1
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Avila A, Zhang SL. A circadian clock regulates the blood-brain barrier across phylogeny. VITAMINS AND HORMONES 2024; 126:241-287. [PMID: 39029975 DOI: 10.1016/bs.vh.2024.04.004] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 07/21/2024]
Abstract
As the central regulatory system of an organism, the brain is responsible for overseeing a wide variety of physiological processes essential for an organism's survival. To maintain the environment necessary for neurons to function, the brain requires highly selective uptake and elimination of specific molecules through the blood-brain barrier (BBB). As an organism's activities vary throughout the day, how does the BBB adapt to meet the changing needs of the brain? A mechanism is through temporal regulation of BBB permeability via its circadian clock, which will be the focal point of this chapter. To comprehend the circadian clock's role within the BBB, we will first examine the anatomy of the BBB and the transport mechanisms enabling it to fulfill its role as a restrictive barrier. Next, we will define the circadian clock, and the discussion will encompass an introduction to circadian rhythms, the Transcription-Translation Feedback Loop (TTFL) as the mechanistic basis of circadian timekeeping, and the organization of tissue clocks found in organisms. Then, we will cover the role of the circadian rhythms in regulating the cellular mechanisms and functions of the BBB. We discuss the implications of this regulation in influencing sleep behavior, the progression of neurodegenerative diseases, and finally drug delivery for treatment of neurological diseases.
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Affiliation(s)
- Ashley Avila
- Cell Biology Department, Emory University, Atlanta, GA, United States
| | - Shirley L Zhang
- Cell Biology Department, Emory University, Atlanta, GA, United States.
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2
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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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3
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Keshvari M, Nejadtaghi M, Hosseini-Beheshti F, Rastqar A, Patel N. Exploring the role of circadian clock gene and association with cancer pathophysiology. Chronobiol Int 2019; 37:151-175. [PMID: 31791146 DOI: 10.1080/07420528.2019.1681440] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Abstract
Most of the processes that occur in the mind and body follow natural rhythms. Those with a cycle length of about one day are called circadian rhythms. These rhythms are driven by a system of self-sustained clocks and are entrained by environmental cues such as light-dark cycles as well as food intake. In mammals, the circadian clock system is hierarchically organized such that the master clock in the suprachiasmatic nuclei of the hypothalamus integrates environmental information and synchronizes the phase of oscillators in peripheral tissues.The circadian system is responsible for regulating a variety of physiological and behavioral processes, including feeding behavior and energy metabolism. Studies revealed that the circadian clock system consists primarily of a set of clock genes. Several genes control the biological clock, including BMAL1, CLOCK (positive regulators), CRY1, CRY2, PER1, PER2, and PER3 (negative regulators) as indicators of the peripheral clock.Circadian has increasingly become an important area of medical research, with hundreds of studies pointing to the body's internal clocks as a factor in both health and disease. Thousands of biochemical processes from sleep and wakefulness to DNA repair are scheduled and dictated by these internal clocks. Cancer is an example of health problems where chronotherapy can be used to improve outcomes and deliver a higher quality of care to patients.In this article, we will discuss knowledge about molecular mechanisms of the circadian clock and the role of clocks in physiology and pathophysiology of concerns.
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Affiliation(s)
- Mahtab Keshvari
- Department of Pharmacology and Physiology, Faculty of Medicine and Health Sciences, University of Sherbrooke, Sherbrooke, Canada
| | - Mahdieh Nejadtaghi
- Department of Medical Genetics, faculty of Medical Sciences, Tarbiat Modares University, Tehran, Iran
| | | | - Ali Rastqar
- Department of Psychiatry and Neuroscience, Université Laval, Quebec, Canada
| | - Niraj Patel
- Centre de Recherche CERVO, Université Laval, Québec, Canada
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4
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Analysis of the circadian transcriptome of the Antarctic krill Euphausia superba. Sci Rep 2019; 9:13894. [PMID: 31554872 PMCID: PMC6761102 DOI: 10.1038/s41598-019-50282-1] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/21/2019] [Accepted: 09/10/2019] [Indexed: 11/09/2022] Open
Abstract
Antarctic krill (Euphausia superba) is a high latitude pelagic organism which plays a central role in the Southern Ocean ecosystem. E. superba shows daily and seasonal rhythms in physiology and behaviour, which are synchronized with the environmental cycles of its habitat. Recently, the main components of the krill circadian machinery have been identified and characterized. However, the exact mechanisms through which the endogenous timing system operates the control and regulation of the overt rhythms remains only partially understood. Here we investigate the involvement of the circadian clock in the temporal orchestration of gene expression by using a newly developed version of a krill microarray platform. The analysis of transcriptome data from krill exposed to both light-dark cycles (LD 18:6) and constant darkness (DD), has led to the identification of 1,564 putative clock-controlled genes. A remarkably large proportion of such genes, including several clock components (clock, period, cry2, vrille, and slimb), show oscillatory expression patterns in DD, with a periodicity shorter than 24 hours. Energy-storage pathways appear to be regulated by the endogenous clock in accordance with their ecological relevance in daily energy managing and overwintering. Our results provide the first representation of the krill circadian transcriptome under laboratory, free-running conditions.
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5
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FRQ-CK1 interaction determines the period of circadian rhythms in Neurospora. Nat Commun 2019; 10:4352. [PMID: 31554810 PMCID: PMC6761100 DOI: 10.1038/s41467-019-12239-w] [Citation(s) in RCA: 25] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/01/2019] [Accepted: 08/28/2019] [Indexed: 01/25/2023] Open
Abstract
Circadian clock mechanisms have been extensively investigated but the main rate-limiting step that determines circadian period remains unclear. Formation of a stable complex between clock proteins and CK1 is a conserved feature in eukaryotic circadian mechanisms. Here we show that the FRQ-CK1 interaction, but not FRQ stability, correlates with circadian period in Neurospora circadian clock mutants. Mutations that specifically affect the FRQ-CK1 interaction lead to severe alterations in circadian period. The FRQ-CK1 interaction has two roles in the circadian negative feedback loop. First, it determines the FRQ phosphorylation profile, which regulates FRQ stability and also feeds back to either promote or reduce the interaction itself. Second, it determines the efficiency of circadian negative feedback process by mediating FRQ-dependent WC phosphorylation. Our conclusions are further supported by mathematical modeling and in silico experiments. Together, these results suggest that the FRQ-CK1 interaction is a major rate-limiting step in circadian period determination. Circadian clocks control daily rhythms of molecular and physiological activities. Here, the authors show that the interaction between proteins FRQ and CK1, rather than FRQ stability, is a major rate-limiting step in circadian period determination in the model fungus Neurospora.
