Relevant bibliographies by topics / Circadian clock

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  1. Journal articles
  2. Dissertations / Theses
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  4. Book chapters
  5. Conference papers
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Academic literature on the topic 'Circadian clock'

Author: Grafiati
Published: 4 June 2021
Last updated: 7 July 2024

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Journal articles on the topic "Circadian clock"

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Xiao, Yangbo, Ye Yuan, Mariana Jimenez, Neeraj Soni, and Swathi Yadlapalli. "Clock proteins regulate spatiotemporal organization of clock genes to control circadian rhythms." Proceedings of the National Academy of Sciences 118, no. 28 (July 7, 2021): e2019756118. http://dx.doi.org/10.1073/pnas.2019756118.

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Circadian clocks regulate ∼24-h oscillations in gene expression, behavior, and physiology. While the genetic and molecular mechanisms of circadian rhythms are well characterized, what remains poorly understood are the intracellular dynamics of circadian clock components and how they affect circadian rhythms. Here, we elucidate how spatiotemporal organization and dynamics of core clock proteins and genes affect circadian rhythms in Drosophila clock neurons. Using high-resolution imaging and DNA-fluorescence in situ hybridization techniques, we demonstrate that Drosophila clock proteins (PERIOD and CLOCK) are organized into a few discrete foci at the nuclear envelope during the circadian repression phase and play an important role in the subnuclear localization of core clock genes to control circadian rhythms. Specifically, we show that core clock genes, period and timeless, are positioned close to the nuclear periphery by the PERIOD protein specifically during the repression phase, suggesting that subnuclear localization of core clock genes might play a key role in their rhythmic gene expression. Finally, we show that loss of Lamin B receptor, a nuclear envelope protein, leads to disruption of PER foci and per gene peripheral localization and results in circadian rhythm defects. These results demonstrate that clock proteins play a hitherto unexpected role in the subnuclear reorganization of core clock genes to control circadian rhythms, revealing how clocks function at the subcellular level. Our results further suggest that clock protein foci might regulate dynamic clustering and spatial reorganization of clock-regulated genes over the repression phase to control circadian rhythms in behavior and physiology.
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Costello, Hannah M., and Michelle L. Gumz. "Circadian Rhythm, Clock Genes, and Hypertension: Recent Advances in Hypertension." Hypertension 78, no. 5 (November 2021): 1185–96. http://dx.doi.org/10.1161/hypertensionaha.121.14519.

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Accumulating evidence suggests that the molecular circadian clock is crucial in blood pressure (BP) control. Circadian rhythms are controlled by the central clock, which resides in the suprachiasmatic nucleus of the hypothalamus and peripheral clocks throughout the body. Both light and food cues entrain these clocks but whether these cues are important for the circadian rhythm of BP is a growing area of interest. The peripheral clocks in the smooth muscle, perivascular adipose tissue, liver, adrenal gland, and kidney have been recently implicated in the regulation of BP rhythm. Dysregulation of the circadian rhythm of BP is associated with adverse cardiorenal outcomes and increased risk of cardiovascular mortality. In this review, we summarize the most recent advances in peripheral clocks as BP regulators, highlight the adverse outcomes of disrupted circadian BP rhythm in hypertension, and provide insight into potential future work in areas exploring the circadian clock in BP control and chronotherapy. A better understanding of peripheral clock function in regulating the circadian rhythm of BP will help pave the way for targeted therapeutics in the treatment of circadian BP dysregulation and hypertension.
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Myung, Jihwan, Mei-Yi Wu, Chun-Ya Lee, Amalia Ridla Rahim, Vuong Hung Truong, Dean Wu, Hugh David Piggins, and Mai-Szu Wu. "The Kidney Clock Contributes to Timekeeping by the Master Circadian Clock." International Journal of Molecular Sciences 20, no. 11 (June 5, 2019): 2765. http://dx.doi.org/10.3390/ijms20112765.

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The kidney harbors one of the strongest circadian clocks in the body. Kidney failure has long been known to cause circadian sleep disturbances. Using an adenine-induced model of chronic kidney disease (CKD) in mice, we probe the possibility that such sleep disturbances originate from aberrant circadian rhythms in kidney. Under the CKD condition, mice developed unstable behavioral circadian rhythms. When observed in isolation in vitro, the pacing of the master clock, the suprachiasmatic nucleus (SCN), remained uncompromised, while the kidney clock became a less robust circadian oscillator with a longer period. We find this analogous to the silencing of a strong slave clock in the brain, the choroid plexus, which alters the pacing of the SCN. We propose that the kidney also contributes to overall circadian timekeeping at the whole-body level, through bottom-up feedback in the hierarchical structure of the mammalian circadian clocks.
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Clark, Amelia M., and Brian J. Altman. "Circadian control of macrophages in the tumor microenvironment." Journal of Immunology 208, no. 1_Supplement (May 1, 2022): 165.06. http://dx.doi.org/10.4049/jimmunol.208.supp.165.06.

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Abstract Introduction All leukocytes tested to date have functional circadian clocks, and nearly every arm of the immune response is subject to circadian regulation. Circadian clocks instruct the time-of-day-dependent, rhythmic expression of genes in a tissue- and cell-specific manner. In macrophages (mΦs), the circadian clock regulates several factors that are critical to executing effective immune responses. Tumor-associated mΦs are major contributors to immune suppression in the tumor microenvironment (TME). Evidence suggests that metabolically stressful factors in the TME such as acidic pH and nutrient limitation promote mΦ-mediated immune suppression, and recent data point to dysregulation of the circadian clock downstream of metabolic stress. Methods We study the effect of TME-associated metabolic stress on the circadian clock of mΦs in vitro by culturing bone marrow-derived mΦs in conditions mimicking acidic pH and nutrient limitations that have been observed in the TME. To study the impact of mΦ-intrinsic circadian rhythms on tumorigenesis in vivo, we use mice genetically engineered to have a myeloid cell-specific disruption of the circadian clock via deletion of the key clock protein BMAL1. Results Oscillation of core clock proteins is altered in mΦs subjected to TME-associated metabolic stress. Additionally, we observe increased tumor growth in mice co-injected with mΦs whose circadian clocks were disrupted compared to mice co-injected with mΦs whose circadian clocks were functional. Conclusion Our data suggests that stressful conditions associated with the TME can alter the mΦ circadian clock, and that a functional circadian clock in mΦs can suppress tumor growth in a syngeneic murine tumor model of pancreatic cancer. This research has been supported by the following fellowships and grants: 2021-Current: Wilmot Predoctoral Cancer Research Fellowship, Wilmot Cancer Institute, University of Rochester Medical Center, Rochester, NY 2020-2021: NIH T32 Training Grant in Cellular, Biochemical & Molecular Sciences, University of Rochester Medical Center, Rochester, NY
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Shakhmantsir, Iryna, and Amita Sehgal. "Splicing the Clock to Maintain and Entrain Circadian Rhythms." Journal of Biological Rhythms 34, no. 6 (August 7, 2019): 584–95. http://dx.doi.org/10.1177/0748730419868136.

