1
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Tabuloc CA, Cai YD, Kwok RS, Chan EC, Hidalgo S, Chiu JC. CLOCK and TIMELESS regulate rhythmic occupancy of the BRAHMA chromatin-remodeling protein at clock gene promoters. PLoS Genet 2023; 19:e1010649. [PMID: 36809369 PMCID: PMC9983840 DOI: 10.1371/journal.pgen.1010649] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/17/2022] [Revised: 03/03/2023] [Accepted: 02/02/2023] [Indexed: 02/23/2023] Open
Abstract
Circadian clock and chromatin-remodeling complexes are tightly intertwined systems that regulate rhythmic gene expression. The circadian clock promotes rhythmic expression, timely recruitment, and/or activation of chromatin remodelers, while chromatin remodelers regulate accessibility of clock transcription factors to the DNA to influence expression of clock genes. We previously reported that the BRAHMA (BRM) chromatin-remodeling complex promotes the repression of circadian gene expression in Drosophila. In this study, we investigated the mechanisms by which the circadian clock feeds back to modulate daily BRM activity. Using chromatin immunoprecipitation, we observed rhythmic BRM binding to clock gene promoters despite constitutive BRM protein expression, suggesting that factors other than protein abundance are responsible for rhythmic BRM occupancy at clock-controlled loci. Since we previously reported that BRM interacts with two key clock proteins, CLOCK (CLK) and TIMELESS (TIM), we examined their effect on BRM occupancy to the period (per) promoter. We observed reduced BRM binding to the DNA in clk null flies, suggesting that CLK is involved in enhancing BRM occupancy to initiate transcriptional repression at the conclusion of the activation phase. Additionally, we observed reduced BRM binding to the per promoter in flies overexpressing TIM, suggesting that TIM promotes BRM removal from DNA. These conclusions are further supported by elevated BRM binding to the per promoter in flies subjected to constant light and experiments in Drosophila tissue culture in which the levels of CLK and TIM are manipulated. In summary, this study provides new insights into the reciprocal regulation between the circadian clock and the BRM chromatin-remodeling complex.
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Affiliation(s)
- Christine A. Tabuloc
- Department of Entomology and Nematology, College of Agricultural and Environmental Sciences, University of California Davis, Davis, California, United States of America
| | - Yao D. Cai
- Department of Entomology and Nematology, College of Agricultural and Environmental Sciences, University of California Davis, Davis, California, United States of America
| | - Rosanna S. Kwok
- Department of Entomology and Nematology, College of Agricultural and Environmental Sciences, University of California Davis, Davis, California, United States of America
| | - Elizabeth C. Chan
- Department of Entomology and Nematology, College of Agricultural and Environmental Sciences, University of California Davis, Davis, California, United States of America
| | - Sergio Hidalgo
- Department of Entomology and Nematology, College of Agricultural and Environmental Sciences, University of California Davis, Davis, California, United States of America
| | - Joanna C. Chiu
- Department of Entomology and Nematology, College of Agricultural and Environmental Sciences, University of California Davis, Davis, California, United States of America
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2
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Reynolds M, de Oliveira L, Vosburg C, Paris T, Massimino C, Norus J, Ortiz Y, Espino M, Davis N, Masse R, Neiman A, Holcomb R, Gervais K, Kemp M, Hoang M, Shippy TD, Hosmani PS, Flores-Gonzalez M, Pelz-Stelinski K, Qureshi JA, Mueller LA, Hunter WB, Benoit JB, Brown SJ, D’Elia T, Saha S. Annotation of putative circadian rhythm-associated genes in Diaphorina citri (Hemiptera: Liviidae). GIGABYTE 2022; 2022:gigabyte48. [PMID: 36824532 PMCID: PMC9662589 DOI: 10.46471/gigabyte.48] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/10/2021] [Accepted: 03/28/2022] [Indexed: 11/09/2022] Open
Abstract
The circadian rhythm involves multiple genes that generate an internal molecular clock, allowing organisms to anticipate environmental conditions produced by the Earth's rotation on its axis. Here, we present the results of the manual curation of 27 genes that are associated with circadian rhythm in the genome of Diaphorina citri, the Asian citrus psyllid. This insect is the vector for the bacterial pathogen Candidatus Liberibacter asiaticus (CLas), the causal agent of citrus greening disease (Huanglongbing). This disease severely affects citrus industries and has drastically decreased crop yields worldwide. Based on cry1 and cry2 identified in the psyllid genome, D. citri likely possesses a circadian model similar to the lepidopteran butterfly, Danaus plexippus. Manual annotation will improve the quality of circadian rhythm gene models, allowing the future development of molecular therapeutics, such as RNA interference or antisense technologies, to target these genes to disrupt the psyllid biology.
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Affiliation(s)
- Max Reynolds
- Indian River State College, Fort Pierce, FL 34981, USA
| | | | - Chad Vosburg
- Indian River State College, Fort Pierce, FL 34981, USA,Department of Plant Pathology and Environmental Microbiology, Pennsylvania State University, University Park, PA 16802, USA
| | - Thomson Paris
- Entomology and Nematology Department, University of Florida, North Florida Research and Education Center, Research Road, Quincy 32351, Florida, USA
| | | | - Jordan Norus
- Indian River State College, Fort Pierce, FL 34981, USA
| | - Yasmin Ortiz
- Indian River State College, Fort Pierce, FL 34981, USA
| | | | - Nina Davis
- Indian River State College, Fort Pierce, FL 34981, USA
| | - Ron Masse
- Indian River State College, Fort Pierce, FL 34981, USA
| | - Alan Neiman
- Indian River State College, Fort Pierce, FL 34981, USA
| | | | - Kylie Gervais
- Indian River State College, Fort Pierce, FL 34981, USA
| | - Melissa Kemp
- Indian River State College, Fort Pierce, FL 34981, USA
| | - Maria Hoang
- Indian River State College, Fort Pierce, FL 34981, USA
| | - Teresa D. Shippy
- Division of Biology, Kansas State University, Manhattan, KS 66506, USA
| | | | | | - Kirsten Pelz-Stelinski
- Department of Entomology and Nematology, University of Florida, Lake Alfred, FL 33850, USA
| | - Jawwad A. Qureshi
- Indian River Research and Education Center, University of Florida, IFAS, 2199 South Rock Road, Fort Pierce, FL 34945-3138, USA,Southwest Florida Research and Education Center, University of Florida, IFAS, 2685 State Road 29 North, Immokalee, FL 34142, USA
| | | | - Wayne B. Hunter
- USDA-ARS, US Horticultural Research Laboratory, Fort Pierce, FL 34945, USA
| | - Joshua B. Benoit
- Department of Biological Sciences, University of Cincinnati, Cincinnati, OH 45221, USA
| | - Susan J. Brown
- Division of Biology, Kansas State University, Manhattan, KS 66506, USA
| | - Tom D’Elia
- Indian River State College, Fort Pierce, FL 34981, USA
| | - Surya Saha
- Boyce Thompson Institute, Ithaca, NY 14853, USA,Animal and Comparative Biomedical Sciences, University of Arizona, Tucson, AZ 85721, USA, Corresponding author. E-mail:
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3
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Cai YD, Chiu JC. Timeless in animal circadian clocks and beyond. FEBS J 2021; 289:6559-6575. [PMID: 34699674 PMCID: PMC9038958 DOI: 10.1111/febs.16253] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/01/2021] [Revised: 10/09/2021] [Accepted: 10/26/2021] [Indexed: 12/13/2022]
Abstract
TIMELESS (TIM) was first identified as a molecular cog in the Drosophila circadian clock. Almost three decades of investigations have resulted in an insightful model describing the critical role of Drosophila TIM (dTIM) in circadian timekeeping in insects, including its function in mediating light entrainment and temperature compensation of the molecular clock. Furthermore, exciting discoveries on its sequence polymorphism and thermosensitive alternative RNA splicing have also established its role in regulating seasonal biology. Although mammalian TIM (mTIM), its mammalian paralog, was first identified as a potential circadian clock component in 1990s due to sequence similarity to dTIM, its role in clock regulation has been more controversial. Mammalian TIM has now been characterized as a DNA replication fork component and has been shown to promote fork progression and participate in cell cycle checkpoint signaling in response to DNA damage. Despite defective circadian rhythms displayed by mtim mutants, it remains controversial whether the regulation of circadian clocks by mTIM is direct, especially given the interconnection between the cell cycle and circadian clocks. In this review, we provide a historical perspective on the identification of animal tim genes, summarize the roles of TIM proteins in biological timing and genomic stability, and draw parallels between dTIM and mTIM despite apparent functional divergence.