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6
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Millius A, Ode KL, Ueda HR. A period without PER: understanding 24-hour rhythms without classic transcription and translation feedback loops. F1000Res 2019; 8. [PMID: 31031966 PMCID: PMC6468715 DOI: 10.12688/f1000research.18158.1] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Accepted: 04/09/2019] [Indexed: 01/08/2023] Open
Abstract
Since Ronald Konopka and Seymour Benzer's discovery of the gene Period in the 1970s, the circadian rhythm field has diligently investigated regulatory mechanisms and intracellular transcriptional and translation feedback loops involving Period, and these investigations culminated in a 2017 Nobel Prize in Physiology or Medicine for Michael W. Young, Michael Rosbash, and Jeffrey C. Hall. Although research on 24-hour behavior rhythms started with Period, a series of discoveries in the past decade have shown us that post-transcriptional regulation and protein modification, such as phosphorylation and oxidation, are alternatives ways to building a ticking clock.
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Affiliation(s)
- Arthur Millius
- Laboratory for Synthetic Biology, RIKEN Center for Biosystems Dynamics Research, 1-3 Yamadaoka, Suita, Osaka, 565-0871, Japan.,Laboratory of Systems Immunology and Laboratory of Host Defense, Immunology Frontier Research Center, Osaka University, Suita, Osaka, 565-0871, Japan
| | - Koji L Ode
- Department of Systems Pharmacology, Graduate School of Medicine, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo, 113-0033, Japan
| | - Hiroki R Ueda
- Laboratory for Synthetic Biology, RIKEN Center for Biosystems Dynamics Research, 1-3 Yamadaoka, Suita, Osaka, 565-0871, Japan.,Department of Systems Pharmacology, Graduate School of Medicine, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo, 113-0033, Japan
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7
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Loros JJ. Principles of the animal molecular clock learned from Neurospora. Eur J Neurosci 2019; 51:19-33. [PMID: 30687965 DOI: 10.1111/ejn.14354] [Citation(s) in RCA: 25] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/31/2018] [Revised: 12/10/2018] [Accepted: 12/13/2018] [Indexed: 12/28/2022]
Abstract
Study of Neurospora, a model system evolutionarily related to animals and sharing a circadian system having nearly identical regulatory architecture to that of animals, has advanced our understanding of all circadian rhythms. Work on the molecular bases of the Oscillator began in Neurospora before any clock genes were cloned and provided the second example of a clock gene, frq, as well as the first direct experimental proof that the core of the Oscillator was built around a transcriptional translational negative feedback loop (TTFL). Proof that FRQ was a clock component provided the basis for understanding how light resets the clock, and this in turn provided the generally accepted understanding for how light resets all animal and fungal clocks. Experiments probing the mechanism of light resetting led to the first identification of a heterodimeric transcriptional activator as the positive element in a circadian feedback loop, and to the general description of the fungal/animal clock as a single step TTFL. The common means through which DNA damage impacts the Oscillator in fungi and animals was first described in Neurospora. Lastly, the systematic study of Output was pioneered in Neurospora, providing the vocabulary and conceptual framework for understanding how Output works in all cells. This model system has contributed to the current appreciation of the role of Intrinsic Disorder in clock proteins and to the documentation of the essential roles of protein post-translational modification, as distinct from turnover, in building a circadian clock.
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Affiliation(s)
- Jennifer J Loros
- Department of Biochemistry and Cell Biology, Geisel School of Medicine at Dartmouth, Hanover, New Hampshire.,Department of Molecular and Systems Biology, Geisel School of Medicine at Dartmouth, Hanover, New Hampshire
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8
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Venkatesan A, Fan JY, Bouyain S, Price JL. The Circadian tau Mutation in Casein Kinase 1 Is Part of a Larger Domain That Can Be Mutated to Shorten Circadian Period. Int J Mol Sci 2019; 20:E813. [PMID: 30769795 PMCID: PMC6412653 DOI: 10.3390/ijms20040813] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/31/2019] [Revised: 01/31/2019] [Accepted: 02/11/2019] [Indexed: 01/21/2023] Open
Abstract
Drosophila Double-time (DBT) phosphorylates the circadian protein Period (PER). The period-altering mutation tau, identified in hamster casein kinase I (CKIε) and created in Drosophila DBT, has been shown to shorten the circadian period in flies, as it does in hamsters. Since CKI often phosphorylates downstream of previously phosphorylated residues and the tau amino acid binds a negatively charged ion in X-ray crystal structures, this amino acid has been suggested to contribute to a phosphate recognition site for the substrate. Alternatively, the tau amino acid may affect a nuclear localization signal (NLS) with which it interacts. We mutated the residues that were close to or part of the phosphate recognition site or NLS. Flies expressing DBT with mutations of amino acids close to or part of either of these motifs produced a shortening of period, suggesting that a domain, including the phosphate recognition site or the NLS, can be mutated to produce the short period phenotype. Mutation of residues affecting internally placed residues produced a longer period, suggesting that a specific domain on the surface of the kinase might generate an interaction with a substrate or regulator, with short periods produced when the interaction is disrupted.
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Affiliation(s)
- Anandakrishnan Venkatesan
- Division of Molecular Biology and Biochemistry, School of Biological Sciences, University of Missouri-Kansas City, Kansas City, MO 64110, USA.
| | - Jin-Yuan Fan
- Division of Molecular Biology and Biochemistry, School of Biological Sciences, University of Missouri-Kansas City, Kansas City, MO 64110, USA.
| | - Samuel Bouyain
- Division of Molecular Biology and Biochemistry, School of Biological Sciences, University of Missouri-Kansas City, Kansas City, MO 64110, USA.
| | - Jeffrey L Price
- Division of Molecular Biology and Biochemistry, School of Biological Sciences, University of Missouri-Kansas City, Kansas City, MO 64110, USA.
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9
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Kim JK. Protein sequestration versus Hill-type repression in circadian clock models. IET Syst Biol 2018; 10:125-35. [PMID: 27444022 DOI: 10.1049/iet-syb.2015.0090] [Citation(s) in RCA: 59] [Impact Index Per Article: 9.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022] Open
Abstract
Circadian (∼24 h) clocks are self-sustained endogenous oscillators with which organisms keep track of daily and seasonal time. Circadian clocks frequently rely on interlocked transcriptional-translational feedback loops to generate rhythms that are robust against intrinsic and extrinsic perturbations. To investigate the dynamics and mechanisms of the intracellular feedback loops in circadian clocks, a number of mathematical models have been developed. The majority of the models use Hill functions to describe transcriptional repression in a way that is similar to the Goodwin model. Recently, a new class of models with protein sequestration-based repression has been introduced. Here, the author discusses how this new class of models differs dramatically from those based on Hill-type repression in several fundamental aspects: conditions for rhythm generation, robust network designs and the periods of coupled oscillators. Consistently, these fundamental properties of circadian clocks also differ among Neurospora, Drosophila, and mammals depending on their key transcriptional repression mechanisms (Hill-type repression or protein sequestration). Based on both theoretical and experimental studies, this review highlights the importance of careful modelling of transcriptional repression mechanisms in molecular circadian clocks.
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Affiliation(s)
- Jae Kyoung Kim
- Department of Mathematical Sciences, Korea Advanced Institute of Science and Technology, 291 Daehak-ro Yuseong-gu, Daejeon, 34141, Korea.
