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  • 1
    UID:
    b3kat_BV004352393
    Format: 205 S. , graph. Darst.
    ISBN: 3055007093
    Series Statement: Wissenschaftliche Taschenbücher 309 : Reihe Mathematik und Physik
    Note: Literaturverz. S. 185 - 200
    Language: German
    Subjects: Physics , Mathematics , Philosophy
    RVK:
    RVK:
    RVK:
    Keywords: Selbstorganisation ; Synergetik ; Zeit ; Selbstorganisation ; Nichtlineares System
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  • 2
    UID:
    b3kat_BV048474136
    Format: Foto (schwarz/weiß) , 8° / 10 x 15
    Additional Edition: Elektronische Reproduktion Berlin : Humboldt-Universität zu Berlin, Universitätsbibliothek, [zwischen 2000 und 2020]
    Language: Undetermined
    URL: Vollständiger Inhalt  (kostenfrei)
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  • 3
    Online Resource
    Online Resource
    Berlin : Humboldt-Universität zu Berlin
    UID:
    edochu_18452_26007
    Format: 1 Online-Ressource (19 Seiten)
    Content: The circadian clock is an endogenous oscillator that controls daily rhythms in metabolism, physiology, and behavior. Although the timekeeping components differ among species, a common design principle is a transcription-translation negative feedback loop. However, it is becoming clear that other mechanisms can contribute to the generation of 24 h rhythms. Peroxiredoxins (Prxs) exhibit 24 h rhythms in their redox state in all kingdoms of life. In mammalian adrenal gland, heart and brown adipose tissue, such rhythms are generated as a result of an inactivating hyperoxidation reaction that is reduced by coordinated import of sulfiredoxin (Srx) into the mitochondria. However, a quantitative description of the Prx/Srx oscillating system is still missing. We investigate the basic principles that generate mitochondrial Prx/Srx rhythms using computational modeling. We observe that the previously described delay in mitochondrial Srx import, in combination with an appropriate separation of fast and slow reactions, is sufficient to generate robust self-sustained relaxation-like oscillations. We find that our conceptual model can be regarded as a series of three consecutive phases and two temporal switches, highlighting the importance of delayed negative feedback and switches in the generation of oscillations.
    Content: Peer Reviewed
    In: Basel : Molecular Diversity Preservation International, 20,9
    Language: English
    URL: Volltext  (kostenfrei)
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  • 4
    Online Resource
    Online Resource
    Berlin : Humboldt-Universität zu Berlin
    UID:
    edochu_18452_26015
    Format: 1 Online-Ressource (11 Seiten)
    Content: Circadian rhythms are biological rhythms with a period close to 24 h. They become entrained to the Earth’s solar day via different periodic cues, so-called zeitgebers. The entrainment of circadian rhythms to a single zeitgeber was investigated in many mathematical clock models of different levels of complexity, ranging from the Poincaré oscillator and the Goodwin model to biologically more detailed models of multiple transcriptional translational feedback loops. However, circadian rhythms are exposed to multiple coexisting zeitgebers in nature. Therefore, we study synergistic effects of two coexisting zeitgebers on different components of the circadian clock. We investigate the induction of period genes by light together with modulations of nuclear receptor activities by drugs and metabolism. Our results show that the entrainment of a circadian rhythm to two coexisting zeitgebers depends strongly on the phase difference between the two zeitgebers. Synergistic interactions of zeitgebers can strengthen diurnal rhythms to reduce detrimental effects of shift-work and jet lag. Medical treatment strategies which aim for stable circadian rhythms should consider interactions of multiple zeitgebers.
