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Ligand-independent requirements of steroid receptors EcR and USP for cell survival. Cell Death Differ 2015; 23:405-16. [PMID: 26250909 DOI: 10.1038/cdd.2015.108] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/09/2014] [Revised: 06/29/2015] [Accepted: 07/01/2015] [Indexed: 02/07/2023] Open
Abstract
The active form of the Drosophila steroid hormone ecdysone, 20-hydroxyecdysone (20E), binds the heterodimer EcR/USP nuclear receptor to regulate target genes that elicit proliferation, cell death and differentiation during insect development. Although the 20E effects are relatively well known, the physiological relevance of its receptors remains poorly understood. We show here that the prothoracic gland (PG), the major steroid-producing organ of insect larvae, requires EcR and USP to survive in a critical period previous to metamorphosis, and that this requirement is 20E-independent. The cell death induced by the downregulation of these receptors involves the activation of the JNK-encoding basket gene and it can be rescued by upregulating EcR isoforms which are unable to respond to 20E. Also, while PG cell death prevents ecdysone production, blocking hormone synthesis or secretion in normal PG does not lead to cell death, demonstrating further the ecdysone-independent nature of the receptor-deprivation cell death. In contrast to PG cells, wing disc or salivary glands cells do not require these receptors for survival, revealing their cell and developmental time specificity. Exploring the potential use of this feature of steroid receptors in cancer, we assayed tumor overgrowth induced by altered yorkie signaling. This overgrowth is suppressed by EcR downregulation in PG, but not in wing disc, cells. The mechanism of all these cell death features is based on the transcriptional regulation of reaper. These novel and context-dependent functional properties for EcR and USP receptors may help to understand the heterogeneous responses to steroid-based therapies in human pathologies.
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2
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Zhang C, Robinson BS, Xu W, Yang L, Yao B, Zhao H, Byun PK, Jin P, Veraksa A, Moberg KH. The ecdysone receptor coactivator Taiman links Yorkie to transcriptional control of germline stem cell factors in somatic tissue. Dev Cell 2015; 34:168-80. [PMID: 26143992 DOI: 10.1016/j.devcel.2015.05.010] [Citation(s) in RCA: 33] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/28/2014] [Revised: 04/25/2015] [Accepted: 05/14/2015] [Indexed: 12/16/2022]
Abstract
The Hippo pathway is a conserved signaling cascade that modulates tissue growth. Although its core elements are well defined, factors modulating Hippo transcriptional outputs remain elusive. Here we show that components of the steroid-responsive ecdysone (Ec) pathway modulate Hippo transcriptional effects in imaginal disc cells. The Ec receptor coactivator Taiman (Tai) interacts with the Hippo transcriptional coactivator Yorkie (Yki) and promotes expression of canonical Yki-responsive genes. Tai enhances Yki-driven growth, while Tai loss, or a form of Tai unable to bind Yki, suppresses Yki-driven tissue growth. This growth suppression is not correlated with impaired induction of canonical Hippo-responsive genes but with suppression of a distinct pro-growth program of Yki-induced/Tai-dependent genes, including the germline stem cell factors nanos and piwi. These data reveal Hippo/Ec pathway crosstalk in the form a Yki-Tai complex that collaboratively induces germline genes as part of a transcriptional program that is normally repressed in developing somatic epithelia.
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Affiliation(s)
- Can Zhang
- Department of Cell Biology, Emory University School of Medicine, Atlanta, GA 30322, USA
| | - Brian S Robinson
- Department of Cell Biology, Emory University School of Medicine, Atlanta, GA 30322, USA; Department of Pathology & Laboratory Medicine, Emory University School of Medicine, Atlanta, GA 30322, USA
| | - Wenjian Xu
- Department of Biology, University of Massachusetts Boston, Boston, MA 02125, USA
| | - Liu Yang
- Department of Biology, University of Massachusetts Boston, Boston, MA 02125, USA
| | - Bing Yao
- Department of Human Genetics, Emory University School of Medicine, Atlanta, GA 30322, USA
| | - Heya Zhao
- Department of Biology, University of Massachusetts Boston, Boston, MA 02125, USA
| | - Phil K Byun
- Department of Cell Biology, Emory University School of Medicine, Atlanta, GA 30322, USA; Graduate Program in Genetics and Molecular Biology, Emory University School of Medicine, Atlanta, GA 30322, USA
| | - Peng Jin
- Department of Human Genetics, Emory University School of Medicine, Atlanta, GA 30322, USA
| | - Alexey Veraksa
- Department of Biology, University of Massachusetts Boston, Boston, MA 02125, USA
| | - Kenneth H Moberg
- Department of Cell Biology, Emory University School of Medicine, Atlanta, GA 30322, USA.