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10
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Ode KL, Ueda HR. Design Principles of Phosphorylation-Dependent Timekeeping in Eukaryotic Circadian Clocks. Cold Spring Harb Perspect Biol 2018; 10:cshperspect.a028357. [PMID: 29038116 DOI: 10.1101/cshperspect.a028357] [Citation(s) in RCA: 23] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
The circadian clock in cyanobacteria employs a posttranslational oscillator composed of a sequential phosphorylation-dephosphorylation cycle of KaiC protein, in which the dynamics of protein structural changes driven by temperature-compensated KaiC's ATPase activity are critical for determining the period. On the other hand, circadian clocks in eukaryotes employ transcriptional feedback loops as a core mechanism. In this system, the dynamics of protein accumulation and degradation affect the circadian period. However, recent studies of eukaryotic circadian clocks reveal that the mechanism controlling the circadian period can be independent of the regulation of protein abundance. Instead, the circadian substrate is often phosphorylated at multiple sites at flexible protein regions to induce structural changes. The phosphorylation is catalyzed by kinases that induce sequential multisite phosphorylation such as casein kinase 1 (CK1) with temperature-compensated activity. We propose that the design principles of phosphorylation-dependent circadian-period determination in eukaryotes may share characteristics with the posttranslational oscillator in cyanobacteria.
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Affiliation(s)
- Koji L Ode
- Department of Systems Pharmacology, Graduate School of Medicine, The University of Tokyo, Hongo 7-3-1, Bunkyo-ku, Tokyo 113-0033, Japan.,Laboratory for Synthetic Biology, RIKEN Quantitative Biology Center, 1-3 Yamadaoka, Suita, Osaka 565-0871, Japan
| | - Hiroki R Ueda
- Department of Systems Pharmacology, Graduate School of Medicine, The University of Tokyo, Hongo 7-3-1, Bunkyo-ku, Tokyo 113-0033, Japan.,Laboratory for Synthetic Biology, RIKEN Quantitative Biology Center, 1-3 Yamadaoka, Suita, Osaka 565-0871, Japan
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11
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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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12
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Wang Q, Abruzzi KC, Rosbash M, Rio DC. Striking circadian neuron diversity and cycling of Drosophila alternative splicing. eLife 2018; 7:35618. [PMID: 29863472 PMCID: PMC6025963 DOI: 10.7554/elife.35618] [Citation(s) in RCA: 22] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/01/2018] [Accepted: 05/31/2018] [Indexed: 11/13/2022] Open
Abstract
Although alternative pre-mRNA splicing (AS) significantly diversifies the neuronal proteome, the extent of AS is still unknown due in part to the large number of diverse cell types in the brain. To address this complexity issue, we used an annotation-free computational method to analyze and compare the AS profiles between small specific groups of Drosophila circadian neurons. The method, the Junction Usage Model (JUM), allows the comprehensive profiling of both known and novel AS events from specific RNA-seq libraries. The results show that many diverse and novel pre-mRNA isoforms are preferentially expressed in one class of clock neuron and also absent from the more standard Drosophila head RNA preparation. These AS events are enriched in potassium channels important for neuronal firing, and there are also cycling isoforms with no detectable underlying transcriptional oscillations. The results suggest massive AS regulation in the brain that is also likely important for circadian regulation.
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Affiliation(s)
- Qingqing Wang
- Department of Molecular and Cell Biology, University of California, Berkeley, Berkeley, United States.,Center for RNA Systems Biology (CRSB), University of California, Berkeley, Berkeley, United States.,California Institute for Quantitative Biosciences (QB3), University of California, Berkeley, Berkeley, United States
| | - Katharine C Abruzzi
- Department of Biology, Howard Hughes Medical Institute, Brandeis University, Waltham, United States.,National Center for Behavior Genomics, Brandeis University, Waltham, United States
| | - Michael Rosbash
- Department of Biology, Howard Hughes Medical Institute, Brandeis University, Waltham, United States.,National Center for Behavior Genomics, Brandeis University, Waltham, United States
| | - Donald C Rio
- Department of Molecular and Cell Biology, University of California, Berkeley, Berkeley, United States.,Center for RNA Systems Biology (CRSB), University of California, Berkeley, Berkeley, United States.,California Institute for Quantitative Biosciences (QB3), University of California, Berkeley, Berkeley, United States
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13
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Top D, O'Neil JL, Merz GE, Dusad K, Crane BR, Young MW. CK1/Doubletime activity delays transcription activation in the circadian clock. eLife 2018; 7:32679. [PMID: 29611807 PMCID: PMC5882363 DOI: 10.7554/elife.32679] [Citation(s) in RCA: 20] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/10/2017] [Accepted: 03/02/2018] [Indexed: 01/08/2023] Open
Abstract
In the Drosophila circadian clock, Period (PER) and Timeless (TIM) proteins inhibit Clock-mediated transcription of per and tim genes until PER is degraded by Doubletime/CK1 (DBT)-mediated phosphorylation, establishing a negative feedback loop. Multiple regulatory delays within this feedback loop ensure ~24 hr periodicity. Of these delays, the mechanisms that regulate delayed PER degradation (and Clock reactivation) remain unclear. Here we show that phosphorylation of certain DBT target sites within a central region of PER affect PER inhibition of Clock and the stability of the PER/TIM complex. Our results indicate that phosphorylation of PER residue S589 stabilizes and activates PER inhibitory function in the presence of TIM, but promotes PER degradation in its absence. The role of DBT in regulating PER activity, stabilization and degradation ensures that these events are chronologically and biochemically linked, and contributes to the timing of an essential delay that influences the period of the circadian clock. Many behaviors, such as when we fall asleep or wake up, follow the rhythm of day and night. This is regulated in part by our ‘circadian clock’, which controls biological processes through the timed activation of hundreds of genes over the 24-hour day. In fruit flies, the proteins that form the core of the circadian clock activate and repress each other in such a way that their expression oscillates over a 24-hour cycle. During the late afternoon and early evening, the Clock protein initiates the production of proteins Period and Timeless: these two molecules then accumulate in the cell, and after binding to each other, they are transported into the nucleus. During the late night and early morning, this Period/Timeless complex inhibits the activity of Clock. After a delay, Period and Timeless are degraded. This allows Clock to be reactivated, restarting the cycle for the next day. Period is critical to help maintain the 24-hour oscillation shown by these proteins. A protein called Doubletime is responsible for making a number of chemical modifications on Period. It is unclear how these changes interact with each other, and how they influence the stability and function of Period when it is associated with Timeless. Here, Top et al. generate mutations in the fruit fly gene period to study these processes, and develop a new biomolecular technique to monitor the stability and activity of Period protein in insect cells grown in the laboratory. The experiments reveal new roles for the chemical changes made by Doubletime to Period. First, after Period associates with Timeless, Doubletime triggers certain modifications that lead to Period being able to inactivate Clock. Second, Doubletime makes another change in a nearby region of Period that results in the Period/Timeless complex being stabilized. Both sets of modifications help the complex to stay active and keep inhibiting Clock for long enough such that a 24-hour rhythm can be maintained. Finally, when Timeless is degraded, Period is released from the complex. At this time, the modifications made by Doubletime promote the degradation of Period, resetting the clock. Fruit flies with mutations that block this mechanism perceive the day as shorter. This shows that the smallest change to clock genes can disorganize behavior. Indeed in humans, health problems such as sleep or mental health disorders are associated with irregular circadian clocks. Understanding the biochemical mechanisms that keep the body clocks ticking could help to find new therapeutic targets for these conditions.