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Circadian clocks drive daily rhythms of physiology and behavior in multiple organisms and synchronize these rhythms to environmental cycles of light and temperature. The basic mechanism of the clock consists of a transcription-translation feedback loop, in which key clock proteins negatively regulate their own transcription. Although much of the focus with respect to clock mechanisms has been on the regulation of transcription and on the stability and activity of clock proteins, it is clear that other regulatory processes also have to be involved to explain aspects of clock function. Here, we review the role of alternative splicing in circadian clocks. Starting with a discussion of the Drosophila clock and then extending to other major circadian model systems, we describe how the control of alternative splicing enables organisms to maintain their circadian clocks as well as to respond to environmental inputs, in particular to temperature changes.
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Fu, Minnie, and Xiaoyong Yang. "The sweet tooth of the circadian clock." Biochemical Society Transactions 45, no. 4 (July 3, 2017): 871–84. http://dx.doi.org/10.1042/bst20160183.

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The endogenous circadian clock is a key regulator of daily metabolic processes. On the other hand, circadian clocks in a broad range of tissues can be tuned by extrinsic and intrinsic metabolic cues. The bidirectional interaction between circadian clocks and metabolism involves both transcriptional and post-translational mechanisms. Nuclear receptors exemplify the transcriptional programs that couple molecular clocks to metabolism. The post-translational modifications of the core clock machinery are known to play a key role in metabolic entrainment of circadian clocks. O-linked N-acetylglucosamine modification (O-GlcNAcylation) of intracellular proteins is a key mediator of metabolic response to nutrient availability. This review highlights our current understanding of the role of protein O-GlcNAcylation in mediating metabolic input and output of the circadian clock.
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Helfrich-Förster, Charlotte, Michael N. Nitabach, and Todd C. Holmes. "Insect circadian clock outputs." Essays in Biochemistry 49 (June 30, 2011): 87–101. http://dx.doi.org/10.1042/bse0490087.

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Insects display an impressive variety of daily rhythms, which are most evident in their behaviour. Circadian timekeeping systems that generate these daily rhythms of physiology and behaviour all involve three interacting elements: the timekeeper itself (i.e. the clock), inputs to the clock through which it entrains and otherwise responds to environmental cues such as light and temperature, and outputs from the clock through which it imposes daily rhythms on various physiological and behavioural parameters. In insects, as in other animals, cellular clocks are embodied in clock neurons capable of sustained autonomous circadian rhythmicity, and those clock neurons are organized into clock circuits. Drosophila flies spend their entire lives in small areas near the ground, and use their circadian brain clock to regulate daily rhythms of rest and activity, so as to organize their behaviour appropriately to the daily rhythms of their local environment. Migratory locusts and butterflies, on the other hand, spend substantial portions of their lives high up in the air migrating long distances (sometimes thousands of miles) and use their circadian brain clocks to provide time-compensation to their sun-compass navigational systems. Interestingly, however, there appear to be substantial similarities in the cellular and network mechanisms that underlie circadian outputs in all insects.
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Wu, Yiyang. "The Evolutionary Pathways of the Circadian Rhythms through Phylogenetical Analysis of Basal Circadian Genes." Highlights in Science, Engineering and Technology 54 (July 4, 2023): 367–76. http://dx.doi.org/10.54097/hset.v54i.9795.

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Circadian rhythm is the endogenous clock in organisms that regulates the performance of various physiological and metabolic events in accordance with the periodic oscillating changes in the environment, especially the periodic light-dark cycle. The clock has endowed organisms with the ability in anticipating environmental changes allowing them to adjust their survival strategies accordingly, promoting their selective fitness. However, the evolutionary path and the emergence of such an intricate and vital system remain elusive. The article aims to analyse the molecular architecture and components of the circadian clock among three kingdoms of plants, animals, fungi, and their unicellular ancestors, revealing the possible emergence of the circadian clock from the primordial circadian rhythm of prokaryotes to complicated rhythms seen in multicellular organisms. In comparative genetic analyses of the circadian clocks, researchers have identified homologs in the circadian genes of multicellular organisms with their unicellular ancestors, indicating prior emergence of the circadian clock than multicellularity. In addition, comparative genetic studies among fungi, animal, and plant circadian clocks implied that the emergence of circadian rhythms across the kingdoms resulted from convergent evolution due to the significant selective advantages concomitant with the circadian clock. Furthermore, the article also reviewed methods of gene transferring laterally, including horizontal gene transfer and endosymbiotic gene transfer, which may explain the overall similarities in the transcription-translation feedback mechanism among the many circadian rhythms. However, while genetic transfer among distantly related organisms enhanced biodiversity and biological innovations in nature, whether the horizontal changes of genetic materials contribute to the similar feedback loop of the circadian clock still requires further research to determine.
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Li, Meina, Lijun Cao, Musoki Mwimba, Yan Zhou, Ling Li, Mian Zhou, Patrick S. Schnable, Jamie A. O’Rourke, Xinnian Dong, and Wei Wang. "Comprehensive mapping of abiotic stress inputs into the soybean circadian clock." Proceedings of the National Academy of Sciences 116, no. 47 (November 1, 2019): 23840–49. http://dx.doi.org/10.1073/pnas.1708508116.

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The plant circadian clock evolved to increase fitness by synchronizing physiological processes with environmental oscillations. Crop fitness was artificially selected through domestication and breeding, and the circadian clock was identified by both natural and artificial selections as a key to improved fitness. Despite progress in Arabidopsis, our understanding of the crop circadian clock is still limited, impeding its rational improvement for enhanced fitness. To unveil the interactions between the crop circadian clock and various environmental cues, we comprehensively mapped abiotic stress inputs to the soybean circadian clock using a 2-module discovery pipeline. Using the “molecular timetable” method, we computationally surveyed publicly available abiotic stress-related soybean transcriptomes to identify stresses that have strong impacts on the global rhythm. These findings were then experimentally confirmed using a multiplexed RNA sequencing technology. Specific clock components modulated by each stress were further identified. This comprehensive mapping uncovered inputs to the plant circadian clock such as alkaline stress. Moreover, short-term iron deficiency targeted different clock components in soybean and Arabidopsis and thus had opposite effects on the clocks of these 2 species. Comparing soybean varieties with different iron uptake efficiencies suggests that phase modulation might be a mechanism to alleviate iron deficiency symptoms in soybean. These unique responses in soybean demonstrate the need to directly study crop circadian clocks. Our discovery pipeline may serve as a broadly applicable tool to facilitate these explorations.
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Bailey, Shannon M. "Emerging role of circadian clock disruption in alcohol-induced liver disease." American Journal of Physiology-Gastrointestinal and Liver Physiology 315, no. 3 (September 1, 2018): G364—G373. http://dx.doi.org/10.1152/ajpgi.00010.2018.