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3
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Jusiak B, Karandikar UC, Kwak SJ, Wang F, Wang H, Chen R, Mardon G. Regulation of Drosophila eye development by the transcription factor Sine oculis. PLoS One 2014; 9:e89695. [PMID: 24586968 PMCID: PMC3934907 DOI: 10.1371/journal.pone.0089695] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/27/2013] [Accepted: 01/21/2014] [Indexed: 11/18/2022] Open
Abstract
Homeodomain transcription factors of the Sine oculis (SIX) family direct multiple regulatory processes throughout the metazoans. Sine oculis (So) was first characterized in the fruit fly Drosophila melanogaster, where it is both necessary and sufficient for eye development, regulating cell survival, proliferation, and differentiation. Despite its key role in development, only a few direct targets of So have been described previously. In the current study, we aim to expand our knowledge of So-mediated transcriptional regulation in the developing Drosophila eye using ChIP-seq to map So binding regions throughout the genome. We find 7,566 So enriched regions (peaks), estimated to map to 5,952 genes. Using overlap between the So ChIP-seq peak set and genes that are differentially regulated in response to loss or gain of so, we identify putative direct targets of So. We find So binding enrichment in genes not previously known to be regulated by So, including genes that encode cell junction proteins and signaling pathway components. In addition, we analyze a subset of So-bound novel genes in the eye, and find eight genes that have previously uncharacterized eye phenotypes and may be novel direct targets of So. Our study presents a greatly expanded list of candidate So targets and serves as basis for future studies of So-mediated gene regulation in the eye.
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Affiliation(s)
- Barbara Jusiak
- Program in Developmental Biology, Baylor College of Medicine, Houston, Texas, United States of America
| | - Umesh C. Karandikar
- Department of Pathology and Immunology, Baylor College of Medicine, Houston, Texas, United States of America
| | - Su-Jin Kwak
- Department of Pathology and Immunology, Baylor College of Medicine, Houston, Texas, United States of America
| | - Feng Wang
- Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, Texas, United States of America
- Human Genome Sequencing Center, Baylor College of Medicine, Houston, Texas, United States of America
| | - Hui Wang
- Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, Texas, United States of America
- Human Genome Sequencing Center, Baylor College of Medicine, Houston, Texas, United States of America
| | - Rui Chen
- Program in Developmental Biology, Baylor College of Medicine, Houston, Texas, United States of America
- Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, Texas, United States of America
- Human Genome Sequencing Center, Baylor College of Medicine, Houston, Texas, United States of America
| | - Graeme Mardon
- Program in Developmental Biology, Baylor College of Medicine, Houston, Texas, United States of America
- Department of Pathology and Immunology, Baylor College of Medicine, Houston, Texas, United States of America
- Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, Texas, United States of America
- Department of Neuroscience, Baylor College of Medicine, Houston, Texas, United States of America
- Department of Ophthalmology, Baylor College of Medicine, Houston, Texas, United States of America
- Program in Cell and Molecular Biology, Baylor College of Medicine, Houston, Texas, United States of America
- * E-mail:
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Chauhan C, Zraly CB, Parilla M, Diaz MO, Dingwall AK. Histone recognition and nuclear receptor co-activator functions of Drosophila cara mitad, a homolog of the N-terminal portion of mammalian MLL2 and MLL3. Development 2012; 139:1997-2008. [PMID: 22569554 DOI: 10.1242/dev.076687] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/20/2023]
Abstract