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Affiliation(s)
- Yao D Cai
- Department of Entomology and Nematology, College of Agricultural and Environmental Sciences, University of California Davis, CA, USA
| | - Joanna C Chiu
- Department of Entomology and Nematology, College of Agricultural and Environmental Sciences, University of California Davis, CA, USA
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4
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Yan J, Kim YJ, Somers DE. Post-Translational Mechanisms of Plant Circadian Regulation. Genes (Basel) 2021; 12:325. [PMID: 33668215 PMCID: PMC7995963 DOI: 10.3390/genes12030325] [Citation(s) in RCA: 20] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/01/2021] [Revised: 02/21/2021] [Accepted: 02/22/2021] [Indexed: 12/15/2022] Open
Abstract
The molecular components of the circadian system possess the interesting feature of acting together to create a self-sustaining oscillator, while at the same time acting individually, and in complexes, to confer phase-specific circadian control over a wide range of physiological and developmental outputs. This means that many circadian oscillator proteins are simultaneously also part of the circadian output pathway. Most studies have focused on transcriptional control of circadian rhythms, but work in plants and metazoans has shown the importance of post-transcriptional and post-translational processes within the circadian system. Here we highlight recent work describing post-translational mechanisms that impact both the function of the oscillator and the clock-controlled outputs.
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Affiliation(s)
| | | | - David E. Somers
- Department of Molecular Genetics, The Ohio State University; Columbus, OH 43210, USA; (J.Y.); (Y.J.K.)
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5
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Cai YD, Xue Y, Truong CC, Del Carmen-Li J, Ochoa C, Vanselow JT, Murphy KA, Li YH, Liu X, Kunimoto BL, Zheng H, Zhao C, Zhang Y, Schlosser A, Chiu JC. CK2 Inhibits TIMELESS Nuclear Export and Modulates CLOCK Transcriptional Activity to Regulate Circadian Rhythms. Curr Biol 2021; 31:502-514.e7. [PMID: 33217322 PMCID: PMC7878342 DOI: 10.1016/j.cub.2020.10.061] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/21/2020] [Revised: 09/25/2020] [Accepted: 10/20/2020] [Indexed: 11/06/2022]
Abstract
Circadian clocks orchestrate daily rhythms in organismal physiology and behavior to promote optimal performance and fitness. In Drosophila, key pacemaker proteins PERIOD (PER) and TIMELESS (TIM) are progressively phosphorylated to perform phase-specific functions. Whereas PER phosphorylation has been extensively studied, systematic analysis of site-specific TIM phosphorylation is lacking. Here, we identified phosphorylation sites of PER-bound TIM by mass spectrometry, given the importance of TIM as a modulator of PER function in the pacemaker. Among the 12 TIM phosphorylation sites we identified, at least two of them are critical for circadian timekeeping as mutants expressing non-phosphorylatable mutations exhibit altered behavioral rhythms. In particular, we observed that CK2-dependent phosphorylation of TIM(S1404) promotes nuclear accumulation of PER-TIM heterodimers by inhibiting the interaction of TIM and nuclear export component, Exportin 1 (XPO1). We propose that proper level of nuclear PER-TIM accumulation is necessary to facilitate kinase recruitment for the regulation of daily phosphorylation rhythm and phase-specific transcriptional activity of CLOCK (CLK). Our results highlight the contribution of phosphorylation-dependent nuclear export of PER-TIM heterodimers to the maintenance of circadian periodicity and identify a new mechanism by which the negative elements of the circadian clock (PER-TIM) regulate the positive elements (CLK-CYC). Finally, because the molecular phenotype of tim(S1404A) non-phosphorylatable mutant exhibits remarkable similarity to that of a mutation in human timeless that underlies familial advanced sleep phase syndrome (FASPS), our results revealed an unexpected parallel between the functions of Drosophila and human TIM and may provide new insights into the molecular mechanisms underlying human FASPS. Organisms in all domains of life exhibit circadian rhythms. Cai et al. reveal that phosphorylation of TIMELESS modulates kinase accessibility to CLOCK in the nucleus. This mechanism is important in controlling daily phosphorylation rhythm of CLOCK, which is critical for its function as a key regulator of circadian rhythms.
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Affiliation(s)
- Yao D Cai
- Department of Entomology and Nematology, College of Agricultural and Environmental Sciences, University of California, Davis, One Shields Avenue, Davis, CA 95616, USA
| | - Yongbo Xue
- Department of Biology, University of Nevada, Reno, NV 89557, USA
| | - Cindy C Truong
- Department of Entomology and Nematology, College of Agricultural and Environmental Sciences, University of California, Davis, One Shields Avenue, Davis, CA 95616, USA
| | - Jose Del Carmen-Li
- Department of Entomology and Nematology, College of Agricultural and Environmental Sciences, University of California, Davis, One Shields Avenue, Davis, CA 95616, USA
| | - Christopher Ochoa
- Department of Entomology and Nematology, College of Agricultural and Environmental Sciences, University of California, Davis, One Shields Avenue, Davis, CA 95616, USA
| | - Jens T Vanselow
- Rudolf Virchow Center for Experimental Biomedicine, University of Wurzburg, Wurzburg, Germany
| | - Katherine A Murphy
- Department of Entomology and Nematology, College of Agricultural and Environmental Sciences, University of California, Davis, One Shields Avenue, Davis, CA 95616, USA
| | - Ying H Li
- Department of Entomology and Nematology, College of Agricultural and Environmental Sciences, University of California, Davis, One Shields Avenue, Davis, CA 95616, USA
| | - Xianhui Liu
- Department of Entomology and Nematology, College of Agricultural and Environmental Sciences, University of California, Davis, One Shields Avenue, Davis, CA 95616, USA
| | - Ben L Kunimoto
- Department of Entomology and Nematology, College of Agricultural and Environmental Sciences, University of California, Davis, One Shields Avenue, Davis, CA 95616, USA
| | - Haiyan Zheng
- Biological Mass Spectrometry Facility, Robert Wood Johnson Medical School and Rutgers, the State University of New Jersey, Piscataway, NJ 08854, USA
| | - Caifeng Zhao
- Biological Mass Spectrometry Facility, Robert Wood Johnson Medical School and Rutgers, the State University of New Jersey, Piscataway, NJ 08854, USA
| | - Yong Zhang
- Department of Biology, University of Nevada, Reno, NV 89557, USA
| | - Andreas Schlosser
- Rudolf Virchow Center for Experimental Biomedicine, University of Wurzburg, Wurzburg, Germany
| | - Joanna C Chiu
- Department of Entomology and Nematology, College of Agricultural and Environmental Sciences, University of California, Davis, One Shields Avenue, Davis, CA 95616, USA.
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6
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Kula-Eversole E, Lee DH, Samba I, Yildirim E, Levine DC, Hong HK, Lear BC, Bass J, Rosbash M, Allada R. Phosphatase of Regenerating Liver-1 Selectively Times Circadian Behavior in Darkness via Function in PDF Neurons and Dephosphorylation of TIMELESS. Curr Biol 2021; 31:138-149.e5. [PMID: 33157022 PMCID: PMC7855481 DOI: 10.1016/j.cub.2020.10.013] [Citation(s) in RCA: 11] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/13/2020] [Revised: 08/25/2020] [Accepted: 10/07/2020] [Indexed: 12/31/2022]
Abstract
The timing of behavior under natural light-dark conditions is a function of circadian clocks and photic input pathways, but a mechanistic understanding of how these pathways collaborate in animals is lacking. Here we demonstrate in Drosophila that the Phosphatase of Regenerating Liver-1 (PRL-1) sets period length and behavioral phase gated by photic signals. PRL-1 knockdown in PDF clock neurons dramatically lengthens circadian period. PRL-1 mutants exhibit allele-specific interactions with the light- and clock-regulated gene timeless (tim). Moreover, we show that PRL-1 promotes TIM accumulation and dephosphorylation. Interestingly, the PRL-1 mutant period lengthening is suppressed in constant light, and PRL-1 mutants display a delayed phase under short, but not long, photoperiod conditions. Thus, our studies reveal that PRL-1-dependent dephosphorylation of TIM is a core mechanism of the clock that sets period length and phase in darkness, enabling the behavioral adjustment to change day-night cycles.
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Affiliation(s)
| | - Da Hyun Lee
- Department of Neurobiology, Northwestern University, Evanston, IL 60208, USA
| | - Ima Samba
- Department of Neurobiology, Northwestern University, Evanston, IL 60208, USA
| | - Evrim Yildirim
- Department of Neurobiology, Northwestern University, Evanston, IL 60208, USA
| | - Daniel C Levine
- Department of Medicine, Northwestern University, Chicago, IL 60611, USA
| | - Hee-Kyung Hong
- Department of Medicine, Northwestern University, Chicago, IL 60611, USA
| | - Bridget C Lear
- Department of Neurobiology, Northwestern University, Evanston, IL 60208, USA
| | - Joseph Bass
- Department of Medicine, Northwestern University, Chicago, IL 60611, USA
| | - Michael Rosbash
- Howard Hughes Medical Institute, Department of Biology, Brandeis University, Waltham, MA 02445, USA
| | - Ravi Allada
- Department of Neurobiology, Northwestern University, Evanston, IL 60208, USA.