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Affiliation(s)
- Deniz Top
- Laboratory of Genetics, The Rockefeller University, New York, United States
| | - Jenna L O'Neil
- Laboratory of Genetics, The Rockefeller University, New York, United States
| | - Gregory E Merz
- Department of Chemistry and Chemical Biology, Cornell University, New York, United States
| | - Kritika Dusad
- Department of Chemistry and Chemical Biology, Cornell University, New York, United States
| | - Brian R Crane
- Department of Chemistry and Chemical Biology, Cornell University, New York, United States
| | - Michael W Young
- Laboratory of Genetics, The Rockefeller University, New York, United States
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14
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Dunlap JC, Loros JJ. Just-So Stories and Origin Myths: Phosphorylation and Structural Disorder in Circadian Clock Proteins. Mol Cell 2017; 69:165-168. [PMID: 29276084 DOI: 10.1016/j.molcel.2017.11.028] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/16/2017] [Revised: 10/19/2017] [Accepted: 11/20/2017] [Indexed: 11/28/2022]
Abstract
Some longstanding dogmas in the circadian field warrant reexamination in light of recent studies focused on the role of post-translational modifications and intrinsic disorder in core circadian clock proteins of mice and fungi. Such dogmas include the role of turnover in circadian feedback loops and the origin myths describing evolutionary relatedness among circadian clocks. In this Essay, the authors recapitulate recent findings on circadian clock protein regulation by taking an unconventional approach in the form of a dialog between Wizard and Apprentice.
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Affiliation(s)
- Jay C Dunlap
- Department of Molecular and Systems Biology, Geisel School of Medicine at Dartmouth, Hanover, NH 03755.
| | - Jennifer J Loros
- Department of Biochemistry and Cell Biology, Geisel School of Medicine at Dartmouth, Hanover, NH 03755
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15
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Dunlap JC, Loros JJ. Making Time: Conservation of Biological Clocks from Fungi to Animals. Microbiol Spectr 2017; 5:10.1128/microbiolspec.FUNK-0039-2016. [PMID: 28527179 PMCID: PMC5446046 DOI: 10.1128/microbiolspec.funk-0039-2016] [Citation(s) in RCA: 81] [Impact Index Per Article: 11.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/12/2016] [Indexed: 01/03/2023] Open
Abstract
The capacity for biological timekeeping arose at least three times through evolution, in prokaryotic cyanobacteria, in cells that evolved into higher plants, and within the group of organisms that eventually became the fungi and the animals. Neurospora is a tractable model system for understanding the molecular bases of circadian rhythms in the last of these groups, and is perhaps the most intensively studied circadian cell type. Rhythmic processes described in fungi include growth rate, stress responses, developmental capacity, and sporulation, as well as much of metabolism; fungi use clocks to anticipate daily environmental changes. A negative feedback loop comprises the core of the circadian system in fungi and animals. In Neurospora, the best studied fungal model, it is driven by two transcription factors, WC-1 and WC-2, that form the White Collar Complex (WCC). WCC elicits expression of the frq gene. FRQ complexes with other proteins, physically interacts with the WCC, and reduces its activity; the kinetics of these processes is strongly influenced by progressive phosphorylation of FRQ. When FRQ becomes sufficiently phosphorylated that it loses the ability to influence WCC activity, the circadian cycle starts again. Environmental cycles of light and temperature influence frq and FRQ expression and thereby reset the internal circadian clocks. The molecular basis of circadian output is also becoming understood. Taken together, molecular explanations are emerging for all the canonical circadian properties, providing a molecular and regulatory framework that may be extended to many members of the fungal and animal kingdoms, including humans.
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Affiliation(s)
- Jay C Dunlap
- Department of Molecular and Systems Biology, Geisel School of Medicine at Dartmouth, Hanover, NH 03755
| | - Jennifer J Loros
- Department of Molecular and Systems Biology, Geisel School of Medicine at Dartmouth, Hanover, NH 03755
- Department of Biochemistry and Cell Biology, Geisel School of Medicine at Dartmouth, Hanover, NH 03755
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16
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Mendoza-Viveros L, Bouchard-Cannon P, Hegazi S, Cheng AH, Pastore S, Cheng HYM. Molecular modulators of the circadian clock: lessons from flies and mice. Cell Mol Life Sci 2017; 74:1035-1059. [PMID: 27689221 PMCID: PMC11107503 DOI: 10.1007/s00018-016-2378-8] [Citation(s) in RCA: 65] [Impact Index Per Article: 9.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/16/2016] [Revised: 09/03/2016] [Accepted: 09/22/2016] [Indexed: 12/16/2022]
Abstract
Circadian timekeeping is a ubiquitous mechanism that enables organisms to maintain temporal coordination between internal biological processes and time of the local environment. The molecular basis of circadian rhythms lies in a set of transcription-translation feedback loops (TTFLs) that drives the rhythmic transcription of core clock genes, whose level and phase of expression serve as the marker of circadian time. However, it has become increasingly evident that additional regulatory mechanisms impinge upon the TTFLs to govern the properties and behavior of the circadian clock. Such mechanisms include changes in chromatin architecture, interactions with other transcription factor networks, post-transcriptional control by RNA modifications, alternative splicing and microRNAs, and post-translational regulation of subcellular trafficking and protein degradation. In this review, we will summarize the current knowledge of circadian clock regulation-from transcriptional to post-translational-drawing from literature pertaining to the Drosophila and murine circadian systems.
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Affiliation(s)
- Lucia Mendoza-Viveros
- Department of Biology, University of Toronto Mississauga, 3359 Mississauga Road, Mississauga, ON, L5L 1C6, Canada
- Department of Cell and Systems Biology, University of Toronto, 25 Harbord Street, Toronto, ON, M5S 3G5, Canada
| | - Pascale Bouchard-Cannon
- Department of Biology, University of Toronto Mississauga, 3359 Mississauga Road, Mississauga, ON, L5L 1C6, Canada
- Department of Cell and Systems Biology, University of Toronto, 25 Harbord Street, Toronto, ON, M5S 3G5, Canada
| | - Sara Hegazi
- Department of Biology, University of Toronto Mississauga, 3359 Mississauga Road, Mississauga, ON, L5L 1C6, Canada
- Department of Cell and Systems Biology, University of Toronto, 25 Harbord Street, Toronto, ON, M5S 3G5, Canada
| | - Arthur H Cheng
- Department of Biology, University of Toronto Mississauga, 3359 Mississauga Road, Mississauga, ON, L5L 1C6, Canada
- Department of Cell and Systems Biology, University of Toronto, 25 Harbord Street, Toronto, ON, M5S 3G5, Canada
| | - Stephen Pastore
- Department of Biology, University of Toronto Mississauga, 3359 Mississauga Road, Mississauga, ON, L5L 1C6, Canada
- Department of Cell and Systems Biology, University of Toronto, 25 Harbord Street, Toronto, ON, M5S 3G5, Canada
| | - Hai-Ying Mary Cheng
- Department of Biology, University of Toronto Mississauga, 3359 Mississauga Road, Mississauga, ON, L5L 1C6, Canada.