MLL2 and MLL3 histone lysine methyltransferases are conserved components of COMPASS-like co-activator complexes. In vertebrates, the paralogous MLL2 and MLL3 contain multiple domains required for epigenetic reading and writing of the histone code involved in hormone-stimulated gene programming, including receptor-binding motifs, SET methyltransferase, HMG and PHD domains. The genes encoding MLL2 and MLL3 arose from a common ancestor. Phylogenetic analyses reveal that the ancestral gene underwent a fission event in some Brachycera dipterans, including Drosophila species, creating two independent genes corresponding to the N- and C-terminal portions. In Drosophila, the C-terminal SET domain is encoded by trithorax-related (trr), which is required for hormone-dependent gene activation. We identified the cara mitad (cmi) gene, which encodes the previously undiscovered N-terminal region consisting of PHD and HMG domains and receptor-binding motifs. The cmi gene is essential and its functions are dosage sensitive. CMI associates with TRR, as well as the EcR-USP receptor, and is required for hormone-dependent transcription. Unexpectedly, although the CMI and MLL2 PHDf3 domains could bind histone H3, neither showed preference for trimethylated lysine 4. Genetic tests reveal that cmi is required for proper global trimethylation of H3K4 and that hormone-stimulated transcription requires chromatin binding by CMI, methylation of H3K4 by TRR and demethylation of H3K27 by the demethylase UTX. The evolutionary split of MLL2 into two distinct genes in Drosophila provides important insight into distinct epigenetic functions of conserved readers and writers of the histone code.
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Affiliation(s)
- Chhavi Chauhan
- Oncology Institute, Stritch School of Medicine, Loyola University of Chicago, Maywood, IL 60153, USA
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Delanoue R, Slaidina M, Léopold P. The steroid hormone ecdysone controls systemic growth by repressing dMyc function in Drosophila fat cells. Dev Cell 2010; 18:1012-21. [PMID: 20627082 DOI: 10.1016/j.devcel.2010.05.007] [Citation(s) in RCA: 140] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/25/2009] [Revised: 02/11/2010] [Accepted: 03/23/2010] [Indexed: 12/31/2022]
Abstract
How steroid hormones shape animal growth remains poorly understood. In Drosophila, the main steroid hormone, ecdysone, limits systemic growth during juvenile development. Here we show that ecdysone controls animal growth rate by specifically acting on the fat body, an organ that retains endocrine and storage functions of the vertebrate liver and fat. We demonstrate that fat body-targeted loss of function of the Ecdysone receptor (EcR) increases dMyc expression and its cellular functions such as ribosome biogenesis. Moreover, changing dMyc levels in this tissue is sufficient to affect animal growth rate. Finally, the growth increase induced by silencing EcR in the fat body is suppressed by cosilencing dMyc. In conclusion, the present work reveals an unexpected function of dMyc in the systemic control of growth in response to steroid hormone signaling.
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Affiliation(s)
- Rénald Delanoue
- Institute of Developmental Biology and Cancer, University of Nice-Sophia Antipolis, CNRS, Parc Valrose, 06108 Nice, France
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Cranna N, Quinn L. Impact of steroid hormone signals on Drosophila cell cycle during development. Cell Div 2009; 4:3. [PMID: 19154610 PMCID: PMC2647916 DOI: 10.1186/1747-1028-4-3] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/22/2008] [Accepted: 01/20/2009] [Indexed: 11/30/2022] Open
Abstract
Metamorphosis of Drosophila involves proliferation, differentiation and death of larval tissues in order to form the adult fly. The major steroid hormone implicated in the larval-pupal transition and adult tissue modelling is ecdysone. Previous reviews have draw together studies connecting ecdysone signaling to the processes of apoptosis and differentiation. Here we discuss those reports connecting the ecdysone pulse to developmentally regulated cell cycle progression.
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Affiliation(s)
- Nicola Cranna
- Department of Anatomy and Cell Biology, University of Melbourne, Parkville 3010, Melbourne, Australia.
