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Matagne V, Kim JG, Ryu BJ, Hur MK, Kim MS, Kim K, Park BS, Damante G, Smiley G, Lee BJ, Ojeda SR. Thyroid transcription factor 1, a homeodomain containing transcription factor, contributes to regulating periodic oscillations in GnRH gene expression. J Neuroendocrinol 2012; 24:916-29. [PMID: 22356123 PMCID: PMC3350608 DOI: 10.1111/j.1365-2826.2012.02302.x] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Thyroid transcription factor 1 (TTF1), a member of the Nkx family of transcription factors required for basal forebrain morphogenesis, functions in the postnatal hypothalamus as a transcriptional regulator of genes encoding neuromodulators and hypophysiotrophic peptides. One of these peptides is gonadotrophin-releasing hormone (GnRH). In the present study, we show that Ttf1 mRNA abundance varies in a diurnal and melatonin-dependent fashion in the preoptic area of the rat, with maximal Ttf1 expression attained during the dark phase of the light/dark cycle, preceding the nocturnal peak in GnRH mRNA content. GnRH promoter activity oscillates in a circadian manner in GT1-7 cells, and this pattern is enhanced by TTF1 and blunted by small interfering RNA-mediated Ttf1 gene silencing. TTF1 transactivates GnRH transcription by binding to two sites in the GnRH promoter. Rat GnRH neurones in situ contain key proteins components of the positive (BMAL1, CLOCK) and negative (PER1) limbs of the circadian oscillator, and these proteins repress Ttf1 promoter activity in vitro. By contrast, Ttf1 transcription is activated by CRY1, a clock component required for circadian rhythmicity. In turn, TTF1 represses transcription of Rev-erbα, a heme receptor that controls circadian transcription within the positive limb of the circadian oscillator. These findings suggest that TTF1 is a component of the molecular machinery controlling circadian oscillations in GnRH gene transcription.
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Affiliation(s)
- Valerie Matagne
- Division of Neuroscience, Oregon National Primate Research Center/Oregon Health Sciences University, Beaverton, Oregon 97006, USA
| | - Jae Geun Kim
- Department of Biological Sciences, University of Ulsan, Ulsan 680-749
| | - Byung Jun Ryu
- Department of Biological Sciences, University of Ulsan, Ulsan 680-749
| | - Min Kyu Hur
- Department of Biological Sciences, University of Ulsan, Ulsan 680-749
| | - Min Sung Kim
- Department of Biological Sciences, University of Ulsan, Ulsan 680-749
| | - Kyungjin Kim
- School of Biological Sciences, Seoul National University, Seoul 151-742, South Korea
| | - Byong Seo Park
- Department of Biological Sciences, University of Ulsan, Ulsan 680-749
| | - Giuseppe Damante
- Department of Medical and Biological Sciences, University of Udine, 33100, Italy
| | - Gregory Smiley
- Division of Neuroscience, Oregon National Primate Research Center/Oregon Health Sciences University, Beaverton, Oregon 97006, USA
| | - Byung Ju Lee
- Department of Biological Sciences, University of Ulsan, Ulsan 680-749
| | - Sergio R. Ojeda
- Division of Neuroscience, Oregon National Primate Research Center/Oregon Health Sciences University, Beaverton, Oregon 97006, USA
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Pfeffer M, Rauch A, Korf HW, von Gall C. The endogenous melatonin (MT) signal facilitates reentrainment of the circadian system to light-induced phase advances by acting upon MT2 receptors. Chronobiol Int 2012; 29:415-29. [PMID: 22489607 DOI: 10.3109/07420528.2012.667859] [Citation(s) in RCA: 48] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
The indolamine melatonin is an important rhythmic endocrine signal in the circadian system. Exogenous melatonin can entrain circadian rhythms in physiology and behavior, but the role of endogenous melatonin and the two membrane-bound melatonin receptor types, MT1 and MT2, in reentrainment of daily rhythms to light-induced phase shifts is not understood. The present study analyzed locomotor activity rhythms and clock protein levels in the suprachiasmatic nuclei (SCN) of melatonin-deficient (C57BL/6J) and melatonin-proficient (C3H/HeN) mice, as well as in melatonin-proficient (C3H/HeN) mice with targeted deletion of the MT1, MT2, or both receptors, to determine effects associated with phase delays or phase advances of the light/dark (LD) cycle. In all mouse strains and genotypes, reentrainment of locomotor activity rhythms was significantly faster after a 6-h phase delay than a 6-h phase advance. Reentrainment after the phase advance was, however, significantly slower than in melatonin-deficient animals and in mice lacking functional MT2 receptors than melatonin-proficient animals with intact MT2 receptors. To investigate whether these behavioral differences coincide with differences in reentrainment of clock protein levels in the SCN, mPER1, mCRY1 immunoreactions were compared between control mice kept under the original LD cycle and killed at zeitgeber time 04 (ZT04) or at ZT10, respectively, and experimental mice subjected to a 6-h phase advance of the LD cycle and sacrificed at ZT10 on the third day after phase advance. This ZT corresponds to ZT04 of the original LD cycle. Under the original LD cycle, the numbers of mPER1- and mCRY1-immunoreactive cell nuclei were low at ZT04 and high at ZT10 in the SCN of all mouse strains and genotypes investigated. Notably, mouse strains with intact melatonin signaling and functional MT2 receptors showed a significant increase in the number of mPER1- and mCRY1-immunoreactive cell nuclei at the new ZT10 as compared to the former ZT04. These data suggest the endogenous melatonin signal facilitates reentrainment of the circadian system to phase advances on the level of the SCN molecular clockwork by acting upon MT2 receptors.
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Affiliation(s)
- Martina Pfeffer
- Dr. Senckenbergische Anatomie, Institut Fachbereich Medizin, Goethe-Universität Frankfurt, Frankfurt am Main, Germany.
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Abstract
The antidiuretic hormone vasopressin (VP) promotes water reabsorption from the kidney and levels of circulating VP are normally related linearly to plasma osmolality, aiming to maintain the latter close to a predetermined set point. Interestingly, VP levels rise also in the absence of an increase in osmolality during late sleep in various mammals, including rats and humans. This circadian rhythm is functionally important because the absence of a late night VP surge results in polyuria and disrupts sleep in humans. Previous work has indicated that the VP surge may be caused by facilitation of the central processes mediating the osmotic control of VP release, and the mechanism by which this occurs was recently studied in angled slices of rat hypothalamus that preserve intact network interactions between the suprachiasmatic nucleus (SCN; the biological clock), the organum vasculosum lamina terminalis (OVLT; the central osmosensory nucleus) and the supraoptic nucleus (SON; which contains VP-releasing neurohypophysial neurones). These studies confirmed that the electrical activity of SCN clock neurones is higher during the middle sleep period (MSP) than during the late sleep period (LSP). Moreover, they revealed that the excitation of SON neurones caused by hyperosmotic stimulation of the OVLT was greater during the LSP than during the MSP. Activation of clock neurones by repetitive electrical stimulation, or by injection of glutamate into the SCN, caused a presynaptic inhibition of glutamatergic synapses made between the axon terminals of OVLT neurones and SON neurones. Consistent with this effect, activation of clock neurones with glutamate also reduced the excitation of SON neurones caused by hyperosmotic stimulation of the OVLT. These results suggest that clock neurones in the SCN can mediate an increase in VP release through a disinhibition of excitatory synapses between the OVLT and the SON during the LSP.
