificity is mediated by interactions with distinct cofactors in different domains: the Hox cofactor Exd acts in the proximal domain and is necessary for Scr to bind many of its paralog-specific targets, while in the distal leg domain, the homeodomain protein Distal-less (Dll) enhances Scr binding to a different subset of loci. These findings reveal how Hox paralogs, and perhaps paralogs of other transcription factor families, orchestrate alternative downstream gene regulatory networks with the help of multiple, context-specific cofactors.
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Affiliation(s)
- Siqian Feng
- Department of Biochemistry and Molecular Biophysics, Columbia University, New York, NY, USA
- Mortimer B. Zuckerman Mind Brain Behavior Institute, Columbia University, New York, NY, USA
| | - Chaitanya Rastogi
- Department of Biological Sciences, Columbia University, New York, NY, USA
| | - Ryan Loker
- Department of Biochemistry and Molecular Biophysics, Columbia University, New York, NY, USA
- Mortimer B. Zuckerman Mind Brain Behavior Institute, Columbia University, New York, NY, USA
- Department of Genetics and Development, Columbia University, New York, NY, USA
- Department of Biology, New York University, New York, NY, USA
| | - William J Glassford
- Department of Biochemistry and Molecular Biophysics, Columbia University, New York, NY, USA
- Mortimer B. Zuckerman Mind Brain Behavior Institute, Columbia University, New York, NY, USA
| | - H Tomas Rube
- Department of Biological Sciences, Columbia University, New York, NY, USA
- Department of Bioengineering, University of California, Merced, CA, USA
| | - Harmen J Bussemaker
- Department of Biological Sciences, Columbia University, New York, NY, USA
- Department of Systems Biology, Columbia University, New York, NY, 10027, USA
| | - Richard S Mann
- Department of Biochemistry and Molecular Biophysics, Columbia University, New York, NY, USA.
- Mortimer B. Zuckerman Mind Brain Behavior Institute, Columbia University, New York, NY, USA.
- Department of Systems Biology, Columbia University, New York, NY, 10027, USA.
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Bi H, Merchant A, Gu J, Li X, Zhou X, Zhang Q. CRISPR/Cas9-Mediated Mutagenesis of Abdominal-A and Ultrabithorax in the Asian Corn Borer, Ostrinia furnacalis. INSECTS 2022; 13:insects13040384. [PMID: 35447826 PMCID: PMC9031573 DOI: 10.3390/insects13040384] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 03/14/2022] [Revised: 04/02/2022] [Accepted: 04/09/2022] [Indexed: 11/16/2022]
Abstract
Simple Summary Homeotic genes encode transcription factors that coordinated the anatomical structure formation during the early embryonic development of organisms. In this study, we functionally characterized two homeotic genes, Abdominal-A (Abd-A) and Ultrabithorax (Ubx), in the Asian corn borer, Ostrinia furnacalis (a maize pest that has devastated the Asia-Pacific region) by using a CRISPR/Cas9 genome editing system. Our results show that the mutagenesis of OfAbd-A and OfUbx led to severe morphological defects in O. furnacalis, which included fused segments and segmental twist during the larval stage, and hollowed and incision-like segments during the pupal stage in OfAbd-A mutants, as well as defects in the wing-pad development in pupal and adult OfUbx mutants. Overall, knocking out Abd-A and Ubx in O. furnacalis resulted in the embryonic lethality to, and pleiotropic impact on, other homeotic genes. This study not only confirms the conserved body planning functions in OfAbd-A and OfUbx, but it also strengthens the control implications of these homeotic genes for lepidopteran pests. Abstract (1) Background: Abdominal-A (Abd-A) and Ultrabithorax (Ubx) are homeotic genes that determine the identity and morphology of the thorax and abdomen in insects. The Asian corn borer, Ostrinia furnacalis (Guenée) (Lepidoptera: Pyralidae), is a devastating maize pest throughout Asia, the Western Pacific, and Australia. Building on previous knowledge, we hypothesized that the knockout of Abd-A and Ubx would disrupt the abdominal body planning in O. furnacalis. (2) Methods: CRISPR/Cas9-targeted mutagenesis was employed to decipher the functions of these homeotic genes. (3) Results: Knockout insects demonstrated classical homeotic transformations. Specifically, the mutagenesis of OfAbd-A resulted in: (1) Fused segments and segmental twist during the larval stage; (2) Embryonic lethality; and (3) The pleiotropic upregulation of other homeotic genes, including Lab, Pd, Dfd, Antp, and Abd-B. The mutagenesis of OfUbx led to: (1) Severe defects in the wing pads, which limited the ability of the adults to fly and mate; (2) Female sterility; and (3) The pleiotropic upregulation of other homeotic genes, including Dfd, Abd-B, and Wnt1. (4) Conclusions: These combined results not only support our hypothesis, but they also strengthen the potential of using homeotic genes as molecular targets for the genetic control of this global insect pest.
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Affiliation(s)
- Honglun Bi
- College of Plant Protection, Shenyang Agricultural University, Shenyang 110866, China; (H.B.); (J.G.)
- State Key Laboratory of Cotton Biology, Key Laboratory of Plant Stress Biology, School of Life Sciences, Henan University, Kaifeng 475004, China
| | - Austin Merchant
- Department of Entomology, University of Kentucky, Lexington, KY 40546, USA; (A.M.); (X.Z.)
| | - Junwen Gu
- College of Plant Protection, Shenyang Agricultural University, Shenyang 110866, China; (H.B.); (J.G.)
| | - Xiaowei Li
- Key Laboratory of Insect Developmental and Evolutionary Biology, Institute of Plant Physiology and Ecology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai 200032, China;
| | - Xuguo Zhou
- Department of Entomology, University of Kentucky, Lexington, KY 40546, USA; (A.M.); (X.Z.)
| | - Qi Zhang
- College of Plant Protection, Shenyang Agricultural University, Shenyang 110866, China; (H.B.); (J.G.)
- Correspondence: ; Tel.: +86-13609876667
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Essay the (unusual) heuristic value of Hox gene clusters; a matter of time? Dev Biol 2022; 484:75-87. [PMID: 35182536 DOI: 10.1016/j.ydbio.2022.02.007] [Citation(s) in RCA: 14] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/24/2022] [Revised: 02/11/2022] [Accepted: 02/14/2022] [Indexed: 12/22/2022]
Abstract
Ever since their first report in 1984, Antennapedia-type homeobox (Hox) genes have been involved in such a series of interesting observations, in particular due to their conserved clustered organization between vertebrates and arthropods, that one may legitimately wonder about the origin of this heuristic value. In this essay, I first consider different examples where Hox gene clusters have been instrumental in providing conceptual advances, taken from various fields of research and mostly involving vertebrate embryos. These examples touch upon our understanding of genomic evolution, the revisiting of 19th century views on the relationships between development and evolution and the building of a new framework to understand long-range and pleiotropic gene regulation during development. I then discuss whether the high value of the Hox gene family, when considered as an epistemic object, is related to its clustered structure (and the absence thereof in some animal species) and, if so, what is it in such particular genetic oddities that made them so generous in providing the scientific community with interesting information.
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Cain B, Gebelein B. Mechanisms Underlying Hox-Mediated Transcriptional Outcomes. Front Cell Dev Biol 2021; 9:787339. [PMID: 34869389 PMCID: PMC8635045 DOI: 10.3389/fcell.2021.787339] [Citation(s) in RCA: 11] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/30/2021] [Accepted: 10/28/2021] [Indexed: 11/13/2022] Open
Abstract
Metazoans differentially express multiple Hox transcription factors to specify diverse cell fates along the developing anterior-posterior axis. Two challenges arise when trying to understand how the Hox transcription factors regulate the required target genes for morphogenesis: First, how does each Hox factor differ from one another to accurately activate and repress target genes required for the formation of distinct segment and regional identities? Second, how can a Hox factor that is broadly expressed in many tissues within a segment impact the development of specific organs by regulating target genes in a cell type-specific manner? In this review, we highlight how recent genomic, interactome, and cis-regulatory studies are providing new insights into answering these two questions. Collectively, these studies suggest that Hox factors may differentially modify the chromatin of gene targets as well as utilize numerous interactions with additional co-activators, co-repressors, and sequence-specific transcription factors to achieve accurate segment and cell type-specific transcriptional outcomes.
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Affiliation(s)
- Brittany Cain
- Division of Developmental Biology, Cincinnati Children's Hospital Medical Center, Cincinnati, OH, United States
| | - Brian Gebelein
- Division of Developmental Biology, Cincinnati Children's Hospital Medical Center, Cincinnati, OH, United States.,Department of Pediatrics, University of Cincinnati College of Medicine, Cincinnati, OH, United States
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Hajirnis N, Mishra RK. Homeotic Genes: Clustering, Modularity, and Diversity. Front Cell Dev Biol 2021; 9:718308. [PMID: 34458272 PMCID: PMC8386295 DOI: 10.3389/fcell.2021.718308] [Citation(s) in RCA: 15] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/31/2021] [Accepted: 07/22/2021] [Indexed: 11/13/2022] Open
Abstract
Hox genes code for transcription factors and are evolutionarily conserved. They regulate a plethora of downstream targets to define the anterior-posterior (AP) body axis of a developing bilaterian embryo. Early work suggested a possible role of clustering and ordering of Hox to regulate their expression in a spatially restricted manner along the AP axis. However, the recent availability of many genome assemblies for different organisms uncovered several examples that defy this constraint. With recent advancements in genomics, the current review discusses the arrangement of Hox in various organisms. Further, we revisit their discovery and regulation in Drosophila melanogaster. We also review their regulation in different arthropods and vertebrates, with a significant focus on Hox expression in the crustacean Parahyale hawaiensis. It is noteworthy that subtle changes in the levels of Hox gene expression can contribute to the development of novel features in an organism. We, therefore, delve into the distinct regulation of these genes during primary axis formation, segment identity, and extra-embryonic roles such as in the formation of hair follicles or misregulation leading to cancer. Toward the end of each section, we emphasize the possibilities of several experiments involving various organisms, owing to the advancements in the field of genomics and CRISPR-based genome engineering. Overall, we present a holistic view of the functioning of Hox in the animal world.