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The detrimental health effects of excessive alcohol consumption are well documented. Alcohol-induced liver disease (ALD) is the leading cause of death from chronic alcohol use. As with many diseases, the etiology of ALD is influenced by how the liver responds to other secondary insults. The molecular circadian clock is an intrinsic cellular timing system that helps organisms adapt and synchronize metabolism to changes in their environment. The clock also influences how tissues respond to toxic, environmental, and metabolic stressors, like alcohol. Consistent with the essential role for clocks in maintaining health, genetic and environmental disruption of the circadian clock contributes to disease. While a large amount of rich literature is available showing that alcohol disrupts circadian-driven behaviors and that circadian clock disruption increases alcohol drinking and preference, very little is known about the role circadian clocks play in alcohol-induced tissue injuries. In this review, recent studies examining the effect alcohol has on the circadian clock in peripheral tissues (liver and intestine) and the impact circadian clock disruption has on development of ALD are presented. This review also highlights some of the rhythmic metabolic processes in the liver that are disrupted by alcohol and potential mechanisms through which alcohol disrupts the liver clock. Improved understanding of the mechanistic links between the circadian clock and alcohol will hopefully lead to the development of new therapeutic approaches for treating ALD and other alcohol-related organ pathologies.
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Dissertations / Theses on the topic "Circadian clock"

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Brettschneider, Christian. "The cyanobacterial circadian clock." Doctoral thesis, Humboldt-Universität zu Berlin, Mathematisch-Naturwissenschaftliche Fakultät I, 2011. http://dx.doi.org/10.18452/16385.

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Cyanobakterien zŠhlen zu den Šltesten Lebewesen auf der Erde. Diese Bakterien, auch Blaualgen genannt, trugen wesentlich zur Sauerstoffanreicherung der Erde bei, da sie eine ausgeprŠgte FŠhigkeit zur Photosynthese besitzen. Der produzerte Sauerstoff der Photosynthese hemmt jedoch eine weitere AktivitŠt von Cyanobakterien, die Stickstofffixierung. Um die Hemmung zu vermeiden, werden diese AktivitŠten zeitlich getrennt und optimal dem tŠglichen Hell-Dunkel-Rhythmus angepasst. Ein evolutionŠrer Vorteil wird erzielt, wenn der Organismus diesen Rhythmus antizipiert und sich darauf vorbereitet. Aus diesem Grund haben Cyanobakterien eine innere Uhr entwickelt, deren Rhythmus zirkadian ist, ãzirka diemÒ bedeutet ãungefŠhr ein TagÒ. Cyanobakterien der Spezies Synechococcus elongatus PCC 7942 haben sich als Modellorganismus etabliert, weil in ihnen die ersten bakteriellen zirkadianen Oszillationen auf molekularer Ebene entdeckt worden sind. Ihre zirkadiane Uhr entspringt dreier, auf der DNS beieinanderliegenden, Gene (kaiA, kaiB, kaiC) und ihrer dazugehšrigen Proteine. Phosphorylierte KaiC-Proteine Ÿben eine RŸckkopplung auf die Transkription von kaiB und kaiC aus, wodurch die AktivitŠt des kaiBC-Promotors zirkadian oszilliert. Eines der wichtigsten Experimente der letzten Jahre hat gezeigt, dass dieser Transkriptions-Translations-Oszillator mit einem weiteren Oszillator gekoppelt ist, der nicht von Transkription und Translation abhŠngt. Das Experiment des Kondo Labors rekonstruiert zirkadiane Oszillationen mit nur drei Proteinen KaiA, KaiB, KaiC und ATP. Die Proteine bilden Komplexe verschiedener Stoichiometrie, die durchschnittliche Phosphorylierung des Proteins KaiC zeigt stabile Oszillationen mit einer zirkadianen Periode. Da ein Entfernen von einem der Proteine zum Verlust der Oszillationen fŸhrt, wird dieser Post-Translations-Oszillator auch als Kernoszillator bezeichnet. Der Phosphorylierungszyklus von KaiC wird bestimmt durch fortlaufende Phosphorylierung und Dephosphorylierung an zwei Positionen des Proteins, den AminosŠuren Serin 431 und Threonin 432. Die Phase des Kernoszillators kann an der Verteilung der vier PhosphorylierungszustŠnde (nicht-, serin-, threonin- und doppeltphosphoryliert) abgelesen werden. KaiC wechselwirkt mit KaiA und KaiB, damit verschieden phosphorylierte KaiC synchronisieren und die Uhr Ÿber mehrere Tage konstante Oszillationen zeigt. Die Details dieser Wechselwirkung sind jedoch unbekannt. In dieser Dissertation erstelle ich ein mathematisches Modell des Kernoszillators und simuliere die vorliegenden Experimente des O''Shea Labors. Die Simulation reproduziert den KaiC Phosphorylierungszyklus der Uhr quantitativ. Um die wichtigsten experimentellen Nebenbedingungen zu erfŸllen, muss das theoretische Modell zwei molekulare Eigenschaften von KaiC berŸcksichtigen, wodurch ich wichtige Vorhersagen treffe. Die erste Nebenbedingung ist durch die Robustheit des Systems gegeben. Die KaiC-Phosphorylierung Šndert sich nicht, wenn die Gesamtkonzentrationen der drei Proteine in gleicher Weise variiert werden. Um diese Bedingung zu erfŸllen, muss das Modell zwei verschiedenartige Komplexe von KaiA und KaiC berŸcksichtigen. ZusŠtzlich zu einem KaiAC Komplex, der die Autophosphorylierung von KaiC unterstŸtzt, muss KaiC den grš§ten Teil von KaiA unabhŠngig vom Phosphorylierungszustand sequestrieren. Diese zweite Bindestelle ist meine erste theoretische Vorhersage. Die zweite Nebenbedingung ist durch das Ÿbergangsverhalten nach Hinzugabe von KaiB gegeben. KaiB induziert eine Dephosphorylierung von KaiC, die abhŠngig vom Phosphorylierungsniveau ist. Ein Umschalten zwischen phosphoylierendem und dephosphorylierendem KaiC ist deshalb nur in bestimmten Zeitfenstern mšglich. Um die gemessenen Zeitfenster in der Simulation zu reproduzieren, postuliere ich im Modell, dass sechsfach Serin phosphorylierte KaiBC Komplexe KaiA inaktivieren. Diese hochgradig nichtlineare RŸckkopplung ist meine zweite theoretische Vorhersage. Die beiden Vorhersagen werden anschlie§end experimentell ŸberprŸft. HierfŸr werden aufgereinigte Kai-Proteine mit ATP gemischt. Proben an ausgewŠhlten Zeitpunkten werden mit der nativen Massenspektrometrie untersucht. Diese ist eine neuartige Methode, die es erlaubt, intakte Proteinkomplexe zu untersuchen. Die Spektren bestŠtigen sowohl die zweite KaiAC-Bindestelle als auch die nichtlineare RŸckkopplung. Das mathematische Modell erlaubt es au§erdem, die drei definierenden Prinzipien von zirkadianen Uhren fŸr den Kernoszillator zu erklŠren. Erstens sichern konstante Phosphorylierungs- und Dephosphorylierungsraten von KaiC und ein pŸnktliches Umschalten zwischen beiden Phasen den Freilauf des Oszillators. Dieser Freilauf bewirkt, dass die zirkadiane Uhr auch unter konstanten Bedingungen, vor allem gleichbleibenden LichtverhŠltnissen, weiterlaufen kann. Zweitens muss die Periodendauer des Oszillators zu unterschiedlichen Šu§eren Bedingungen erhalten bleiben (Temperaturkompensation). Diese Bedingung wird realisiert, indem temperaturabhŠngige Dissoziationskonstanten von KaiAC und KaiBC Komplexen Phasenverschiebungen erzeugen, die sich gegenseitig kompensieren. Drittens muss die Phase des Oszillators sich dem Tagesrhythmus anpassen kšnnen. Diese Anpassung folgt aus einem Šu§eren Warm-Kalt-Rhythmus, der die drei temperaturabhŠngigen Phasenverschiebungen nur zum Teil einschaltet und damit die Kompensation verhindert. Eine in silico Evolutionsanalyse zeigt, dass eine zweite phosphorylierbare AminosŠure einen evolutionŠren Vorteil bringt und die Verteilung der PhosphorylierungszustŠnde optimiert ist, um eindeutig die Zeit zu bestimmen. Das Ergebnis weist darauf hin, dass diese Verteilung die physiologisch wichtige Ausgangsgrš§e der Uhr ist und die vier PhosphroylierungszustŠnde die Funktionen der zirkadianen Uhr von Cyanobakterien sichern.
Biological activities in cyanobacteria are coordinated by an internal clock. The rhythm of the cyanobacterium Synechococcus elongatus PCC 7942 originates from the kai gene cluster and its corresponding proteins. In a test tube, the proteins KaiA, KaiB and KaiC form complexes of various stoichiometry and the average phosphorylation level of KaiC exhibits robust circadian oscillations in the presence of ATP. The characteristic cycle of individual KaiC proteins is determined by phosphorylation of serine 431 and threonine 432. Differently phosphorylated KaiC synchronize due to an interaction with KaiA and KaiB. However, the details of this interaction are unknown. Here, I quantitatively investigate the experimentally observed characteristic phosphorylation cycle of the KaiABC clockwork using mathematical modeling. I thereby predict the binding properties of KaiA to both KaiC and KaiBC complexes by analyzing the two most important experimental constraints for the model. In order to reproduce the KaiB-induced dephosphorylation of KaiC a highly non-linear feedback loop has been identified. This feedback originates from KaiBC complexes, which are exclusively phosphorylated at the serine residue. The observed robustness of the KaiC phosphorylation level to concerted changes of the total protein concentrations demands an inclusion of two KaiC binding sites to KaiA in the mathematical model. Besides the formation of KaiAC complexes enhancing the autophosphorylation activity of KaiC, the model accounts for a KaiC binding site, which constantly sequestrates a large fraction of free KaiA. These theoretical predictions have been confirmed by the novel method of native mass spectrometry, which was applied in collaboration with the Heck laboratory. The mathematical model elucidates the mechanism by which the circadian clock satisfies three defining principles. First, the highly non-linear feedback loop assures a rapid and punctual switch to dephosphorylation which is essential for a precise period of approximately 24 h (free-running rhythm). Second, the dissociation of the protein complexes increases with increasing temperatures. These perturbations induce opposing phase shifts, which exactly compensate during one period (temperature compensation). Third, a shifted external rhythm of low and high temperature affects only a part of the three compensating phase perturbations, which leads to phase shifts (phase entrainment). An in silico evolution analysis shows that the existing second phosphorylatable residue of KaiC is not necessary for the existence of sustained oscillations but provides an evolutionary benefit. The analysis demonstrates that the distribution of four phosphorylated states of KaiC is optimized in order for the organism to uniquely distinguish between dusk and dawn. Consequently, this thesis emphasizes the importance of the four phosphorylated states of KaiC, which assure the outstanding performance of the core oscillator.
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Smith, Karen Lynn. "Entrainment of the circadian clock." Thesis, University of Cambridge, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.624358.