    Content: Peer Reviewed
    In: Lausanne : Frontiers Media, 1
    Language: English
    URL: Volltext  (kostenfrei)
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  • 5
    UID:
    edochu_18452_26448
    Format: 1 Online-Ressource (17 Seiten)
    Content: The circadian clock modulates key physiological processes in many organisms. This widespread role of circadian rhythms is typically characterized at the molecular level by profiling the transcriptome at multiple time points. Subsequent analysis identifies transcripts with altered rhythms between control and perturbed conditions, that is, are differentially rhythmic (DiffR). Commonly, Venn diagram analysis (VDA) compares lists of rhythmic transcripts to catalog transcripts with rhythms in both conditions, or that have gained or lost rhythms. However, unavoidable errors in rhythmicity detection propagate to the final DiffR classification resulting in overestimated DiffR. We show using artificial experiments on biological data that VDA indeed produces excessive false DiffR hits both in the presence and absence of true DiffR transcripts. We review and benchmark hypothesis testing and model selection approaches that instead compare circadian amplitude and phase of transcripts between the two conditions. These methods identify transcripts that ‘gain’, ‘lose’, ‘change’, or have the ‘same’ rhythms; the third category is missed by VDA. We reanalyzed three studies on the interplay between metabolism and the clock in the mouse liver that used VDA. We found not only fewer DiffR transcripts than originally reported, but VDA overlooked many relevant DiffR transcripts. Our analyses confirmed some and contradicted other conclusions in the original studies and also generated novel insights. Our conclusions equally apply to circadian studies using other omics technologies. We believe that avoiding Venn diagrams and using our convenient r‐package comparerhythms will improve the reliability of analyses in chronobiology.
    Content: Comparing rhythms with and without an intervention reveals the functioning of the circadian system. High‐throughput studies of clock outputs (transcripts, proteins, etc.) typically compare lists of rhythmic outputs in each condition using Venn diagrams. This approach incorrectly predicts too many altered rhythms, while also overlooking some rhythm changes. Direct comparison of amplitudes and phases using R‐package comparerhythms fixes this problem and reveals limited circadian remodeling due to metabolic changes. image
    Content: Peer Reviewed
    In: Oxford : Wiley-Blackwell, 289,21, Seiten 6605-6621
    Language: English
    URL: Volltext  (kostenfrei)
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  • 6
    Online Resource
    Online Resource
    Berlin : Humboldt-Universität zu Berlin
    UID:
    edochu_18452_23083
    Format: 1 Online-Ressource (12 Seiten)
    Content: Entrainment denotes a process of coordinating the internal circadian clock to external rhythmic time-cues (Zeitgeber), mainly light. It is facilitated by stronger Zeitgeber signals and smaller period differences between the internal clock and the external Zeitgeber. The phase of entrainment ψ is a result of this process on the side of the circadian clock. On Earth, the period of the day-night cycle is fixed to 24 h, while the periods of circadian clocks distribute widely due to natural variation within and between species. The strength and duration of light depend locally on season and geographic latitude. Therefore, entrainment characteristics of a circadian clock vary under a local light environment and distribute along geoecological settings. Using conceptual models of circadian clocks, we investigate how local conditions of natural light shape global patterning of entrainment through seasons. This clock-side entrainment paradigm enables us to predict systematic changes in the global distribution of chronotypes.
    Content: Peer Reviewed
    In: Lausanne : Frontiers Media S.A., 11
    Language: English
    URL: Volltext  (kostenfrei)
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  • 7
    UID:
    edochu_18452_23138
    Format: 1 Online-Ressource (10 Seiten)
    Content: Understanding entrainment of circadian rhythms is a central goal of chronobiology. Many factors, such as period, amplitude, Zeitgeber strength, and daylength, govern entrainment ranges and phases of entrainment. We have tested whether simple amplitude-phase models can provide insight into the control of entrainment phases. Using global optimization, we derived conceptual models with just three free parameters (period, amplitude, and relaxation rate) that reproduce known phenotypic features of vertebrate clocks: phase response curves (PRCs) with relatively small phase shifts, fast re-entrainment after jet lag, and seasonal variability to track light onset or offset. Since optimization found multiple sets of model parameters, we could study this model ensemble to gain insight into the underlying design principles. We found complex associations between model parameters and entrainment features. Arnold onions of representative models visualize strong dependencies of entrainment on periods, relative Zeitgeber strength, and photoperiods. Our results support the use of oscillator theory as a framework for understanding the entrainment of circadian clocks.