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Affiliation(s)
- E Trudel
- Centre for Research in Neuroscience, McGill University and Montreal General Hospital, Montreal, Canada
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Williams WP, Kriegsfeld LJ. Circadian control of neuroendocrine circuits regulating female reproductive function. Front Endocrinol (Lausanne) 2012; 3:60. [PMID: 22661968 PMCID: PMC3356853 DOI: 10.3389/fendo.2012.00060] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/10/2011] [Accepted: 04/13/2012] [Indexed: 01/14/2023] Open
Abstract
Female reproduction requires the precise temporal organization of interacting, estradiol-sensitive neural circuits that converge to optimally drive hypothalamo-pituitary-gonadal (HPG) axis functioning. In mammals, the master circadian pacemaker in the suprachiasmatic nucleus (SCN) of the anterior hypothalamus coordinates reproductively relevant neuroendocrine events necessary to maximize reproductive success. Likewise, in species where periods of fertility are brief, circadian oversight of reproductive function ensures that estradiol-dependent increases in sexual motivation coincide with ovulation. Across species, including humans, disruptions to circadian timing (e.g., through rotating shift work, night shift work, poor sleep hygiene) lead to pronounced deficits in ovulation and fecundity. Despite the well-established roles for the circadian system in female reproductive functioning, the specific neural circuits and neurochemical mediators underlying these interactions are not fully understood. Most work to date has focused on the direct and indirect communication from the SCN to the gonadotropin-releasing hormone (GnRH) system in control of the preovulatory luteinizing hormone (LH) surge. However, the same clock genes underlying circadian rhythms at the cellular level in SCN cells are also common to target cell populations of the SCN, including the GnRH neuronal network. Exploring the means by which the master clock synergizes with subordinate clocks in GnRH cells and its upstream modulatory systems represents an exciting opportunity to further understand the role of endogenous timing systems in female reproduction. Herein we provide an overview of the state of knowledge regarding interactions between the circadian timing system and estradiol-sensitive neural circuits driving GnRH secretion and the preovulatory LH surge.
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Affiliation(s)
- Wilbur P. Williams
- Department of Psychology, Helen Wills Neuroscience Institute, University of CaliforniaBerkeley, CA, USA
| | - Lance J. Kriegsfeld
- Department of Psychology, Helen Wills Neuroscience Institute, University of CaliforniaBerkeley, CA, USA
- *Correspondence: Lance J. Kriegsfeld, Neurobiology Laboratory, Department of Psychology, Helen Wills Neuroscience Institute, University of California, 3210 Tolman Hall, #1650, Berkeley, CA 94720-1650, USA. e-mail:
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Atkinson SE, Maywood ES, Chesham JE, Wozny C, Colwell CS, Hastings MH, Williams SR. Cyclic AMP signaling control of action potential firing rate and molecular circadian pacemaking in the suprachiasmatic nucleus. J Biol Rhythms 2011; 26:210-20. [PMID: 21628548 DOI: 10.1177/0748730411402810] [Citation(s) in RCA: 43] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
Circadian pacemaking in suprachiasmatic nucleus (SCN) neurons revolves around transcriptional/posttranslational feedback loops, driven by protein products of "clock" genes. These loops are synchronized and sustained by intercellular signaling, involving vasoactive intestinal peptide (VIP) via its VPAC2 receptor, which positively regulates cAMP synthesis. In turn, SCN cells communicate circadian time to the brain via a daily rhythm in electrophysiological activity. To investigate the mechanisms whereby VIP/VPAC2/cAMP signaling controls SCN molecular and electrical pacemaking, we combined bioluminescent imaging of circadian gene expression and whole-cell electrophysiology in organotypic SCN slices. As a potential direct target of cAMP, we focused on hyperpolarization-activated, cyclic nucleotide-gated (HCN) channels. Mutations of VIP-ergic signaling compromised the SCN molecular pacemaker, diminishing the amplitude and intercellular synchrony of circadian gene expression. These deficits were transiently reversed by elevation of cAMP. Similarly, cellular synchrony in electrical firing rates was lost in SCN slices lacking the VPAC2 receptor for VIP. Whole-cell current-clamp recordings in wild-type (WT) slices revealed voltage responses shaped by the conductance I(h), which is mediated by HCN channel activity. The influence of I(h) on voltage responses showed a modest peak in early circadian day, identifying HCN channels as a putative mediator of cAMP-dependent circadian effects on firing rate. I(h), however, was unaffected by loss of VIP-ergic signaling in VPAC2-null slices, and inhibition of cAMP synthesis had no discernible effect on I(h) but did suppress gene expression and SCN firing rates. Moreover, only sustained but not acute, pharmacological blockade of HCN channels reduced action potential (AP) firing. Thus, our evidence suggests that in the SCN, cAMP-mediated signaling is not a principal regulator of HCN channel function and that HCN is not a determinant of AP firing rate. VIP/cAMP-dependent signaling sustains the SCN molecular oscillator and action potential firing via mechanisms yet to be identified.
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Affiliation(s)
- Susan E Atkinson
- Division of Neurobiology, Medical Research Council Laboratory of Molecular Biology, Cambridge, United Kingdom
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56
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King HA, Hoelz A, Crane BR, Young MW. Structure of an enclosed dimer formed by the Drosophila period protein. J Mol Biol 2011; 413:561-72. [PMID: 21907720 DOI: 10.1016/j.jmb.2011.08.048] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/04/2011] [Revised: 08/19/2011] [Accepted: 08/23/2011] [Indexed: 11/18/2022]
Abstract
Period (PER) is the major transcription inhibitor in metazoan circadian clocks and lies at the center of several feedback loops that regulate gene expression. Dimerization of Drosophila PER influences nuclear translocation, repressor activity, and behavioral rhythms. The structure of a central, 346-residue PER fragment reveals two associated PAS (Per-Arnt-Sim) domains followed by a protruding α-helical extension (αF). A closed, pseudo-symmetric dimer forms from a cross handshake interaction of the N-terminal PAS domain with αF of the opposing subunit. Strikingly, a shift of αF against the PAS β-sheet generates two alternative subunit interfaces in the dimer. Taken together with a previously reported PER structure in which αF extends, these data indicate that αF unlatches to switch association of PER with itself to its partner Timeless. The variable positions of the αF helix provide snapshots of a helix dissociation mechanism that has relevance to other PAS protein systems. Conservation of PER interaction residues among a family of PAS-AB-containing transcription factors suggests that contacts mediating closed PAS-AB dimers serve a general function.
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Affiliation(s)
- Heather A King
- Laboratory of Genetics, The Rockefeller University, New York, NY 10065, USA
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57
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Abstract
Neurons in the suprachiasmatic nucleus (SCN) function as part of a central timing circuit that drives daily changes in our behaviour and underlying physiology. A hallmark feature of SCN neuronal populations is that they are mostly electrically silent during the night, start to fire action potentials near dawn and then continue to generate action potentials with a slow and steady pace all day long. Sets of currents are responsible for this daily rhythm, with the strongest evidence for persistent Na(+) currents, L-type Ca(2+) currents, hyperpolarization-activated currents (I(H)), large-conductance Ca(2+) activated K(+) (BK) currents and fast delayed rectifier (FDR) K(+) currents. These rhythms in electrical activity are crucial for the function of the circadian timing system, including the expression of clock genes, and decline with ageing and disease. This article reviews our current understanding of the ionic and molecular mechanisms that drive the rhythmic firing patterns in the SCN.
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Affiliation(s)
- Christopher S Colwell
- Laboratory of Circadian and Sleep Medicine, Department of Psychiatry and Biobehavioral Sciences, David Geffen School of Medicine, University of California Los Angeles, California 90024, USA.