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Affiliation(s)
- Nikhil Hajirnis
- CSIR – Centre for Cellular and Molecular Biology (CCMB), Hyderabad, India
| | - Rakesh K. Mishra
- CSIR – Centre for Cellular and Molecular Biology (CCMB), Hyderabad, India
- AcSIR – Academy of Scientific and Innovative Research, Ghaziabad, India
- Tata Institute for Genetics and Society (TIGS), Bangalore, India
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Lewin TD, Royall AH, Holland PWH. Dynamic Molecular Evolution of Mammalian Homeobox Genes: Duplication, Loss, Divergence and Gene Conversion Sculpt PRD Class Repertoires. J Mol Evol 2021; 89:396-414. [PMID: 34097121 PMCID: PMC8208926 DOI: 10.1007/s00239-021-10012-6] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/05/2021] [Accepted: 05/11/2021] [Indexed: 11/21/2022]
Abstract
The majority of homeobox genes are highly conserved across animals, but the eutherian-specific ETCHbox genes, embryonically expressed and highly divergent duplicates of CRX, are a notable exception. Here we compare the ETCHbox genes of 34 mammalian species, uncovering dynamic patterns of gene loss and tandem duplication, including the presence of a large tandem array of LEUTX loci in the genome of the European rabbit (Oryctolagus cuniculus). Despite extensive gene gain and loss, all sampled species possess at least two ETCHbox genes, suggesting their collective role is indispensable. We find evidence for positive selection and show that TPRX1 and TPRX2 have been the subject of repeated gene conversion across the Boreoeutheria, homogenising their sequences and preventing divergence, especially in the homeobox region. Together, these results are consistent with a model where mammalian ETCHbox genes are dynamic in evolution due to functional overlap, yet have collective indispensable roles.
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Affiliation(s)
- Thomas D Lewin
- Department of Zoology, University of Oxford, 11a Mansfield Road, Oxford, OX1 3SZ, UK
| | - Amy H Royall
- Department of Zoology, University of Oxford, 11a Mansfield Road, Oxford, OX1 3SZ, UK
| | - Peter W H Holland
- Department of Zoology, University of Oxford, 11a Mansfield Road, Oxford, OX1 3SZ, UK.
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Van der Mude A. Structure encoding in DNA. J Theor Biol 2020; 492:110205. [PMID: 32070719 DOI: 10.1016/j.jtbi.2020.110205] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/16/2019] [Revised: 12/29/2019] [Accepted: 02/14/2020] [Indexed: 12/21/2022]
Abstract
It is proposed that transposons and related long non-coding RNA define the fine structure of body parts. Although morphogens have long been known to direct the formation of many gross structures in early embryonic development, they do not have the necessary precision to define a structure down to the individual cellular level. Using the distinction between procedural and declarative knowledge in information processing as an analogy, it is hypothesized that DNA encodes fine structure in a manner that is different from the genetic code for proteins. The hypothesis states that repeated or near-repeated sequences that are in transposons and non-coding RNA define body part structures. As the cells in a body part go through the epigenetic process of differentiation, the action of methylation serves to inactivate all but the relevant structure definitions and some associated cell type genes. The transposons left active will then physically modify the DNA sequence in the heterochromatin to establish the local context in the three-dimensional body part structure. This brings the encoded definition of the cell type to the histone. The histone code for that cell type starts the regulatory cascade that turns on the genes associated with that particular type of cell, transforming it from a multipotent cell to a fully differentiated cell. This mechanism creates structures in the musculoskeletal system, the organs of the body, the major parts of the brain, and other systems.
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RNA-DNA strand exchange by the Drosophila Polycomb complex PRC2. Nat Commun 2020; 11:1781. [PMID: 32286294 PMCID: PMC7156742 DOI: 10.1038/s41467-020-15609-x] [Citation(s) in RCA: 34] [Impact Index Per Article: 8.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/01/2019] [Accepted: 03/17/2020] [Indexed: 12/21/2022] Open
Abstract
Polycomb Group (PcG) proteins form memory of transient transcriptional repression that is necessary for development. In Drosophila, DNA elements termed Polycomb Response Elements (PREs) recruit PcG proteins. How PcG activities are targeted to PREs to maintain repressed states only in appropriate developmental contexts has been difficult to elucidate. PcG complexes modify chromatin, but also interact with both RNA and DNA, and RNA is implicated in PcG targeting and function. Here we show that R-loops form at many PREs in Drosophila embryos, and correlate with repressive states. In vitro, both PRC1 and PRC2 can recognize R-loops and open DNA bubbles. Unexpectedly, we find that PRC2 drives formation of RNA-DNA hybrids, the key component of R-loops, from RNA and dsDNA. Our results identify R-loop formation as a feature of Drosophila PREs that can be recognized by PcG complexes, and RNA-DNA strand exchange as a PRC2 activity that could contribute to R-loop formation. RNA is implicated in the targeting and function of Polycomb Group (PcG) chromatin regulators. Here the authors show that R-loops, three-stranded nucleic acid structures formed by DNA and RNA, are formed at some PcG binding sites in flies, as they are in mammals. Fly PRC2 can drive formation of RNA-DNA hybrids in vitro.
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Kyrchanova O, Wolle D, Sabirov M, Kurbidaeva A, Aoki T, Maksimenko O, Kyrchanova M, Georgiev P, Schedl P. Distinct Elements Confer the Blocking and Bypass Functions of the Bithorax Fab-8 Boundary. Genetics 2019; 213:865-876. [PMID: 31551239 PMCID: PMC6827379 DOI: 10.1534/genetics.119.302694] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/24/2019] [Accepted: 09/12/2019] [Indexed: 01/05/2023] Open
Abstract
Boundaries in the Drosophila bithorax complex (BX-C) enable the regulatory domains that drive parasegment-specific expression of the three Hox genes to function autonomously. The four regulatory domains (iab-5, iab-6, iab-7, and iab-8) that control the expression of the Abdominal-B (Abd-B) gene are located downstream of the transcription unit, and are delimited by the Mcp, Fab-6, Fab-7, and Fab-8 boundaries. These boundaries function to block cross talk between neighboring regulatory domains. In addition, three of the boundaries (Fab-6, Fab-7, and Fab-8) must also have bypass activity so that regulatory domains distal to the boundaries can contact the Abd-B promoter. In the studies reported here, we have undertaken a functional dissection of the Fab-8 boundary using a boundary-replacement strategy. Our studies indicate that the Fab-8 boundary has two separable subelements. The distal subelement blocks cross talk, but cannot support bypass. The proximal subelement has only minimal blocking activity but is able to mediate bypass. A large multiprotein complex, the LBC (large boundary complex), binds to sequences in the proximal subelement and contributes to its bypass activity. The same LBC complex has been implicated in the bypass activity of the Fab-7 boundary.
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Affiliation(s)
- Olga Kyrchanova
- Department of the Control of Genetic Processes, Institute of Gene Biology Russian Academy of Sciences, Moscow 119334, Russia
| | - Daniel Wolle
- Department of Molecular Biology, Princeton University, New Jersey 08544
| | - Marat Sabirov
- Department of the Control of Genetic Processes, Institute of Gene Biology Russian Academy of Sciences, Moscow 119334, Russia
| | - Amina Kurbidaeva
- Department of Molecular Biology, Princeton University, New Jersey 08544
| | - Tsutomu Aoki
- Department of Molecular Biology, Princeton University, New Jersey 08544
| | - Oksana Maksimenko
- Department of the Control of Genetic Processes, Institute of Gene Biology Russian Academy of Sciences, Moscow 119334, Russia
| | - Maria Kyrchanova
- Department of the Control of Genetic Processes, Institute of Gene Biology Russian Academy of Sciences, Moscow 119334, Russia
| | - Pavel Georgiev
- Department of the Control of Genetic Processes, Institute of Gene Biology Russian Academy of Sciences, Moscow 119334, Russia
| | - Paul Schedl
- Department of Molecular Biology, Princeton University, New Jersey 08544
- Laboratory of Gene Expression Regulation in Development, Institute of Gene Biology Russian Academy of Sciences, Moscow 119334, Russia
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13
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Tian L, Rahman SR, Ezray BD, Franzini L, Strange JP, Lhomme P, Hines HM. A homeotic shift late in development drives mimetic color variation in a bumble bee. Proc Natl Acad Sci U S A 2019; 116:11857-11865. [PMID: 31043564 PMCID: PMC6575597 DOI: 10.1073/pnas.1900365116] [Citation(s) in RCA: 29] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022] Open
Abstract
Natural phenotypic radiations, with their high diversity and convergence, are well-suited for informing how genomic changes translate to natural phenotypic variation. New genomic tools enable discovery in such traditionally nonmodel systems. Here, we characterize the genomic basis of color pattern variation in bumble bees (Hymenoptera, Apidae, Bombus), a group that has undergone extensive convergence of setal color patterns as a result of Müllerian mimicry. In western North America, multiple species converge on local mimicry patterns through parallel shifts of midabdominal segments from red to black. Using genome-wide association, we establish that a cis-regulatory locus between the abdominal fate-determining Hox genes, abd-A and Abd-B, controls the red-black color switch in a western species, Bombus melanopygus Gene expression analysis reveals distinct shifts in Abd-B aligned with the duration of setal pigmentation at the pupal-adult transition. This results in atypical anterior Abd-B expression, a late developmental homeotic shift. Changing expression of Hox genes can have widespread effects, given their important role across segmental phenotypes; however, the late timing reduces this pleiotropy, making Hox genes suitable targets. Analysis of this locus across mimics and relatives reveals that other species follow independent genetic routes to obtain the same phenotypes.
