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Aryal RP, Kwak PB, Tamayo AG, Gebert M, Chiu PL, Walz T, Weitz CJ. Macromolecular Assemblies of the Mammalian Circadian Clock. Mol Cell 2017; 67:770-782.e6. [PMID: 28886335 PMCID: PMC5679067 DOI: 10.1016/j.molcel.2017.07.017] [Citation(s) in RCA: 161] [Impact Index Per Article: 23.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/17/2017] [Revised: 06/14/2017] [Accepted: 07/13/2017] [Indexed: 10/18/2022]
Abstract
The mammalian circadian clock is built on a feedback loop in which PER and CRY proteins repress their own transcription. We found that in mouse liver nuclei all three PERs, both CRYs, and Casein Kinase-1δ (CK1δ) are present together in an ∼1.9-MDa repressor assembly that quantitatively incorporates its CLOCK-BMAL1 transcription factor target. Prior to incorporation, CLOCK-BMAL1 exists in an ∼750-kDa complex. Single-particle electron microscopy (EM) revealed nuclear PER complexes purified from mouse liver to be quasi-spherical ∼40-nm structures. In the cytoplasm, PERs, CRYs, and CK1δ were distributed into several complexes of ∼0.9-1.1 MDa that appear to constitute an assembly pathway regulated by GAPVD1, a cytoplasmic trafficking factor. Single-particle EM of two purified cytoplasmic PER complexes revealed ∼20-nm and ∼25-nm structures, respectively, characterized by flexibly tethered globular domains. Our results define the macromolecular assemblies comprising the circadian feedback loop and provide an initial structural view of endogenous eukaryotic clock machinery.
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Affiliation(s)
- Rajindra P Aryal
- Department of Neurobiology, Harvard Medical School, Boston, MA 02115, USA
| | - Pieter Bas Kwak
- Department of Neurobiology, Harvard Medical School, Boston, MA 02115, USA
| | - Alfred G Tamayo
- Department of Neurobiology, Harvard Medical School, Boston, MA 02115, USA
| | - Michael Gebert
- Department of Neurobiology, Harvard Medical School, Boston, MA 02115, USA
| | - Po-Lin Chiu
- Department of Cell Biology, Harvard Medical School, Boston, MA 02115, USA
| | - Thomas Walz
- Laboratory of Molecular Electron Microscopy, Rockefeller University, New York, NY 10065, USA
| | - Charles J Weitz
- Department of Neurobiology, Harvard Medical School, Boston, MA 02115, USA.
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Islam ZU, Bishop SC, Savill NJ, Rowland RRR, Lunney JK, Trible B, Doeschl-Wilson AB. Quantitative analysis of porcine reproductive and respiratory syndrome (PRRS) viremia profiles from experimental infection: a statistical modelling approach. PLoS One 2013; 8:e83567. [PMID: 24358295 PMCID: PMC3866253 DOI: 10.1371/journal.pone.0083567] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/17/2013] [Accepted: 11/13/2013] [Indexed: 11/18/2022] Open
Abstract
Porcine reproductive and respiratory syndrome (PRRS) is one of the most economically significant viral diseases facing the global swine industry. Viremia profiles of PRRS virus challenged pigs reflect the severity and progression of infection within the host and provide crucial information for subsequent control measures. In this study we analyse the largest longitudinal PRRS viremia dataset from an in-vivo experiment. The primary objective was to provide a suitable mathematical description of all viremia profiles with biologically meaningful parameters for quantitative analysis of profile characteristics. The Wood's function, a gamma-type function, and a biphasic extended Wood's function were fit to the individual profiles using Bayesian inference with a likelihood framework. Using maximum likelihood inference and numerous fit criteria, we established that the broad spectrum of viremia trends could be adequately represented by either uni- or biphasic Wood's functions. Three viremic categories emerged: cleared (uni-modal and below detection within 42 days post infection(dpi)), persistent (transient experimental persistence over 42 dpi) and rebound (biphasic within 42 dpi). The convenient biological interpretation of the model parameters estimates, allowed us not only to quantify inter-host variation, but also to establish common viremia curve characteristics and their predictability. Statistical analysis of the profile characteristics revealed that persistent profiles were distinguishable already within the first 21 dpi, whereas it is not possible to predict the onset of viremia rebound. Analysis of the neutralizing antibody(nAb) data indicated that there was a ubiquitous strong response to the homologous PRRSV challenge, but high variability in the range of cross-protection of the nAbs. Persistent pigs were found to have a significantly higher nAb cross-protectivity than pigs that either cleared viremia or experienced rebound within 42 dpi. Our study provides novel insights into the nature and degree of variation of hosts' responses to infection as well as new informative traits for subsequent genomic and modelling studies.