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7
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Pelham JF, Dunlap JC, Hurley JM. Intrinsic disorder is an essential characteristic of components in the conserved circadian circuit. Cell Commun Signal 2020; 18:181. [PMID: 33176800 PMCID: PMC7656774 DOI: 10.1186/s12964-020-00658-y] [Citation(s) in RCA: 29] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/09/2020] [Accepted: 09/06/2020] [Indexed: 12/12/2022] Open
Abstract
INTRODUCTION The circadian circuit, a roughly 24 h molecular feedback loop, or clock, is conserved from bacteria to animals and allows for enhanced organismal survival by facilitating the anticipation of the day/night cycle. With circadian regulation reportedly impacting as high as 80% of protein coding genes in higher eukaryotes, the protein-based circadian clock broadly regulates physiology and behavior. Due to the extensive interconnection between the clock and other cellular systems, chronic disruption of these molecular rhythms leads to a decrease in organismal fitness as well as an increase of disease rates in humans. Importantly, recent research has demonstrated that proteins comprising the circadian clock network display a significant amount of intrinsic disorder. MAIN BODY In this work, we focus on the extent of intrinsic disorder in the circadian clock and its potential mechanistic role in circadian timing. We highlight the conservation of disorder by quantifying the extent of computationally-predicted protein disorder in the core clock of the key eukaryotic circadian model organisms Drosophila melanogaster, Neurospora crassa, and Mus musculus. We further examine previously published work, as well as feature novel experimental evidence, demonstrating that the core negative arm circadian period drivers FREQUENCY (Neurospora crassa) and PERIOD-2 (PER2) (Mus musculus), possess biochemical characteristics of intrinsically disordered proteins. Finally, we discuss the potential contributions of the inherent biophysical principals of intrinsically disordered proteins that may explain the vital mechanistic roles they play in the clock to drive their broad evolutionary conservation in circadian timekeeping. CONCLUSION The pervasive conservation of disorder amongst the clock in the crown eukaryotes suggests that disorder is essential for optimal circadian timing from fungi to animals, providing vital homeostatic cellular maintenance and coordinating organismal physiology across phylogenetic kingdoms. Video abstract.
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Affiliation(s)
- Jacqueline F. Pelham
- Department of Biological Sciences, Rensselaer Polytechnic Institute, Troy, NY 12180 USA
| | - Jay C. Dunlap
- Department of Molecular and Systems Biology, Geisel School of Medicine at Dartmouth, Hanover, NH 03755 USA
| | - Jennifer M. Hurley
- Department of Biological Sciences, Rensselaer Polytechnic Institute, Troy, NY 12180 USA
- Center for Biotechnology and Interdisciplinary Sciences, Rensselaer Polytechnic Institute, Troy, NY 12018 USA
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8
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A Symphony of Signals: Intercellular and Intracellular Signaling Mechanisms Underlying Circadian Timekeeping in Mice and Flies. Int J Mol Sci 2019; 20:ijms20092363. [PMID: 31086044 PMCID: PMC6540063 DOI: 10.3390/ijms20092363] [Citation(s) in RCA: 19] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/01/2019] [Revised: 05/10/2019] [Accepted: 05/10/2019] [Indexed: 12/11/2022] Open
Abstract
The central pacemakers of circadian timekeeping systems are highly robust yet adaptable, providing the temporal coordination of rhythms in behavior and physiological processes in accordance with the demands imposed by environmental cycles. These features of the central pacemaker are achieved by a multi-oscillator network in which individual cellular oscillators are tightly coupled to the environmental day-night cycle, and to one another via intercellular coupling. In this review, we will summarize the roles of various neurotransmitters and neuropeptides in the regulation of circadian entrainment and synchrony within the mammalian and Drosophila central pacemakers. We will also describe the diverse functions of protein kinases in the relay of input signals to the core oscillator or the direct regulation of the molecular clock machinery.
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9
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Top D, Young MW. Coordination between Differentially Regulated Circadian Clocks Generates Rhythmic Behavior. Cold Spring Harb Perspect Biol 2018; 10:a033589. [PMID: 28893860 PMCID: PMC6028074 DOI: 10.1101/cshperspect.a033589] [Citation(s) in RCA: 48] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
Abstract
Specialized groups of neurons in the brain are key mediators of circadian rhythms, receiving daily environmental cues and communicating those signals to other tissues in the organism for entrainment and to organize circadian physiology. In Drosophila, the "circadian clock" is housed in seven neuronal clusters, which are defined by their expression of the main circadian proteins, Period, Timeless, Clock, and Cycle. These clusters are distributed across the fly brain and are thereby subject to the respective environments associated with their anatomical locations. While these core components are universally expressed in all neurons of the circadian network, additional regulatory proteins that act on these components are differentially expressed, giving rise to "local clocks" within the network that nonetheless converge to regulate coherent behavioral rhythms. In this review, we describe the communication between the neurons of the circadian network and the molecular differences within neurons of this network. We focus on differences in protein-expression patterns and discuss how such variation can impart functional differences in each local clock. Finally, we summarize our current understanding of how communication within the circadian network intersects with intracellular biochemical mechanisms to ultimately specify behavioral rhythms. We propose that additional efforts are required to identify regulatory mechanisms within each neuronal cluster to understand the molecular basis of circadian behavior.
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Affiliation(s)
- Deniz Top
- Laboratory of Genetics, The Rockefeller University, New York, New York 10065
| | - Michael W Young
- Laboratory of Genetics, The Rockefeller University, New York, New York 10065
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10
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Biscontin A, Wallach T, Sales G, Grudziecki A, Janke L, Sartori E, Bertolucci C, Mazzotta G, De Pittà C, Meyer B, Kramer A, Costa R. Functional characterization of the circadian clock in the Antarctic krill, Euphausia superba. Sci Rep 2017; 7:17742. [PMID: 29255161 PMCID: PMC5735174 DOI: 10.1038/s41598-017-18009-2] [Citation(s) in RCA: 22] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/03/2017] [Accepted: 12/05/2017] [Indexed: 11/30/2022] Open
Abstract
Antarctic krill (Euphausia superba) is a key species in Southern Ocean ecosystem where it plays a central role in the Antarctic food web. Available information supports the existence of an endogenous timing system in krill enabling it to synchronize metabolism and behavior with an environment characterized by extreme seasonal changes in terms of day length, food availability, and surface ice extent. A screening of our transcriptome database “KrillDB” allowed us to identify the putative orthologues of 20 circadian clock components. Mapping of conserved domains and phylogenetic analyses strongly supported annotations of the identified sequences. Luciferase assays and co-immunoprecipitation experiments allowed us to define the role of the main clock components. Our findings provide an overall picture of the molecular mechanisms underlying the functioning of the endogenous circadian clock in the Antarctic krill and shed light on their evolution throughout crustaceans speciation. Interestingly, the core clock machinery shows both mammalian and insect features that presumably contribute to an evolutionary strategy to cope with polar environment’s challenges. Moreover, despite the extreme variability characterizing the Antarctic seasonal day length, the conserved light mediated degradation of the photoreceptor EsCRY1 suggests a persisting pivotal role of light as a Zeitgeber.
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Affiliation(s)
- Alberto Biscontin
- Charité-Universitätsmedizin Berlin, Laboratory of Chronobiology, D-10117, Berlin, Germany.,Department of Biology, University of Padova, 35121, Padova, Italy
| | - Thomas Wallach
- Charité-Universitätsmedizin Berlin, Laboratory of Chronobiology, D-10117, Berlin, Germany
| | - Gabriele Sales
- Department of Biology, University of Padova, 35121, Padova, Italy
| | - Astrid Grudziecki
- Charité-Universitätsmedizin Berlin, Laboratory of Chronobiology, D-10117, Berlin, Germany
| | - Leonard Janke
- Charité-Universitätsmedizin Berlin, Laboratory of Chronobiology, D-10117, Berlin, Germany
| | - Elena Sartori
- Department of Biology, University of Padova, 35121, Padova, Italy
| | - Cristiano Bertolucci
- Department of Life Sciences and Biotechnology, University of Ferrara, 44121, Ferrara, Italy
| | | | | | - Bettina Meyer
- Alfred Wegener Polar Biological Oceanography, 27570, Bremerhaven, Germany.,Carl von Ossietzky University of Oldenburg, Institute for Chemistry and Biology of the Marine Environment, 26129, Oldenburg, Germany.,Helmholtz Institute for Functional Marine Biodiversity Oldenburg (HIFMB), 26129, Oldenburg, Germany
| | - Achim Kramer
- Charité-Universitätsmedizin Berlin, Laboratory of Chronobiology, D-10117, Berlin, Germany.
| | - Rodolfo Costa
- Department of Biology, University of Padova, 35121, Padova, Italy.