- Department of Cell and Systems Biology, University of Toronto, 25 Harbord Street, Toronto, ON, M5S 3G5, Canada.
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Hurley JM, Loros JJ, Dunlap JC. Circadian Oscillators: Around the Transcription-Translation Feedback Loop and on to Output. Trends Biochem Sci 2016; 41:834-846. [PMID: 27498225 DOI: 10.1016/j.tibs.2016.07.009] [Citation(s) in RCA: 128] [Impact Index Per Article: 16.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/12/2016] [Revised: 07/10/2016] [Accepted: 07/14/2016] [Indexed: 12/20/2022]
Abstract
From cyanobacteria to mammals, organisms have evolved timing mechanisms to adapt to environmental changes in order to optimize survival and improve fitness. To anticipate these regular daily cycles, many organisms manifest ∼24h cell-autonomous oscillations that are sustained by transcription-translation-based or post-transcriptional negative-feedback loops that control a wide range of biological processes. With an eye to identifying emerging common themes among cyanobacterial, fungal, and animal clocks, some major recent developments in the understanding of the mechanisms that regulate these oscillators and their output are discussed. These include roles for antisense transcription, intrinsically disordered proteins, codon bias in clock genes, and a more focused discussion of post-transcriptional and translational regulation as a part of both the oscillator and output.
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Affiliation(s)
- Jennifer M Hurley
- Department of Biological Sciences, Rensselaer Polytechnic Institute, Troy, NY 12180, USA.
| | - Jennifer J Loros
- Department of Biochemistry and Cell Biology, Geisel School of Medicine at Dartmouth, Hanover, NH 03755, USA
| | - Jay C Dunlap
- Department of Molecular and Systems Biology, Geisel School of Medicine at Dartmouth, Hanover, NH 03755, USA.
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18
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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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19
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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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Proietto M, Bianchi MM, Ballario P, Brenna A. Epigenetic and Posttranslational Modifications in Light Signal Transduction and the Circadian Clock in Neurospora crassa. Int J Mol Sci 2015; 16:15347-83. [PMID: 26198228 PMCID: PMC4519903 DOI: 10.3390/ijms160715347] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/12/2015] [Revised: 06/24/2015] [Accepted: 06/30/2015] [Indexed: 12/15/2022] Open
Abstract
Blue light, a key abiotic signal, regulates a wide variety of physiological processes in many organisms. One of these phenomena is the circadian rhythm presents in organisms sensitive to the phase-setting effects of blue light and under control of the daily alternation of light and dark. Circadian clocks consist of autoregulatory alternating negative and positive feedback loops intimately connected with the cellular metabolism and biochemical processes. Neurospora crassa provides an excellent model for studying the molecular mechanisms involved in these phenomena. The White Collar Complex (WCC), a blue-light receptor and transcription factor of the circadian oscillator, and Frequency (FRQ), the circadian clock pacemaker, are at the core of the Neurospora circadian system. The eukaryotic circadian clock relies on transcriptional/translational feedback loops: some proteins rhythmically repress their own synthesis by inhibiting the activity of their transcriptional factors, generating self-sustained oscillations over a period of about 24 h. One of the basic mechanisms that perpetuate self-sustained oscillations is post translation modification (PTM). The acronym PTM generically indicates the addition of acetyl, methyl, sumoyl, or phosphoric groups to various types of proteins. The protein can be regulatory or enzymatic or a component of the chromatin. PTMs influence protein stability, interaction, localization, activity, and chromatin packaging. Chromatin modification and PTMs have been implicated in regulating circadian clock function in Neurospora. Research into the epigenetic control of transcription factors such as WCC has yielded new insights into the temporal modulation of light-dependent gene transcription. Here we report on epigenetic and protein PTMs in the regulation of the Neurospora crassa circadian clock. We also present a model that illustrates the molecular mechanisms at the basis of the blue light control of the circadian clock.
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Affiliation(s)
- Marco Proietto
- Department of Biology and Biotechnologies "Charles Darwin", Sapienza-University of Rome, Piazzale Aldo Moro 5, Rome 00185, Italy.
| | - Michele Maria Bianchi
- Department of Biology and Biotechnologies "Charles Darwin", Sapienza-University of Rome, Piazzale Aldo Moro 5, Rome 00185, Italy.
| | - Paola Ballario
- Department of Biology and Biotechnologies "Charles Darwin", Sapienza-University of Rome, Piazzale Aldo Moro 5, Rome 00185, Italy.
- Pasteur Institute, Cenci Bolognetti Foundation and Department of Biology and Biotechnology "Charles Darwin", Sapienza-University of Rome, Piazzale Aldo Moro 5, Rome 00185, Italy.
| | - Andrea Brenna
- Department of Biology and Biotechnologies "Charles Darwin", Sapienza-University of Rome, Piazzale Aldo Moro 5, Rome 00185, Italy.
- Pasteur Institute, Cenci Bolognetti Foundation and Department of Biology and Biotechnology "Charles Darwin", Sapienza-University of Rome, Piazzale Aldo Moro 5, Rome 00185, Italy.
- Department of Biology, Division of Biochemistry, University of Fribourg, Chemin du Musée 5, Fribourg 1700, Switzerland.
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21
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Venkatesan A, Fan JY, Nauman C, Price JL. A Doubletime Nuclear Localization Signal Mediates an Interaction with Bride of Doubletime to Promote Circadian Function. J Biol Rhythms 2015; 30:302-17. [PMID: 26082158 DOI: 10.1177/0748730415588189] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
Abstract
Doubletime (DBT) has an essential circadian role in Drosophila melanogaster because it phosphorylates Period (PER). To determine if DBT antagonism can produce distinct effects in the cytosol and nucleus, forms of a dominant negative DBT(K/R) with these 2 alternative localizations were produced. DBT has a putative nuclear localization signal (NLS), and mutation of this signal confers cytosolic localization of DBT in the lateral neurons of Drosophila clock cells in the brain. By contrast, addition of a strong NLS domain (e.g., SV40 NLS) to DBT's C terminus leads to more nuclear localization. Expression of DBT(K/R) with the mutated NLS (DBT(K/R) NLS(-)) using a timGAL4 driver does not alter the circadian period of locomotor activity, and the daily oscillations of PER detected by immunoblot and immunofluorescence persist, like those of wild-type flies. By contrast, expression of DBT(K/R) with the strong NLS (DBT(K/R) stNLS) using the timGAL4 driver lengthens period more strongly than DBT(K/R), with damped oscillations of PER phosphorylation and localization. Both DBT(K/R) and DBT(WT) without the NLS fail to interact with Bride of Doubletime (BDBT) protein, which is related to FK506-binding proteins and shown to interact with DBT to enhance its circadian function. This result suggests that the DBT(K/R) NLS(-) has lost its dominant negative property because it does not form normal clock protein complexes. DBT(WT) proteins with the same changes (NLS(-) and stNLS) also produce equivalent changes in localization that do not produce opposite period phenotypes. Additionally, a DBT(K/R) protein with both the stNLS and NLS(-) mutation does not affect circadian period, although it is nuclear, demonstrating that the lack of a dominant negative for the DBT(K/R) NLS(-) is not due to failure to localize to nuclei. Finally, bdbt RNAi increases the cytosolic localization of DBT(K/R) but not of DBT(WT), suggesting a role for BDBT in DBT kinase-dependent nuclear localization of DBT.