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Affiliation(s)
- Li Tian
- Department of Biology, The Pennsylvania State University, University Park, PA 16802
| | | | - Briana D Ezray
- Department of Entomology, The Pennsylvania State University, University Park, PA 16802
| | - Luca Franzini
- Department of Entomology, The Pennsylvania State University, University Park, PA 16802
| | - James P Strange
- United States Department of Agriculture-Agricultural Research Service Pollinating Insects Research Unit, Utah State University, Logan, UT 84322
| | - Patrick Lhomme
- Department of Biology, The Pennsylvania State University, University Park, PA 16802
- Biodiversity and Crop Improvement Program, International Center of Agricultural Research in the Dry Areas, 10112 Rabat, Morocco
| | - Heather M Hines
- Department of Biology, The Pennsylvania State University, University Park, PA 16802;
- Department of Entomology, The Pennsylvania State University, University Park, PA 16802
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14
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Mateo LJ, Murphy SE, Hafner A, Cinquini IS, Walker CA, Boettiger AN. Visualizing DNA folding and RNA in embryos at single-cell resolution. Nature 2019; 568:49-54. [PMID: 30886393 PMCID: PMC6556380 DOI: 10.1038/s41586-019-1035-4] [Citation(s) in RCA: 266] [Impact Index Per Article: 53.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/01/2018] [Accepted: 02/25/2019] [Indexed: 01/09/2023]
Abstract
Establishment of cell types during development requires precise interactions between genes and distal regulatory sequences. Our understanding of how these interactions look in three dimensions, vary across cell types in complex tissue, and relate to transcription remains limited. Here we describe optical reconstruction of chromatin architecture (ORCA), a method to trace the DNA path in single cells with nanoscale accuracy and genomic resolution reaching 2 kilobases. We applied ORCA to a Hox gene cluster in cryosectioned Drosophila embryos and labelled ~30 RNA species in parallel. We identified cell-type-specific physical borders between active and Polycomb-repressed DNA, and unexpected Polycomb-independent borders. Deletion of Polycomb-independent borders led to ectopic enhancer-promoter contacts, aberrant gene expression, and developmental defects. Together, these results illustrate an approach for high-resolution, single-cell DNA domain analysis in vivo, reveal domain structures that change with cell identity, and show that border elements contribute to formation of physical domains in Drosophila.
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Affiliation(s)
- Leslie J Mateo
- Department of Developmental Biology, Stanford University, Stanford, CA, USA
| | - Sedona E Murphy
- Department of Developmental Biology, Stanford University, Stanford, CA, USA.,Department of Genetics, Stanford University, Stanford, CA, USA
| | - Antonina Hafner
- Department of Developmental Biology, Stanford University, Stanford, CA, USA
| | - Isaac S Cinquini
- Department of Developmental Biology, Stanford University, Stanford, CA, USA.,Department of Computer Science, Stanford University, Stanford, CA, USA
| | - Carly A Walker
- Department of Developmental Biology, Stanford University, Stanford, CA, USA
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15
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16
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Lakhotia SC. From Heterochromatin to Long Noncoding RNAs in Drosophila: Expanding the Arena of Gene Function and Regulation. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2018; 1008:75-118. [PMID: 28815537 DOI: 10.1007/978-981-10-5203-3_3] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
Abstract
Recent years have witnessed a remarkable interest in exploring the significance of pervasive noncoding transcripts in diverse eukaryotes. Classical cytogenetic studies using the Drosophila model system unraveled the perplexing attributes and "functions" of the "gene"-poor heterochromatin. Recent molecular studies in the fly model are likewise revealing the very diverse and significant roles played by long noncoding RNAs (lncRNAs) in development, gene regulation, chromatin organization, cell and nuclear architecture, etc. There has been a rapid increase in the number of identified lncRNAs, although a much larger number still remains unknown. The diversity of modes of actions and functions of the limited number of Drosophila lncRNAs, which have been examined, already reflects the profound roles of such RNAs in generating and sustaining the biological complexities of eukaryotes. Several of the known Drosophila lncRNAs originate as independent sense or antisense transcripts from promoter or intergenic, intronic, or 5'/3'-UTR regions, while many of them are independent genes that produce only lncRNAs or coding as well as noncoding RNAs. The different lncRNAs affect chromatin organization (local or large-scale pan-chromosomal), transcription, RNA processing/stability, or translation either directly through interaction with their target DNA sequences or indirectly by acting as intermediary molecules for specific regulatory proteins or may act as decoys/sinks, or storage sites for specific proteins or groups of proteins, or may provide a structural framework for the assembly of substructures in nucleus/cytoplasm. It is interesting that many of the "functions" alluded to heterochromatin in earlier cytogenetic studies appear to find correlates with the known subtle as well as far-reaching actions of the different small and long noncoding RNAs. Further studies exploiting the very rich and powerful genetic and molecular resources available for the Drosophila model are expected to unravel the mystery underlying the long reach of ncRNAs.
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Affiliation(s)
- Subhash C Lakhotia
- Cytogenetics Laboratory, Department of Zoology, Banaras Hindu University, Varanasi, 221005, India.
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17
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Dutta P, Li WX. The SERTAD protein Taranis plays a role in Polycomb-mediated gene repression. PLoS One 2017; 12:e0180026. [PMID: 28665982 PMCID: PMC5493352 DOI: 10.1371/journal.pone.0180026] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/02/2016] [Accepted: 06/08/2017] [Indexed: 11/19/2022] Open
Abstract
The Polycomb group (PcG) proteins have been implicated in epigenetic transcriptional repression in development, stem cell maintenance and in cancer. The chromodomain protein Polycomb (Pc) is a key member of the PcG. Pc binds to the histone mark, trimethylated histone 3 lysine 27 (H3K27me3), to initiate transcriptional repression. How PcG proteins are recruited to target loci is not fully understood. Here we show that the Drosophila SERTA domain protein Taranis (Tara) is involved in transcriptional regulation of Pc target genes. Embryos lacking Tara exhibit a partial homeotic transformation of cuticular the segments, a phenotype associated with the loss of Pc function. Moreover, Drosophila embryos homozygous for a tara hypomorphic allele also misexpress engrailed, a Pc-regulated gene, and this phenotype is associated with the loss of Pc binding to the cis response element in the engrailed enhancer. In relation to that, Pc recruitment is reduced on the salivary gland polytene chromosomes and specifically at the engrailed locus. These results suggest that Tara might be required for positioning Pc to a subset of its target genes.
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Affiliation(s)
- Pranabananda Dutta
- Department of Medicine, University of California San Diego, La Jolla, California, United States of America
- Department of Biomedical Genetics, University of Rochester Medical Center, Rochester, New York, United States of America
- * E-mail:
| | - Willis X. Li
- Department of Medicine, University of California San Diego, La Jolla, California, United States of America
- Department of Biomedical Genetics, University of Rochester Medical Center, Rochester, New York, United States of America
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18
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Narendra V, Bulajić M, Dekker J, Mazzoni EO, Reinberg D. CTCF-mediated topological boundaries during development foster appropriate gene regulation. Genes Dev 2017; 30:2657-2662. [PMID: 28087711 PMCID: PMC5238725 DOI: 10.1101/gad.288324.116] [Citation(s) in RCA: 105] [Impact Index Per Article: 15.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/31/2016] [Accepted: 12/12/2016] [Indexed: 12/11/2022]
Abstract
The genome is organized into repeating topologically associated domains (TADs), each of which is spatially isolated from its neighbor by poorly understood boundary elements thought to be conserved across cell types. Here, we show that deletion of CTCF (CCCTC-binding factor)-binding sites at TAD and sub-TAD topological boundaries that form within the HoxA and HoxC clusters during differentiation not only disturbs local chromatin domain organization and regulatory interactions but also results in homeotic transformations typical of Hox gene misregulation. Moreover, our data suggest that CTCF-dependent boundary function can be modulated by competing forces, such as the self-assembly of polycomb domains within the nucleus. Therefore, CTCF boundaries are not merely static structural components of the genome but instead are locally dynamic regulatory structures that control gene expression during development.
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Affiliation(s)
- Varun Narendra
- Howard Hughes Medical Institute, New York, New York 10016, USA.,Department of Biochemistry and Molecular Pharmacology, New York University School of Medicine, New York, New York 10016, USA
| | - Milica Bulajić
- Department of Biology, New York University, New York, New York 10003, USA
| | - Job Dekker
- Howard Hughes Medical Institute, New York, New York 10016, USA.,Program in Systems Biology, Department of Biochemistry and Molecular Pharmacology, University of Massachusetts Medical School, Worcester, Massachusetts 01605, USA
| | - Esteban O Mazzoni
- Department of Biology, New York University, New York, New York 10003, USA
| | - Danny Reinberg
- Howard Hughes Medical Institute, New York, New York 10016, USA.,Department of Biochemistry and Molecular Pharmacology, New York University School of Medicine, New York, New York 10016, USA
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19
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Pervasive Behavioral Effects of MicroRNA Regulation in Drosophila. Genetics 2017; 206:1535-1548. [PMID: 28468905 PMCID: PMC5500149 DOI: 10.1534/genetics.116.195776] [Citation(s) in RCA: 24] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/14/2016] [Accepted: 04/23/2017] [Indexed: 11/18/2022] Open
Abstract
Picao-Osorio et al. reveal pervasive effects of microRNA regulation on complex locomotor behaviors in Drosophila larvae: over 40% of microRNAs display... The effects of microRNA (miRNA) regulation on the genetic programs underlying behavior remain largely unexplored. Despite this, recent work in Drosophila shows that mutation of a single miRNA locus (miR-iab4/iab8) affects the capacity of the larva to correct its orientation if turned upside down (self-righting, SR), suggesting that other miRNAs might also be involved in behavioral control. Here we explore this possibility, studying early larval SR behavior in a collection of 81 Drosophila miRNA mutants covering almost the entire miRNA complement of the late embryo. Unexpectedly, we observe that >40% of all miRNAs tested significantly affect SR time, revealing pervasive behavioral effects of miRNA regulation in the early larva. Detailed analyses of those miRNAs affecting SR behavior (SR-miRNAs) show that individual miRNAs can affect movement in different ways, suggesting that specific molecular and cellular elements are affected by individual miRNA mutations. Furthermore, gene expression analysis shows that the Hox gene Abdominal-B (Abd-B) represents one of the targets deregulated by several SR-miRNAs. Our work thus reveals pervasive effects of miRNA regulation on a complex innate behavior in Drosophila and suggests that miRNAs may be core components of the genetic programs underlying behavioral control in other animals too.
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20
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Chetverina DA, Elizar’ev PV, Lomaev DV, Georgiev PG, Erokhin MM. Control of the gene activity by polycomb and trithorax group proteins in Drosophila. RUSS J GENET+ 2017. [DOI: 10.1134/s1022795417020028] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
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21
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Rux DR, Wellik DM. Hox genes in the adult skeleton: Novel functions beyond embryonic development. Dev Dyn 2017; 246:310-317. [PMID: 28026082 DOI: 10.1002/dvdy.24482] [Citation(s) in RCA: 65] [Impact Index Per Article: 9.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/30/2016] [Revised: 12/13/2016] [Accepted: 12/16/2016] [Indexed: 12/20/2022] Open
Abstract
Hox genes encode evolutionarily conserved transcription factors that control skeletal patterning in the developing embryo. They are expressed in regionally restricted domains and function to regulate the morphology of specific vertebral and long bone elements. Recent work has provided evidence that Hox genes continue to be regionally expressed in adult tissues. Fibroblasts cultured from adult tissues show broadly maintained Hox gene expression patterns. In the adult skeleton, Hox genes are expressed in progenitor-enriched populations of mesenchymal stem/stromal cells (MSCs), and genetic loss-of-function analyses have provided evidence that Hox genes function during the fracture healing process. This review will highlight our current understanding of Hox expression in the adult animal and its function in skeletal regeneration. Developmental Dynamics 246:310-317, 2017. © 2016 Wiley Periodicals, Inc.