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11
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Zwarts L, Vulsteke V, Buhl E, Hodge JJL, Callaerts P. SlgA, encoded by the homolog of the human schizophrenia-associated gene PRODH, acts in clock neurons to regulate Drosophila aggression. Dis Model Mech 2017; 10:705-716. [PMID: 28331058 PMCID: PMC5483002 DOI: 10.1242/dmm.027151] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/18/2016] [Accepted: 03/09/2017] [Indexed: 12/11/2022] Open
Abstract
Mutations in the proline dehydrogenase gene PRODH are linked to behavioral alterations in schizophrenia and as part of DiGeorge and velo-cardio-facial syndromes, but the role of PRODH in their etiology remains unclear. Here, we establish a Drosophila model to study the role of PRODH in behavioral disorders. We determine the distribution of the Drosophila PRODH homolog slgA in the brain and show that knockdown and overexpression of human PRODH and slgA in the lateral neurons ventral (LNv) lead to altered aggressive behavior. SlgA acts in an isoform-specific manner and is regulated by casein kinase II (CkII). Our data suggest that these effects are, at least partially, due to effects on mitochondrial function. We thus show that precise regulation of proline metabolism is essential to drive normal behavior and we identify Drosophila aggression as a model behavior relevant for the study of the mechanisms that are impaired in neuropsychiatric disorders. Editors' choice: A Drosophila model to study the role of PRODH, a schizophrenia-associated gene, in behavioral disorders.
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Affiliation(s)
- Liesbeth Zwarts
- KU Leuven - University of Leuven, Department of Human Genetics, Laboratory of Behavioral and Developmental Genetics, Leuven B-3000, Belgium.,VIB Center for the Biology of Disease, Laboratory of Behavioral and Developmental Genetics, Leuven B-3000, Belgium
| | - Veerle Vulsteke
- KU Leuven - University of Leuven, Department of Human Genetics, Laboratory of Behavioral and Developmental Genetics, Leuven B-3000, Belgium.,VIB Center for the Biology of Disease, Laboratory of Behavioral and Developmental Genetics, Leuven B-3000, Belgium
| | - Edgar Buhl
- University of Bristol, School of Physiology, Pharmacology and Neuroscience, Bristol BS8 1TD, UK
| | - James J L Hodge
- University of Bristol, School of Physiology, Pharmacology and Neuroscience, Bristol BS8 1TD, UK
| | - Patrick Callaerts
- KU Leuven - University of Leuven, Department of Human Genetics, Laboratory of Behavioral and Developmental Genetics, Leuven B-3000, Belgium .,VIB Center for the Biology of Disease, Laboratory of Behavioral and Developmental Genetics, Leuven B-3000, Belgium
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12
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Top D, Harms E, Syed S, Adams EL, Saez L. GSK-3 and CK2 Kinases Converge on Timeless to Regulate the Master Clock. Cell Rep 2016; 16:357-367. [PMID: 27346344 PMCID: PMC4945451 DOI: 10.1016/j.celrep.2016.06.005] [Citation(s) in RCA: 35] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/29/2016] [Revised: 04/27/2016] [Accepted: 05/25/2016] [Indexed: 10/21/2022] Open
Abstract
The molecular clock relies on a delayed negative feedback loop of transcriptional regulation to generate oscillating gene expression. Although the principal components of the clock are present in all circadian neurons, different neuronal clusters have varying effects on rhythmic behavior, suggesting that the clocks they house are differently regulated. Combining biochemical and genetic techniques in Drosophila, we identify a phosphorylation program native to the master pacemaker neurons that regulates the timing of nuclear accumulation of the Period/Timeless repressor complex. GSK-3/SGG binds and phosphorylates Period-bound Timeless, triggering a CK2-mediated phosphorylation cascade. Mutations that block the hierarchical phosphorylation of Timeless in vitro also delay nuclear accumulation in both tissue culture and in vivo and predictably change rhythmic behavior. This two-kinase phosphorylation cascade is anatomically restricted to the eight master pacemaker neurons, distinguishing the regulatory mechanism of the molecular clock within these neurons from the other clocks that cooperate to govern behavioral rhythmicity.
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Affiliation(s)
- Deniz Top
- Laboratory of Genetics, The Rockefeller University, 1230 York Avenue, Box 288, New York, NY 10065, USA.
| | - Emily Harms
- Laboratory of Genetics, The Rockefeller University, 1230 York Avenue, Box 288, New York, NY 10065, USA
| | - Sheyum Syed
- Department of Physics, The University of Miami, 1320 Campo Sano Avenue, Coral Gables, FL 33146, USA
| | - Eliza L Adams
- Laboratory of Genetics, The Rockefeller University, 1230 York Avenue, Box 288, New York, NY 10065, USA
| | - Lino Saez
- Laboratory of Genetics, The Rockefeller University, 1230 York Avenue, Box 288, New York, NY 10065, USA
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13
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Fischer R, Helfrich-Förster C, Peschel N. GSK-3 Beta Does Not Stabilize Cryptochrome in the Circadian Clock of Drosophila. PLoS One 2016; 11:e0146571. [PMID: 26741981 PMCID: PMC4704813 DOI: 10.1371/journal.pone.0146571] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/15/2015] [Accepted: 12/08/2015] [Indexed: 11/19/2022] Open
Abstract
Cryptochrome (CRY) is the primary photoreceptor of Drosophila’s circadian clock. It resets the circadian clock by promoting light-induced degradation of the clock protein Timeless (TIM) in the proteasome. Under constant light, the clock stops because TIM is absent, and the flies become arrhythmic. In addition to TIM degradation, light also induces CRY degradation. This depends on the interaction of CRY with several proteins such as the E3 ubiquitin ligases Jetlag (JET) and Ramshackle (BRWD3). However, CRY can seemingly also be stabilized by interaction with the kinase Shaggy (SGG), the GSK-3 beta fly orthologue. Consequently, flies with SGG overexpression in certain dorsal clock neurons are reported to remain rhythmic under constant light. We were interested in the interaction between CRY, Ramshackle and SGG and started to perform protein interaction studies in S2 cells. To our surprise, we were not able to replicate the results, that SGG overexpression does stabilize CRY, neither in S2 cells nor in the relevant clock neurons. SGG rather does the contrary. Furthermore, flies with SGG overexpression in the dorsal clock neurons became arrhythmic as did wild-type flies. Nevertheless, we could reproduce the published interaction of SGG with TIM, since flies with SGG overexpression in the lateral clock neurons shortened their free-running period. We conclude that SGG does not directly interact with CRY but rather with TIM. Furthermore we could demonstrate, that an unspecific antibody explains the observed stabilization effects on CRY.
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Affiliation(s)
- Robin Fischer
- Neurobiology and Genetics, Biocenter, University of Würzburg, Würzburg, Germany
| | | | - Nicolai Peschel
- Neurobiology and Genetics, Biocenter, University of Würzburg, Würzburg, Germany
- * E-mail:
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14
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Tormey D, Colbourne JK, Mockaitis K, Choi JH, Lopez J, Burkhart J, Bradshaw W, Holzapfel C. Evolutionary divergence of core and post-translational circadian clock genes in the pitcher-plant mosquito, Wyeomyia smithii. BMC Genomics 2015; 16:754. [PMID: 26444857 PMCID: PMC4594641 DOI: 10.1186/s12864-015-1937-y] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/27/2015] [Accepted: 09/19/2015] [Indexed: 01/25/2023] Open
Abstract
BACKGROUND Internal circadian (circa, about; dies, day) clocks enable organisms to maintain adaptive timing of their daily behavioral activities and physiological functions. Eukaryotic clocks consist of core transcription-translation feedback loops that generate a cycle and post-translational modifiers that maintain that cycle at about 24 h. We use the pitcher-plant mosquito, Wyeomyia smithii (subfamily Culicini, tribe Sabethini), to test whether evolutionary divergence of the circadian clock genes in this species, relative to other insects, has involved primarily genes in the core feedback loops or the post-translational modifiers. Heretofore, there is no reference transcriptome or genome sequence for any mosquito in the tribe Sabethini, which includes over 375 mainly circumtropical species. METHODS We sequenced, assembled and annotated the transcriptome of W. smithii containing nearly 95 % of conserved single-copy orthologs in animal genomes. We used the translated contigs and singletons to determine the average rates of circadian clock-gene divergence in W. smithii relative to three other mosquito genera, to Drosophila, to the butterfly, Danaus, and to the wasp, Nasonia. RESULTS Over 1.08 million cDNA sequence reads were obtained consisting of 432.5 million nucleotides. Their assembly produced 25,904 contigs and 54,418 singletons of which 62 % and 28 % are annotated as protein-coding genes, respectively, sharing homology with other animal proteomes. DISCUSSION The W. smithii transcriptome includes all nine circadian transcription-translation feedback-loop genes and all eight post-translational modifier genes we sought to identify (Fig. 1). After aligning translated W. smithii contigs and singletons from this transcriptome with other insects, we determined that there was no significant difference in the average divergence of W. smithii from the six other taxa between the core feedback-loop genes and post-translational modifiers. CONCLUSIONS The characterized transcriptome is sufficiently complete and of sufficient quality to have uncovered all of the insect circadian clock genes we sought to identify (Fig. 1). Relative divergence does not differ between core feedback-loop genes and post-translational modifiers of those genes in a Sabethine species (W. smithii) that has experienced a continual northward dispersal into temperate regions of progressively longer summer day lengths as compared with six other insect taxa. An associated microarray platform derived from this work will enable the investigation of functional genomics of circadian rhythmicity, photoperiodic time measurement, and diapause along a photic and seasonal geographic gradient.