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Galvanin, Silvia. "Circadian Clock Study Through Frequency-Encoded Entrainment Stimulations." Doctoral thesis, Università degli studi di Padova, 2018. http://hdl.handle.net/11577/3422301.

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Circadian clocks are intrinsic, time-tracking systems that enable organisms to maintain their physiological state and their synchrony with the 24-hour rotation of the Earth, by partitioning behavioural and metabolic processes according to time of day within each tissue. They are entrained to the external environment by light/dark cycles and by food timing, which act as clock synchronizers. Emerging evidence suggests that circadian regulation is intimately linked to metabolic homeostasis and that dysregulation of circadian rhythms can contribute to disease. Conversely, metabolic signals also feed back into the circadian system, modulating circadian gene expression and behaviour. Conventional experimental approach of circadian clock in vitro studies is based on single-pulse stimulation of only one metabolite or hormone, while in vivo peripheral tissues are exposed to periodic oscillating stimuli of a large number of metabolites and hormones, whose variations are in most cases interconnected, as for example glucose and insulin. Moreover, only one or few clock genes are generally considered, while it is known that a large number of genes, thus biological processes, are under circadian regulation. Therefore, this Ph.D. research work is aimed at the development of technologies and data analysis tools to investigate the entrainment of peripheral mammalian circadian clock to frequency-encoded metabolic stimuli, which well mimic physiological oscillations at which peripheral tissues are exposed in vivo. Technologies, and, more specifically, microtechnologies have been developed to investigate the effects of periodic metabolic entrainment, showing that in murine fibroblasts oscillatory periodic metabolic stimulations entrain the expression of Per2, one of the core genes of the circadian molecular mechanism. Moreover, it has been proven that only by metabolic oscillations it is possible to completely reset the phase of cell-autonomous clocks. In order to develop a physiological and pathological in vitro model, achieving a high spatio-temporal control of cell culture microenvironment, frequency-encoded perturbations have been automated in a newly designed microfluidic platform for circadian applications. Finally, to broaden the description of genes expressed with a circadian temporal pattern, a new data analysis method has been proposed and characterized, that allows to identify circadian genes in whole transcriptome data, to group genes based on the phase of their expression, to visualize transcriptome data at a glance and clearly identifying modifications at the transcriptome level from one biological condition to another one.
I ritmi circadiani sono meccanismi biologici di organizzazione temporale intrinseci e autosostenuti, che consentono agli organismi di anticipare i cambiamenti ambientali e permettono loro di adattare il loro comportamento e la loro fisiologia nell’arco della giornata. L’orologio circadiano è sincronizzato dai cicli luce/buio e dall’ora dei pasti. La funzione biologica essenziale del ritmo circadiano è mantenere lo stato fisiologico dell’organismo e la sua sincronia comportamentale e metabolica con l’ambiente esterno. Recentemente è stato dimostrato che l’orologio circadiano garantisce il mantenimento dell’omeostasi metabolica, e che una distruzione del ritmo circadiano è causa di numerose malattie. L’approccio sperimentale convenzionale per lo studio dell’orologio circadiano in vitro è basato su una singola stimolazione di un solo metabolita o ormone, mentre in vivo i tessuti sono esposti in continuo a stimoli oscillatori periodici di una grande vastità di metaboliti e ormoni, le cui variazioni sono spesso interconnesse, come nel caso di glucosio e insulina. Inoltre, nell’analisi sperimentale convenzionale, sono studiati solo uno o pochi geni noti per essere implicati nell’orologio circadiano, mentre è noto che un elevato numero di geni sono espressi in modo circadiano. Lo scopo di questo progetto di ricerca è quindi sviluppare tecnologie e metodi di analisi per studiare l’effetto di stimoli metabolici in frequenza sull’orologio circadiano di tessuti periferici. Questi stimoli riproducono infatti in vitro le oscillazioni metaboliche a cui i tessuti sono esposti in vivo. Tecnologie, e più nello specifico, microtecnologie sono state sviluppate per studiare gli effetti di stimoli metabolici oscillatori, ed è stato dimostrato che in fibroblasti murini l’espressione di Per2 (uno dei geni principali del meccanismo molecolare dell’orologio circadiano) è sincronizzata da stimoli metabolici oscillatori. Inoltre, è stato dimostrato che le oscillazioni metaboliche sono di per sé sufficienti per allineare l’orologio circadiano nei tessuti periferici. Per sviluppare un modello che riproducesse in vitro condizioni sia fisiologiche che patologiche, raggiungendo un controllo spazio-temporale preciso del microambiente cellulare, le stimolazioni in frequenza sono state automatizzate in un dispositivo microfluidico progettato in modo dedicato per studi del ritmo circadiano. Infine, per estendere lo studio ai geni espressi con un pattern temporale circadiano, un nuovo metodo di analisi è stato proposto e caratterizzato. Il metodo permette di identificare geni circadiani da dati di trascrittomica, di suddividere i geni basandosi sulla fase della loro espressione, di visualizzare dati di trascrittomica nel loro complesso e di individuare rapidamente e in modo semplice modifiche a livello trascrizionale da una condizione biologica ad un’altra.
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Gegnaw, Shumet T. "The connection between circadian clock impairment and retinal disease." Electronic Thesis or Diss., Strasbourg, 2023. http://www.theses.fr/2023STRAJ120.