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Affiliation(s)
- Anandakrishnan Venkatesan
- School of Biological Sciences, Division of Molecular Biology and Biochemistry, University of Missouri-Kansas City, Kansas City, Missouri Department of Physiology, The University of Texas Health Science Center at San Antonio STRF-Greehey North Campus, San Antonio, Texas
| | - Jin-Yuan Fan
- School of Biological Sciences, Division of Molecular Biology and Biochemistry, University of Missouri-Kansas City, Kansas City, Missouri
| | - Christopher Nauman
- School of Biological Sciences, Division of Molecular Biology and Biochemistry, University of Missouri-Kansas City, Kansas City, Missouri
| | - Jeffrey L Price
- School of Biological Sciences, Division of Molecular Biology and Biochemistry, University of Missouri-Kansas City, Kansas City, Missouri School of Medicine, Department of Neurology and Cognitive Neuroscience, University of Missouri-Kansas City, Kansas City, Missouri
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22
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Larrondo LF, Olivares-Yañez C, Baker CL, Loros JJ, Dunlap JC. Circadian rhythms. Decoupling circadian clock protein turnover from circadian period determination. Science 2015; 347:1257277. [PMID: 25635104 DOI: 10.1126/science.1257277] [Citation(s) in RCA: 106] [Impact Index Per Article: 11.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
The mechanistic basis of eukaryotic circadian oscillators in model systems as diverse as Neurospora, Drosophila, and mammalian cells is thought to be a transcription-and-translation-based negative feedback loop, wherein progressive and controlled phosphorylation of one or more negative elements ultimately elicits their own proteasome-mediated degradation, thereby releasing negative feedback and determining circadian period length. The Neurospora crassa circadian negative element FREQUENCY (FRQ) exemplifies such proteins; it is progressively phosphorylated at more than 100 sites, and strains bearing alleles of frq with anomalous phosphorylation display abnormal stability of FRQ that is well correlated with altered periods or apparent arrhythmicity. Unexpectedly, we unveiled normal circadian oscillations that reflect the allelic state of frq but that persist in the absence of typical degradation of FRQ. This manifest uncoupling of negative element turnover from circadian period length determination is not consistent with the consensus eukaryotic circadian model.
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Affiliation(s)
- Luis F Larrondo
- Millennium Nucleus for Fungal Integrative and Synthetic Biology, Departamento de Genética Molecular y Microbiología, Facultad de Ciencias Biológicas, Pontificia Universidad Católica de Chile, Casilla 114-D, Santiago, Chile. Department of Genetics, Geisel School of Medicine at Dartmouth, Hanover, NH 03755, USA.
| | - Consuelo Olivares-Yañez
- Millennium Nucleus for Fungal Integrative and Synthetic Biology, Departamento de Genética Molecular y Microbiología, Facultad de Ciencias Biológicas, Pontificia Universidad Católica de Chile, Casilla 114-D, Santiago, Chile
| | - Christopher L Baker
- Department of Genetics, Geisel School of Medicine at Dartmouth, Hanover, NH 03755, USA
| | - Jennifer J Loros
- Department of Genetics, Geisel School of Medicine at Dartmouth, Hanover, NH 03755, USA. Department of Biochemistry, Geisel School of Medicine at Dartmouth, Hanover, NH 03755, USA
| | - Jay C Dunlap
- Department of Genetics, Geisel School of Medicine at Dartmouth, Hanover, NH 03755, USA.
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23
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Crane BR, Young MW. Interactive features of proteins composing eukaryotic circadian clocks. Annu Rev Biochem 2015; 83:191-219. [PMID: 24905781 DOI: 10.1146/annurev-biochem-060713-035644] [Citation(s) in RCA: 87] [Impact Index Per Article: 9.7] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Research into the molecular mechanisms of eukaryotic circadian clocks has proceeded at an electrifying pace. In this review, we discuss advances in our understanding of the structures of central molecular players in the timing oscillators of fungi, insects, and mammals. A series of clock protein structures demonstrate that the PAS (Per/Arnt/Sim) domain has been used with great variation to formulate the transcriptional activators and repressors of the clock. We discuss how posttranslational modifications and external cues, such as light, affect the conformation and function of core clock components. Recent breakthroughs have also revealed novel interactions among clock proteins and new partners that couple the clock to metabolic and developmental pathways. Overall, a picture of clock function has emerged wherein conserved motifs and structural platforms have been elaborated into a highly dynamic collection of interacting molecules that undergo orchestrated changes in chemical structure, conformational state, and partners.
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Affiliation(s)
- Brian R Crane
- Department of Chemistry and Chemical Biology, Cornell University, Ithaca, New York 14853;
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24
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Abstract
Casein kinase 1, known as DOUBLETIME (DBT) in Drosophila melanogaster, is a critical component of the circadian clock that phosphorylates and promotes degradation of the PERIOD (PER) protein. However, other functions of DBT in circadian regulation are not clear, in part because severe reduction of dbt causes preadult lethality. Here we report the molecular and behavioral phenotype of a viable dbt(EY02910) loss-of-function mutant. We found that DBT protein levels are dramatically reduced in adult dbt(EY02910) flies, and the majority of mutant flies display arrhythmic behavior, with a few showing weak, long-period (∼32 h) rhythms. Peak phosphorylation of PER is delayed, and both hyper- and hypophosphorylated forms of the PER and CLOCK proteins are present throughout the day. In addition, molecular oscillations of the circadian clock are dampened. In the central brain, PER and TIM expression is heterogeneous and decoupled in the canonical clock neurons of the dbt(EY02910) mutants. We also report an interaction between dbt and the signaling pathway involving pigment dispersing factor (PDF), a synchronizing peptide in the clock network. These data thus demonstrate that overall reduction of DBT causes long and arrhythmic behavior, and they reveal an unexpected role of DBT in promoting synchrony of the circadian clock network.