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Affiliation(s)
- Duncan Tormey
- Institute of Ecology and Evolution, University of Oregon, Eugene, OR, USA.,Stowers Institute for Medical Research, Kansas City, MO, USA
| | - John K Colbourne
- Center for Genomics and Bioinformatics, Indiana University, Bloomington, IN, USA.,School of Biosciences, University of Birmingham, Birmingham, UK
| | - Keithanne Mockaitis
- Center for Genomics and Bioinformatics, Indiana University, Bloomington, IN, USA.,Pervasive Technology Institute, Indiana University, Bloomington, IN, USA
| | - Jeong-Hyeon Choi
- Center for Genomics and Bioinformatics, Indiana University, Bloomington, IN, USA.,GRU Cancer Center, Georgia Regents University, Augusta, GA, USA
| | - Jacqueline Lopez
- Center for Genomics and Bioinformatics, Indiana University, Bloomington, IN, USA.,Department of Biological Sciences, Notre Dame University, Notre Dame, IN, USA
| | - Joshua Burkhart
- Institute of Ecology and Evolution, University of Oregon, Eugene, OR, USA.,Burke E. Porter Machinery, Grand Rapids, MI, USA
| | - William Bradshaw
- Institute of Ecology and Evolution, University of Oregon, Eugene, OR, USA.
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15
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Andreazza S, Bouleau S, Martin B, Lamouroux A, Ponien P, Papin C, Chélot E, Jacquet E, Rouyer F. Daytime CLOCK Dephosphorylation Is Controlled by STRIPAK Complexes in Drosophila. Cell Rep 2015; 11:1266-79. [PMID: 25981041 DOI: 10.1016/j.celrep.2015.04.033] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/08/2014] [Revised: 02/23/2015] [Accepted: 04/16/2015] [Indexed: 11/29/2022] Open
Abstract
In the Drosophila circadian oscillator, the CLOCK/CYCLE complex activates transcription of period (per) and timeless (tim) in the evening. PER and TIM proteins then repress CLOCK (CLK) activity during the night. The pace of the oscillator depends upon post-translational regulation that affects both positive and negative components of the transcriptional loop. CLK protein is highly phosphorylated and inactive in the morning, whereas hypophosphorylated active forms are present in the evening. How this critical dephosphorylation step is mediated is unclear. We show here that two components of the STRIPAK complex, the CKA regulatory subunit of the PP2A phosphatase and its interacting protein STRIP, promote CLK dephosphorylation during the daytime. In contrast, the WDB regulatory PP2A subunit stabilizes CLK without affecting its phosphorylation state. Inhibition of the PP2A catalytic subunit and CKA downregulation affect daytime CLK similarly, suggesting that STRIPAK complexes are the main PP2A players in producing transcriptionally active hypophosphorylated CLK.
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Affiliation(s)
- Simonetta Andreazza
- Université Paris-Saclay, Université Paris-Sud, CNRS, UMR 9197, Institut des Neurosciences Paris-Saclay, 91190 Gif-sur-Yvette, France
| | - Sylvina Bouleau
- Université Paris-Saclay, Université Paris-Sud, CNRS, UMR 9197, Institut des Neurosciences Paris-Saclay, 91190 Gif-sur-Yvette, France
| | - Béatrice Martin
- Université Paris-Saclay, Université Paris-Sud, CNRS, UMR 9197, Institut des Neurosciences Paris-Saclay, 91190 Gif-sur-Yvette, France
| | - Annie Lamouroux
- Université Paris-Saclay, Université Paris-Sud, CNRS, UMR 9197, Institut des Neurosciences Paris-Saclay, 91190 Gif-sur-Yvette, France
| | - Prishila Ponien
- Institut de Chimie des Substances Naturelles, CNRS, UPR 2301, 91190 Gif-sur-Yvette, France
| | - Christian Papin
- Université Paris-Saclay, Université Paris-Sud, CNRS, UMR 9197, Institut des Neurosciences Paris-Saclay, 91190 Gif-sur-Yvette, France
| | - Elisabeth Chélot
- Université Paris-Saclay, Université Paris-Sud, CNRS, UMR 9197, Institut des Neurosciences Paris-Saclay, 91190 Gif-sur-Yvette, France
| | - Eric Jacquet
- Institut de Chimie des Substances Naturelles, CNRS, UPR 2301, 91190 Gif-sur-Yvette, France
| | - François Rouyer
- Université Paris-Saclay, Université Paris-Sud, CNRS, UMR 9197, Institut des Neurosciences Paris-Saclay, 91190 Gif-sur-Yvette, France.
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16
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Jang AR, Moravcevic K, Saez L, Young MW, Sehgal A. Drosophila TIM binds importin α1, and acts as an adapter to transport PER to the nucleus. PLoS Genet 2015; 11:e1004974. [PMID: 25674790 PMCID: PMC4335507 DOI: 10.1371/journal.pgen.1004974] [Citation(s) in RCA: 46] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/11/2014] [Accepted: 12/23/2014] [Indexed: 02/07/2023] Open
Abstract
Regulated nuclear entry of clock proteins is a conserved feature of eukaryotic circadian clocks and serves to separate the phase of mRNA activation from mRNA repression in the molecular feedback loop. In Drosophila, nuclear entry of the clock proteins, PERIOD (PER) and TIMELESS (TIM), is tightly controlled, and impairments of this process produce profound behavioral phenotypes. We report here that nuclear entry of PER-TIM in clock cells, and consequently behavioral rhythms, require a specific member of a classic nuclear import pathway, Importin α1 (IMPα1). In addition to IMPα1, rhythmic behavior and nuclear expression of PER-TIM require a specific nuclear pore protein, Nup153, and Ran-GTPase. IMPα1 can also drive rapid and efficient nuclear expression of TIM and PER in cultured cells, although the effect on PER is mediated by TIM. Mapping of interaction domains between IMPα1 and TIM/PER suggests that TIM is the primary cargo for the importin machinery. This is supported by attenuated interaction of IMPα1 with TIM carrying a mutation previously shown to prevent nuclear entry of TIM and PER. TIM is detected at the nuclear envelope, and computational modeling suggests that it contains HEAT-ARM repeats typically found in karyopherins, consistent with its role as a co-transporter for PER. These findings suggest that although PER is the major timekeeper of the clock, TIM is the primary target of nuclear import mechanisms. Thus, the circadian clock uses specific components of the importin pathway with a novel twist in that TIM serves a karyopherin-like role for PER. In Drosophila, circadian rhythms are driven by a negative feedback loop that includes the key regulators, period (per) and timeless (tim). To generate this feedback loop, PER and TIM proteins first accumulate in the cytoplasm and then translocate to the nucleus where PER represses transcription. Thus, the nuclear import of PER-TIM proteins is a critical step to separate the phases of activation and repression of mRNA synthesis. In this study, we discovered that a member of the nuclear import machinery, importin α1 is an essential component of this feedback loop. Flies lacking importin α1 (IMPα1) display arrhythmic behavior and cytoplasmic expression of both PER and TIM at all times. In cultured S2 cells, IMPα1 expression directly facilitates nuclear import of TIM, but the effect on PER appears to be indirect. TIM expression is detected at the nuclear envelope and it interacts with other components of the nuclear transport machinery, which we show are also required for nuclear expression of TIM-PER and for behavioral rhythms. Our results thus suggest that TIM functions to link PER to the nuclear import machinery through IMPα1. Altogether, this study provides the mechanistic basis of a crucial step in the circadian clock mechanism.