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Affiliation(s)
- Danielle R Rux
- Department of Cell and Developmental Biology, University of Michigan, Ann Arbor, Michigan
| | - Deneen M Wellik
- Department of Cell and Developmental Biology, University of Michigan, Ann Arbor, Michigan.,Department of Internal Medicine, Division of Molecular Medicine and Genetics, University of Michigan, Ann Arbor, Michigan
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22
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Wang H, Tong X, Liu M, Hu H, Li Z, Xiang Z, Dai F, Lu C. Fine Mapping of a Degenerated Abdominal Legs Mutant (Edl) in Silkworm, Bombyx mori. PLoS One 2017; 12:e0169224. [PMID: 28081147 PMCID: PMC5231277 DOI: 10.1371/journal.pone.0169224] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/31/2016] [Accepted: 12/13/2016] [Indexed: 12/05/2022] Open
Abstract
In insects, abdominal appendages, also called prolegs, vary due to adaptive evolution. Mutations on prolegs within species provide insights to better understand the mechanisms underlying appendage development and diversity. In silkworm Bombyx mori, extra-crescents and degenerated abdominal legs (Edl) mutant, belonging to the E pseudoallele group, is a spontaneous mutation that adds crescents and degenerates prolegs on the third abdominal segment (A3). This mutation may be a homeotic transformation of A3 to A2. In this study, the Edl locus was mapped within approximately a 211 Kb region that is 10 Kb upstream of Bmabdominal-A (Bmabd-A). RT-quantitative PCR (RT-qPCR) and Western blot analysis of Bmabd-A expression showed a slight but significant decrease, while the expression of BmUltrabithorax (BmUbx) was up-regulated in the Edl mutant compared to wildtype (Dazao). Moreover, we also found that BmDistal-less (BmDll), which regulated the development of distal proleg structures, was missing at the tips of the A3 prolegs in the Edl mutant compared to BmDll expression in normally developed prolegs in both the wildtype and mutant. Collectively, we identified approximately a 211 Kb region in the Edl locus that regulates BmUbx and Bmabd-A expression and found that changes in BmUbx and Bmabd-A expression may lead to the loss of distal proleg structures in B. mori.
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Affiliation(s)
- Honglei Wang
- State Key Laboratory of Silkworm Genome Biology, Key Laboratory for Sericulture Functional Genomics and Biotechnology of Agricultural Ministry, Southwest University, Chongqing, China
| | - Xiaoling Tong
- State Key Laboratory of Silkworm Genome Biology, Key Laboratory for Sericulture Functional Genomics and Biotechnology of Agricultural Ministry, Southwest University, Chongqing, China
| | - Meijing Liu
- State Key Laboratory of Silkworm Genome Biology, Key Laboratory for Sericulture Functional Genomics and Biotechnology of Agricultural Ministry, Southwest University, Chongqing, China
| | - Hai Hu
- State Key Laboratory of Silkworm Genome Biology, Key Laboratory for Sericulture Functional Genomics and Biotechnology of Agricultural Ministry, Southwest University, Chongqing, China
| | - Zhiquan Li
- State Key Laboratory of Silkworm Genome Biology, Key Laboratory for Sericulture Functional Genomics and Biotechnology of Agricultural Ministry, Southwest University, Chongqing, China
| | - Zhonghuai Xiang
- State Key Laboratory of Silkworm Genome Biology, Key Laboratory for Sericulture Functional Genomics and Biotechnology of Agricultural Ministry, Southwest University, Chongqing, China
| | - Fangyin Dai
- State Key Laboratory of Silkworm Genome Biology, Key Laboratory for Sericulture Functional Genomics and Biotechnology of Agricultural Ministry, Southwest University, Chongqing, China
- * E-mail: (FD); (CL)
| | - Cheng Lu
- State Key Laboratory of Silkworm Genome Biology, Key Laboratory for Sericulture Functional Genomics and Biotechnology of Agricultural Ministry, Southwest University, Chongqing, China
- * E-mail: (FD); (CL)
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23
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Kyrchanova O, Mogila V, Wolle D, Deshpande G, Parshikov A, Cléard F, Karch F, Schedl P, Georgiev P. Functional Dissection of the Blocking and Bypass Activities of the Fab-8 Boundary in the Drosophila Bithorax Complex. PLoS Genet 2016; 12:e1006188. [PMID: 27428541 PMCID: PMC4948906 DOI: 10.1371/journal.pgen.1006188] [Citation(s) in RCA: 34] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/03/2015] [Accepted: 06/22/2016] [Indexed: 12/16/2022] Open
Abstract
Functionally autonomous regulatory domains direct the parasegment-specific expression of the Drosophila Bithorax complex (BX-C) homeotic genes. Autonomy is conferred by boundary/insulator elements that separate each regulatory domain from its neighbors. For six of the nine parasegment (PS) regulatory domains in the complex, at least one boundary is located between the domain and its target homeotic gene. Consequently, BX-C boundaries must not only block adventitious interactions between neighboring regulatory domains, but also be permissive (bypass) for regulatory interactions between the domains and their gene targets. To elucidate how the BX-C boundaries combine these two contradictory activities, we have used a boundary replacement strategy. We show that a 337 bp fragment spanning the Fab-8 boundary nuclease hypersensitive site and lacking all but 83 bp of the 625 bp Fab-8 PTS (promoter targeting sequence) fully rescues a Fab-7 deletion. It blocks crosstalk between the iab-6 and iab-7 regulatory domains, and has bypass activity that enables the two downstream domains, iab-5 and iab-6, to regulate Abdominal-B (Abd-B) transcription in spite of two intervening boundary elements. Fab-8 has two dCTCF sites and we show that they are necessary both for blocking and bypass activity. However, CTCF sites on their own are not sufficient for bypass. While multimerized dCTCF (or Su(Hw)) sites have blocking activity, they fail to support bypass. Moreover, this bypass defect is not rescued by the full length PTS. Finally, we show that orientation is critical for the proper functioning the Fab-8 replacement. Though the inverted Fab-8 boundary still blocks crosstalk, it disrupts the topology of the Abd-B regulatory domains and does not support bypass. Importantly, altering the orientation of the Fab-8 dCTCF sites is not sufficient to disrupt bypass, indicating that orientation dependence is conferred by other factors. Boundary elements in the Bithorax complex have two seemingly contradictory activities. They must block crosstalk between neighboring regulatory domains, but at the same time be permissive (insulator bypass) for regulatory interactions between the domains and the BX-C homeotic genes. We have used a replacement strategy to investigate how they carry out these two functions. We show that a 337 bp fragment spanning the Fab-8 boundary nuclease hypersensitive site is sufficient to fully rescue a Fab-7 boundary deletion. It blocks crosstalk and supports bypass. As has been observed in transgene assays, blocking activity requires the Fab-8 dCTCF sites, while full bypass activity requires the dCTCF sites plus a small part of PTS. In transgene assays, bypass activity typically depends on the orientation of the two insulators relative to each other. A similar orientation dependence is observed for the Fab-8 replacement in BX-C. When the orientation of the Fab-8 boundary is reversed, bypass activity is lost, while blocking is unaffected. Interestingly, unlike what has been observed in mammals, reversing the orientation of only the Fab-8 dCTCF sites does not affect boundary function. This finding indicates that other Fab-8 factors must play a critical role in determining orientation. Taken together, our findings argue that carrying out the paradoxical functions of the BX-C boundaries does not require any unusual or special properties; rather BX-C boundaries utilize generic blocking and insulator bypass activities that are appropriately adapted to their regulatory context. Thus making them a good model for studying the functional properties of boundaries/insulators in their native setting.
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Affiliation(s)
- Olga Kyrchanova
- Department of Genetics, Institute of Gene Biology, Russian Academy of Sciences, Moscow, Russia
- * E-mail: (OK); (PG)
| | - Vladic Mogila
- Department of Genetics, Institute of Gene Biology, Russian Academy of Sciences, Moscow, Russia
| | - Daniel Wolle
- Department of Molecular Biology, Princeton University, Princeton, New Jersey, United States of America
| | - Girish Deshpande
- Department of Molecular Biology, Princeton University, Princeton, New Jersey, United States of America
| | - Alexander Parshikov
- Department of Genetics, Institute of Gene Biology, Russian Academy of Sciences, Moscow, Russia
| | - Fabienne Cléard
- Department of Genetics and Evolution, University of Geneva, Geneva, Switzerland
| | - Francois Karch
- Department of Genetics and Evolution, University of Geneva, Geneva, Switzerland
| | - Paul Schedl
- Department of Genetics, Institute of Gene Biology, Russian Academy of Sciences, Moscow, Russia
- Department of Molecular Biology, Princeton University, Princeton, New Jersey, United States of America
| | - Pavel Georgiev
- Department of Genetics, Institute of Gene Biology, Russian Academy of Sciences, Moscow, Russia
- * E-mail: (OK); (PG)
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24
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Kyrchanova O, Mogila V, Wolle D, Magbanua JP, White R, Georgiev P, Schedl P. The boundary paradox in the Bithorax complex. Mech Dev 2015; 138 Pt 2:122-132. [PMID: 26215349 PMCID: PMC4890074 DOI: 10.1016/j.mod.2015.07.002] [Citation(s) in RCA: 29] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/13/2015] [Revised: 07/08/2015] [Accepted: 07/09/2015] [Indexed: 02/08/2023]
Abstract
The parasegment-specific expression of the three Drosophila Bithorax complex homeotic genes is orchestrated by nine functionally autonomous regulatory domains. Functional autonomy depends upon special elements called boundaries or insulators that are located between each domain. The boundaries ensure the independent activity of each domain by blocking adventitious interactions with initiators, enhancers and silencers in the neighboring domains. However, this blocking activity poses a regulatory paradox--the Bithorax boundaries are also able to insulate promoters from regulatory interactions with enhancers and silencers and six of the nine Bithorax regulatory domains are separated from their target genes by at least one boundary element. Here we consider several mechanisms that have been suggested for how the Bithorax regulatory domains are able to bypass intervening boundary elements and direct the appropriate parasegment-specific temporal and spatial expression of their target gene.