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Cette thèse a étudié comment une dérégulation de l'horloge circadienne, qui n'avait pas été clairement associée à une maladie rétinienne jusqu'à présent, pourrait contribuer à la dégénérescence et influencer le développement et la fonction de la rétine. L'inactivation spécifique du gène horloge Bmal1 (rod-Bmal1KO) dans la lignée de souris portant la mutation P23H de la rhodopsine aggrave les symptômes de dégénérescence rétinienne, tels que la réduction de la réponse ERG et la perte de bâtonnets, induits par la seule mutation P23H. Ces observations ont été corroborées par l'analyse RNA-Seq qui a révélé des changements majeurs dans l'expression des gènes, liés à la phototransduction et aux processus métaboliques, entre le double mutant (rod-Bmal1KO/P23H) et les rétines P23H. Nous avons montré qu'au cours du développement, l’invalidation des gènes horloge Per1 et Per2 chez la souris affecte de manière significative l'expression des gènes de la phototransduction et du cycle cellulaire. Nous avons observé que les souris adultes déficientes en Per1 et Per2 ne modulent pas quotidiennement leur sensibilité à la lumière, dans des conditions scotopiques et mésopiques. Nous avons également constaté une altération de la régulation journalière de la sensibilité à la lumière chez les souris déficientes en gène d'horloge Bmal1 dans les bâtonnets. De plus, nous avons investigué comment la dégénérescence des bâtonnets pourrait influencer la capacité rythmique globale de la rétine en mesurant les rythmes de bioluminescence PER2::LUC chez des souris P23H. Nos résultats montrent que l'horloge rétinienne chez les souris hétérozygotes P23H/+ présente des rythmes circadiens avec une robustesse et une amplitude significativement accrues. Ces effets impliquent probablement l’activation des cellules gliales
This thesis investigated how circadian clock misregulation, which has not been clearly associated with retinal genetic disease so far, could contribute to degeneration and influence development and function in the retina. The rod-specific knockout of Bmal1 clock gene (rod-Bmal1KO) from the mouse line carrying the P23H mutation of rhodopsin exacerbated the retinal degeneration phenotypes, such as reduction in ERG response and rods loss, induced by the P23H mutation alone. These observations were corroborated by RNA-Seq analysis, where we found major changes in expression of genes related to phototransduction and metabolic processes, between the (rod-Bmal1KO/P23H) double mutant and P23H retinas. We showed that during development, Per1 and Per2 clock genes deficiency in mice significantly affects gene expression of phototransduction and cell cycle components. We found that adult mice deficient for Per1 and Per2 genes lack a daily modulation of light sensitivity, under scotopic and mesopic conditions. We also found an impaired daily modulation of light sensitivity in mice deficient for Bmal1 clock gene in rods. Additionally, we investigated how rod degeneration could impact on the global rhythmic capacity of the retina by measuring PER2::LUC bioluminescence rhythms in P23H mice. We showed that the retinal clock in P23H/+ heterozygous mice displays circadian rhythms with significantly increased robustness and amplitude. These effects likely involve activation of glial cells
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Gesto, João Silveira Moledo. "Circadian clock genes and seasonal behaviour." Thesis, University of Leicester, 2011. http://hdl.handle.net/2381/10266.

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Circadian and photoperiodic phenomena serve to organize the temporal pattern of various biological processes. While the former generates endogenous daily rhythms, the latter is related to seasonality. In Drosophila melanogaster, the gene timeless (tim) encodes a cardinal component of the circadian clock and also contributes to photoperiodism, which is observed as an adult reproductive diapause. In this work, natural tim variants were examined for diapause across different temperatures and photoperiods. The newly derived allele, ls-tim, exhibited consistently higher diapause levels than the ancestral one, s-tim, implicating a putative adaptive advantage in the seasonal European environment and providing a perfect substrate for the recently proposed scenario of directional selection. To investigate further genetic links between circadian and photoperiodic mechanisms, classical clock mutations and transgenes were placed on a natural congenic background and assayed for locomotor activity behaviour and diapause response. Surprisingly, the results not only highlighted the importance of tim, and its natural alleles, but also revealed the participation of other clock components in diapause, suggesting that both daily and seasonal timers might have molecularly coevolved. The phenotypic effects promoted by ls-tim arise from the protein isoform LTIM, which expresses an additional N-terminal fragment. To study the adaptive significance of the N-terminal residues, including putative phosphorylation sites, a number of mutagenized TIM constructs were generated and functionally analysed. At the molecular level, it was demonstrated that both the N-terminus length and the order of its residues are important variables modulating the interaction dynamics between TIM and CRYPTOCHROME (CRY). At the behaviour level, the overall amino acid composition, rather than a particular order, appeared to be more critical for the phaseshift responses. Interestingly, despite the functional importance of the N-terminus, a deletion mapping analysis revealed that CRY directly binds to a protein sequence located at TIM C-terminus.
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Curran, Jack. "Ageing and the Drosophila circadian clock." Thesis, University of Bristol, 2019. http://hdl.handle.net/1983/7b02ec7c-f6a2-4640-b50f-ce97a66a5a11.