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Affiliation(s)
- A. Reum Jang
- Howard Hughes Medical Institute, Perelman School of Medicine at the University of Pennsylvania, Philadelphia, Pennsylvania, United States of America
| | - Katarina Moravcevic
- Howard Hughes Medical Institute, Perelman School of Medicine at the University of Pennsylvania, Philadelphia, Pennsylvania, United States of America
| | - Lino Saez
- Laboratory of Genetics, The Rockefeller University, New York, New York, United States of America
| | - Michael W. Young
- Laboratory of Genetics, The Rockefeller University, New York, New York, United States of America
| | - Amita Sehgal
- Howard Hughes Medical Institute, Perelman School of Medicine at the University of Pennsylvania, Philadelphia, Pennsylvania, United States of America
- * E-mail:
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17
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Tataroglu O, Emery P. The molecular ticks of the Drosophila circadian clock. CURRENT OPINION IN INSECT SCIENCE 2015; 7:51-57. [PMID: 26120561 PMCID: PMC4480617 DOI: 10.1016/j.cois.2015.01.002] [Citation(s) in RCA: 81] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/04/2023]
Abstract
Drosophila is a powerful model to understand the mechanisms underlying circadian rhythms. The Drosophila molecular clock is comprised of transcriptional feedback loops. The expressions of the critical transcriptional activator CLK and its repressors PER and TIM are under tight transcriptional control. However, posttranslational modification of these proteins and regulation of their stability are critical to their function and to the generation of 24-hr period rhythms. We review here recent progress made in our understanding of PER, TIM and CLK posttranslational control. We also review recent studies that are uncovering the importance of novel regulatory mechanisms that affect mRNA stability and translation of circadian pacemaker proteins and their output.
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18
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Lee E, Kim EY. A role for timely nuclear translocation of clock repressor proteins in setting circadian clock speed. Exp Neurobiol 2014; 23:191-9. [PMID: 25258565 PMCID: PMC4174609 DOI: 10.5607/en.2014.23.3.191] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/25/2014] [Revised: 04/17/2014] [Accepted: 04/19/2014] [Indexed: 11/19/2022] Open
Abstract
By means of a circadian clock system, all the living organisms on earth including human beings can anticipate the environmental rhythmic changes such as light/dark and warm/cold periods in a daily as well as in a yearly manner. Anticipating such environmental changes provide organisms with survival benefits via manifesting behavior and physiology at an advantageous time of the day and year. Cell-autonomous circadian oscillators, governed by transcriptional feedback loop composed of positive and negative elements, are organized into a hierarchical system throughout the organisms and generate an oscillatory expression of a clock gene by itself as well as clock controlled genes (ccgs) with a 24 hr periodicity. In the feedback loop, hetero-dimeric transcription factor complex induces the expression of negative regulatory proteins, which in turn represses the activity of transcription factors to inhibit their own transcription. Thus, for robust oscillatory rhythms of the expression of clock genes as well as ccgs, the precise control of subcellular localization and/or timely translocation of core clock protein are crucial. Here, we discuss how sub-cellular localization and nuclear translocation are controlled in a time-specific manner focusing on the negative regulatory clock proteins.
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Affiliation(s)
- Euna Lee
- Department of Biomedical Sciences, Department of Brain Science, Ajou University School of Medicine, Suwon 443-380, Korea
| | - Eun Young Kim
- Department of Biomedical Sciences, Department of Brain Science, Ajou University School of Medicine, Suwon 443-380, Korea
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19
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Mulekar JJ, Huq E. Expanding roles of protein kinase CK2 in regulating plant growth and development. JOURNAL OF EXPERIMENTAL BOTANY 2014; 65:2883-93. [PMID: 24307718 DOI: 10.1093/jxb/ert401] [Citation(s) in RCA: 37] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/17/2023]
Abstract
Protein kinase CK2 (formerly known as casein kinase II) is a ubiquitious Ser/Thr kinase present in all eukaryotes. The α (catalytic) and β (regulatory) subunits of CK2 exist both as a tetrameric holoenzyme and as monomers in eukaryotic cells. CK2 has been implicated in multiple developmental and stress-responsive pathways including light signalling and circadian clock in plants. Recent studies using CK2 knockout and dominant negative mutants in Arabidopsis have uncovered new roles for this enzyme. CK2 substrates that have been identified so far are primarily transcription factors or regulatory proteins. CK2-mediated phosphorylation of these factors often results in alteration of the protein function including changes in the DNA-binding affinity, dimerization, stability, protein-protein interactions, and subcellular localization. CK2 has evolved as an essential housekeeping kinase in plants that modifies protein function in a dynamic way. This review summarizes the current knowledge of the role of CK2 in plant development.
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Affiliation(s)
- Jidnyasa Jayant Mulekar
- Department of Molecular Biosciences and Institute for Cellular and Molecular Biology, University of Texas at Austin, Austin, TX 78712, USA
| | - Enamul Huq
- Department of Molecular Biosciences and Institute for Cellular and Molecular Biology, University of Texas at Austin, Austin, TX 78712, USA
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20
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Drosophila mbm is a nucleolar myc and casein kinase 2 target required for ribosome biogenesis and cell growth of central brain neuroblasts. Mol Cell Biol 2014; 34:1878-91. [PMID: 24615015 DOI: 10.1128/mcb.00658-13] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Proper cell growth is a prerequisite for maintaining repeated cell divisions. Cells need to translate information about intracellular nutrient availability and growth cues from energy-sensing organs into growth-promoting processes, such as sufficient supply with ribosomes for protein synthesis. Mutations in the mushroom body miniature (mbm) gene impair proliferation of neural progenitor cells (neuroblasts) in the central brain of Drosophila melanogaster. Yet the molecular function of Mbm has so far been unknown. Here we show that mbm does not affect the molecular machinery controlling asymmetric cell division of neuroblasts but instead decreases their cell size. Mbm is a nucleolar protein required for small ribosomal subunit biogenesis in neuroblasts. Accordingly, levels of protein synthesis are reduced in mbm neuroblasts. Mbm expression is transcriptionally regulated by Myc, which, among other functions, relays information from nutrient-dependent signaling pathways to ribosomal gene expression. At the posttranslational level, Mbm becomes phosphorylated by casein kinase 2 (CK2), which has an impact on localization of the protein. We conclude that Mbm is a new part of the Myc target network involved in ribosome biogenesis, which, together with CK2-mediated signals, enables neuroblasts to synthesize sufficient amounts of proteins required for proper cell growth.
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21
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Garbe DS, Fang Y, Zheng X, Sowcik M, Anjum R, Gygi SP, Sehgal A. Cooperative interaction between phosphorylation sites on PERIOD maintains circadian period in Drosophila. PLoS Genet 2013; 9:e1003749. [PMID: 24086144 PMCID: PMC3784489 DOI: 10.1371/journal.pgen.1003749] [Citation(s) in RCA: 48] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/15/2013] [Accepted: 07/10/2013] [Indexed: 12/26/2022] Open
Abstract
Circadian rhythms in Drosophila rely on cyclic regulation of the period (per) and timeless (tim) clock genes. The molecular cycle requires rhythmic phosphorylation of PER and TIM proteins, which is mediated by several kinases and phosphatases such as Protein Phosphatase-2A (PP2A) and Protein Phosphatase-1 (PP1). Here, we used mass spectrometry to identify 35 “phospho-occupied” serine/threonine residues within PER, 24 of which are specifically regulated by PP1/PP2A. We found that cell culture assays were not good predictors of protein function in flies and so we generated per transgenes carrying phosphorylation site mutations and tested for rescue of the per01 arrhythmic phenotype. Surprisingly, most transgenes restore wild type rhythms despite carrying mutations in several phosphorylation sites. One particular transgene, in which T610 and S613 are mutated to alanine, restores daily rhythmicity, but dramatically lengthens the period to ∼30 hrs. Interestingly, the single S613A mutation extends the period by 2–3 hours, while the single T610A mutation has a minimal effect, suggesting these phospho-residues cooperate to control period length. Conservation of S613 from flies to humans suggests that it possesses a critical clock function, and mutational analysis of residues surrounding T610/S613 implicates the entire region in determining circadian period. Biochemical and immunohistochemical data indicate defects in overall phosphorylation and altered timely degradation of PER carrying the double or single S613A mutation(s). The PER-T610A/S613A mutant also alters CLK phosphorylation and CLK-mediated output. Lastly, we show that a mutation at a previously identified site, S596, is largely epistatic to S613A, suggesting that S613 negatively regulates phosphorylation at S596. Together these data establish functional significance for a new domain of PER, demonstrate that cooperativity between phosphorylation sites maintains PER function, and support a model in which specific phosphorylated regions regulate others to control circadian period. Circadian rhythms coordinate an organism's activities with its environment to ensure appropriate physiology and behavior at the relevant times of day. In Drosophila melanogaster, the central molecular clock is regulated by transcriptional and translational feedback loops that drive rhythmic waves of gene expression. Additionally, the clock is controlled by post-translational modifications, including phosphorylation of a core negative regulator, PERIOD (PER). Using a proteomic approach, we identified two key phosphorylation sites within PER that cooperate to establish proper daily rhythms. Mutation of both residues results in a period of ∼30 hrs, whereas single mutant phenotypes are less severe suggesting these sites normally cooperate to control the pace of the clock. Biochemical and immunohistochemical data demonstrate that altered PER phosphorylation and changes in protein stability give rise to behavioral defects. Other mutations in the vicinity of the two sites above also alter circadian period, thereby confirming a new regulatory domain of PER. Our results also suggest that the phospho-residues identified in this study regulate phosphorylation in another important domain of PER. Together our data establish that cooperativity between neighboring phospho-sites as well as interactions between different phosphorylated domains of PER control its stability and overall circadian periodicity.