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Tan A, Palli SR. Ecdysone [corrected] receptor isoforms play distinct roles in controlling molting and metamorphosis in the red flour beetle, Tribolium castaneum. Mol Cell Endocrinol 2008; 291:42-9. [PMID: 18583027 PMCID: PMC2595142 DOI: 10.1016/j.mce.2008.05.006] [Citation(s) in RCA: 87] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/20/2007] [Revised: 05/01/2008] [Accepted: 05/06/2008] [Indexed: 10/22/2022]
Abstract
Ecdysteroids regulate insect growth and development through a heterodimeric complex of nuclear receptors consisting of ecdysone receptor (EcR) and ultraspiracle (USP). In the red flour beetle, Tribolium castaneum, two isoforms each of EcR and USP have been identified. Quantitative real-time reverse-transcriptase PCR (qRT-PCR) analysis showed isoform-specific developmental expression of both EcR and USP in the epidermis and the midgut dissected from the final instar larvae and pupae. Injection of double-stranded RNA (dsRNA) prepared using the common or isoform-specific regions of EcR or USP as templates caused derailment of development. EcR common region (EcRC) or EcRA dsRNA caused more severe effects, and most of the treated larvae died prior to pupation. EcRB dsRNA caused less severe effects and most of the treated larvae became pupae but showed developmental defects. Only dsRNA prepared against USP common region but not against USPA or USPB isoform-specific region caused developmental defects during larval-pupal metamorphosis. Determination of mRNA levels of EcR isoforms and 20-hydroxyecdysone-response (20E) genes (broad, E75, E74, HR3 and FTZ-F1) by qRT-PCR in the larvae injected with EcRA, EcRB or EcRC dsRNA showed that EcRA initiates ecdysteroid action by regulation the expression of EcRB and 20E-response genes. These data suggest that the EcR but not USP isoforms play distinct roles during the larval-pupal metamorphosis and EcRA plays a dominant role in transduction of ecdysteroid response in T. castaneum.
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Affiliation(s)
| | - Subba Reddy Palli
- Corresponding Author. Tel: +1 859 257 4962; fax: +1859 323 1120. E-mail address:
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Costantino BFB, Bricker DK, Alexandre K, Shen K, Merriam JR, Antoniewski C, Callender JL, Henrich VC, Presente A, Andres AJ. A novel ecdysone receptor mediates steroid-regulated developmental events during the mid-third instar of Drosophila. PLoS Genet 2008; 4:e1000102. [PMID: 18566664 PMCID: PMC2413497 DOI: 10.1371/journal.pgen.1000102] [Citation(s) in RCA: 68] [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: 01/28/2008] [Accepted: 05/20/2008] [Indexed: 11/18/2022] Open
Abstract
The larval salivary gland of Drosophila melanogaster synthesizes and secretes glue glycoproteins that cement developing animals to a solid surface during metamorphosis. The steroid hormone 20-hydroxyecdysone (20E) is an essential signaling molecule that modulates most of the physiological functions of the larval gland. At the end of larval development, it is known that 20E--signaling through a nuclear receptor heterodimer consisting of EcR and USP--induces the early and late puffing cascade of the polytene chromosomes and causes the exocytosis of stored glue granules into the lumen of the gland. It has also been reported that an earlier pulse of hormone induces the temporally and spatially specific transcriptional activation of the glue genes; however, the receptor responsible for triggering this response has not been characterized. Here we show that the coordinated expression of the glue genes midway through the third instar is mediated by 20E acting to induce genes of the Broad Complex (BRC) through a receptor that is not an EcR/USP heterodimer. This result is novel because it demonstrates for the first time that at least some 20E-mediated, mid-larval, developmental responses are controlled by an uncharacterized receptor that does not contain an RXR-like component.