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It is well established that elderly individuals have increased difficulty sleeping at night combined with falling asleep and waking up earlier. Although these age-related declines in circadian output are clearly observable in activity recordings of laboratory animals, the underlying changes in molecular and neuronal activity remain unknown. The fruit fly, Drosophila melanogaster, has long been used as a model for studying the circadian system and for ageing research. In this thesis Drosophila was used as a model to study the effect of ageing on circadian and sleep behaviour. Circadian behaviour was measured using the Drosophila Activity Monitoring system, recording activity of flies at various stages of the ageing process, demonstrating a linear decline in rhythm strength with age combined with an increase in period length. Weakened circadian output is combined with significant alterations of diurnal behaviour of Drosophila, namely a reduction in morning and evening anticipatory behaviour. Ageing also has a significant impact on sleep behaviour, significantly increasing sleep duration whilst reducing latency, with larger effects observed on day- time sleep. Age-related changes in neuronal activity were investigated using whole-cell patch clamp electrophysiology to record from large lateral ventral (l-LNV) clock neurons, finding that ageing was associated with a significant decrease in input resistance, but no significant changes in spontaneous electrical activity or membrane potential. Manipulating the electrical properties of the circadian system by knocking down expression of candidate ion channels in all clock neurons had significant effects on behaviour, linking electrical activity with clock outputs. The results presented in this thesis demonstrate the suitability of Drosophila as a model to interrogate how ageing effects the circadian clock, identifying Alterations in the electrical properties of the l-LNV neurons may underlie observed changes in diurnal activity and sleep, while decreased remodelling of the s-LNV neurons can explain weakened circadian behaviour.
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Beynon, Amy Louise. "Neuroimmune modulation of the circadian clock." Thesis, Swansea University, 2011. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.678517.

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Jaeger, Cassie Danielle. "Chronic Circadian Misalignment Disrupts the Circadian Clock and Promotes Metabolic Syndrome." OpenSIUC, 2015. https://opensiuc.lib.siu.edu/dissertations/1081.

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Obesity, metabolic syndrome, and diabetes represent a major source of morbidity and mortality in the United States and worldwide. Chronic misalignment of an organism’s internal circadian clock with diurnal, cyclic changes in the external environment, prevalent in professions that require shift work, contributes significantly to Type 2 Diabetes development. Experimentally, only short-term models of circadian disruption have been explored. Therefore, the goal of this study was to establish an animal model of chronic circadian disruption, which would more closely mimic the harmful misalignment associated with metabolic syndrome in clinical studies. Moreover, since high fat diet consumption alters circadian behavior and rhythmic gene expression, contributing to the diet-induced phenotype, I hypothesized that chronic circadian disruption interacts with a high fat diet to worsen metabolic syndrome. To investigate circadian misalignment and diet-induced metabolic syndrome, I examined the contribution of the Aryl Hydrocarbon Receptor (AhR). AhR has similar PAS domain containing motifs as circadian clock proteins allowing for protein/protein interactions and crosstalk between AhR signaling and circadian rhythms. Furthermore, AhR activation is implicated in Type 2 Diabetes risk. To examine chronic circadian disruption, male wild-type (WT; C57Bl/6J) and AhR +/- mice were entrained to 12/12-hour light/dark cycles where lights were on from 10pm-10am and off from 10am-10pm. Misalignment was initiated by delaying the time of lights on by 8 hours on Monday. Mice were exposed to the misalignment schedule Monday-Friday then returned to the entrainment schedule Saturday and Sunday to mimic readjustment to society during the weekend. Circadian misaligned mice were exposed to the altered light schedule for 15 weeks and control animals remained on the12/12-hour light/dark cycle. Mice were fed a normal chow diet (10% fat) or a high fat diet (60% fat). Animals were sacrificed and samples were collected at 4-hour intervals on day 2 of the weekend. Exposure to chronic circadian misalignment by light disruption or high fat diet altered circadian rhythms of behavior, metabolic outputs, and expression of circadian clock, clock-controlled nuclear receptor, and lipid metabolism genes. A combination of light misalignment and high fat diet exacerbated the effects of either treatment alone further disrupting behavior, enhancing % body fat and fasting glucose, and dampening circadian clock gene expression. AhR +/- mice also were protected from the metabolic consequences of chronic misalignment and a high fat diet by resistance to altered behavioral and molecular circadian rhythms and disruption of metabolic outputs. With metabolic syndrome and Type 2 Diabetes occurrence on the rise, it is important to understand all contributing factors, including circadian disruption. Differences between chronic circadian misalignment and high fat diet-induced obesity in WT and AhR +/- mice furthers our understanding of the complex mechanisms that underlie Type 2 Diabetes development and advocates the discovery of potential therapeutic targets for the development of novel treatment options.
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Cotter, Sean. "Characterisation of the circadian clock in barley." Thesis, University of Liverpool, 2010. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.548780.

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Reddy, Akhilesh Basi. "Molecular Neurobiology of the mammalian circadian clock." Thesis, University of Cambridge, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.619684.

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Books on the topic "Circadian clock"

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Albrecht, Urs, ed. The Circadian Clock. New York, NY: Springer New York, 2010. http://dx.doi.org/10.1007/978-1-4419-1262-6.

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Engmann, Olivia, and Marco Brancaccio, eds. Circadian Clock in Brain Health and Disease. Cham: Springer International Publishing, 2021. http://dx.doi.org/10.1007/978-3-030-81147-1.

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Björn, Lemmer, and Rensing Ludger, eds. From the biological clock to chronopharmacology. Stuttgart: Medpharm, 1996.

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C, Klein D., Moore Robert Y, and Reppert Steven M, eds. Suprachiasmatic nucleus: The mind's clock. New York: Oxford University Press, 1991.

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Csernus, Valér. The avian pineal gland: A model of the biological clock. Budapest: Akadémiai Kiadó, 2004.

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Derek, Chadwick, Ackrill Kate, and Symposium on Circadian Clocks and Their Adjustment (1993 : Ciba Foundation), eds. Circadian clocks and their adjustment. Chichester: Wiley, 1995.

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Hirota, Tsuyoshi, Megumi Hatori, and Satchidananda Panda, eds. Circadian Clocks. New York, NY: Springer US, 2022. http://dx.doi.org/10.1007/978-1-0716-2577-4.

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Brown, Steven A., ed. Circadian Clocks. New York, NY: Springer US, 2021. http://dx.doi.org/10.1007/978-1-0716-0381-9.

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Kramer, Achim, and Martha Merrow, eds. Circadian Clocks. Berlin, Heidelberg: Springer Berlin Heidelberg, 2013. http://dx.doi.org/10.1007/978-3-642-25950-0.