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Affiliation(s)
- Zeenath U. Islam
- The Roslin Institute & R(D)SVS, University of Edinburgh, Edinburgh, Midlothian, United Kingdom
- * E-mail:
| | - Stephen C. Bishop
- The Roslin Institute & R(D)SVS, University of Edinburgh, Edinburgh, Midlothian, United Kingdom
| | - Nicholas J. Savill
- Institute of Immunology and Infection Research, University of Edinburgh, Edinburgh, United Kingdom
| | - Raymond R. R. Rowland
- Department of Diagnostic Medicine and Pathobiology, College of Veterinary Medicine, Kansas State University, Manhattan, Kansas, United States of America
| | - Joan K. Lunney
- United State Department of Agriculture, Beltsville Agricultural Research Center, Beltsville, Maryland, United States of America
| | - Benjamin Trible
- Department of Diagnostic Medicine and Pathobiology, College of Veterinary Medicine, Kansas State University, Manhattan, Kansas, United States of America
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3
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A cybernetic perspective on food protection in rats: simple rules can generate complex and adaptable behaviour. Anim Behav 2011. [DOI: 10.1016/j.anbehav.2011.06.016] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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4
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Maex R, Steuber V. The first second: models of short-term memory traces in the brain. Neural Netw 2009; 22:1105-12. [PMID: 19635658 DOI: 10.1016/j.neunet.2009.07.022] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/25/2009] [Revised: 05/26/2009] [Accepted: 07/14/2009] [Indexed: 10/20/2022]
Abstract
Many network models in computational neuroscience rise to the challenge of explaining behavioural phenomena ranging from microseconds to tens of seconds using components operating mostly on a time-scale of milliseconds. These models have in common that the underlying system has a memory, which implies that its output depends on its past input history. In this review we compare how such memory traces or delayed responses may be implemented in different brain areas supporting a diversity of functions.
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Affiliation(s)
- Reinoud Maex
- Science and Technology Research Institute, University of Hertfordshire, College Lane, Hatfield, Hertfordshire, United Kingdom.
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Youan BBC. Chronopharmaceutics: gimmick or clinically relevant approach to drug delivery? J Control Release 2004; 98:337-53. [PMID: 15312991 DOI: 10.1016/j.jconrel.2004.05.015] [Citation(s) in RCA: 87] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/09/2004] [Accepted: 05/25/2004] [Indexed: 10/26/2022]
Abstract
Due to advances in chronobiology, chronopharmacology, and global market constraints, the traditional goal of pharmaceutics (e.g. design drug delivery systems with a constant drug release rate) is becoming obsolete. However, the major bottleneck in the development of drug delivery systems that match the circadian rhythm (chronopharmaceutical drug delivery systems: ChrDDS) may be the availability of appropriate technology. The last decade has witnessed the emergence of ChrDDS against several diseases. The increasing research interest surrounding ChrDDS may lead to the creation of a new sub-discipline in pharmaceutics known as chronopharmaceutics. This review introduces the concept of chronopharmaceutics, addresses theoretical/formal approaches to this sub-discipline, underscores potential disease-targets, revisits existing technologies and examples of ChrDDS. Future development in chronopharmaceutics may be made at the interface of other emerging disciplines such as system biology and nanomedicine. Such novel and more biological approaches to drug delivery may lead to safer and more efficient disease therapy in the future.
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Affiliation(s)
- Bi-Botti C Youan
- Department of Pharmaceutical Sciences, School of Pharmacy, Texas Tech University Health Sciences Center School of Pharmacy, Amarillo 1300, Coulter, TX 79106, USA.