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Affiliation(s)
- Olga Kyrchanova
- Laboratory of Gene Expression Regulation in Development, Institute of Gene Biology, Russian Academy of Sciences, Moscow, Russia
| | - Vladic Mogila
- Department of the Control of Genetic Processes, Institute of Gene Biology, Russian Academy of Sciences, Moscow, Russia; Nikolaev V.A. Sukhomlinsky National University, Department of Biology, Ukraine
| | - Daniel Wolle
- Department of Molecular Biology, Princeton University, Princeton, NJ, USA
| | - Jose Paolo Magbanua
- Department of Physiology, Development and Neuroscience, University of Cambridge, Cambridge, UK
| | - Robert White
- Department of Physiology, Development and Neuroscience, University of Cambridge, Cambridge, UK
| | - Pavel Georgiev
- Department of the Control of Genetic Processes, Institute of Gene Biology, Russian Academy of Sciences, Moscow, Russia
| | - Paul Schedl
- Laboratory of Gene Expression Regulation in Development, Institute of Gene Biology, Russian Academy of Sciences, Moscow, Russia; Department of Molecular Biology, Princeton University, Princeton, NJ, USA.
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25
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The quest for mammalian Polycomb response elements: are we there yet? Chromosoma 2015; 125:471-96. [PMID: 26453572 PMCID: PMC4901126 DOI: 10.1007/s00412-015-0539-4] [Citation(s) in RCA: 62] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/08/2015] [Revised: 08/31/2015] [Accepted: 09/02/2015] [Indexed: 12/12/2022]
Abstract
A long-standing mystery in the field of Polycomb and Trithorax regulation is how these proteins, which are highly conserved between flies and mammals, can regulate several hundred equally highly conserved target genes, but recognise these targets via cis-regulatory elements that appear to show no conservation in their DNA sequence. These elements, termed Polycomb/Trithorax response elements (PRE/TREs or PREs), are relatively well characterised in flies, but their mammalian counterparts have proved to be extremely difficult to identify. Recent progress in this endeavour has generated a wealth of data and raised several intriguing questions. Here, we ask why and to what extent mammalian PREs are so different to those of the fly. We review recent advances, evaluate current models and identify open questions in the quest for mammalian PREs.
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26
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Maeda RK, Karch F. The open for business model of the bithorax complex in Drosophila. Chromosoma 2015; 124:293-307. [PMID: 26067031 PMCID: PMC4548009 DOI: 10.1007/s00412-015-0522-0] [Citation(s) in RCA: 62] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/16/2015] [Revised: 05/19/2015] [Accepted: 05/19/2015] [Indexed: 01/13/2023]
Abstract
After nearly 30 years of effort, Ed Lewis published his 1978 landmark paper in which he described the analysis of a series of mutations that affect the identity of the segments that form along the anterior-posterior (AP) axis of the fly (Lewis 1978). The mutations behaved in a non-canonical fashion in complementation tests, forming what Ed Lewis called a "pseudo-allelic" series. Because of this, he never thought that the mutations represented segment-specific genes. As all of these mutations were grouped to a particular area of the Drosophila third chromosome, the locus became known of as the bithorax complex (BX-C). One of the key findings of Lewis' article was that it revealed for the first time, to a wide scientific audience, that there was a remarkable correlation between the order of the segment-specific mutations along the chromosome and the order of the segments they affected along the AP axis. In Ed Lewis' eyes, the mutants he discovered affected "segment-specific functions" that were sequentially activated along the chromosome as one moves from anterior to posterior along the body axis (the colinearity concept now cited in elementary biology textbooks). The nature of the "segment-specific functions" started to become clear when the BX-C was cloned through the pioneering chromosomal walk initiated in the mid 1980s by the Hogness and Bender laboratories (Bender et al. 1983a; Karch et al. 1985). Through this molecular biology effort, and along with genetic characterizations performed by Gines Morata's group in Madrid (Sanchez-Herrero et al. 1985) and Robert Whittle's in Sussex (Tiong et al. 1985), it soon became clear that the whole BX-C encoded only three protein-coding genes (Ubx, abd-A, and Abd-B). Later, immunostaining against the Ubx protein hinted that the segment-specific functions could, in fact, be cis-regulatory elements regulating the expression of the three protein-coding genes. In 1987, Peifer, Karch, and Bender proposed a comprehensive model of the functioning of the BX-C, in which the "segment-specific functions" appear as segment-specific enhancers regulating, Ubx, abd-A, or Abd-B (Peifer et al. 1987). Key to their model was that the segmental address of these enhancers was not an inherent ability of the enhancers themselves, but was determined by the chromosomal location in which they lay. In their view, the sequential activation of the segment-specific functions resulted from the sequential opening of chromatin domains along the chromosome as one moves from anterior to posterior. This model soon became known of as the open for business model. While the open for business model is quite easy to visualize at a conceptual level, molecular evidence to validate this model has been missing for almost 30 years. The recent publication describing the outstanding, joint effort from the Bender and Kingston laboratories now provides the missing proof to support this model (Bowman et al. 2014). The purpose of this article is to review the open for business model and take the reader through the genetic arguments that led to its elaboration.
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Affiliation(s)
- Robert K. Maeda
- Department of Genetics and Evolution, University of Geneva, 30 quai E. Ansermet, 1211 Geneva-4, Switzerland
| | - François Karch
- Department of Genetics and Evolution, University of Geneva, 30 quai E. Ansermet, 1211 Geneva-4, Switzerland
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Srivastava S, Dhawan J, Mishra RK. Epigenetic mechanisms and boundaries in the regulation of mammalian Hox clusters. Mech Dev 2015; 138 Pt 2:160-169. [PMID: 26254900 DOI: 10.1016/j.mod.2015.07.015] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/01/2015] [Revised: 07/29/2015] [Accepted: 07/30/2015] [Indexed: 01/07/2023]
Abstract
Hox gene expression imparts segment identity to body structures along the anterior-posterior axis and is tightly governed by higher order chromatin mechanisms. Chromatin regulatory features of the homeotic complex are best defined in Drosophila melanogaster, where multiple cis-regulatory elements have been identified that ensure collinear Hox gene expression patterns in accordance with their genomic organization. Recent studies focused on delineating the epigenetic features of the vertebrate Hox clusters have helped reveal their dynamic chromatin organization and its impact on gene expression. Enrichment for the 'activating' H3K4me3 and 'repressive' H3K27me3 histone modifications is a particularly strong read-out for transcriptional status and correlates well with the evidence for chromatin loop domain structures and stage specific topological changes at these loci. However, it is not clear how such distinct domains are imposed and regulated independent of each other. Comparative analysis of the chromatin structure and organization of the homeotic gene clusters in fly and mammals is increasingly revealing the functional conservation of chromatin mediated mechanisms. Here we discuss the case for interspersed boundary elements existing within mammalian Hox clusters along with their possible roles and mechanisms of action. Recent studies suggest a role for factors other than the well characterized vertebrate boundary factor CTCF, such as the GAGA binding factor (GAF), in maintaining chromatin domains at the Hox loci. We also present data demonstrating how such regulatory elements may be involved in organizing higher order structure and demarcating active domains of gene expression at the mammalian Hox clusters.
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Affiliation(s)
- Surabhi Srivastava
- Centre for Cellular and Molecular Biology, Uppal Road, Hyderabad 500007, India.
| | - Jyotsna Dhawan
- Centre for Cellular and Molecular Biology, Uppal Road, Hyderabad 500007, India
| | - Rakesh K Mishra
- Centre for Cellular and Molecular Biology, Uppal Road, Hyderabad 500007, India
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Meinhardt H. Models for patterning primary embryonic body axes: The role of space and time. Semin Cell Dev Biol 2015; 42:103-17. [PMID: 26126935 DOI: 10.1016/j.semcdb.2015.06.005] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/10/2015] [Accepted: 06/23/2015] [Indexed: 11/19/2022]
Abstract
Models for the generation and interpretation of spatial patterns are discussed. Crucial for these processes is an intimate link between self-enhancing and antagonistic reactions. For spatial patterning, long-ranging antagonistic reactions are required that restrict the self-enhancing reactions to generate organizing regions. Self-enhancement is also required for a permanent switch-like activation of genes. This self-enhancement is antagonized by the mutual repression of genes, making sure that in a particular cell only one gene of a set of possible genes become activated - a long range inhibition in the 'gene space'. The understanding how the main body axes are initiated becomes more straightforward if the evolutionary ancestral head/brain pattern and the trunk pattern is considered separately. To activate a specific gene at particular concentration of morphogenetic gradient, observations are compatible with a systematic and time-requiring 'promotion' from one gene to the next until the local concentration is insufficient to accomplish a further promotion. The achieved determination is stable against a fading of the morphogen, as required to allow substantial growth. Minor modifications lead to a purely time-dependent activation of genes; both mechanisms are involved to pattern the anteroposterior axis. A mutual activation of cell states that locally exclude each other accounts for many features of the segmental patterning of the trunk. A possible scenario for the evolutionary invention of segmentation is discussed that is based on a reemployment of interactions involved in asexual reproduction.
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Affiliation(s)
- Hans Meinhardt
- Max-Planck-Institut für Entwicklungsbiologie, Spemannstr. 35, D-72076 Tübingen, Germany.