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Affiliation(s)
- Benjamin F. B. Costantino
- School of Life Sciences, University of Nevada Las Vegas, Las Vegas, Nevada, United States of America
| | - Daniel K. Bricker
- School of Life Sciences, University of Nevada Las Vegas, Las Vegas, Nevada, United States of America
| | - Kelly Alexandre
- School of Life Sciences, University of Nevada Las Vegas, Las Vegas, Nevada, United States of America
| | - Kate Shen
- School of Life Sciences, University of Nevada Las Vegas, Las Vegas, Nevada, United States of America
| | - John R. Merriam
- Department of Molecular, Cell and Developmental Biology, University of California Los Angeles, Los Angeles, California, United States of America
| | | | - Jenna L. Callender
- Center for Biotechnology, Genomics, and Health Research, University of North Carolina Greensboro, Greensboro, North Carolina, United States of America
| | - Vincent C. Henrich
- Center for Biotechnology, Genomics, and Health Research, University of North Carolina Greensboro, Greensboro, North Carolina, United States of America
| | - Asaf Presente
- School of Life Sciences, University of Nevada Las Vegas, Las Vegas, Nevada, United States of America
| | - Andrew J. Andres
- School of Life Sciences, University of Nevada Las Vegas, Las Vegas, Nevada, United States of America
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9
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Beatty J, Fauth T, Callender JL, Spindler-Barth M, Henrich VC. Analysis of transcriptional activity mediated by Drosophila melanogaster ecdysone receptor isoforms in a heterologous cell culture system. INSECT MOLECULAR BIOLOGY 2006; 15:785-95. [PMID: 17201771 DOI: 10.1111/j.1365-2583.2006.00683.x] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/13/2023]
Abstract
Ecdysteroid regulation of gene transcription in Drosophila melanogaster and other insects is mediated by a heterodimer comprised of Ultraspiracle (USP) and one of three ecdysone receptor (EcR) isoforms (A, B1 and B2). This study revealed that the EcR/USP heterodimer displays isoform-specific capabilities. EcRB1 is normally induced with a form of USP that is missing its DNA-binding domain (DBD), although potentiation by juvenile hormone (JH) III is reduced. The EcRA and B2 isoforms, however, display almost no response to ecdysteroids with the DBD(-) USP. A mutation, K497E, in the shared ligand-binding domain of the EcR isoforms caused elevated EcRB2-specific affinity for a canonical ecdysone response element. The effects of directed modification and mutagenesis offer a strategy for developing hypotheses and considerations for studying in vivo function.
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Affiliation(s)
- J Beatty
- Center for Biotechnology, Genomics and Health Research, University of North Carolina-Greensboro, Greensboro, NC 27402-6170, USA
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Pool JE, Bauer DuMont V, Mueller JL, Aquadro CF. A scan of molecular variation leads to the narrow localization of a selective sweep affecting both Afrotropical and cosmopolitan populations of Drosophila melanogaster. Genetics 2006; 172:1093-105. [PMID: 16322515 PMCID: PMC1456208 DOI: 10.1534/genetics.105.049973] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/23/2005] [Accepted: 11/10/2005] [Indexed: 11/18/2022] Open
Abstract
Drosophila melanogaster originated in tropical Africa but has achieved a cosmopolitan distribution in association with human habitation. Cosmopolitan populations of D. melanogaster are known to have reduced genetic variation, particularly on the X chromosome. However, the relative importance of population bottlenecks and selective sweeps in explaining this reduction is uncertain. We surveyed variation at 31 microsatellites across a 330-kb section of the X chromosome located between the white and kirre genes. Two linked clusters of loci were observed with reduced variation and a skew toward rare alleles in both an Ecuador and a Zimbabwe population sample. Examining Zimbabwe DNA sequence polymorphism within one of these regions allowed us to localize a selective sweep to a 361-bp window within the 5' regulatory region of the roughest gene, with one nucleotide substitution representing the best candidate for the target of selection. Estimates of sweep age suggested that this fixation event occurred prior to the expansion of D. melanogaster from sub-Saharan Africa. For both putative sweep regions in our data set, cosmopolitan populations showed wider footprints of selection compared to those in Zimbabwe. This pattern appears consistent with the demographic amplification of preexisting sweep signals due to one or more population bottlenecks.
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Affiliation(s)
- John E Pool
- Department of Molecular Biology and Genetics, Cornell University, Ithaca, New York 14853, USA.
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Abstract
Nuclear receptors are ancient ligand-regulated transcription factors that control key metabolic and developmental pathways. The fruitfly Drosophila melanogaster has only 18 nuclear-receptor genes - far fewer than any other genetic model organism and representing all 6 subfamilies of vertebrate receptors. These unique attributes establish the fly as an ideal system for studying the regulation and function of nuclear receptors during development. Here, we review recent breakthroughs in our understanding of D. melanogaster nuclear receptors, and interpret these results in light of findings from their evolutionarily conserved vertebrate homologues.