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6
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Farhy LS, Veldhuis JD. Putative GH pulse renewal: periventricular somatostatinergic control of an arcuate-nuclear somatostatin and GH-releasing hormone oscillator. Am J Physiol Regul Integr Comp Physiol 2004; 286:R1030-42. [PMID: 14988084 DOI: 10.1152/ajpregu.00473.2003] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Growth hormone (GH) pulsatility requires periventricular-nuclear somatostatin(SRIF(PeV)), arcuate-nuclear (ArC) GH-releasing hormone (GHRH), and systemic GH autofeedback. However, no current formalism interlinks these regulatory loci in a manner that generates self-renewable GH dynamics. The latter must include in the adult rat 1) infrequent volleys of high-amplitude GH peaks in the male, 2) frequent discrete low-amplitude GH pulses in the female, 3) disruption of the male pattern by severing SRIF(PeV) outflow to ArC, 4) stimulation of GHRH and GH secretion by central nervous system delivery of SRIF, 5) inhibition of GH release by central exposure to GHRH, and 6) a reboundlike burst of GHRH secretion induced by stopping peripheral infusion of SRIF. The present study validates by computer-assisted simulations a simplified ensemble formulation that predicts each of the foregoing six outcomes, wherein 1) blood-borne GH stimulates SRIF(PeV) secretion after a long time latency, 2) SRIF(PeV) inhibits both pituitary GH and ArC GHRH release, 3) ArC GHRH and SRIF(ArC) oscillate reciprocally with brief time delay, and 4) SRIF(PeV) represses and disinhibits the putative GHRH-SRIF(ArC) oscillator. According to the present analytic construction, time-delayed feedforward and feedback signaling among SRIF(PeV), ArC GHRH, and SRIF(ArC) could endow the complex physiological patterns of GH secretion in the male and female.
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Affiliation(s)
- Leon S Farhy
- Division of Endocrinology and Metabolism, Department of Internal Medicine, School of Medicine, University of Virginia, Charlottesville, 22908, USA
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Farhy LS, Veldhuis JD. Joint pituitary-hypothalamic and intrahypothalamic autofeedback construct of pulsatile growth hormone secretion. Am J Physiol Regul Integr Comp Physiol 2003; 285:R1240-9. [PMID: 12869363 DOI: 10.1152/ajpregu.00086.2003] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Growth hormone (GH) secretion is vividly pulsatile in all mammalian species studied. In a simplified model, self-renewable GH pulsatility can be reproduced by assuming individual, reversible, time-delayed, and threshold-sensitive hypothalamic outflow of GH-releasing hormone (GHRH) and GH release-inhibiting hormone (somatostatin; SRIF). However, this basic concept fails to explicate an array of new experimental observations. Accordingly, here we formulate and implement a novel fourfold ensemble construct, wherein 1) systemic GH pulses stimulate long-latency, concentration-dependent secretion of periventricular-nuclear SRIF, thereby initially quenching and then releasing multiphasic GH volleys (recurrent every 3-3.5 h); 2) SRIF delivered to the anterior pituitary gland competitively antagonizes exocytotic release, but not synthesis, of GH during intervolley intervals; 3) arcuate-nucleus GHRH pulses drive the synthesis and accumulation of GH in saturable somatotrope stores; and 4) a purely intrahypothalamic mechanism sustains high-frequency GH pulses (intervals of 30-60 min) within a volley, assuming short-latency reciprocal coupling between GHRH and SRIF neurons (stimulatory direction) and SRIF and GHRH neurons (inhibitory direction). This two-oscillator formulation explicates (but does not prove) 1) the GHRH-sensitizing action of prior SRIF exposure; 2) a three-site (intrahypothalamic, hypothalamo-pituitary, and somatotrope GH store dependent) mechanism driving rebound-like GH secretion after SRIF withdrawal in the male; 3) an obligatory role for pituitary GH stores in representing rebound GH release in the female; 4) greater irregularity of SRIF than GH release profiles; and 5) a basis for the paradoxical GH-inhibiting action of centrally delivered GHRH.