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29
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Kyrchanova OV, Georgiev PG. The bithorax complex of Drosophila melanogaster as a model for studying specific long-distance interactions between enhancers and promoters. RUSS J GENET+ 2015. [DOI: 10.1134/s1022795415050038] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
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30
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A. De Souza D, Wang Y, Kaftanoglu O, De Jong D, V. Amdam G, S. Gonçalves L, M. Francoy T. Morphometric Identification of Queens, Workers and Intermediates in In Vitro Reared Honey Bees (Apis mellifera). PLoS One 2015; 10:e0123663. [PMID: 25894528 PMCID: PMC4404332 DOI: 10.1371/journal.pone.0123663] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/29/2014] [Accepted: 03/06/2015] [Indexed: 11/22/2022] Open
Abstract
In vitro rearing is an important and useful tool for honey bee (Apis mellifera L.) studies. However, it often results in intercastes between queens and workers, which are normally are not seen in hive-reared bees, except when larvae older than three days are grafted for queen rearing. Morphological classification (queen versus worker or intercastes) of bees produced by this method can be subjective and generally depends on size differences. Here, we propose an alternative method for caste classification of female honey bees reared in vitro, based on weight at emergence, ovariole number, spermatheca size and size and shape, and features of the head, mandible and basitarsus. Morphological measurements were made with both traditional morphometric and geometric morphometrics techniques. The classifications were performed by principal component analysis, using naturally developed queens and workers as controls. First, the analysis included all the characters. Subsequently, a new analysis was made without the information about ovariole number and spermatheca size. Geometric morphometrics was less dependent on ovariole number and spermatheca information for caste and intercaste identification. This is useful, since acquiring information concerning these reproductive structures requires time-consuming dissection and they are not accessible when abdomens have been removed for molecular assays or in dried specimens. Additionally, geometric morphometrics divided intercastes into more discrete phenotype subsets. We conclude that morphometric geometrics are superior to traditional morphometrics techniques for identification and classification of honey bee castes and intermediates.
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Affiliation(s)
- Daiana A. De Souza
- Departamento de Genética, Faculdade de Medicina de Ribeirão Preto, Universidade de São Paulo, Ribeirão Preto, São Paulo, Brazil
- * E-mail:
| | - Ying Wang
- School of Life Sciences, Arizona State University, Tempe, Arizona, United States of America
| | - Osman Kaftanoglu
- School of Life Sciences, Arizona State University, Tempe, Arizona, United States of America
| | - David De Jong
- Departamento de Genética, Faculdade de Medicina de Ribeirão Preto, Universidade de São Paulo, Ribeirão Preto, São Paulo, Brazil
| | - Gro V. Amdam
- School of Life Sciences, Arizona State University, Tempe, Arizona, United States of America
- Norwegian University of Life Sciences, Department of Chemistry, Biotechnology and Food Science, Aas, Norway
| | - Lionel S. Gonçalves
- Departamento de Biologia, Faculdade de Filosofia Ciências e Letras de Ribeirão Preto, Universidade de São Paulo, Ribeirão Preto, São Paulo, Brazil
- Universidade Federal do Semi-árido, Mossoró, Rio Grande do Norte, Brazil
| | - Tiago M. Francoy
- Departamento de Genética, Faculdade de Medicina de Ribeirão Preto, Universidade de São Paulo, Ribeirão Preto, São Paulo, Brazil
- Escola de Artes, Ciências e Humanidades, Universidade de São Paulo, São Paulo, São Paulo, Brazil
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Coutelis JB, González-Morales N, Géminard C, Noselli S. Diversity and convergence in the mechanisms establishing L/R asymmetry in metazoa. EMBO Rep 2014; 15:926-37. [PMID: 25150102 DOI: 10.15252/embr.201438972] [Citation(s) in RCA: 45] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023] Open
Abstract
Differentiating left and right hand sides during embryogenesis represents a major event in body patterning. Left-Right (L/R) asymmetry in bilateria is essential for handed positioning, morphogenesis and ultimately the function of organs (including the brain), with defective L/R asymmetry leading to severe pathologies in human. How and when symmetry is initially broken during embryogenesis remains debated and is a major focus in the field. Work done over the past 20 years, in both vertebrate and invertebrate models, has revealed a number of distinct pathways and mechanisms important for establishing L/R asymmetry and for spreading it to tissues and organs. In this review, we summarize our current knowledge and discuss the diversity of L/R patterning from cells to organs during evolution.
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Affiliation(s)
- Jean-Baptiste Coutelis
- Institut de Biologie Valrose University of Nice Sophia Antipolis, Nice, France CNRS Institut de Biologie Valrose UMR 7277, Nice, France INSERM Institut de Biologie Valrose U1091, Nice, France
| | - Nicanor González-Morales
- Institut de Biologie Valrose University of Nice Sophia Antipolis, Nice, France CNRS Institut de Biologie Valrose UMR 7277, Nice, France INSERM Institut de Biologie Valrose U1091, Nice, France
| | - Charles Géminard
- Institut de Biologie Valrose University of Nice Sophia Antipolis, Nice, France CNRS Institut de Biologie Valrose UMR 7277, Nice, France INSERM Institut de Biologie Valrose U1091, Nice, France
| | - Stéphane Noselli
- Institut de Biologie Valrose University of Nice Sophia Antipolis, Nice, France CNRS Institut de Biologie Valrose UMR 7277, Nice, France INSERM Institut de Biologie Valrose U1091, Nice, France
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32
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Maksimenko O, Kyrchanova O, Bonchuk A, Stakhov V, Parshikov A, Georgiev P. Highly conserved ENY2/Sus1 protein binds to Drosophila CTCF and is required for barrier activity. Epigenetics 2014; 9:1261-70. [PMID: 25147918 DOI: 10.4161/epi.32086] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Abstract
Chromatin insulators affect interactions between promoters and enhancers/silencers and function as barriers for the spreading of repressive chromatin. Drosophila insulator protein dCTCF marks active promoters and boundaries of many histone H3K27 trimethylation domains associated with repressed chromatin. In particular, dCTCF binds to such boundaries between the parasegment-specific regulatory domains of the Bithorax complex. Here we demonstrate that the evolutionarily conserved protein ENY2 is recruited to the zinc-finger domain of dCTCF and is required for the barrier activity of dCTCF-dependent insulators in transgenic lines. Inactivation of ENY2 by RNAi in BG3 cells leads to the spreading of H3K27 trimethylation and Pc protein at several dCTCF boundaries. The results suggest that evolutionarily conserved ENY2 is responsible for barrier activity mediated by the dCTCF protein.
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Affiliation(s)
- Oksana Maksimenko
- Laboratory of Gene Expression Regulation in Development; Institute of Gene Biology; Russian Academy of Sciences; Moscow, Russia
| | - Olga Kyrchanova
- Group of Transcriptional Regulation; Institute of Gene Biology; Russian Academy of Sciences; Moscow, Russia
| | - Artem Bonchuk
- Group of Transcriptional Regulation; Institute of Gene Biology; Russian Academy of Sciences; Moscow, Russia
| | - Viacheslav Stakhov
- Laboratory of Gene Expression Regulation in Development; Institute of Gene Biology; Russian Academy of Sciences; Moscow, Russia
| | - Alexander Parshikov
- Department of the Control of Genetic Processes; Institute of Gene Biology; Russian Academy of Sciences; Moscow, Russia
| | - Pavel Georgiev
- Department of the Control of Genetic Processes; Institute of Gene Biology; Russian Academy of Sciences; Moscow, Russia
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33
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Bowman SK, Deaton AM, Domingues H, Wang PI, Sadreyev RI, Kingston RE, Bender W. H3K27 modifications define segmental regulatory domains in the Drosophila bithorax complex. eLife 2014; 3:e02833. [PMID: 25082344 PMCID: PMC4139060 DOI: 10.7554/elife.02833] [Citation(s) in RCA: 89] [Impact Index Per Article: 8.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022] Open
Abstract
The bithorax complex (BX-C) in Drosophila melanogaster is a cluster of homeotic genes that determine body segment identity. Expression of these genes is governed by cis-regulatory domains, one for each parasegment. Stable repression of these domains depends on Polycomb Group (PcG) functions, which include trimethylation of lysine 27 of histone H3 (H3K27me3). To search for parasegment-specific signatures that reflect PcG function, chromatin from single parasegments was isolated and profiled. The H3K27me3 profiles across the BX-C in successive parasegments showed a 'stairstep' pattern that revealed sharp boundaries of the BX-C regulatory domains. Acetylated H3K27 was broadly enriched across active domains, in a pattern complementary to H3K27me3. The CCCTC-binding protein (CTCF) bound the borders between H3K27 modification domains; it was retained even in parasegments where adjacent domains lack H3K27me3. These findings provide a molecular definition of the homeotic domains, and implicate precisely positioned H3K27 modifications as a central determinant of segment identity.
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Affiliation(s)
- Sarah K Bowman
- Department of Molecular Biology, Massachusetts General Hospital, Boston, United States Department of Genetics, Harvard Medical School, Boston, United States
| | - Aimee M Deaton
- Department of Molecular Biology, Massachusetts General Hospital, Boston, United States Department of Genetics, Harvard Medical School, Boston, United States
| | - Heber Domingues
- Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, United States
| | - Peggy I Wang
- Department of Molecular Biology, Massachusetts General Hospital, Boston, United States Department of Genetics, Harvard Medical School, Boston, United States
| | - Ruslan I Sadreyev
- Department of Molecular Biology, Massachusetts General Hospital, Boston, United States Department of Pathology, Harvard Medical School, Boston, United States
| | - Robert E Kingston
- Department of Molecular Biology, Massachusetts General Hospital, Boston, United States Department of Genetics, Harvard Medical School, Boston, United States
| | - Welcome Bender
- Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, United States
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34
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Hox gene regulation and timing in embryogenesis. Semin Cell Dev Biol 2014; 34:76-84. [PMID: 24930771 DOI: 10.1016/j.semcdb.2014.06.005] [Citation(s) in RCA: 51] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/07/2014] [Revised: 05/15/2014] [Accepted: 06/05/2014] [Indexed: 11/22/2022]
Abstract
Hox genes are critical regulators of embryonic development in bilaterian animals. They exhibit a unique mode of transcriptional regulation where the position of the genes along the chromosome corresponds to the time and place of their expression during development. The sequential temporal activation of these genes in the primitive streak helps determining their subsequent pattern of expression along the anterior-posterior axis of the embryo, yet the precise correspondence between these two collinear processes is not fully understood. In addition, vertebrate Hox genes evolved similar modes of regulation along secondary body axes, such as the developing limbs. We review the current understanding of the mechanisms operating during activation, maintenance and silencing of Hox gene expression in these various contexts, and discuss the evolutionary significance of their genomic organization.