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25
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van Ooijen G, Martin SF, Barrios-Llerena ME, Hindle M, Le Bihan T, O'Neill JS, Millar AJ. Functional analysis of the rodent CK1tau mutation in the circadian clock of a marine unicellular alga. BMC Cell Biol 2013; 14:46. [PMID: 24127907 PMCID: PMC3852742 DOI: 10.1186/1471-2121-14-46] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/29/2013] [Accepted: 10/04/2013] [Indexed: 11/18/2022] Open
Abstract
Background Casein Kinase 1 (CK1) is one of few proteins known to affect cellular timekeeping across metazoans, and the naturally occurring CK1tau mutation shortens circadian period in mammals. Functional conservation of a timekeeping function for CK1 in the green lineage was recently identified in the green marine unicell Ostreococcus tauri, in spite of the absence of CK1's transcriptional targets known from other species. The short-period phenotype of CK1tau mutant in mammals depends specifically on increased CK1 activity against PERIOD proteins. To understand how CK1 acts differently upon the algal clock, we analysed the cellular and proteomic effects of CK1tau overexpression in O. tauri. Results Overexpression of the CK1tau in O. tauri induces period lengthening identical to overexpression of wild-type CK1, in addition to resistance to CK1 inhibitor IC261. Label-free quantitative mass spectrometry of CK1tau overexpressing algae revealed a total of 58 unique phospho-sites that are differentially responsive to CK1tau. Combined with CK1 phosphorylation site prediction tools and previously published wild-type CK1-responsive peptides, this study results in a highly stringent list of upregulated phospho-sites, derived from proteins containing ankyrin repeats, kinase proteins, and phosphoinositide-binding proteins. Conclusions The identical phenotype for overexpression of wild-type CK1 and CK1tau is in line with the absence of critical targets for rodent CK1tau in O. tauri. Proteomic analyses reveal that two thirds of previously reported CK1 overexpression-responsive phospho-sites are shared with CK1tau. These results indicate that the two alleles are functionally indiscriminate in O. tauri, and verify the identified cellular CK1 target proteins in a minimal circadian model organism.
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Affiliation(s)
- Gerben van Ooijen
- SynthSys, University of Edinburgh, Waddington Building, The King's Buildings, Mayfield Road, Edinburgh EH9 3JD, UK.
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26
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van Ooijen G, Hindle M, Martin SF, Barrios-Llerena M, Sanchez F, Bouget FY, O’Neill JS, Le Bihan T, Millar AJ. Functional analysis of Casein Kinase 1 in a minimal circadian system. PLoS One 2013; 8:e70021. [PMID: 23936135 PMCID: PMC3723912 DOI: 10.1371/journal.pone.0070021] [Citation(s) in RCA: 33] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/06/2013] [Accepted: 06/14/2013] [Indexed: 12/04/2022] Open
Abstract
The Earth's rotation has driven the evolution of cellular circadian clocks to facilitate anticipation of the solar cycle. Some evidence for timekeeping mechanism conserved from early unicellular life through to modern organisms was recently identified, but the components of this oscillator are currently unknown. Although very few clock components appear to be shared across higher species, Casein Kinase 1 (CK1) is known to affect timekeeping across metazoans and fungi, but has not previously been implicated in the circadian clock in the plant kingdom. We now show that modulation of CK1 function lengthens circadian rhythms in Ostreococcustauri, a unicellular marine algal species at the base of the green lineage, separated from humans by ~1.5 billion years of evolution. CK1 contributes to timekeeping in a phase-dependent manner, indicating clock-mediated gating of CK1 activity. Label-free proteomic analyses upon overexpression as well as inhibition revealed CK1-responsive phosphorylation events on a set of target proteins, including highly conserved potentially clock-relevant cellular regulator proteins. These results have major implications for our understanding of cellular timekeeping and can inform future studies in any circadian organism.
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Affiliation(s)
- Gerben van Ooijen
- SynthSys, University of Edinburgh, Edinburgh, United Kingdom
- Institute for Molecular Plant Sciences, University of Edinburgh, Edinburgh, United Kingdom
- Institute of Structural and Molecular Biology, University of Edinburgh, Edinburgh, United Kingdom
| | - Matthew Hindle
- SynthSys, University of Edinburgh, Edinburgh, United Kingdom
| | - Sarah F. Martin
- SynthSys, University of Edinburgh, Edinburgh, United Kingdom
| | | | - Frédéric Sanchez
- Centre National de la Recherche Scientifique, Université Pierre et Marie Curie, Paris, France
- Laboratoire d’Océanographie Microbienne, Observatoire Océanologique, Banyuls-sur-Mer, France
| | - François-Yves Bouget
- Centre National de la Recherche Scientifique, Université Pierre et Marie Curie, Paris, France
- Laboratoire d’Océanographie Microbienne, Observatoire Océanologique, Banyuls-sur-Mer, France
| | - John S. O’Neill
- Medical Research Council Laboratory for Molecular Biology, Cambridge, United Kingdom
| | - Thierry Le Bihan
- SynthSys, University of Edinburgh, Edinburgh, United Kingdom
- Institute of Structural and Molecular Biology, University of Edinburgh, Edinburgh, United Kingdom
| | - Andrew J. Millar
- SynthSys, University of Edinburgh, Edinburgh, United Kingdom
- Institute of Structural and Molecular Biology, University of Edinburgh, Edinburgh, United Kingdom
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27
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Hsu PY, Devisetty UK, Harmer SL. Accurate timekeeping is controlled by a cycling activator in Arabidopsis. eLife 2013. [PMID: 23638299 DOI: 10.7554/elife.00473.018] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/16/2023] Open
Abstract
Transcriptional feedback loops are key to circadian clock function in many organisms. Current models of the Arabidopsis circadian network consist of several coupled feedback loops composed almost exclusively of transcriptional repressors. Indeed, a central regulatory mechanism is the repression of evening-phased clock genes via the binding of morning-phased Myb-like repressors to evening element (EE) promoter motifs. We now demonstrate that a related Myb-like protein, REVEILLE8 (RVE8), is a direct transcriptional activator of EE-containing clock and output genes. Loss of RVE8 and its close homologs causes a delay and reduction in levels of evening-phased clock gene transcripts and significant lengthening of clock pace. Our data suggest a substantially revised model of the circadian oscillator, with a clock-regulated activator essential both for clock progression and control of clock outputs. Further, our work suggests that the plant clock consists of a highly interconnected, complex regulatory network rather than of coupled morning and evening feedback loops. DOI:http://dx.doi.org/10.7554/eLife.00473.001.