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58
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Mohawk JA, Takahashi JS. Cell autonomy and synchrony of suprachiasmatic nucleus circadian oscillators. Trends Neurosci 2011; 34:349-58. [PMID: 21665298 DOI: 10.1016/j.tins.2011.05.003] [Citation(s) in RCA: 156] [Impact Index Per Article: 12.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/16/2011] [Revised: 05/04/2011] [Accepted: 05/10/2011] [Indexed: 11/18/2022]
Abstract
The suprachiasmatic nucleus (SCN) of the hypothalamus is the site of the master circadian pacemaker in mammals. The individual cells of the SCN are capable of functioning independently from one another and therefore must form a cohesive circadian network through intercellular coupling. The network properties of the SCN lead to coordination of circadian rhythms among its neurons and neuronal subpopulations. There is increasing evidence for multiple interconnected oscillators within the SCN, and in this review we will highlight recent advances in our knowledge of the complex organization and function of the cellular and network-level SCN clock. Understanding the way in which synchrony is achieved between cells in the SCN will provide insight into the means by which this important nucleus orchestrates circadian rhythms throughout the organism.
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Affiliation(s)
- Jennifer A Mohawk
- Department of Neuroscience and Howard Hughes Medical Institute, University of Texas Southwestern Medical Center, Dallas, TX 75390-9111, USA
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59
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Xu K, DiAngelo JR, Hughes ME, Hogenesch JB, Sehgal A. The circadian clock interacts with metabolic physiology to influence reproductive fitness. Cell Metab 2011; 13:639-54. [PMID: 21641546 PMCID: PMC3152999 DOI: 10.1016/j.cmet.2011.05.001] [Citation(s) in RCA: 124] [Impact Index Per Article: 9.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/07/2010] [Revised: 12/21/2010] [Accepted: 03/18/2011] [Indexed: 10/18/2022]
Abstract
Circadian rhythms are regulated by a synchronized system of central and peripheral clocks. Here, we show that a clock in the Drosophila fat body drives rhythmic expression of genes involved in metabolism, detoxification, the immune response, and steroid hormone regulation. Some of these genes cycle even when the fat body clock is disrupted, indicating that they are regulated by exogenous factors. Food is an important stimulus, as limiting food availability to a 6 hr interval each day drives rhythmic expression of genes in the fat body. Restricting food to a time of day when consumption is typically low desynchronizes internal rhythms because it alters the phase of rhythmic gene expression in the fat body without affecting the brain clock. Flies maintained on this paradigm produce fewer eggs than those restricted to food at the normal time. These data suggest that desynchrony of endogenous rhythms, caused by aberrant feeding patterns, affects reproductive fitness.
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Affiliation(s)
- Kanyan Xu
- Department of Neuroscience, Howard Hughes Medical Institute, University of Pennsylvania School of Medicine, Philadelphia, PA 19104, USA
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60
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Foley NC, Tong TY, Foley D, LeSauter J, Welsh DK, Silver R. Characterization of orderly spatiotemporal patterns of clock gene activation in mammalian suprachiasmatic nucleus. Eur J Neurosci 2011; 33:1851-65. [PMID: 21488990 PMCID: PMC3423955 DOI: 10.1111/j.1460-9568.2011.07682.x] [Citation(s) in RCA: 58] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Abstract
Because we can observe oscillation within individual cells and in the tissue as a whole, the suprachiasmatic nucleus (SCN) presents a unique system in the mammalian brain for the analysis of individual cells and the networks of which they are a part. While dispersed cells of the SCN sustain circadian oscillations in isolation, they are unstable oscillators that require network interactions for robust cycling. Using cluster analysis to assess bioluminescence in acute brain slices from PERIOD2::Luciferase (PER2::LUC) knockin mice, and immunochemistry of SCN from animals harvested at various circadian times, we assessed the spatiotemporal activation patterns of PER2 to explore the emergence of a coherent oscillation at the tissue level. The results indicate that circadian oscillation is characterized by a stable daily cycle of PER2 expression involving orderly serial activation of specific SCN subregions, followed by a silent interval, with substantial symmetry between the left and right side of the SCN. The biological significance of the clusters identified in living slices was confirmed by co-expression of LUC and PER2 in fixed, immunochemically stained brain sections, with the spatiotemporal pattern of LUC expression resembling that revealed in the cluster analysis of bioluminescent slices. We conclude that the precise timing of PER2 expression within individual neurons is dependent on their location within the nucleus, and that small groups of neurons within the SCN give rise to distinctive and identifiable subregions. We propose that serial activation of these subregions is the basis of robustness and resilience of the daily rhythm of the SCN.
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Affiliation(s)
- Nicholas C. Foley
- Department of Cognitive and Neural Systems, Boston University, Boston, MA, USA
| | - Tina Y. Tong
- Department of Psychology, Barnard College of Columbia University, New York, NY, USA
| | - Duncan Foley
- Department of Economics, New School for Social Research, New York, NY, USA
| | - Joseph LeSauter
- Department of Psychology, Barnard College of Columbia University, New York, NY, USA
| | - David K. Welsh
- Department of Psychiatry and Center for Chronobiology, University of California, San Diego, La Jolla, CA, USA
- Veterans Affairs San Diego Healthcare System, San Diego, CA, USA
| | - Rae Silver
- Department of Psychology, Barnard College of Columbia University, New York, NY, USA
- Department of Psychology, Columbia University, New York, NY, USA
- Department of Pathology and Cell Biology, Columbia University Health Sciences, New York, NY, USA
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Iwashina I, Mochizuki K, Inamochi Y, Goda T. Clock genes regulate the feeding schedule-dependent diurnal rhythm changes in hexose transporter gene expressions through the binding of BMAL1 to the promoter/enhancer and transcribed regions. J Nutr Biochem 2011; 22:334-43. [PMID: 20688499 DOI: 10.1016/j.jnutbio.2010.02.012] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/25/2009] [Revised: 02/02/2010] [Accepted: 02/23/2010] [Indexed: 10/19/2022]
Abstract
The expression of hexose transporter genes (SGLT1, GLUT5 and GLUT2) in mice with ad libitum feeding under light (7:00-19:00)-dark (19:00-7:00) cycle gradually increased from a basal level at 7:00 and reached a maximum at 19:00, coinciding with the start of dark phase feeding. The peaks of these gene expressions were shifted to 7:00 in mice that were subjected to a restricted feeding schedule from 9:00 to 17:00. The expression of BMAL1, a transcription factor driving the central feedback loop of the clock genes, was followed by the increase of hexose transporter gene expressions. The expressions of Per1-3, genes related to negative regulation of BMAL1, were the highest at or just after the time of maximal expression of the hexose transporter genes in both the group fed ad libitum and the restricted feeding group. Furthermore, chromatin immunoprecipitation assays revealed that the binding of BMAL1 to the promoter and/or transcribed regions of hexose transporters and Per 2 genes was associated with changes in their expressions. These results suggest that diurnal changes in expression of hexose transporter genes depend on the feeding schedule and are directly regulated by a feedback loop of clock genes.