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35
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Chetverina D, Aoki T, Erokhin M, Georgiev P, Schedl P. Making connections: insulators organize eukaryotic chromosomes into independent cis-regulatory networks. Bioessays 2013; 36:163-72. [PMID: 24277632 DOI: 10.1002/bies.201300125] [Citation(s) in RCA: 76] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
Insulators play a central role in subdividing the chromosome into a series of discrete topologically independent domains and in ensuring that enhancers and silencers contact their appropriate target genes. In this review we first discuss the general characteristics of insulator elements and their associated protein factors. A growing collection of insulator proteins have been identified including a family of proteins whose expression is developmentally regulated. We next consider several unexpected discoveries that require us to completely rethink how insulators function (and how they can best be assayed). These discoveries also require a reevaluation of how insulators might restrict or orchestrate (by preventing or promoting) interactions between regulatory elements and their target genes. We conclude by connecting these new insights into the mechanisms of insulator action to dynamic changes in the three-dimensional topology of the chromatin fiber and the generation of specific patterns of gene activity during development and differentiation.
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Affiliation(s)
- Darya Chetverina
- Institute of Gene Biology, Russian Academy of Sciences, Moscow, Russia
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36
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Mallo M, Alonso CR. The regulation of Hox gene expression during animal development. Development 2013; 140:3951-63. [PMID: 24046316 DOI: 10.1242/dev.068346] [Citation(s) in RCA: 223] [Impact Index Per Article: 20.3] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
Hox genes encode a family of transcriptional regulators that elicit distinct developmental programmes along the head-to-tail axis of animals. The specific regional functions of individual Hox genes largely reflect their restricted expression patterns, the disruption of which can lead to developmental defects and disease. Here, we examine the spectrum of molecular mechanisms controlling Hox gene expression in model vertebrates and invertebrates and find that a diverse range of mechanisms, including nuclear dynamics, RNA processing, microRNA and translational regulation, all concur to control Hox gene outputs. We propose that this complex multi-tiered regulation might contribute to the robustness of Hox expression during development.
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Affiliation(s)
- Moisés Mallo
- Instituto Gulbenkian de Ciência, Rua da Quinta Grande 6, 2780-156 Oeiras, Portugal
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37
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Kyrchanova O, Georgiev P. Chromatin insulators and long-distance interactions in Drosophila. FEBS Lett 2013; 588:8-14. [PMID: 24211836 DOI: 10.1016/j.febslet.2013.10.039] [Citation(s) in RCA: 70] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/19/2013] [Revised: 10/25/2013] [Accepted: 10/25/2013] [Indexed: 12/31/2022]
Abstract
Data on long-distance enhancer-mediated activation of gene promoters and complex regulation of gene expression by multiple enhancers have prompted the hypothesis that the action of enhancers is restricted by insulators. Studies with transgenic lines have shown that insulators are responsible for establishing proper local interactions between regulatory elements, but not for defining independent transcriptional domains that restrict the activity of enhancers. It has also become apparent that enhancer blocking is only one of several functional activities of known insulator proteins, which also contribute to the organization of chromosome architecture and the integrity of regulatory elements.
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Affiliation(s)
- Olga Kyrchanova
- Group of Transcriptional Regulation, Institute of Gene Biology, Russian Academy of Sciences, Moscow, Russia
| | - Pavel Georgiev
- Department of the Control of Genetic Processes, Institute of Gene Biology, Russian Academy of Sciences, 34/5 Vavilov St., Moscow 119334, Russia.
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38
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Fujioka M, Sun G, Jaynes JB. The Drosophila eve insulator Homie promotes eve expression and protects the adjacent gene from repression by polycomb spreading. PLoS Genet 2013; 9:e1003883. [PMID: 24204298 PMCID: PMC3814318 DOI: 10.1371/journal.pgen.1003883] [Citation(s) in RCA: 41] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/12/2013] [Accepted: 08/29/2013] [Indexed: 12/18/2022] Open
Abstract
Insulators can block the action of enhancers on promoters and the spreading of repressive chromatin, as well as facilitating specific enhancer-promoter interactions. However, recent studies have called into question whether the activities ascribed to insulators in model transgene assays actually reflect their functions in the genome. The Drosophila even skipped (eve) gene is a Polycomb (Pc) domain with a Pc-group response element (PRE) at one end, flanked by an insulator, an arrangement also seen in other genes. Here, we show that this insulator has three major functions. It blocks the spreading of the eve Pc domain, preventing repression of the adjacent gene, TER94. It prevents activation of TER94 by eve regulatory DNA. It also facilitates normal eve expression. When Homie is deleted in the context of a large transgene that mimics both eve and TER94 regulation, TER94 is repressed. This repression depends on the eve PRE. Ubiquitous TER94 expression is “replaced” by expression in an eve pattern when Homie is deleted, and this effect is reversed when the PRE is also removed. Repression of TER94 is attributable to spreading of the eve Pc domain into the TER94 locus, accompanied by an increase in histone H3 trimethylation at lysine 27. Other PREs can functionally replace the eve PRE, and other insulators can block PRE-dependent repression in this context. The full activity of the eve promoter is also dependent on Homie, and other insulators can promote normal eve enhancer-promoter communication. Our data suggest that this is not due to preventing promoter competition, but is likely the result of the insulator organizing a chromosomal conformation favorable to normal enhancer-promoter interactions. Thus, insulator activities in a native context include enhancer blocking and enhancer-promoter facilitation, as well as preventing the spread of repressive chromatin. Insulators are specialized DNA elements that can separate the genome into functional units. Most of the current thinking about these elements comes from studies done with model transgenes. Studies of insulators within the specialized Hox gene complexes have suggested that model transgenes can reflect the normal functions of these elements in their native context. However, recent genome-wide studies have called this into question. This work analyzes the native function of an insulator that resides between the Drosophila genes eve and TER94, which are expressed in very different patterns. Also, the eve gene is a Polycomb (Pc) domain, a specialized type of chromatin that is found in many places throughout the genome. We show that this insulator has three major functions. It blocks the spreading of the eve Pc domain, preventing repression of TER94. It prevents activation of TER94 by eve regulatory DNA. It also facilitates normal eve expression. Each of these activities are consistent with those seen with model transgenes, and other known insulators can provide these functions in this context. This work provides a novel and convincing example of the normal role of insulators in regulating the eukaryotic genome, as well as providing insights into their mechanisms of action.
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Affiliation(s)
- Miki Fujioka
- Department of Biochemistry and Molecular Biology and the Kimmel Cancer Center, Thomas Jefferson University, Philadelphia, Pennsylvania, United States of America
| | - Guizhi Sun
- Department of Biochemistry and Molecular Biology and the Kimmel Cancer Center, Thomas Jefferson University, Philadelphia, Pennsylvania, United States of America
| | - James B. Jaynes
- Department of Biochemistry and Molecular Biology and the Kimmel Cancer Center, Thomas Jefferson University, Philadelphia, Pennsylvania, United States of America
- * E-mail:
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Chen P, Tong XL, Li DD, Liang PF, Fu MY, Li CF, Hu H, Xiang ZH, Lu C, Dai FY. Fine mapping of a supernumerary proleg mutant (E(Cs) -l) and comparative expression analysis of the abdominal-A gene in silkworm, Bombyx mori. INSECT MOLECULAR BIOLOGY 2013; 22:497-504. [PMID: 23803144 DOI: 10.1111/imb.12039] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/02/2023]
Abstract
Patterning and phenotypic variations of appendages in insects provide important clues on developmental genetics. In the silkworm Bombyx mori, morphological variations associated with the E complex, an analogue of the Drosophila melanogaster bithorax complex, mainly determine the shape and number of prolegs on abdominal segments. Here, we report the identification and characterization of the allele responsible for the supernumerary crescents and legs-like (E(Cs) -l) mutant, a model derived from spontaneous mutation of the E complex, with supernumerary legs and extra crescents. Fine mapping with 1605 individuals revealed a ∼68 kb sequence in the upstream intergenic region of B. mori abdominal-A (Bmabd-A) clustered with the E(Cs) -l locus. Quantitative real-time PCR (qRT-PCR) and Western blotting analyses disclosed a marked increase in Bmabd-A expression in the E(Cs) -l mutant at both the transcriptional and translational levels, compared to wild-type Dazao. Furthermore, we observed ectopic expression of the Bmabd-A protein in the second abdominal segment (A2) of the E(Cs) -l mutant. Our results collectively suggest that the 68 kb region contains important regulatory elements of the Bmabd-A gene, and provide evidence that the gene is required for limb development in abdominal segments in the silkworm.
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Affiliation(s)
- P Chen
- State Key Laboratory of Silkworm Genome Biology, Southwest University, Chongqing, China
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40
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Abstract
RNA transcripts without obvious coding potential are widespread in many creatures, including the fruit fly, Drosophila melanogaster. Several noncoding RNAs have been identified within the Drosophila bithorax complex. These first appear in blastoderm stage embryos, and their expression patterns indicate that they are transcribed only from active domains of the bithorax complex. It has been suggested that these noncoding RNAs have a role in establishing active domains, perhaps by setting the state of Polycomb Response Elements A comprehensive survey across the proximal half of the bithorax complex has now revealed nine distinct noncoding RNA transcripts, including four within the Ultrabithorax transcription unit. At the blastoderm stage, the noncoding transcripts collectively span ∼75% of the 135 kb surveyed. Recombination-mediated cassette exchange was used to invert the promoter of one of the noncoding RNAs, a 23-kb transcript from the bxd domain of the bithorax complex. The resulting animals fail to make the normal bxd noncoding RNA and show no transcription across the bxd Polycomb Response Element in early embryos. The mutant flies look normal; the regulation of the bxd domain appears unaffected. Thus, the bxd noncoding RNA has no apparent function.
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Soshnikova N. Hox genes regulation in vertebrates. Dev Dyn 2013; 243:49-58. [PMID: 23832853 DOI: 10.1002/dvdy.24014] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/22/2013] [Revised: 06/30/2013] [Accepted: 07/01/2013] [Indexed: 12/16/2022] Open
Abstract
Hox genes encode transcription factors defining cellular identities along the major and secondary body axes. Their coordinated expression in both space and time is critical for embryonic patterning. Accordingly, Hox genes transcription is tightly controlled at multiple levels, and involves an intricate combination of local and long-range cis-regulatory elements. Recent studies revealed that in addition to transcription factors, dynamic patterns of histone marks and higher-order chromatin structure are important determinants of Hox gene regulation. Furthermore, the emerging picture suggests an involvement of various species of non-coding RNA in targeting activating and repressive complexes to Hox clusters. I review these recent developments and discuss their relevance to the control of Hox gene expression in vivo, as well as to our understanding of transcriptional regulatory mechanisms.