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Affiliation(s)
- Polly Yingshan Hsu
- Department of Plant Biology , University of California, Davis , Davis , United States
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28
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Hsu PY, Devisetty UK, Harmer SL. Accurate timekeeping is controlled by a cycling activator in Arabidopsis. eLife 2013; 2:e00473. [PMID: 23638299 PMCID: PMC3639509 DOI: 10.7554/elife.00473] [Citation(s) in RCA: 130] [Impact Index Per Article: 11.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/17/2012] [Accepted: 03/24/2013] [Indexed: 12/19/2022] Open
Abstract
Transcriptional feedback loops are key to circadian clock function in many organisms. Current models of the Arabidopsis circadian network consist of several coupled feedback loops composed almost exclusively of transcriptional repressors. Indeed, a central regulatory mechanism is the repression of evening-phased clock genes via the binding of morning-phased Myb-like repressors to evening element (EE) promoter motifs. We now demonstrate that a related Myb-like protein, REVEILLE8 (RVE8), is a direct transcriptional activator of EE-containing clock and output genes. Loss of RVE8 and its close homologs causes a delay and reduction in levels of evening-phased clock gene transcripts and significant lengthening of clock pace. Our data suggest a substantially revised model of the circadian oscillator, with a clock-regulated activator essential both for clock progression and control of clock outputs. Further, our work suggests that the plant clock consists of a highly interconnected, complex regulatory network rather than of coupled morning and evening feedback loops. DOI:http://dx.doi.org/10.7554/eLife.00473.001 We live in a world with a 24-hr cycle in which day follows night follows day with complete predictability. Life on earth has evolved to take advantage of this predictability by using circadian clocks to prepare for the coming of night (or day), and plants are no exception. Even in constant darkness, characteristics such as leaf movements show a constant cycle of around 24 hr. Most circadian clocks rely on negative feedback loops involving various genes and proteins to keep track of time. In one of these feedback loops, certain genes—called morning-phased genes—are expressed as proteins during the day, and these proteins prevent other genes—called evening-phased genes—from producing proteins. As night approaches, however, a second feedback loop acts to stop the morning-phased genes being expressed, thus allowing the evening-phased genes to produce proteins. And as day approaches, expression of these genes is stopped and the whole cycle starts again. Many of the genes and proteins involved in the circadian system of Arabidopsis thaliana, a small flowering plant that is widely used as a model organism, have been identified, and its circadian clock was thought to rely almost entirely on proteins called repressors that block the transcription of genes. Now, Hsu et al. have shown that the Arabidopsis clock also involves proteins that increase the expression of certain genes at specific times of the day. Hsu et al. focused on the promoter regions of evening-phased genes: these regions are stretches of DNA that proteins called transcription factors bind to and either encourage the expression of a gene (if the protein is a transcriptional activator) or block its expression (as a transcriptional repressor). In particular, they focused on a protein called RVE8 that is most strongly expressed in the afternoon and, based on previous research, is thought to activate the transcription of genes. Using genetically modified plants in which the gene for RVE8 can be turned on and off, they found that this protein led to increases in the expression of some genes, and reductions in the expression of others. Further analysis showed that RVE8 was able to activate the expression of evening-phased genes directly, without requiring that new proteins be made first. By contrast, morning-expressed genes were likely to be suppressed by RVE8 via an indirect mechanism that involved other proteins that had previously been activated by RVE8. The expression of RVE8 itself is regulated by other clock genes and also by an undefined post-transcriptional process. Therefore rather than consisting of a morning feedback loop coupled to an evening feedback loop, with both loops being based on repressors, the plant clock is instead better viewed as a highly connected network of activators and repressors. Further research is clearly necessary to understand this unexpected complexity in the circadian clock of Arabidopsis. DOI:http://dx.doi.org/10.7554/eLife.00473.002
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Affiliation(s)
- Polly Yingshan Hsu
- Department of Plant Biology , University of California, Davis , Davis , United States
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29
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van Ooijen G, Millar AJ. Non-transcriptional oscillators in circadian timekeeping. Trends Biochem Sci 2012; 37:484-92. [PMID: 22917814 DOI: 10.1016/j.tibs.2012.07.006] [Citation(s) in RCA: 56] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/16/2012] [Revised: 07/20/2012] [Accepted: 07/26/2012] [Indexed: 01/10/2023]
Abstract
Circadian clocks have evolved as an adaptation to life on a rotating planet, and orchestrate rhythmic changes in physiology to match the time of day. For decades, cellular circadian rhythms were considered to solely result from feedback between the products of rhythmically expressed genes. These transcriptional/translational feedback loops (TTFLs) have been ubiquitously studied, and explain the majority of circadian outputs. In recent years, however, non-transcriptional processes were shown to be major contributors to circadian rhythmicity. These key findings have profound implications on our understanding of the evolution and mechanistic basis of cellular circadian timekeeping. This review summarises and discusses these results and the experimental and theoretical evidence of a possible relation between non-transcriptional oscillator (NTO) mechanisms and TTFL oscillations.
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Affiliation(s)
- Gerben van Ooijen
- SynthSys, University of Edinburgh, The Kings Buildings, Mayfield Road, EH9 3JD, Edinburgh, UK
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Speed control: cogs and gears that drive the circadian clock. Trends Neurosci 2012; 35:574-85. [PMID: 22748426 DOI: 10.1016/j.tins.2012.05.007] [Citation(s) in RCA: 58] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/20/2012] [Revised: 05/09/2012] [Accepted: 05/31/2012] [Indexed: 01/29/2023]
Abstract
In most organisms, an intrinsic circadian (~24-h) timekeeping system drives rhythms of physiology and behavior. Within cells that contain a circadian clock, specific transcriptional activators and repressors reciprocally regulate each other to generate a basic molecular oscillator. A mismatch of the period generated by this oscillator with the external environment creates circadian disruption, which can have adverse effects on neural function. Although several clock genes have been extensively characterized, a fundamental question remains: how do these genes work together to generate a ~24-h period? Period-altering mutations in clock genes can affect any of multiple regulated steps in the molecular oscillator. In this review, we examine the regulatory mechanisms that contribute to setting the pace of the circadian oscillator.
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Modelling the effect of phosphorylation on the circadian clock of Drosophila. J Theor Biol 2012; 307:53-61. [PMID: 22588022 DOI: 10.1016/j.jtbi.2012.05.003] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/23/2011] [Revised: 04/30/2012] [Accepted: 05/03/2012] [Indexed: 11/22/2022]
Abstract
It is by now well known that, at the molecular level, the core of the circadian clock of most living species is a negative feedback loop where some proteins inhibit their own transcription. However, it has recently been shown that post-translational processes, such as phosphorylations, are essential for a correct timing of the clock. Depending on which sites of a circadian protein are phosphorylated, different properties such as degradation, nuclear localization and repressing power can be altered. Furthermore, phosphorylation domains can be related in a positive way, giving rise to consecutive phosphorylations, or in a negative way, hindering phosphorylation at other domains. Here we present a simple mathematical model of a circadian protein having two mutually exclusive domains of phosphorylation. We show that the system has limit cycles that arise from a unique fixed point through a Hopf bifurcation. We find a set of parameters, with realistic values, for which the limit cycle has the same period as the wild type circadian oscillations of the fruit fly. The domains act as a switch, in the sense that alterations in their phosphorylation can alter the period of circadian oscillation in opposite ways, increasing or decreasing the period of the wild type oscillations. In particular, we show that our model is able to reproduce some of the experimental results found for switch-like phosphorylations of the PER protein of the circadian clock of the fly Drosophila melanogaster.
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