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Affiliation(s)
- Kirst King-Jones
- Howard Hughes Medical Institute, Department of Human Genetics, University of Utah School of Medicine, 15 North 2030 East, Room 5100, Salt Lake City, Utah 84112-5331, USA.
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Sedkov Y, Cho E, Petruk S, Cherbas L, Smith ST, Jones RS, Cherbas P, Canaani E, Jaynes JB, Mazo A. Methylation at lysine 4 of histone H3 in ecdysone-dependent development of Drosophila. Nature 2003; 426:78-83. [PMID: 14603321 PMCID: PMC2743927 DOI: 10.1038/nature02080] [Citation(s) in RCA: 130] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/23/2003] [Accepted: 09/15/2003] [Indexed: 11/08/2022]
Abstract
Steroid hormones fulfil important functions in animal development. In Drosophila, ecdysone triggers moulting and metamorphosis through its effects on gene expression. Ecdysone works by binding to a nuclear receptor, EcR, which heterodimerizes with the retinoid X receptor homologue Ultraspiracle. Both partners are required for binding to ligand or DNA. Like most DNA-binding transcription factors, nuclear receptors activate or repress gene expression by recruiting co-regulators, some of which function as chromatin-modifying complexes. For example, p160 class coactivators associate with histone acetyltransferases and arginine histone methyltransferases. The Trithorax-related gene of Drosophila encodes the SET domain protein TRR. Here we report that TRR is a histone methyltransferases capable of trimethylating lysine 4 of histone H3 (H3-K4). trr acts upstream of hedgehog (hh) in progression of the morphogenetic furrow, and is required for retinal differentiation. Mutations in trr interact in eye development with EcR, and EcR and TRR can be co-immunoprecipitated on ecdysone treatment. TRR, EcR and trimethylated H3-K4 are detected at the ecdysone-inducible promoters of hh and BR-C in cultured cells, and H3-K4 trimethylation at these promoters is decreased in embryos lacking a functional copy of trr. We propose that TRR functions as a coactivator of EcR by altering the chromatin structure at ecdysone-responsive promoters.
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Affiliation(s)
- Yurii Sedkov
- Kimmel Cancer Center, Thomas Jefferson University, Philadelphia, Pennsylvania 19107, USA
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Cherbas L, Hu X, Zhimulev I, Belyaeva E, Cherbas P. EcR isoforms in Drosophila: testing tissue-specific requirements by targeted blockade and rescue. Development 2003; 130:271-84. [PMID: 12466195 DOI: 10.1242/dev.00205] [Citation(s) in RCA: 251] [Impact Index Per Article: 12.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
The three Drosophila EcR isoforms differ only at their N termini; thus, they share the conserved ligand-binding domain transcriptional activation function (AF2) and only differ in the unconserved A/B region, which contains a second, isoform-specific, activation function (AF1). We have developed a dominant-negative mutant EcR (EcR-DN), expressed it in flies with the GAL4/UAS system, and used it to block ecdysone signaling in eight tissues or groups of tissues. Localized EcR-DN arrests ecdysone-dependent development in the target cells and often--because of a molting checkpoint--arrests development globally. Simultaneously expressing individual wild-type EcR isoforms in the same target tissues suppresses the EcR-DN phenotype and identifies the rescuing isoform as sufficient to support the development of the target. Every isoform, and even an N-terminal truncated EcR that lacks any AF1, supports development in the fat body, eye discs, salivary glands, EH-secreting neurosecretory cells and in the dpp expression domain, implying that AF1 is dispensable in these tissues. By contrast, only EcR-A is able to support development in the margins of the wing discs, and only EcR-B2 can do so in the larval epidermis and the border cells of the developing egg chamber. In light of our results, the simplest explanations for the widespread spatial and temporal variations in EcR isoform titers appear untenable.
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Affiliation(s)
- Lucy Cherbas
- Department of Biology, Indiana University, Bloomington, IN 47405, USA.
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