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Affiliation(s)
- Ikumi Iwashina
- Laboratory of Nutritional Physiology and School of Food and Nutritional Sciences, The University of Shizuoka and Global COE, 52-1 Yada, Shizuoka-shi, Shizuoka 422–8526, Japan
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Hayasaka N, Aoki K, Kinoshita S, Yamaguchi S, Wakefield JK, Tsuji-Kawahara S, Horikawa K, Ikegami H, Wakana S, Murakami T, Ramabhadran R, Miyazawa M, Shibata S. Attenuated food anticipatory activity and abnormal circadian locomotor rhythms in Rgs16 knockdown mice. PLoS One 2011; 6:e17655. [PMID: 21408016 PMCID: PMC3052372 DOI: 10.1371/journal.pone.0017655] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/12/2011] [Accepted: 02/04/2011] [Indexed: 11/18/2022] Open
Abstract
Regulators of G protein signaling (RGS) are a multi-functional protein family, which functions in part as GTPase-activating proteins (GAPs) of G protein α-subunits to terminate G protein signaling. Previous studies have demonstrated that the Rgs16 transcripts exhibit robust circadian rhythms both in the suprachiasmatic nucleus (SCN), the master circadian light-entrainable oscillator (LEO) of the hypothalamus, and in the liver. To investigate the role of RGS16 in the circadian clock in vivo, we generated two independent transgenic mouse lines using lentiviral vectors expressing short hairpin RNA (shRNA) targeting the Rgs16 mRNA. The knockdown mice demonstrated significantly shorter free-running period of locomotor activity rhythms and reduced total activity as compared to the wild-type siblings. In addition, when feeding was restricted during the daytime, food-entrainable oscillator (FEO)-driven elevated food-anticipatory activity (FAA) observed prior to the scheduled feeding time was significantly attenuated in the knockdown mice. Whereas the restricted feeding phase-advanced the rhythmic expression of the Per2 clock gene in liver and thalamus in the wild-type animals, the above phase shift was not observed in the knockdown mice. This is the first in vivo demonstration that a common regulator of G protein signaling is involved in the two separate, but interactive circadian timing systems, LEO and FEO. The present study also suggests that liver and/or thalamus regulate the food-entrained circadian behavior through G protein-mediated signal transduction pathway(s).
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Affiliation(s)
- Naoto Hayasaka
- Department of Anatomy and Neurobiology, Kinki University School of Medicine, Osaka-Sayama, Osaka, Japan.
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63
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Abstract
In mammals, most metabolic processes are influenced by biological clocks and feeding rhythms. The mechanisms that couple metabolism to circadian oscillators are just emerging. NAD-dependent enzymes (e.g., Sirtuins and poly[ADP-ribose] polymerases), redox- and/or temperature-dependent transcription factors (e.g., CLOCK, NPAS2, and HSF1), nutrient-sensing transcriptional regulatory proteins (e.g., CREB-CBP-CRCT2, FOXO-p300, nuclear receptors, PGC-1, and SP1 family members) and protein kinases (e.g., AMPK), are plausible candidates for conveying a cell's metabolic state to the core clock circuitry. The intertwining between these acute regulators and circadian clock components is so tight that the discrimination between metabolic and circadian oscillations may be somewhat arbitrary.
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64
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Urbanski HF. Role of circadian neuroendocrine rhythms in the control of behavior and physiology. Neuroendocrinology 2011; 93:211-22. [PMID: 21508622 PMCID: PMC3128131 DOI: 10.1159/000327399] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/01/2010] [Accepted: 03/13/2011] [Indexed: 12/27/2022]
Abstract
Hormones play a major role in regulating behavior and physiology, and their efficacy is often dependent on the temporal pattern in which they are secreted. Significant insights into the mechanisms underlying rhythmic hormone secretion have been gained from transgenic rodent models, suggesting that many of the body's rhythmic functions are regulated by a coordinated network of central and peripheral circadian pacemakers. Some neuroendocrine rhythms are driven by transcriptional-posttranslational feedback circuits comprising 'core clock genes', while others represent a cyclic cascade of neuroendocrine events. This review focuses on recent data from the rhesus macaque, a non-human primate model with high clinical translation potential. With primary emphasis on adrenal and gonadal steroids, it illustrates the rhythmic nature of hormone secretion, and discusses the impact that fluctuating hormone levels have on the accuracy of clinical diagnoses and on the design of effective hormone replacement therapies in the elderly. In addition, this minireview raises awareness of the rhythmic expression patterns shown by many genes, and discusses how this could impact interpretation of data obtained from gene profiling studies, especially from nocturnal rodents.
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Affiliation(s)
- Henryk F Urbanski
- Division of Neuroscience, Oregon National Primate Research Center, Department of Behavioral Neuroscience, Oregon Health & Science University, Portland, Oreg., USA.
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65
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Girardet C, Becquet D, Blanchard MP, François-Bellan AM, Bosler O. Neuroglial and synaptic rearrangements associated with photic entrainment of the circadian clock in the suprachiasmatic nucleus. Eur J Neurosci 2010; 32:2133-42. [DOI: 10.1111/j.1460-9568.2010.07520.x] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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66
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Walker JJ, Terry JR, Tsaneva-Atanasova K, Armstrong SP, McArdle CA, Lightman SL. Encoding and decoding mechanisms of pulsatile hormone secretion. J Neuroendocrinol 2010; 22:1226-38. [PMID: 21054582 DOI: 10.1111/j.1365-2826.2010.02087.x] [Citation(s) in RCA: 56] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/22/2023]
Abstract
Ultradian pulsatile hormone secretion underlies the activity of most neuroendocrine systems, including the hypothalamic-pituitary adrenal (HPA) and gonadal (HPG) axes, and this pulsatile mode of signalling permits the encoding of information through both amplitude and frequency modulation. In the HPA axis, glucocorticoid pulse amplitude increases in anticipation of waking, and, in the HPG axis, changing gonadotrophin-releasing hormone pulse frequency is the primary means by which the body alters its reproductive status during development (i.e. puberty). The prevalence of hormone pulsatility raises two crucial questions: how are ultradian pulses encoded (or generated) by these systems, and how are these pulses decoded (or interpreted) at their target sites? We have looked at mechanisms within the HPA axis responsible for encoding the pulsatile mode of glucocorticoid signalling that we observe in vivo. We review evidence regarding the 'hypothalamic pulse generator' hypothesis, and describe an alternative model for pulse generation, which involves steroid feedback-dependent endogenous rhythmic activity throughout the HPA axis. We consider the decoding of hormone pulsatility by taking the HPG axis as a model system and focussing on molecular mechanisms of frequency decoding by pituitary gonadotrophs.
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Affiliation(s)
- J J Walker
- Henry Wellcome Laboratories for Integrative Neuroscience and Endocrinology, University of Bristol, Bristol, UK.
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67
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Abstract
Neuroactive peptides and the intracellular calcium concentration ([Ca(2+) ](i) ) play important roles in light-induced modulation of gene expression in the suprachiasmatic nucleus (SCN) neurons that ultimately control behavioral rhythms. Vasoactive intestinal peptide (VIP) and arginine vasopressin (AVP) are expressed rhythmically within populations of SCN neurons. Pituitary adenylate cyclase-activating peptide (PACAP) is released from retinohypothalamic tract (RHT) terminals synapsing on SCN neurons. Nociceptin/orphanin FQ (OFQ) receptors are functionally expressed in the SCN. We examined the role of several neuropeptides on Ca(2+) signaling, simultaneously imaging multiple neurons within the SCN neural network. VIP reduced the [Ca(2+) ](i) in populations of SCN neurons during the day, but had little effect at night. Stimulation of the RHT at frequencies that simulate light input signaling evoked transient [Ca(2+) ](i) elevations that were not altered by VIP. AVP elevated the [Ca(2+) ](i) during both the day and night, PACAP produced variable responses, and OFQ induced a reduction in the [Ca(2+) ](i) similar to VIP. During the day, VIP lowered the [Ca(2+) ](i) to near nighttime levels, while AVP elevated [Ca(2+) ](i) during both the day and night, suggesting that the VIP effects on [Ca(2+) ](i) were dependent, and the AVP effects independent of the action potential firing activity state of the neuron. We hypothesize that VIP and AVP regulate, at least in part, Ca(2+) homeostasis in SCN neurons and may be a major point of regulation for SCN neuronal synchronization.
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Affiliation(s)
- Robert P Irwin
- Center for Research on Occupational and Environmental Toxicology (CROET), Oregon Health & Science University, L-606, Portland, OR, 97239 USA.