    Content: Peer Reviewed
    In: Lausanne : Frontiers Research Foundation, 11
    Language: English
    URL: Volltext  (kostenfrei)
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  • 8
    UID:
    edochu_18452_21440
    Format: 1 Online-Ressource (10 Seiten)
    Content: The human CD4+FOXP3+ T cell population is heterogeneous and consists of various subpopulations which remain poorly defined. Anergy and suppression are two main functional characteristics of FOXP3+Treg cells. We used the anergic behavior of FOXP3+Treg cells for a better discrimination and characterization of such subpopulations. We compared IL-2-expressing with IL-2-non-expressing cells within the memory FOXP3+ T cell population. In contrast to IL-2-non-expressing FOXP3+ cells, IL-2-expressing FOXP3+ cells exhibit intermediate characteristics of Treg and Th cells concerning the Treg cell markers CD25, GITR, and Helios. Besides lower levels of FOXP3, they also have higher levels of the transcription factors NFATc2, c-Fos, NF-κBp65, and c-Jun. An approach combining flow cytometric measurements with statistical interpretation for quantitative transcription factor analysis suggests that the physiological expression levels not only of FOXP3 but also of NFATc2, c-Jun, c-Fos, and NF-κBp65 are limiting for the decision whether IL-2 is expressed or not in activated peripheral human memory FOXP3+ cells. These findings demonstrate that concomitant high levels of NFATc2, c-Jun, c-Fos, and NF-κBp65 lead in addition to potential IL-2 expression in those FOXP3+ cells with low levels of FOXP3. We hypothesize that not only the level of FOXP3 expression but also the amounts of the four transcription factors studied represent determining factors for the anergic phenotype of FOXP3+ Treg cells.
    Content: Peer Reviewed
    In: Lausanne : Frontiers Research Foundation, 3
    Language: English
    URL: Volltext  (kostenfrei)
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  • 9
    UID:
    edochu_18452_28810
    Format: 1 Online-Ressource (11 Seiten)
    Content: The skin is the largest human organ with a circadian clock that regulates its function. Although circadian rhythms in specific functions are known, rhythms in the proximal clock output, gene expression, in human skin have not been thoroughly explored. This work reports 24 h gene expression rhythms in two skin layers, epidermis and dermis, in a cohort of young, healthy adults, who maintained natural, regular sleep-wake schedules. 10% of the expressed genes showed such diurnal rhythms at the population level, of which only a third differed between the two layers. Amplitude and phases of diurnal gene expression varied more across subjects than layers, with amplitude being more variable than phases. Expression amplitudes in the epidermis were larger and more subject-variable, while they were smaller and more consistent in the dermis. Core clock gene expression was similar across layers at the population-level, but were heterogeneous in their variability across subjects. We also identified small sets of biomarkers for internal clock phase in each layer, which consisted of layer-specific non-core clock genes. This work provides a valuable resource to advance our understanding of human skin and presents a novel methodology to quantify sources of variability in human circadian rhythms.
    Content: Peer Reviewed
    In: Oxford : Oxford University Press, 4,4
    Language: English
    URL: Volltext  (kostenfrei)
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  • 10
    UID:
    gbv_618041982
    ISSN: 0008-5472
    In: Cancer research, Birmingham, Ala. [u.a.] : AACR, 1941, 70(2010), 1, Seite 12-13, 0008-5472
    In: volume:70
    In: year:2010
    In: number:1
    In: pages:12-13
    Language: English
    Author information: Wolkenhauer, Olaf 1966-
    Author information: Junghanß, Christian 1969-
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