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Affiliation(s)
- Leon S Farhy
- Division of Endocrinology and Metabolism, Dept. of Internal Medicine, Mayo Medical and Graduate Schools of Medicine, General Clinical Research Center, Mayo Clinic, Rochester, MN 55905, USA
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9
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Farhy LS, Straume M, Johnson ML, Kovatchev B, Veldhuis JD. Unequal autonegative feedback by GH models the sexual dimorphism in GH secretory dynamics. Am J Physiol Regul Integr Comp Physiol 2002; 282:R753-64. [PMID: 11832396 DOI: 10.1152/ajpregu.00407.2001] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Growth hormone (GH) secretion, controlled principally by a GH-releasing hormone (GHRH) and GH release-inhibiting hormone [somatostatin (SRIF)] displays vivid sexual dimorphism in many species. We hypothesized that relatively small differences within a dynamic core GH network driven by regulatory interactions among GH, GHRH, and SRIF explain the gender contrast. To investigate this notion, we implemented a minimal biomathematical model based on two coupled oscillators: time-delayed reciprocal interactions between GH and GHRH, which endow high-frequency (40-60 min) GH oscillations, and time-lagged bidirectional GH-SRIF interactions, which mediate low-frequency (occurring every 3.3 h) GH volleys. We show that this basic formulation, sufficient to explain GH dynamics in the male rat [Farhy LS, Straume M, Johnson ML, Kovatchev BP, and Veldhuis JD. Am J Physiol Regulatory Integrative Comp Physiol 281: R38-R51, 2001], emulates the female pattern of GH release, if autofeedback of GH on SRIF is relaxed. Relief of GH-stimulated SRIF release damps the slower volleylike oscillator, allowing emergence of the underlying high-frequency oscillations that are sustained by the GH-GHRH interactions. Concurrently, increasing variability of basal somatostatin outflow introduces quantifiable, sex-specific disorderliness of the release process typical of female GH dynamics. Accordingly, modulation of GH autofeedback on SRIF within the interactive GH-GHRH-SRIF ensemble and heightened basal SRIF variability are sufficient to transform the well-ordered, 3.3-h-interval, multiphasic, volleylike male GH pattern into a femalelike profile with irregular pulses of higher frequency.
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Affiliation(s)
- Leon S Farhy
- Division of Endocrinology and Metabolism, Department of Internal Medicine, The University of Virginia Health System, Charlottesville, Virginia 22908, USA.
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10
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Cellular and Molecular Mechanisms of Circadian Regulation in the Unicellular Dinoflagellate Gonyaulax polyedra. ACTA ACUST UNITED AC 2001. [DOI: 10.1007/978-1-4615-1201-1_12] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register]
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11
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Iwasaki H, Kondo T. The current state and problems of circadian clock studies in cyanobacteria. PLANT & CELL PHYSIOLOGY 2000; 41:1013-20. [PMID: 11100773 DOI: 10.1093/pcp/pcd024] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
Abstract
Circadian rhythms have been observed in innumerable physiological processes in most of organisms. Recent molecular and genetic studies on circadian clocks in many organisms have identified and characterized several molecular regulatory factors that contribute to generation of such rhythms. The cyanobacterium is the simplest organism known to harbor circadian clocks, and it has become one of most successful model organisms for circadian biology. In this review, we will briefly summarize physiological observations and consideration of circadian rhythms in cyanobacteria, molecular genetics of the clock using Synechococcus, and current knowledge of the input and output pathways that support the cellular circadian system. Finally, we will document some current problems in the studies on the cyanobacterial circadian clock.
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Affiliation(s)
- H Iwasaki
- Division of Biological Science, Graduate School of Science, Nagoya University, Chikusa, Japan.
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12
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Murray DB, Engelen F, Lloyd D, Kuriyama H. Involvement of glutathione in the regulation of respiratory oscillation during a continuous culture of Saccharomyces cerevisiae. MICROBIOLOGY (READING, ENGLAND) 1999; 145 ( Pt 10):2739-45. [PMID: 10537195 DOI: 10.1099/00221287-145-10-2739] [Citation(s) in RCA: 57] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
Respiratory oscillation occurred during aerobic continuous culture of Saccharomyces cerevisiae. During oscillation, phase-related changes in NAD(P)H and GSH levels occur. Perturbation of oscillation and inhibition of respiration occurred when GSH or GSSG was injected; however, there was a phase delay in perturbation in the case of an injection during high respiration. The perturbation phase delay was not apparent when a combination of DL-buthionine-(S,R)-sulphoximine, GSH and 5-nitro-2-furaldehyde was injected. Perturbation by GSH injection caused the intracellular GSH concentration to increase, the GSSG concentration to decrease and the cessation of ethanol uptake. NAD(P)H during perturbation was inversely related to dissolved oxygen. Perturbation by calcium pantothenate and pyridoxal-HCl caused a period of enhanced respiration before oscillation returned. These results suggest that the NAD+/NADH redox is not directly involved in oscillation control and regulation involves glutathione metabolism. Possible regulation points include alcohol dehydrogenase inhibition and/or respiratory-chain inhibition.