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68
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Abstract
Mammalian circadian rhythms are controlled by endogenous biological oscillators, including a master clock located in the hypothalamic suprachiasmatic nuclei (SCN). Since the period of this oscillation is of approximately 24 h, to keep synchrony with the environment, circadian rhythms need to be entrained daily by means of Zeitgeber ("time giver") signals, such as the light-dark cycle. Recent advances in the neurophysiology and molecular biology of circadian rhythmicity allow a better understanding of synchronization. In this review we cover several aspects of the mechanisms for photic entrainment of mammalian circadian rhythms, including retinal sensitivity to light by means of novel photopigments as well as circadian variations in the retina that contribute to the regulation of retinal physiology. Downstream from the retina, we examine retinohypothalamic communication through neurotransmitter (glutamate, aspartate, pituitary adenylate cyclase-activating polypeptide) interaction with SCN receptors and the resulting signal transduction pathways in suprachiasmatic neurons, as well as putative neuron-glia interactions. Finally, we describe and analyze clock gene expression and its importance in entrainment mechanisms, as well as circadian disorders or retinal diseases related to entrainment deficits, including experimental and clinical treatments.
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Affiliation(s)
- Diego A Golombek
- Laboratory of Chronobiology, Department of Science and Technology, University of Quilmes/Consejo Nacional de Investigaciones Científicas y Tecnológicas (CONICET), Quilmes, Argentina.
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69
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Wulff K, Gatti S, Wettstein JG, Foster RG. Sleep and circadian rhythm disruption in psychiatric and neurodegenerative disease. Nat Rev Neurosci 2010; 11:589-99. [DOI: 10.1038/nrn2868] [Citation(s) in RCA: 682] [Impact Index Per Article: 48.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
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70
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Chronic treatment with a selective inhibitor of casein kinase I delta/epsilon yields cumulative phase delays in circadian rhythms. Psychopharmacology (Berl) 2010; 210:569-76. [PMID: 20407760 DOI: 10.1007/s00213-010-1860-5] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/23/2010] [Accepted: 03/31/2010] [Indexed: 12/21/2022]
Abstract
INTRODUCTION Casein kinase I epsilon/delta phosphorylates certain clock-related proteins as part of a complex arrangement of transcriptional/translational feedback loops that comprise the circadian oscillator in mammals. Pharmacologic inhibition leads to a delay of the oscillations with the magnitude of this effect dependent upon the timing of drug administration. OBJECTIVE Earlier studies by our lab described the actions of a selective CKI epsilon/delta inhibitor, PF-670462, on circadian behavior following acute dosing; the present work extended these studies to chronic once-daily treatment. METHODS Gross motor activity was used to estimate the circadian rhythms of rats maintained under a 12 L:12 D cycle. PF-670462, 10 or 30 mg/kg/day s.c., was administered once daily for 20 days either at ZT6 or ZT11 (i.e., 6 or 11 h after light onset). RESULTS Chronic administration of PF-670462, performed at a fixed time of day, produced delays in the activity onsets of rats that cumulated with the duration of dosing. Dosing at ZT11 yielded more robust delays than dosing at ZT6 in keeping with earlier phase-response analyses with this agent. CONCLUSIONS The magnitude of the shifts in activity onsets achieved with chronic dosing of PF-670462 appears to be a function of the dose and the previously established phase relationship. Its cumulative effect further suggests that the pharmacodynamic t (1/2) of the drug greatly exceeds its pharmacokinetic one. Most importantly, these changes in circadian behavior occurred in the presence of a fixed L:D cycle, confirming the drug to be a robust modulator of circadian phase in the presence of the natural zeitgeber.
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71
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Yasenkov R, Deboer T. Circadian regulation of sleep and the sleep EEG under constant sleep pressure in the rat. Sleep 2010; 33:631-41. [PMID: 20469805 DOI: 10.1093/sleep/33.5.631] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
STUDY OBJECTIVE Sleep is regulated by homeostatic and circadian processes. Slow wave activity (SWA; 1-4 Hz) in the NREM sleep electroencephalogram (EEG) reflects sleep homeostasis. Activity of faster EEG frequencies (10-25 Hz) is thought to be under influence of circadian factors. The relative contribution of both processes to the distribution of sleep and wakefulness and EEG activity in rodents remains uncertain. DESIGN Continuous EEG recording in rats in constant dark conditions (DD) were performed and a sleep deprivation protocol consisting of 2 h sleep deprivation followed by 2 h of rest (2h/2h) was applied for 48 h to obtain a constant sleep pressure. SETTINGS Basic sleep research laboratory. PATIENTS OR PARTICIPANTS Adult male Wistar rats. INTERVENTION Sleep deprivation. MEASUREMENTS AND RESULTS Under the 2h/2h protocol, the circadian modulation of waking, NREM and REM sleep was markedly reduced compared to the baseline, affecting the frequency of vigilance state episodes and the duration of REM sleep and waking episodes. In contrast, NREM sleep episode duration still showed a daily modulation. Consecutive 2h values of SWA in NREM sleep were stabile during the 2h\2h protocol, while NREM sleep EEG activity within the higher frequencies (7-25 Hz) still demonstrated strong circadian modulation, which did not differ from baseline. CONCLUSIONS In rats, the daily modulation of REM sleep is less pronounced compared to NREM sleep and waking. In contrast to SWA, activity in higher frequencies (7-25 Hz) in the NREM sleep EEG have an endogenous circadian origin and are not influenced by sleep homeostatic mechanisms.
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Affiliation(s)
- Roman Yasenkov
- Laboratory for Neurophysiology, Department of Molecular Cell Biology Leiden University Medical Center, Leiden, The Netherlands
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72
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Bottum K, Poon E, Haley B, Karmarkar S, Tischkau SA. Suprachiasmatic nucleus neurons display endogenous resistance to excitotoxicity. Exp Biol Med (Maywood) 2010; 235:237-46. [PMID: 20404040 DOI: 10.1258/ebm.2009.009244] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
A comprehensive understanding of neuroprotective pathways is essential to progress in the battle against numerous neurodegenerative conditions. The hypothalamic suprachiasmatic nucleus (SCN) is endogenously resistant to glutamate (Glu) excitotoxicity in vivo. This study was designed to determine whether immortalized SCN neurons (SCN2.2 cells) retain this characteristic. We first established that SCN2.2 cells retained the ability to respond to Glu. SCN2.2 cells expressed N-methyl-d-aspartate (NMDA) receptor subtypes NR1 and NR2A/2B, suggesting the presence of functional receptors. mRNA for the NMDA receptor subunits NR2A and NR2B were higher in the SCN2.2 than in the control hypothalamic neurons (GT1-7). Specific NMDA receptor antagonists (+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5,10-imine maleate and d-(-)-2-amino-5-phosphonovaleric acid blocked Glu-induced activation of gene expression. SCN2.2 cells were resistant to Glu excitotoxicity compared with GT1-7 neurons as assessed with a mitochondrial function assay, cell death by trypan blue exclusion and apoptosis by terminal deoxynucleotidyl transferase dUTP nick end labeling. SCN2.2 resistance to Glu excitoxicity was retained in the presence of the broad spectrum Glu transport inhibitor, l-trans-pyrrolidine-2,4 dicarboxylate, excluding glial Glu uptake as a major neuroprotective mechanism. Collectively, these observations demonstrate endogenous neuroprotection in SCN2.2 cells; this cell line is resistant to excitotoxicity under conditions that are toxic to other immortalized cell lines. Thus, the SCN2.2 cell line may provide insights into the molecular mechanisms that confer endogenous neuroprotection in the SCN.