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Montavon T, Duboule D. Chromatin organization and global regulation of Hox gene clusters. Philos Trans R Soc Lond B Biol Sci 2013; 368:20120367. [PMID: 23650639 PMCID: PMC3682730 DOI: 10.1098/rstb.2012.0367] [Citation(s) in RCA: 60] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022] Open
Abstract
During development, a properly coordinated expression of Hox genes, within their different genomic clusters is critical for patterning the body plans of many animals with a bilateral symmetry. The fascinating correspondence between the topological organization of Hox clusters and their transcriptional activation in space and time has served as a paradigm for understanding the relationships between genome structure and function. Here, we review some recent observations, which revealed highly dynamic changes in the structure of chromatin at Hox clusters, in parallel with their activation during embryonic development. We discuss the relevance of these findings for our understanding of large-scale gene regulation.
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Affiliation(s)
- Thomas Montavon
- National Research Centre 'Frontiers in Genetics', School of Life Sciences, Ecole Polytechnique Fédérale, Lausanne, Switzerland
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43
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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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45
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Fujioka M, Jaynes JB. Regulation of a duplicated locus: Drosophila sloppy paired is replete with functionally overlapping enhancers. Dev Biol 2011; 362:309-19. [PMID: 22178246 DOI: 10.1016/j.ydbio.2011.12.001] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/18/2011] [Revised: 11/16/2011] [Accepted: 12/01/2011] [Indexed: 11/28/2022]
Abstract
In order to investigate regulation and redundancy within the sloppy paired (slp) locus, we analyzed 30 kilobases of DNA encompassing the tandem, coordinately regulated slp1 and slp2 transcription units. We found a remarkable array of stripe enhancers with overlapping activities surrounding the slp1 transcription unit, and, unexpectedly, glial cell enhancers surrounding slp2. The slp stripe regulatory region generates 7 stripes at blastoderm, and later 14 stripes that persist throughout embryogenesis. Phylogenetic analysis among drosophilids suggests that the multiplicity of stripe enhancers did not evolve through recent duplication. Most of the direct integration among cis-regulatory modules appears to be simply additive, with one notable exception. Despite the apparent redundancy among stripe enhancers, transgenic rescue suggests that most are required for full function, to maintain wingless expression and parasegment boundaries throughout embryogenesis. Transgenic rescue also reveals indirect positive autoregulation by the 7 early stripes, without which alternate stripes within the 14-stripe pattern are lost, leading to embryos with a pair-rule phenotype.
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Affiliation(s)
- Miki Fujioka
- Dept. of Biochemistry and Molecular Biology, Kimmel Cancer Center, Thomas Jefferson University, Philadelphia, PA 19107, USA
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46
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Peter IS, Davidson EH. Evolution of gene regulatory networks controlling body plan development. Cell 2011; 144:970-85. [PMID: 21414487 DOI: 10.1016/j.cell.2011.02.017] [Citation(s) in RCA: 245] [Impact Index Per Article: 18.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/02/2010] [Revised: 12/16/2010] [Accepted: 02/10/2011] [Indexed: 11/29/2022]
Abstract
Evolutionary change in animal morphology results from alteration of the functional organization of the gene regulatory networks (GRNs) that control development of the body plan. A major mechanism of evolutionary change in GRN structure is alteration of cis-regulatory modules that determine regulatory gene expression. Here we consider the causes and consequences of GRN evolution. Although some GRN subcircuits are of great antiquity, other aspects are highly flexible and thus in any given genome more recent. This mosaic view of the evolution of GRN structure explains major aspects of evolutionary process, such as hierarchical phylogeny and discontinuities of paleontological change.
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Affiliation(s)
- Isabelle S Peter
- Division of Biology 156-29, California Institute of Technology, Pasadena, CA 91125, USA.
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Slattery M, Ma L, Négre N, White KP, Mann RS. Genome-wide tissue-specific occupancy of the Hox protein Ultrabithorax and Hox cofactor Homothorax in Drosophila. PLoS One 2011; 6:e14686. [PMID: 21483663 PMCID: PMC3071676 DOI: 10.1371/journal.pone.0014686] [Citation(s) in RCA: 72] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/07/2011] [Accepted: 01/21/2011] [Indexed: 11/18/2022] Open
Abstract
The Hox genes are responsible for generating morphological diversity along the
anterior-posterior axis during animal development. The
Drosophila Hox gene Ultrabithorax
(Ubx), for example, is required for specifying the identity
of the third thoracic (T3) segment of the adult, which includes the dorsal
haltere, an appendage required for flight, and the ventral T3 leg.
Ubx mutants show homeotic transformations of the T3 leg
towards the identity of the T2 leg and the haltere towards the wing. All Hox
genes, including Ubx, encode homeodomain containing
transcription factors, raising the question of what target genes
Ubx regulates to generate these adult structures. To
address this question, we carried out whole genome ChIP-chip studies to identify
all of the Ubx bound regions in the haltere and T3 leg imaginal discs, which are
the precursors to these adult structures. In addition, we used ChIP-chip to
identify the sites bound by the Hox cofactor, Homothorax (Hth). In contrast to
previous ChIP-chip studies carried out in Drosophila embryos,
these binding studies reveal that there is a remarkable amount of tissue- and
transcription factor-specific binding. Analyses of the putative target genes
bound and regulated by these factors suggest that Ubx regulates many downstream
transcription factors and developmental pathways in the haltere and T3 leg.
Finally, we discovered additional DNA sequence motifs that in some cases are
specific for individual data sets, arguing that Ubx and/or Hth work together
with many regionally expressed transcription factors to execute their functions.
Together, these data provide the first whole-genome analysis of the binding
sites and target genes regulated by Ubx to specify the morphologies of the adult
T3 segment of the fly.
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Affiliation(s)
- Matthew Slattery
- Department of Biochemistry and Molecular
Biophysics, Columbia University, New York, New York, United States of
America
| | - Lijia Ma
- Department of Human Genetics, Department of
Ecology and Evolution, Institute for Genomics and Systems Biology, University of
Chicago, Chicago, Illinois, United States of America
| | - Nicolas Négre
- Department of Human Genetics, Department of
Ecology and Evolution, Institute for Genomics and Systems Biology, University of
Chicago, Chicago, Illinois, United States of America
| | - Kevin P. White
- Department of Human Genetics, Department of
Ecology and Evolution, Institute for Genomics and Systems Biology, University of
Chicago, Chicago, Illinois, United States of America
| | - Richard S. Mann
- Department of Biochemistry and Molecular
Biophysics, Columbia University, New York, New York, United States of
America
- * E-mail:
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48
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Soshnikova N. Dynamics of Polycomb and Trithorax activities during development. ACTA ACUST UNITED AC 2011; 91:781-7. [DOI: 10.1002/bdra.20774] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/03/2010] [Revised: 11/23/2010] [Accepted: 11/25/2010] [Indexed: 12/17/2022]
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Choo SW, Russell S. Genomic approaches to understanding Hox gene function. ADVANCES IN GENETICS 2011; 76:55-91. [PMID: 22099692 DOI: 10.1016/b978-0-12-386481-9.00003-1] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
For many years, biologists have sought to understand how the homeodomain-containing transcriptional regulators encoded by Hox genes are able to control the development of animal morphology. Almost a century of genetics and several decades of molecular biology have defined the conserved organization of homeotic gene clusters in animals and the basic molecular properties of Hox transcription factors. In contrast to these successes, we remain relatively ignorant of how Hox proteins find their target genes in the genome or what sets of genes a Hox protein regulates to direct morphogenesis. The recent deployment of genomic methods, such as whole transcriptome mRNA expression profiling and genome-wide analysis of protein-DNA interactions, begins to shed light on these issues. Results from such studies, principally in the fruit fly, indicate that Hox proteins control the expression of hundreds, if not thousands, of genes throughout the gene regulatory network and that, in many cases, the effects on the expression of individual genes may be quite subtle. Hox proteins regulate both high-level effectors, including other transcription factors and signaling molecules, as well as the cytodifferentiation genes or Realizators at the bottom of regulatory hierarchies. Insights emerging from mapping Hox binding sites in the genome begin to suggest that Hox binding may be strongly influenced by chromatin accessibility rather than binding site affinity. If this is the case, it indicates we need to refocus our efforts at understanding Hox function toward the dynamics of gene regulatory networks and chromatin epigenetics.
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Affiliation(s)
- Siew Woh Choo
- Department of Genetics and Cambridge Systems Biology Centre, University of Cambridge, Cambridge, United Kingdom
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Initiator elements function to determine the activity state of BX-C enhancers. PLoS Genet 2010; 6:e1001260. [PMID: 21203501 PMCID: PMC3009686 DOI: 10.1371/journal.pgen.1001260] [Citation(s) in RCA: 45] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/28/2010] [Accepted: 11/23/2010] [Indexed: 11/19/2022] Open
Abstract
A >300 kb cis-regulatory region is required for the proper expression of the three bithorax complex (BX-C) homeotic genes. Based on genetic and transgenic analysis, a model has been proposed in which the numerous BX-C cis-regulatory elements are spatially restricted through the activation or repression of parasegment-specific chromatin domains. Particular early embryonic enhancers, called initiators, have been proposed to control this complex process. Here, in order to better understand the process of domain activation, we have undertaken a systematic in situ dissection of the iab-6 cis-regulatory domain using a new method, called InSIRT. Using this method, we create and genetically characterize mutations affecting iab-6 function, including mutations specifically modifying the iab-6 initiator. Through our mutagenesis of the iab-6 initiator, we provide strong evidence that initiators function not to directly control homeotic gene expression but rather as domain control centers to determine the activity state of the enhancers and silencers within a cis-regulatory domain. Understanding how genes become activated is one of the primary areas of research in modern biology. In order to decipher the DNA components required for this process, scientists have traditionally turned to transgenic reporter assays, where DNA elements are removed from their native environment and placed next to a simplified reporter gene to monitor transcriptional activation. Although this approach is powerful, it can result in artifacts stemming from the channelization of regulatory element activities into predetermined classes. In this manuscript, we investigate the biological role of elements from the Drosophila bithorax complex, called initiators. In transgenic assays, these elements have been categorized as enhancers. However, genetic analysis suggests that, in situ, these elements perform a far more complex function. Here, using a new method to repeatedly target a genetic locus for mutagenesis, we show that initiators function as control elements that coordinate the activity of nearby enhancers and silencers. Overall, our study highlights how gene expression can be controlled through a hierarchical arrangement of cis-regulatory elements.
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