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Affiliation(s)
- D B Murray
- Microbiology Group, Cardiff School of Biosciences, Cardiff University, Wales, UK
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13
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Murray‐Mcintosh RP. Role of Pulsatility in Hormonal Action. Compr Physiol 1998. [DOI: 10.1002/cphy.cp070119] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
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14
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Risold PY, Thompson RH, Swanson LW. The structural organization of connections between hypothalamus and cerebral cortex. BRAIN RESEARCH. BRAIN RESEARCH REVIEWS 1997; 24:197-254. [PMID: 9385455 DOI: 10.1016/s0165-0173(97)00007-6] [Citation(s) in RCA: 242] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
Motivated behavior requires coordinated somatic, autonomic, and endocrine responses, and may be divided into initiation, procurement, and consummatory phases (Swanson, L.W. and Mogenson, G.J., Neural mechanisms for the functional coupling of autonomic, endocrine and somatomotor responses in adaptative behavior, Brain Res. Rev., 3 (1981) 1-34). Obviously, such behavior may involve the entire central nervous system, although it is important to identify circuitry or systems that mediate the behavior directed toward specific goal objects. This problem has recently been clarified by the identification of hypothalamic subsystems important for the execution of instinctive behaviors related to ingestion, reproduction, and defense. These subsystems are modulated by sensory (reflex), central control (e.g., circadian), and voluntary (cortical) inputs. The latter are dominated by inputs from the ventral temporal lobe and medial prefrontal region, which are both direct and via associated parts of the basal nuclei (ganglia). Hypothalamic output is characterized by descending projections to brainstem and spinal motor systems, and by projections back to the cerebral cortex, which are both direct and via a continuous rostromedial part of the dorsal thalamus. This thalamic region includes the anterior, medial, and midline groups, which in turn innervate a continuous ring of cortex that includes the hippocampal formation and the cingulate, prefrontal, and insular regions. Parts of this thalamic region also innervate the ventral striatum, which receives a massive input from the cortical rings as well.
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Affiliation(s)
- P Y Risold
- Program for Neural, Informational and Behavioral Sciences, University of Southern California, Los Angeles 90089-2520, USA
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15
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Heintzen C, Nater M, Apel K, Staiger D. AtGRP7, a nuclear RNA-binding protein as a component of a circadian-regulated negative feedback loop in Arabidopsis thaliana. Proc Natl Acad Sci U S A 1997; 94:8515-20. [PMID: 9238008 PMCID: PMC22981 DOI: 10.1073/pnas.94.16.8515] [Citation(s) in RCA: 170] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023] Open
Abstract
The endogenous clock that drives circadian rhythms is thought to communicate temporal information within the cell via cycling downstream transcripts. A transcript encoding a glycine-rich RNA-binding protein, Atgrp7, in Arabidopsis thaliana undergoes circadian oscillations with peak levels in the evening. The AtGRP7 protein also cycles with a time delay so that Atgrp7 transcript levels decline when the AtGRP7 protein accumulates to high levels. After AtGRP7 protein concentration has fallen to trough levels, Atgrp7 transcript starts to reaccumulate. Overexpression of AtGRP7 in transgenic Arabidopsis plants severely depresses cycling of the endogenous Atgrp7 transcript. These data establish both transcript and protein as components of a negative feedback circuit capable of generating a stable oscillation. AtGRP7 overexpression also depresses the oscillation of the circadian-regulated transcript encoding the related RNA-binding protein AtGRP8 but does not affect the oscillation of transcripts such as cab or catalase mRNAs. We propose that the AtGRP7 autoregulatory loop represents a "slave" oscillator in Arabidopsis that receives temporal information from a central "master" oscillator, conserves the rhythmicity by negative feedback, and transduces it to the output pathway by regulating a subset of clock-controlled transcripts.