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S, Takahashi Joseph, Turek Fred W, and Moore Robert Y, eds. Circadian clocks. New York: Kluwer Academic/Plenum Publishers, 2001.

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Book chapters on the topic "Circadian clock"

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Levesque, Roger J. R. "Circadian Clock." In Encyclopedia of Adolescence, 421. New York, NY: Springer New York, 2011. http://dx.doi.org/10.1007/978-1-4419-1695-2_460.

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Thiriet, Marc. "Circadian Clock." In Control of Cell Fate in the Circulatory and Ventilatory Systems, 329–56. New York, NY: Springer New York, 2011. http://dx.doi.org/10.1007/978-1-4614-0329-6_5.

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Levesque, Roger J. R. "Circadian Clock." In Encyclopedia of Adolescence, 598–99. Cham: Springer International Publishing, 2018. http://dx.doi.org/10.1007/978-3-319-33228-4_460.

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Michel, Stephan, Gene D. Block, and Johanna H. Meijer. "The Aging Clock." In Circadian Medicine, 321–35. Hoboken, NJ: John Wiley & Sons, Inc, 2015. http://dx.doi.org/10.1002/9781118467831.ch22.

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Daniel Rudic, R. "The Cardiovascular Clock." In Circadian Medicine, 119–33. Hoboken, NJ: John Wiley & Sons, Inc, 2015. http://dx.doi.org/10.1002/9781118467831.ch8.

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Herzog, Erik D., and Paul H. Taghert. "Circadian Neural Networks." In The Circadian Clock, 179–94. New York, NY: Springer New York, 2009. http://dx.doi.org/10.1007/978-1-4419-1262-6_8.

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Daan, Serge. "A History of Chronobiological Concepts." In The Circadian Clock, 1–35. New York, NY: Springer New York, 2009. http://dx.doi.org/10.1007/978-1-4419-1262-6_1.

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Feillet, Céline, and Urs Albrecht. "Clocks, Brain Function, and Dysfunction." In The Circadian Clock, 229–82. New York, NY: Springer New York, 2009. http://dx.doi.org/10.1007/978-1-4419-1262-6_10.

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d’Eysmond, Thomas, and Felix Naef. "Systems Biology and Modeling of Circadian Rhythms." In The Circadian Clock, 283–93. New York, NY: Springer New York, 2009. http://dx.doi.org/10.1007/978-1-4419-1262-6_11.

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Ripperger, Jürgen A., and Steven A. Brown. "Transcriptional Regulation of Circadian Clocks." In The Circadian Clock, 37–78. New York, NY: Springer New York, 2009. http://dx.doi.org/10.1007/978-1-4419-1262-6_2.

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Conference papers on the topic "Circadian clock"

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AXMANN, ILKA M., STEFAN LEGEWIE, and HANSPETER HERZEL. "A MINIMAL CIRCADIAN CLOCK MODEL." In Proceedings of the 7th Annual International Workshop on Bioinformatics and Systems Biology (IBSB 2007). IMPERIAL COLLEGE PRESS, 2007. http://dx.doi.org/10.1142/9781860949920_0006.

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O’Reilly, Steven. "04.22 Circadian clock and fibrosis." In 37th European Workshop for Rheumatology Research 2–4 March 2017 Athens, Greece. BMJ Publishing Group Ltd and European League Against Rheumatism, 2017. http://dx.doi.org/10.1136/annrheumdis-2016-211051.22.

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Naik, A., K. Forrest, S. Gavronski, U. Valekunja, A. Reddy, and S. Sengupta. "Circadian Clock Modulates Lung Repair and Regeneration." In American Thoracic Society 2021 International Conference, May 14-19, 2021 - San Diego, CA. American Thoracic Society, 2021. http://dx.doi.org/10.1164/ajrccm-conference.2021.203.1_meetingabstracts.a4525.

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Lewis, R. D. "A feedback model for an insect circadian clock." In Proceedings of the Annual International Conference of the IEEE Engineering in Medicine and Biology Society. IEEE, 1988. http://dx.doi.org/10.1109/iembs.1988.95054.

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Kurosawa, Gen, Kazuyuki Aihara, and Yoh Iwasa. "Bifurcation analyses in the cyanobacterial circadian clock model." In 2006 IEEE/NLM Life Science Systems and Applications Workshop. IEEE, 2006. http://dx.doi.org/10.1109/lssa.2006.250394.

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Sorkin, Maria. "A Comprehensive Interactome for the Arabidopsis Circadian Clock." In ASPB PLANT BIOLOGY 2020. USA: ASPB, 2020. http://dx.doi.org/10.46678/pb.20.989669.

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Figueiredo, Erika Ciconelli de, and Maria Augusta Justi Pisani. "Office building typologies and circadian potential." In XVII ENCONTRO NACIONAL DE CONFORTO NO AMBIENTE CONSTRUÍDO. ANTAC, 2023. http://dx.doi.org/10.46421/encac.v17i1.3878.

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Circadian rhythms are internal manifestations of the solar day that allow adaptations to environmental-temporal changes. Mood disorders are often associated with disrupted circadian clock-controlled responses, whereas circadian rhythm disruption is correlated to jet lag, night-shift work, or to exposure to artificial light at night. Modern lifestyle patterns lead to circadian rhythm disruption, and it results in several diseases. Circadian rhythm disruption is one of the factors most often investigated, besides smoking, diet, fatigue and quality sleep, increased body mass index and obesity. Lack of enough daylight at daytime and the exposure to electric light at nighttime can disconnect people from the natural environment and lead to psychological issues. The aims of the current research are to analyze the circadian potential of three building models based on WELL Certification, to compare their performance, and to draw design guidelines about circadian rhythm and users’ well-being to be applied to office buildings in São Paulo City, São Paulo State, Brazil. Adaptive Lighting for Alertness (ALFA tool) was used to calculate the Equivalent Melanopic Lux for WELL Certification criteria in the investigated scenarios. Results have indicated that shallow office plans can benefit users by providing them with regular circadian rhythm o help improving their sleep quality, reducing their stress and preventing severe diseases.
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Merlin, Christine. "Circadian clock control of the monarch butterfly seasonal migration." In 2016 International Congress of Entomology. Entomological Society of America, 2016. http://dx.doi.org/10.1603/ice.2016.92863.

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Foo, Mathias, Hee Young Yoo, and Pan-Jun Kim. "System identification of circadian clock in plant Arabidopsis thaliana." In 2013 13th International Conference on Control, Automaton and Systems (ICCAS). IEEE, 2013. http://dx.doi.org/10.1109/iccas.2013.6703901.

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Naik, A., Y. Issah, K. Forrest, D. B. Frank, A. Paris, A. Vaughan, and S. Sengupta. "Role of Circadian Clock in Lung Repair and Regeneration." In American Thoracic Society 2020 International Conference, May 15-20, 2020 - Philadelphia, PA. American Thoracic Society, 2020. http://dx.doi.org/10.1164/ajrccm-conference.2020.201.1_meetingabstracts.a5651.