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Affiliation(s)
- David S. Garbe
- Department of Neuroscience, University of Pennsylvania School of Medicine, Translational Research Center, Philadelphia, Pennsylvania, United States of America
| | - Yanshan Fang
- Department of Neuroscience, University of Pennsylvania School of Medicine, Translational Research Center, Philadelphia, Pennsylvania, United States of America
| | - Xiangzhong Zheng
- Department of Neuroscience, University of Pennsylvania School of Medicine, Translational Research Center, Philadelphia, Pennsylvania, United States of America
| | - Mallory Sowcik
- Department of Neuroscience, University of Pennsylvania School of Medicine, Translational Research Center, Philadelphia, Pennsylvania, United States of America
| | - Rana Anjum
- Department of Cell Biology, Harvard Medical School, Boston, Massachusetts, United States of America
| | - Steven P. Gygi
- Department of Cell Biology, Harvard Medical School, Boston, Massachusetts, United States of America
| | - Amita Sehgal
- Department of Neuroscience, University of Pennsylvania School of Medicine, Translational Research Center, Philadelphia, Pennsylvania, United States of America
- Howard Hughes Medical Institute, University of Pennsylvania School of Medicine, Translational Research Center, Philadelphia, Pennsylvania, United States of America
- * E-mail:
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22
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Szabó Á, Papin C, Zorn D, Ponien P, Weber F, Raabe T, Rouyer F. The CK2 kinase stabilizes CLOCK and represses its activity in the Drosophila circadian oscillator. PLoS Biol 2013; 11:e1001645. [PMID: 24013921 PMCID: PMC3754892 DOI: 10.1371/journal.pbio.1001645] [Citation(s) in RCA: 35] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/11/2013] [Accepted: 07/19/2013] [Indexed: 12/21/2022] Open
Abstract
Phosphorylation is a pivotal regulatory mechanism for protein stability and activity in circadian clocks regardless of their evolutionary origin. It determines the speed and strength of molecular oscillations by acting on transcriptional activators and their repressors, which form negative feedback loops. In Drosophila, the CK2 kinase phosphorylates and destabilizes the PERIOD (PER) and TIMELESS (TIM) proteins, which inhibit CLOCK (CLK) transcriptional activity. Here we show that CK2 also targets the CLK activator directly. Downregulating the activity of the catalytic α subunit of CK2 induces CLK degradation, even in the absence of PER and TIM. Unexpectedly, the regulatory β subunit of the CK2 holoenzyme is not required for the regulation of CLK stability. In addition, downregulation of CK2α activity decreases CLK phosphorylation and increases per and tim transcription. These results indicate that CK2 inhibits CLK degradation while reducing its activity. Since the CK1 kinase promotes CLK degradation, we suggest that CLK stability and transcriptional activity result from counteracting effects of CK1 and CK2.
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Affiliation(s)
- Áron Szabó
- Institut de Neurobiologie Alfred Fessard, Centre National de la Recherche Scientifique Unité Propre de Recherche 3294, Gif-sur-Yvette, France
- Département de Biologie, Université Paris Sud, Orsay, France
| | - Christian Papin
- Institut de Neurobiologie Alfred Fessard, Centre National de la Recherche Scientifique Unité Propre de Recherche 3294, Gif-sur-Yvette, France
- Département de Biologie, Université Paris Sud, Orsay, France
| | - Daniela Zorn
- Heidelberg University, Biochemistry Center (BZH), Im Neuenheimer Feld 328, Heidelberg, Germany
| | - Prishila Ponien
- Institut de Chimie des Substances Naturelles, CNRS UPR2301, Gif-sur-Yvette, France
- IMAGIF, Centre de Recherche de Gif, Gif-sur-Yvette, France
| | - Frank Weber
- Heidelberg University, Biochemistry Center (BZH), Im Neuenheimer Feld 328, Heidelberg, Germany
| | - Thomas Raabe
- University of Wuerzburg, Institute of Medical Radiation and Cell Research, Wuerzburg, Germany
| | - François Rouyer
- Institut de Neurobiologie Alfred Fessard, Centre National de la Recherche Scientifique Unité Propre de Recherche 3294, Gif-sur-Yvette, France
- Département de Biologie, Université Paris Sud, Orsay, France
- * E-mail:
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23
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Di Cara F, King-Jones K. How clocks and hormones act in concert to control the timing of insect development. Curr Top Dev Biol 2013; 105:1-36. [PMID: 23962837 DOI: 10.1016/b978-0-12-396968-2.00001-4] [Citation(s) in RCA: 38] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
During the last century, insect model systems have provided fascinating insights into the endocrinology and developmental biology of all animals. During the insect life cycle, molts and metamorphosis delineate transitions from one developmental stage to the next. In most insects, pulses of the steroid hormone ecdysone drive these developmental transitions by activating signaling cascades in target tissues. In holometabolous insects, ecdysone triggers metamorphosis, the remarkable remodeling of an immature larva into a sexually mature adult. The input from another developmental hormone, juvenile hormone (JH), is required to repress metamorphosis by promoting juvenile fates until the larva has acquired sufficient nutrients to survive metamorphosis. Ecdysone and JH act together as key endocrine timers to precisely control the onset of developmental transitions such as the molts, pupation, or eclosion. In this review, we will focus on the role of the endocrine system and the circadian clock, both individually and together, in temporally regulating insect development. Since this is not a coherent field, we will review recent developments that serve as examples to illuminate this complex topic. First, we will consider studies conducted in Rhodnius that revealed how circadian pathways exert temporal control over the production and release of ecdysone. We will then take a look at molecular and genetic data that revealed the presence of two circadian clocks, located in the brain and the prothoracic gland, that regulate eclosion rhythms in Drosophila. In this context, we will also review recent developments that examined how the ecdysone hierarchy delays the differentiation of the crustacean cardioactive peptide (CCAP) neurons, an event that is critical for the timing of ecdysis and eclosion. Finally, we will discuss some recent findings that transformed our understanding of JH function.
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Affiliation(s)
- Francesca Di Cara
- Department of Biological Sciences, University of Alberta, Edmonton, Alberta, Canada
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CULLIN-3 controls TIMELESS oscillations in the Drosophila circadian clock. PLoS Biol 2012; 10:e1001367. [PMID: 22879814 PMCID: PMC3413713 DOI: 10.1371/journal.pbio.1001367] [Citation(s) in RCA: 46] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/01/2012] [Accepted: 06/14/2012] [Indexed: 12/17/2022] Open
Abstract
The ubiquitin ligases CUL-3 and SLMB collaborate to regulate the Drosophila circadian clock by controlling TIMELESS oscillations. Eukaryotic circadian clocks rely on transcriptional feedback loops. In Drosophila, the PERIOD (PER) and TIMELESS (TIM) proteins accumulate during the night, inhibit the activity of the CLOCK (CLK)/CYCLE (CYC) transcriptional complex, and are degraded in the early morning. The control of PER and TIM oscillations largely depends on post-translational mechanisms. They involve both light-dependent and light-independent pathways that rely on the phosphorylation, ubiquitination, and proteasomal degradation of the clock proteins. SLMB, which is part of a CULLIN-1-based E3 ubiquitin ligase complex, is required for the circadian degradation of phosphorylated PER. We show here that CULLIN-3 (CUL-3) is required for the circadian control of PER and TIM oscillations. Expression of either Cul-3 RNAi or dominant negative forms of CUL-3 in the clock neurons alters locomotor behavior and dampens PER and TIM oscillations in light-dark cycles. In constant conditions, CUL-3 deregulation induces behavioral arrhythmicity and rapidly abolishes TIM cycling, with slower effects on PER. CUL-3 affects TIM accumulation more strongly in the absence of PER and forms protein complexes with hypo-phosphorylated TIM. In contrast, SLMB affects TIM more strongly in the presence of PER and preferentially associates with phosphorylated TIM. CUL-3 and SLMB show additive effects on TIM and PER, suggesting different roles for the two ubiquitination complexes on PER and TIM cycling. This work thus shows that CUL-3 is a new component of the Drosophila clock, which plays an important role in the control of TIM oscillations. Circadian clocks adjust the physiology and behavior of organisms to the day/night cycle and rely on molecular feedback loops that generate daily oscillations of transcription. In the Drosophila fruit fly, the PERIOD (PER) and TIMELESS (TIM) proteins coordinate the clock–they accumulate during the night, form a complex, and repress their own gene expression in the early morning. The temporal control of this oscillation involves the phosphorylation, ubiquitination, and proteasomal degradation of the PER and TIM proteins. The SUPERNUMERARY LIMBS (SLMB) ubiquitin ligase is known to play a key role in controlling the degradation of phosphorylated PER and TIM. In this study we investigated the role of another ubiquitin ligase, CULLIN-3 (CUL-3). We found that inhibition of CUL-3 activity results in the abolition of rest/activity rhythms in flies and flattens the PER and TIM oscillations. CUL-3 physically interacts and forms a complex with a lowphosphorylated version of TIM in the absence of PER, thereby allowing its accumulation during the night. In contrast, when PER is present SLMB preferentially interacts with phosphorylated TIM, favoring its degradation. The results suggest that CUL-3 and SLMB share the work to control the oscillations of the PER and TIM proteins during the day/night cycle.