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Affiliation(s)
- Kathleen Bottum
- Department of Medicine, Division of Internal Medicine and Psychiatry, Southern Illinois School of Medicine, Springfield, IL 62794-9636, USA
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73
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Central clock excites vasopressin neurons by waking osmosensory afferents during late sleep. Nat Neurosci 2010; 13:467-74. [PMID: 20190744 DOI: 10.1038/nn.2503] [Citation(s) in RCA: 74] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/16/2009] [Accepted: 01/08/2010] [Indexed: 02/08/2023]
Abstract
Osmoregulated vasopressin release is facilitated during the late sleep period (LSP) to prevent dehydration and enuresis. Previous work has shown that clock neurons in the suprachiasmatic nucleus (SCN) have low firing rates during the LSP, but it is not known how this reduced activity enhances vasopressin release. We found that synaptic excitation of rat supraoptic nucleus neurons by osmosensory afferents is facilitated during the LSP. Stimulation of the SCN at this time inhibited excitatory synaptic currents induced in supraoptic neurons by activation of osmosensory afferents. This effect was associated with an increased rate of synaptic failures and occurred without changes in frequency facilitation, quantal size or in the ratio of postsynaptic responses mediated by AMPA and NMDA receptors. We conclude that clock neurons mediate an activity-dependent presynaptic silencing of osmosensory afferent synapses onto vasopressin neurons and that osmoregulatory gain is enhanced by removal of this effect during late sleep.
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74
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Girardet C, Blanchard MP, Ferracci G, Lévêque C, Moreno M, François-Bellan AM, Becquet D, Bosler O. Daily changes in synaptic innervation of VIP neurons in the rat suprachiasmatic nucleus: contribution of glutamatergic afferents. Eur J Neurosci 2010; 31:359-70. [PMID: 20074215 DOI: 10.1111/j.1460-9568.2009.07071.x] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
The daily temporal organization of rhythmic functions in mammals, which requires synchronization of the circadian clock to the 24-h light-dark cycle, is believed to involve adjustments of the mutual phasing of the cellular oscillators that comprise the time-keeper within the suprachiasmatic nucleus of the hypothalamus (SCN). Following from a previous study showing that the SCN undergoes day/night rearrangements of its neuronal-glial network that may be crucial for intercellular phasing, we investigated the contribution of glutamatergic synapses, known to play major roles in SCN functioning, to such rhythmic plastic events. Neither expression levels of the vesicular glutamate transporters nor numbers of glutamatergic terminals showed nycthemeral variations in the SCN. However, using quantitative imaging after combined immunolabelling, the density of synapses on neurons expressing vasoactive intestinal peptide, known as targets of the retinal input, increased during the day and both glutamatergic and non-glutamatergic synapses contributed to the increase (+36%). This was not the case for synapses made on vasopressin-containing neurons, the other major source of SCN efferents in the non-retinorecipient region. Together with electron microscope observations showing no differences in the morphometric features of glutamatergic terminals during the day and night, these data show that the light synchronization process in the SCN involves a selective remodelling of synapses at sites of photic integration. They provide a further illustration of how the adult brain may rapidly and reversibly adapt its synaptic architecture to functional needs.
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Affiliation(s)
- Clémence Girardet
- Centre de Recherche en Neurobiologie et Neurophysiologie de Marseille (CRN2M), CNRS-UMR 6231, Université de la Méditerranée, Faculté de Médecine Nord, Marseille, France
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75
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Abstract
The suprachiasmatic nucleus (SCN) is the primary circadian pacemaker in mammals. Individual SCN neurons in dispersed culture can generate independent circadian oscillations of clock gene expression and neuronal firing. However, SCN rhythmicity depends on sufficient membrane depolarization and levels of intracellular calcium and cAMP. In the intact SCN, cellular oscillations are synchronized and reinforced by rhythmic synaptic input from other cells, resulting in a reproducible topographic pattern of distinct phases and amplitudes specified by SCN circuit organization. The SCN network synchronizes its component cellular oscillators, reinforces their oscillations, responds to light input by altering their phase distribution, increases their robustness to genetic perturbations, and enhances their precision. Thus, even though individual SCN neurons can be cell-autonomous circadian oscillators, neuronal network properties are integral to normal function of the SCN.
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Affiliation(s)
- David K Welsh
- Department of Psychiatry, University of California-San Diego, La Jolla, CA 92093, USA.
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76
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Akiyama S, Ohta H, Watanabe S, Moriya T, Hariu A, Nakahata N, Chisaka H, Matsuda T, Kimura Y, Tsuchiya S, Tei H, Okamura K, Yaegashi N. The Uterus Sustains Stable Biological Clock during Pregnancy. TOHOKU J EXP MED 2010; 221:287-98. [DOI: 10.1620/tjem.221.287] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Affiliation(s)
- Shizuko Akiyama
- Center for Perinatal Medicine, Tohoku University Hospital
- Department of Pediatrics, Tohoku University Hospital
| | - Hidenobu Ohta
- Center for Perinatal Medicine, Tohoku University Hospital
- Department of Pediatrics, Tohoku University Hospital
- Department of Obstetrics and Gynecology, Tohoku University Hospital
| | - Shimpei Watanabe
- Center for Perinatal Medicine, Tohoku University Hospital
- Department of Pediatrics, Tohoku University Hospital
| | - Takahiro Moriya
- Department of Cellular Signaling, Graduate School of Pharmaceutical Sciences, Tohoku University
| | - Aya Hariu
- Department of Cellular Signaling, Graduate School of Pharmaceutical Sciences, Tohoku University
| | - Norimichi Nakahata
- Department of Cellular Signaling, Graduate School of Pharmaceutical Sciences, Tohoku University
| | - Hiroshi Chisaka
- Center for Perinatal Medicine, Tohoku University Hospital
- Department of Obstetrics and Gynecology, Tohoku University Hospital
| | - Tadashi Matsuda
- Center for Perinatal Medicine, Tohoku University Hospital
- Department of Pediatrics, Tohoku University Hospital
| | - Yoshitaka Kimura
- Tohoku University Institute for International Advanced Research and Education
| | - Shigeru Tsuchiya
- Department of Obstetrics and Gynecology, Tohoku University Hospital
| | - Hajime Tei
- Kanazawa University Institute of Science and Engineering Faculty of Natural System
| | - Kunihiro Okamura
- Center for Perinatal Medicine, Tohoku University Hospital
- Department of Obstetrics and Gynecology, Tohoku University Hospital
| | - Nobuo Yaegashi
- Center for Perinatal Medicine, Tohoku University Hospital
- Department of Obstetrics and Gynecology, Tohoku University Hospital
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77
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Ospeck MC, Coffey B, Freeman D. Light-dark cycle memory in the mammalian suprachiasmatic nucleus. Biophys J 2009; 97:1513-24. [PMID: 19751655 DOI: 10.1016/j.bpj.2009.06.010] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/23/2008] [Revised: 05/18/2009] [Accepted: 06/08/2009] [Indexed: 11/15/2022] Open
Abstract
The mammalian circadian oscillator, or suprachiasmatic nucleus (SCN), contains several thousand clock neurons in its ventrolateral division, many of which are spontaneous oscillators with period lengths that range from 22 to 28 h. In complete darkness, this network synchronizes through the exchange of action potentials that release vasoactive intestinal polypeptide, striking a compromise, free-running period close to 24 h long. We entrained Siberian hamsters to various light-dark cycles and then tracked their activity into constant darkness to show that they retain a memory of the previous light-dark cycle before returning to their own free-running period. Employing Leloup-Goldbeter mammalian clock neurons we model the ventrolateral SCN network and show that light acting weakly upon a strongly rhythmic vasoactive intestinal polypeptide oscillation can explain the observed light-dark cycle memory. In addition, light is known to initiate a mitogen-activated protein kinase signaling cascade that induces transcription of both per and mkp1 phosphatase. We show that the ensuing phosphatase-kinase interaction can account for the dead zone in the mammalian phase response curve and hypothesize that the SCN behaves like a lock-in amplifier to entrain to the light edges of the circadian day.