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Reports on the topic "Circadian clock"

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Johnson, Carl H. Cell-permeable Circadian Clock Proteins. Fort Belvoir, VA: Defense Technical Information Center, June 2002. http://dx.doi.org/10.21236/ada405529.

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Czeisler, Charles A., and Laura K. Barger. Clinical Trial of Exercise on Circadian Clock Resetting. Fort Belvoir, VA: Defense Technical Information Center, January 2001. http://dx.doi.org/10.21236/ada387100.

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Van Cauter, Eve. Phase-Shifting Effects of Light and Activity on the Human Circadian Clock. Fort Belvoir, VA: Defense Technical Information Center, February 1994. http://dx.doi.org/10.21236/ada281204.

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Van Cauter, Eve. Phase-Shifting Effect of Light and Exercise on the Human Circadian Clock. Fort Belvoir, VA: Defense Technical Information Center, February 1992. http://dx.doi.org/10.21236/ada253012.

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Van Cauter, Eve, Jeppe Sturis, Maria M. Byrne, John D. Blackman, Neal H. Scherberg, Rachel Leproult, Samuel Refetoff, and Olivier Van Reeth. Phase-Shifting Effect of Light and Exercise on the Human Circadian Clock. Fort Belvoir, VA: Defense Technical Information Center, May 1993. http://dx.doi.org/10.21236/ada265732.

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Van Cauter, Eve. Phase Shifting Effects of Light and Activity on the Human Circadian Clock. Fort Belvoir, VA: Defense Technical Information Center, February 1998. http://dx.doi.org/10.21236/ada337545.

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Casey, Therese, Sameer J. Mabjeesh, Avi Shamay, and Karen Plaut. Photoperiod effects on milk production in goats: Are they mediated by the molecular clock in the mammary gland? United States Department of Agriculture, January 2014. http://dx.doi.org/10.32747/2014.7598164.bard.

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US scientists, Dr. Theresa Casey and Dr. Karen Plaut, collaborated with Israeli scientists, Dr. SameerMabjeesh and Dr. AviShamay to conduct studies proposed in the BARD Project No. US-4715-14 Photoperiod effects on milk production in goats: Are they mediated by the molecular clock in the mammary gland over the last 3 years. CLOCK and BMAL1 are core components of the circadian clock and as heterodimers function as a transcription factor to drive circadian-rhythms of gene expression. Studies of CLOCK-mutant mice found impaired mammary development in late pregnancy was related to poor lactation performance post-partum. To gain a better understanding of role of clock in regulation of mammary development studies were conducted with the mammary epithelial cell line HC11. Decreasing CLOCK protein levels using shRNA resulted in increased mammary epithelial cell growth rate and impaired differentiation, with lower expression of differentiation markers including ad herens junction protein and fatty acid synthesis genes. When BMAL1 was knocked out using CRISPR-CAS mammary epithelial cells had greater growth rate, but reached stationary phase at a lower density, with FACS indicating cells were growing and dying at a faster rate. Beta-casein milk protein levels were significantly decreased in BMAL1 knockout cells. ChIP-seq analysis was conducted to identify BMAL1 target genes in mammary epithelial cells. Studies conducted in goats found that photoperiod duration and physiological state affected the dynamics of the mammary clock. Effects were likely independent of the photoperiod effects on prolactin levels. Interestingly, circadian rhythms of core body temperature, which functions as a key synchronizing cue sent out by the central clock in the hypothalamus, were profoundly affected by photoperiod and physiological state. Data support that the clock in the mammary gland regulates genes important to development of the gland and milk synthesis. We also found the clock in the mammary is responsive to changes in physiological state and photoperiod, and thus may serve as a mechanism to establish milk production levels in response to environmental cues.
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Gauger, Michele A. Determining the Effect of Cryptochrome Loss and Circadian Clock Disruption on Tumorigenesis in Mice. Fort Belvoir, VA: Defense Technical Information Center, March 2005. http://dx.doi.org/10.21236/ada435115.

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Gillette, Martha. AASERT-92 Augmentation of Research Training in Chronobiology: Regulation of the Mammalian Circadian Clock by Neurotransmitters. Fort Belvoir, VA: Defense Technical Information Center, May 1994. http://dx.doi.org/10.21236/ada288243.

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Wagner, D. Ry, Eliezer Lifschitz, and Steve A. Kay. Molecular Genetic Analysis of Flowering in Arabidopsis and Tomato. United States Department of Agriculture, May 2002. http://dx.doi.org/10.32747/2002.7585198.bard.

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The primary objectives for the US lab included: the characterization of ELF3 transcription and translation; the creation and characterization of various transgenic lines that misexpress ELF3; defining genetic pathways related to ELF3 function regulating floral initiation in Arabidopsis; and the identification of genes that either interact with or are regulated by ELF3. Light quality, photoperiod, and temperature often act as important and, for some species, essential environmental cues for the initiation of flowering. However, there is relatively little information on the molecular mechanisms that directly regulate the developmental pathway from the reception of the inductive light signals to the onset of flowering and the initiation of floral meristems. The ELF3 gene was identified as possibly having a role in light-mediated floral regulation since elj3 mutants not only flower early, but exhibit light-dependent circadian defects. We began investigating ELF3's role in light signalling and flowering by cloning the ELF3 gene. ELF3 is a novel gene only present in plant species; however, there is an ELF3 homolog within Arabidopsis. The Arabidopsis elj3 mutation causes arrhythmic circadian output in continuous light; however, we show conclusively normal circadian function with no alteration of period length in elj3 mutants in dark conditions and that the light-dependent arrhythmia observed in elj3 mutants is pleiotropic on multiple outputs regardless of phase. Plants overexpressing ELF3 have an increased period length in constant light and flower late in long-days; furthermore, etiolated ELF3-overexpressing seedlings exhibit a decreased acute CAB2 response after a red light pulse, whereas the null mutant is hypersensitive to acute induction. This finding suggests that ELF3 negatively regulates light input to both the clock and its outputs. To determine whether ELF3's action is phase dependent, we examined clock resetting by light pulses and constructed phase response curves. Absence of ELF3 activity causes a significant alteration of the phase response curve during the subjective night, and overexpression of ELF3 results in decreased sensitivity to the resetting stimulus, suggesting that ELF3 antagonizes light input to the clock during the night. Indeed, the ELF3 protein interacts with the photoreceptor PHYB in the yeast two-hybrid assay and in vitro. The phase ofELF3 function correlates with its peak expression levels of transcript and protein in the subjective night. ELF3 action, therefore, represents a mechanism by which the oscillator modulates light resetting. Furthermore, flowering time is dependent upon proper expression ofELF3. Scientifically, we've made a big leap in the understanding of the circadian system and how it is coupled so tightly with light reception in terms of period length and clock resetting. Agriculturally, understanding more about the way in which the clock perceives and relays temporal information to pathways such as those involved in the floral transition can lead to increased crop yields by enabling plants to be grown in suboptimal conditions.
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