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Affiliation(s)
- C Heintzen
- Institute for Plant Sciences, Eidgenössiche Technische Hochschule, CH-8092 Zurich, Switzerland
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16
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Gekakis N, Saez L, Delahaye-Brown AM, Myers MP, Sehgal A, Young MW, Weitz CJ. Isolation of timeless by PER protein interaction: defective interaction between timeless protein and long-period mutant PERL. Science 1995; 270:811-5. [PMID: 7481773 DOI: 10.1126/science.270.5237.811] [Citation(s) in RCA: 265] [Impact Index Per Article: 9.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023]
Abstract
The period (per) gene likely encodes a component of the Drosophila circadian clock. Circadian oscillations in the abundance of per messenger RNA and per protein (PER) are thought to arise from negative feedback control of per gene transcription by PER. A recently identified second clock locus, timeless (tim), apparently regulates entry of PER into the nucleus. Reported here are the cloning of complementary DNAs derived from the tim gene in a two-hybrid screen for PER-interacting proteins and the demonstration of a physical interaction between the tim protein (TIM) and PER in vitro. A restricted segment of TIM binds directly to a part of the PER dimerization domain PAS. PERL, a mutation that causes a temperature-sensitive lengthening of circadian period and a temperature-sensitive delay in PER nuclear entry, exhibits a temperature-sensitive defect in binding to TIM. These results suggest that the interaction between TIM and PER determines the timing of PER nuclear entry and therefore the duration of part of the circadian cycle.
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Affiliation(s)
- N Gekakis
- Department of Neurobiology, Harvard Medical School, Boston, MA 02115, USA
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17
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Analysis of Calcium Fertilization Transients in Mouse Oocytes. ACTA ACUST UNITED AC 1995. [DOI: 10.1016/s1043-9471(06)80042-x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register]
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18
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Systems-Level Analysis of Physiological Regulatory Interactions Controlling Complex Secretory Dynamics of the Growth Hormone Axis: A Dynamical Network Model. ACTA ACUST UNITED AC 1995. [DOI: 10.1016/s1043-9471(06)80037-6] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register]
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19
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Mirmiran M, Koster-Van Hoffen GC, Bos NP. Circadian rhythm generation in the cultured suprachiasmatic nucleus. Brain Res Bull 1995; 38:275-83. [PMID: 7496822 DOI: 10.1016/0361-9230(95)00100-s] [Citation(s) in RCA: 21] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023]
Abstract
The suprachiasmatic nucleus (SCN) of the hypothalamus is involved in the generation and entrainment of circadian rhythms. The results of a series of experiments in long-term cultured organotypic SCN slices suggest that (1) some but not all SCN neurons display circadian rhythmicity in their extracellular discharges. To the extent they could be studied, these neurons did not usually show synchronized high/low levels of activity; (2) simultaneous daily depolarization of these neurons (K+ pulses) to some extent influenced the distribution of the firing rate of SCN neurons around the time of expected daily pulses; (3) extracellular Ca++ and synaptic input is required for the pacemaker activity of the SCN. We conclude that the mammalian biological clock is a heterogeneous neuronal system in which the circadian pacemaker rhythm is generated and entrained via complex interactions among SCN neurons.
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Affiliation(s)
- M Mirmiran
- Netherlands Institute for Brain Research, Amsterdam, The Netherlands
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20
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Abstract
Reciprocal inhibition between neuron pairs is a long-standing model for the mechanism by which circuits generate rhythmic animal movement patterns. This review shows that this model mechanism can explain the origins of cyclic movements in six different preparations for which the neuronal circuits are available. The overall function of reciprocal inhibition, when combined with a variety of dynamic properties in each of the circuits, is to generate stable antiphasic or multiphasic output patterns. Apparent redundancy in the identified circuits may lend additional robustness to the oscillations, but it also increases the difficulty of identifying critical circuit elements.
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Affiliation(s)
- W O Friesen
- Department of Biology, University of Virginia, Charlottesville 22903-2477
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Abstract
Significant advances have been made in understanding the cellular mechanisms for pattern generation in both invertebrate and vertebrate preparations. In a number of preparations, slow neuromodulators have been shown not only to modify network function, but to be intimately involved in development and/or normal function of the neural network and its associated behavior. The mechanisms underlying coordination between multiple pattern-generating networks, including switching of neurons from one network to another, are now being studied. Several new quantitative models of network function have been developed, and modeling is now an important component of research in this field.
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Affiliation(s)
- R M Harris-Warrick
- Section of Neurobiology and Behavior, Cornell University, Ithaca, New York 14853
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