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Affiliation(s)
- Mark C Ospeck
- Physics Department, University of Memphis, Memphis, Tennessee, USA.
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78
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Deery MJ, Maywood ES, Chesham JE, Sládek M, Karp NA, Green EW, Charles PD, Reddy AB, Kyriacou CP, Lilley KS, Hastings MH. Proteomic analysis reveals the role of synaptic vesicle cycling in sustaining the suprachiasmatic circadian clock. Curr Biol 2009; 19:2031-6. [PMID: 19913422 DOI: 10.1016/j.cub.2009.10.024] [Citation(s) in RCA: 80] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/15/2009] [Revised: 10/06/2009] [Accepted: 10/08/2009] [Indexed: 10/20/2022]
Abstract
The central circadian pacemaker of the suprachiasmatic nucleus (SCN) is characterized as a series of transcriptional/posttranslational feedback loops. How this molecular mechanism coordinates daily rhythms in the SCN and hence the organism is poorly understood. We conducted the first systematic exploration of the "circadian intracellular proteome" of the SCN and revealed that approximately 13% of soluble proteins are subject to circadian regulation. Many of these proteins have underlying nonrhythmic mRNAs, so they have not previously been noted as circadian. Circadian proteins of the SCN include rate-limiting factors in metabolism, protein trafficking, and, intriguingly, synaptic vesicle recycling. We investigated the role of this clock-regulated pathway by treating organotypic cultures of SCN with botulinum toxin A or dynasore to block exocytosis and endocytosis. These manipulations of synaptic vesicle recycling compromised circadian gene expression, both across the SCN as a circuit and within individual SCN neurons. These findings reveal how basic cellular processes within the SCN are subject to circadian regulation and how disruption of these processes interferes with SCN cellular pacemaking. Specifically, we highlight synaptic vesicle cycling as a novel point of clock cell regulation in mammals.
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Affiliation(s)
- Michael J Deery
- Cambridge Centre for Proteomics, Department of Biochemistry, University of Cambridge, Tennis Court Road, Cambridge CB2 1QR, UK
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79
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Furness SGB, Whelan F. The pleiotropy of dioxin toxicity--xenobiotic misappropriation of the aryl hydrocarbon receptor's alternative physiological roles. Pharmacol Ther 2009; 124:336-53. [PMID: 19781569 DOI: 10.1016/j.pharmthera.2009.09.004] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/31/2009] [Accepted: 09/01/2009] [Indexed: 10/20/2022]
Abstract
The aryl hydrocarbon receptor is a signal regulated transcription factor that has best been characterised as regulating the xenobiotic response to a variety of planar aromatic hydrocarbons. There is compelling evidence that it mediates most, if not all, of the toxic effects of dioxin (2,3,7,8-tetrachlorodibenzo-p-dioxin). Dioxin exposure results in a wide variety of toxic outcomes including severe wasting syndrome, chloracne, thymic involution, severe immune suppression, reduced fertility, hepatotoxicity, teratogenicity, tumour promotion and death. The pleiotropy of toxic outcomes implies the disruption of a wide range of normal physiological functions. The aryl hydrocarbon receptor has developmentally restricted expression as well as developmental defects in gene-targeted mice. It has a wide range of target genes that do not fit into the classical xenobiotic metabolising gene battery and has recently been shown to interact with NF-kappa B and the estrogen receptor. There is also evidence for its activation in the absence of exogenous ligand, all of which point to various roles outside xenobiotic metabolism. Ligands so far identified display differential activation potential with respect to receptor activity. This article addresses activities of the aryl hydrocarbon receptor that are outside the xenobiotic response. Known physiological roles are discussed as well as how their disruption contributes to the pleiotropic toxicity of TCDD.
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Affiliation(s)
- Sebastian G B Furness
- Drug Discovery Biology Laboratory, Monash Institute of Pharmaceutical Sciences, Monash University, Parkville, Victoria 3052, Australia.
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80
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Zhang X, Dube TJ, Esser KA. Working around the clock: circadian rhythms and skeletal muscle. J Appl Physiol (1985) 2009; 107:1647-54. [PMID: 19696362 DOI: 10.1152/japplphysiol.00725.2009] [Citation(s) in RCA: 42] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The study of the circadian molecular clock in skeletal muscle is in the very early stages. Initial research has demonstrated the presence of the molecular clock in skeletal muscle and that skeletal muscle of a clock-compromised mouse, Clock mutant, exhibits significant disruption in normal expression of many genes required for adult muscle structure and metabolism. In light of the growing association between the molecular clock, metabolism, and metabolic disease, it will also be important to understand the contribution of circadian factors to normal metabolism, metabolic responses to muscle training, and contribution of the molecular clock in muscle-to-muscle disease (e.g., insulin resistance). Consistent with the potential for the skeletal muscle molecular clock modulating skeletal muscle physiology, there are findings in the literature that there is significant time-of-day effects for strength and metabolism. Additionally, there is some recent evidence that temporal specificity is important for optimizing training for muscular performance. While these studies do not prove that the molecular clock in skeletal muscle is important, they are suggestive of a circadian contribution to skeletal muscle function. The application of well-established models of skeletal muscle research in function and metabolism with available genetic models of molecular clock disruption will allow for more mechanistic understanding of potential relationships.
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Affiliation(s)
- Xiping Zhang
- Center for Muscle Biology, Dept. of Physiology, Chandler College of Medicine, Univ. of Kentucky, 800 Rose St., Lexington, KY 40536, USA
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81
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Sleep and circadian rhythm disturbances: multiple genes and multiple phenotypes. Curr Opin Genet Dev 2009; 19:237-46. [PMID: 19423332 DOI: 10.1016/j.gde.2009.03.007] [Citation(s) in RCA: 67] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/22/2009] [Revised: 03/16/2009] [Accepted: 03/20/2009] [Indexed: 11/23/2022]
Abstract
Sleep is regulated by two broad mechanisms: the circadian system, which generates 24-h rhythms of sleep propensity and a wake-dependent homeostatic sleep process whereby sleep pressure increases during wake and dissipates during sleep. These, in turn, regulate multiple brain structures and neurotransmitter systems. In view of the complexity of sleep it is not surprising that there is considerable variation between individuals in both sleep timing and propensity. Furthermore, marked abnormalities in sleep are commonly encountered in psychiatric and neurodegenerative disorders. Teasing apart the genetic versus environmental contributions to normal and abnormal sleep is complex. Here we attempt to summarise what recent progress has been made, and what will be needed in the future to gain a more complete understanding of this fundamental aspect of physiology.
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82
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de Vries GJ, Södersten P. Sex differences in the brain: the relation between structure and function. Horm Behav 2009; 55:589-96. [PMID: 19446075 PMCID: PMC3932614 DOI: 10.1016/j.yhbeh.2009.03.012] [Citation(s) in RCA: 121] [Impact Index Per Article: 8.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/07/2009] [Revised: 03/10/2009] [Accepted: 03/12/2009] [Indexed: 11/24/2022]
Abstract
In the fifty years since the organizational hypothesis was proposed, many sex differences have been found in behavior as well as structure of the brain that depend on the organizational effects of gonadal hormones early in development. Remarkably, in most cases we do not understand how the two are related. This paper makes the case that overstating the magnitude or constancy of sex differences in behavior and too narrowly interpreting the functional consequences of structural differences are significant roadblocks in resolving this issue.