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Özkaya Ö, Rosato E. The Circadian Clock of the Fly: A Neurogenetics Journey Through Time. GENE-ENVIRONMENT INTERPLAY 2012; 77:79-123. [DOI: 10.1016/b978-0-12-387687-4.00004-0] [Citation(s) in RCA: 74] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
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26
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Kinases and phosphatases in the mammalian circadian clock. FEBS Lett 2011; 585:1393-9. [DOI: 10.1016/j.febslet.2011.02.038] [Citation(s) in RCA: 135] [Impact Index Per Article: 10.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/19/2010] [Revised: 02/23/2011] [Accepted: 02/28/2011] [Indexed: 12/28/2022]
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Pegoraro M, Tauber E. Animal clocks: a multitude of molecular mechanisms for circadian timekeeping. WILEY INTERDISCIPLINARY REVIEWS-RNA 2011; 2:312-20. [PMID: 21957012 DOI: 10.1002/wrna.58] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
Studies in various model organisms reveal that the expression level of a substantial part of the transcriptome and the proteome exhibits regular daily oscillations. These oscillations are translated to physiological and behavioral rhythms allowing organisms to efficiently anticipate and respond to the daily and seasonally changing environment (e.g., temperature and light). A rather small subset of evolutionary conserved genes drives these oscillations and constitutes the core molecular circadian clock. Here, we review the multiple mechanisms that coexist at various molecular and cellular levels and are involved in the metazoan circadian clock, including transcription/translation negative feedback loops, post-transcriptional and post-translational modifications, intracellular translocation, and intercellular signaling.
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Affiliation(s)
- Mirko Pegoraro
- Department of Genetics, University of Leicester, Leicester, UK
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28
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Portolés S, Más P. The functional interplay between protein kinase CK2 and CCA1 transcriptional activity is essential for clock temperature compensation in Arabidopsis. PLoS Genet 2010; 6:e1001201. [PMID: 21079791 PMCID: PMC2973838 DOI: 10.1371/journal.pgen.1001201] [Citation(s) in RCA: 86] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/18/2010] [Accepted: 10/07/2010] [Indexed: 01/17/2023] Open
Abstract
Circadian rhythms are daily biological oscillations driven by an endogenous mechanism known as circadian clock. The protein kinase CK2 is one of the few clock components that is evolutionary conserved among different taxonomic groups. CK2 regulates the stability and nuclear localization of essential clock proteins in mammals, fungi, and insects. Two CK2 regulatory subunits, CKB3 and CKB4, have been also linked with the Arabidopsis thaliana circadian system. However, the biological relevance and the precise mechanisms of CK2 function within the plant clockwork are not known. By using ChIP and Double-ChIP experiments together with in vivo luminescence assays at different temperatures, we were able to identify a temperature-dependent function for CK2 modulating circadian period length. Our study uncovers a previously unpredicted mechanism for CK2 antagonizing the key clock regulator CIRCADIAN CLOCK-ASSOCIATED 1 (CCA1). CK2 activity does not alter protein accumulation or subcellular localization but interferes with CCA1 binding affinity to the promoters of the oscillator genes. High temperatures enhance the CCA1 binding activity, which is precisely counterbalanced by the CK2 opposing function. Altering this balance by over-expression, mutation, or pharmacological inhibition affects the temperature compensation profile, providing a mechanism by which plants regulate circadian period at changing temperatures. Therefore, our study establishes a new model demonstrating that two opposing and temperature-dependent activities (CCA1-CK2) are essential for clock temperature compensation in Arabidopsis.
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Affiliation(s)
- Sergi Portolés
- Consortium CSIC-IRTA-UAB, Centre for Research in Agricultural Genomics (CRAG), Department of Plant Molecular Genetics, Barcelona, Spain
| | - Paloma Más
- Consortium CSIC-IRTA-UAB, Centre for Research in Agricultural Genomics (CRAG), Department of Plant Molecular Genetics, Barcelona, Spain
- * E-mail:
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Abstract
Circadian clocks organize behavior and physiology to adapt to daily environmental cycles. Genetic approaches in the fruit fly, Drosophila melanogaster, have revealed widely conserved molecular gears of these 24-h timers. Yet much less is known about how these cell-autonomous clocks confer temporal information to modulate cellular functions. Here we discuss our current knowledge of circadian clock function in Drosophila, providing an overview of the molecular underpinnings of circadian clocks. We then describe the neural network important for circadian rhythms of locomotor activity, including how these molecular clocks might influence neuronal function. Finally, we address a range of behaviors and physiological systems regulated by circadian clocks, including discussion of specific peripheral oscillators and key molecular effectors where they have been described. These studies reveal a remarkable complexity to circadian pathways in this "simple" model organism.
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Affiliation(s)
- Ravi Allada
- Department of Neurobiology and Physiology, Northwestern University, Evanston, IL 60208, USA.
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A role for the PERIOD:PERIOD homodimer in the Drosophila circadian clock. PLoS Biol 2009; 7:e3. [PMID: 19402744 PMCID: PMC2671555 DOI: 10.1371/journal.pbio.1000003] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/06/2008] [Accepted: 11/12/2008] [Indexed: 01/13/2023] Open
Abstract
Circadian clocks in eukaryotes rely on transcriptional feedback loops, in which clock genes repress their own transcription resulting in molecular oscillations with a period of ∼24 h. In Drosophila, the clock proteins Period (PER) and Timeless (TIM) operate in such a feedback loop, whereby they first accumulate in the cytoplasm of clock cells as a heterodimer. Nuclear translocation of the complex or the individual PER and TIM proteins is followed by repression of per and tim transcription, whereby PER seems to act as the prime repressor. We found that in addition to PER:TIM complexes, functional PER:PER homodimers exist in flies. Specific disruption of PER homodimers results in drastically impaired behavioral and molecular rhythmicity, pointing the biological importance of this clock protein complex. Analysis of PER subcellular distribution and repressor competence in the PER dimer mutant revealed defects in PER nuclear translocation and a disruption of rhythmic period transcription. The striking similarity of these phenotypes with that of reduced CKII activity suggests that the formation or function of the PER dimer is closely linked to this kinase. Our results confirm a previous structural model for PER and provide strong evidence that PER homodimers are important for circadian clock function. The current models of circadian clocks in flies and mammals involve the formation of complexes between clock proteins in the cytoplasm. These complexes are usually heterodimers (that is, made up of two different clock proteins) and appear to enter the nucleus at certain times of the circadian day in order to shut down their own gene expression by deactivating specific transcription factors. After progressive phosphorylation the repressor proteins eventually are degraded so that a new cycle of transcription can begin. Here we present evidence that in addition to heterodimeric complexes, the clock protein PERIOD (PER) also forms homodimers (pairs of identical proteins). Based on a structural model a PER mutant was designed, which is not able to form homodimers but can still bind to its partner TIMELESS (TIM). Flies expressing this mutant PER protein show abnormal clock function in regard to PER nuclear translocation, repressor activity, and behavioral rhythms. The circadian clock model in flies therefore needs to be extended by adding the PER:PER homodimer as a functional unit. Recent structural studies with mammalian PER proteins suggest that homodimers between clock proteins are an important general feature of eukaryotic clocks. The circadian molecular clock model needs to be extended by adding the PERIOD:PERIOD homodimer as a functional unit in rhythm generation in Drosophila. Blocking this dimerization leads to faulty nuclear localization, reduced repressor activity, and impaired behavioral rhythms.
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