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Affiliation(s)
- Geert J de Vries
- Department of Psychology and Center for Neuroendocrine Studies, Tobin Hall, University of Massachusetts, Amherst, MA 01003 9333, USA.
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83
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Bosler O, Girardet C, Sage-Ciocca D, Jacomy H, François-Bellan AM, Becquet D. Mécanismes de plasticité structurale associés à la synchronisation photique de l'horloge circadienne au sein du noyau suprachiasmatique. ACTA ACUST UNITED AC 2009; 203:49-63. [DOI: 10.1051/jbio:2009004] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022]
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84
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Abstract
Glucocorticoids, hormones produced by the adrenal gland cortex, perform numerous functions in body homeostasis and the response of the organism to external stressors. One striking feature of their regulation is a diurnal release pattern, with peak levels linked to the start of the activity phase. This release is under control of the circadian clock, an endogenous biological timekeeper that acts to prepare the organism for daily changes in its environment. Circadian control of glucocorticoid production and secretion involves a central pacemaker in the hypothalamus, the suprachiasmatic nucleus, as well as a circadian clock in the adrenal gland itself. Central circadian regulation is mediated via the hypothalamic-pituitary-adrenal axis and the autonomic nervous system, while the adrenal gland clock appears to control sensitivity of the gland to the adrenocorticopic hormone (ACTH). The rhythmically released glucocorticoids in turn might contribute to synchronisation of the cell-autonomous clocks in the body and interact with them to time physiological dynamics in their target tissues around the day.
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Affiliation(s)
- Thomas Dickmeis
- Institute of Toxicology and Genetics, Forschungszentrum Karlsruhe, Eggenstein-Leopoldshafen, Germany.
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85
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Current world literature. Ageing: biology and nutrition. Curr Opin Clin Nutr Metab Care 2009; 12:95-100. [PMID: 19057195 DOI: 10.1097/mco.0b013e32831fd97a] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
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86
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House SB, Li C, Yue C, Gainer H. Effects of ciliary neurotrophic factor and leukemia inhibiting factor on oxytocin and vasopressin magnocellular neuron survival in rat and mouse hypothalamic organotypic cultures. J Neurosci Methods 2008; 178:128-33. [PMID: 19118574 DOI: 10.1016/j.jneumeth.2008.12.004] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/08/2008] [Revised: 12/03/2008] [Accepted: 12/03/2008] [Indexed: 12/16/2022]
Abstract
Organotypic cultures of mouse and rat magnocellular neurons (MCNs) in the hypothalamo-neurohypophysial system (HNS) have served as important experimental models for the molecular and physiological study of this neuronal phenotype. However, it has been difficult to maintain significant numbers of the MCNs, particularly vasopressin MCNs, in these cultures for long periods. In this paper, we describe the use of the neurotrophic factors, leukemia inhibiting factor (LIF) and ciliary neurotrophic factor (CNTF) to rescue rat vasopressin (Avp)- and oxytocin (Oxt)-MCNs from axotomy-induced, programmed cell death in vitro. Quantitative data are presented for the efficacy of the LIF family of neurotrophic factors on the survival of MCNs in three nuclei, the paraventricular (PVN), supraoptic (SON), and accessory (ACC) nuclei in the mouse and rat hypothalamus.
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Affiliation(s)
- Shirley B House
- Molecular Neuroscience Section, Laboratory of Neurochemistry, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD 20892, USA
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87
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Abstract
Circadian rhythms coordinate our physiology at a fundamental level. Over the last 20 years, we have witnessed a paradigm shift in our perception of what the clocks driving such rhythms actually are, moving from 'black boxes' to talking about autoregulatory transcriptional/post-translational feedback loops with identified molecular components. We also now know that the pacemaker of the suprachiasmatic nuclei (SCN) is not our only clock but quite the opposite because circadian clocks abound in our bodies, driving local rhythms of cellular metabolism, and synchronised to each other and to solar time, by cues from the SCN. This discovery of dispersed local clocks has far-reaching implications for understanding our physiology and the pathological consequences of clock dysfunction, revealing that clocks are critical in a variety of metabolic and neurological conditions, all of which have long-term morbidity attributable to them. Without the currently available molecular framework, these insights would have not have been possible. In the circadian future, a growing appreciation of the systems-level functioning of these clocks and their various cerebral and visceral outputs, will likely stimulate the development of novel therapies for major illnesses.
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Affiliation(s)
- M H Hastings
- Division of Neurobiology, MRC Laboratory of Molecular Biology, Cambridge, UK.
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88
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Abstract
A network of feedback loops constitutes the basis for circadian timing in mammals. Complex transcriptional, post-transcriptional and post-translational events are also involved in the ticking of circadian clocks, allowing them to run autonomously with their characteristic, near-24h period. Central to the molecular mechanism is the CLOCK/BMAL1 heterodimer of transcription factors. Recent data using Clock knock-out mice however suggest that CLOCK may not be as mandatory as initially suggested from data gathered in the Clock mutant mouse model. Indeed, it appears that the Clock homolog Npas2 is able to functionally compensate for Clock genetic ablation. Furthermore, real-time imaging techniques using different clock genes knock-out lines established on a PER2 ::Luc knock-in background now demonstrate that persistent rhythmicity in the suprachiasmatic nuclei likely arises as a consequence of combined genetic redundancy and strong intercellular coupling, the latter characteristic being likely weakened in peripheral tissues such as liver or lung. The present review aims at summarizing current knowledge of the molecular basis of circadian clocks and possible differences between central and peripheral clocks in light of recent findings in Clock knock-out mice.
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Affiliation(s)
- Hugues Dardente
- School of Biological Sciences, Zoology Building, Tillydrone Avenue, Aberdeen AB24 2TZ, Ecosse, Royaume-Uni.
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89
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Maywood ES, O'Neill JS, Reddy AB, Chesham JE, Prosser HM, Kyriacou CP, Godinho SIH, Nolan PM, Hastings MH. Genetic and molecular analysis of the central and peripheral circadian clockwork of mice. COLD SPRING HARBOR SYMPOSIA ON QUANTITATIVE BIOLOGY 2007; 72:85-94. [PMID: 18419265 DOI: 10.1101/sqb.2007.72.005] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/26/2023]
Abstract
A hierarchy of interacting, tissue-based clocks controls circadian physiology and behavior in mammals. Preeminent are the suprachiasmatic nuclei (SCN): central hypothalamic pacemakers synchronized to solar time via retinal afferents and in turn responsible for internal synchronization of other clocks present in major organ systems. The SCN and peripheral clocks share essentially the same cellular timing mechanism. This consists of autoregulatory transcriptional/posttranslational feedback loops in which the Period (Per) and Cryptochrome (Cry) "clock" genes are negatively regulated by their protein products. Here, we review recent studies directed at understanding the molecular and cellular bases to the mammalian clock. At the cellular level, we demonstrate the role of F-box protein Fbxl3 (characterized by the afterhours mutation) in directing the proteasomal degradation of Cry and thereby controlling negative feedback and circadian period of the molecular loops. Within SCN neural circuitry, we describe how neuropeptidergic signaling by VIP synchronizes and sustains the cellular clocks. At the hypothalamic level, signaling via a different SCN neuropeptide, prokineticin, is not required for pacemaking but is necessary for control of circadian behavior. Finally, we consider how metabolic pathways are coordinated in time, focusing on liver function and the role of glucocorticoid signals in driving the circadian transcriptome and proteome.
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Affiliation(s)
- E S Maywood
- Division of Neurobiology, MRC Laboratory of Molecular Biology, Cambridge CB2 0QH, United Kingdom
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