Fibroblast PER2 Circadian Rhythmicity Depends on Cell Density

Noguchi, Takaaki; Wang, Lexie; Welsh, David K.

doi:10.1177/0748730413487494

Cited by 50 publications

(58 citation statements)

References 53 publications

(92 reference statements)

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“…Regulation of circadian rhythmicity by excreted factors has also been demonstrated in other cell types. For instance, in fibroblasts, paracrine signaling is essential for maintenance of rhythmicity, but these signals do not have to be rhythmic and do not appear to influence circadian period; in particular, co-culturing PER2::LUC wildtype fibroblasts with non-luminescent Bmal1 −/− or Cry2 −/− fibroblasts to achieve a high-density culture enhanced the rhythmicity of the WT cells but did not affect their period [23]. In contrast, potential paracrine regulators of local coupling in hepatocyte cultures must be circadianly regulated and capable of influencing circadian phase or period.…”

Section: Discussionmentioning

confidence: 99%

Circadian Rhythms of PER2::LUC in Individual Primary Mouse Hepatocytes and Cultures

et al. 2014

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BackgroundHepatocytes, the parenchymal cells of the liver, express core clock genes, such as Period2 and Cryptochrome2, which are involved in the transcriptional/translational feedback loop of the circadian clock. Whether or not the liver is capable of sustaining rhythms independent of a central pacemaker is controversial. Whether and how circadian information may be shared among cells in the liver in order to sustain oscillations is currently unknown.ResultsIn this study we isolated primary hepatocytes from transgenic Per2Luc mice and used bioluminescence as a read-out of the state of the circadian clock. Hepatocytes cultured in a collagen gel sandwich configuration exhibited persistent circadian rhythms for several weeks. The amplitude of the rhythms damped, but medium changes consistently reset the phase and amplitude of the cultures. Cry2−/− Per2Luc cells oscillated robustly and expressed a longer period. Co-culturing with wildtype cells did not significantly shorten the period, indicating that coupling among hepatocytes is insufficient to synchronize cells with significantly differing periods. However, spatial patterns revealed by cellular imaging of wildtype cultures provided evidence of weak local coupling among the hepatocytes.ConclusionsOur results with primary hepatocyte cultures demonstrate that cultured hepatocytes are weakly coupled. While this coupling is not sufficient to sustain global synchrony, it does increase local synchrony, which may stabilize the circadian rhythms of peripheral oscillators, such as the liver, against noise in the entraining signals.

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Section: Discussionmentioning

confidence: 99%

Circadian Rhythms of PER2::LUC in Individual Primary Mouse Hepatocytes and Cultures

et al. 2014

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“…Single-cell mPer2 Luc measurements were carried out as described elsewhere (Noguchi, et al, 2013, Welsh and Noguchi, 2012) with a few modifications. Light from the sample was collected by an Olympus UPlanSApo 10x objective (NA 0.40).…”

Section: Methodsmentioning

confidence: 99%

Cellular circadian oscillators in the suprachiasmatic nucleus remain coupled in the absence of connexin-36

et al. 2017

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In mammals, the master circadian clock resides in the suprachiasmatic nucleus (SCN). The SCN is characterized by robust circadian oscillations of clock gene expression and neuronal firing. The synchronization of circadian oscillations among individual cells in the SCN is attributed to intercellular coupling. Previous studies have shown that gap junctions, specifically those composed of connexin-36 (Cx36) subunits, are required for coupling of electrical firing among SCN neurons at a time scale of milliseconds. However, it remains unknown whether Cx36 gap junctions also contribute to coupling of circadian (~24 h) rhythms of clock gene expression. Here, we investigated circadian expression patterns of the clock gene Period 2 (Per2) in the SCN of Cx36-deficient mice using luminometry and single-cell bioluminescence imaging. Surprisingly, we found that synchronization of circadian PER2 expression rhythms is maintained in SCN explants from Cx36-deficient mice. Since Cx36 expression levels change with age, we also tested circadian running-wheel behavior of juvenile (3–4 weeks old) and adult (9–30 weeks old) Cx36-deficient mice. We found that impact of connexin-36 expression on circadian behavior changes greatly during postnatal development. However, consistent with the intact synchrony among SCN cells in cultured explants, Cx36-deficient mice had intact locomotor circadian rhythms, although adults displayed a lengthened period in constant darkness. Our data indicate that even though Cx36 may be required for electrical coupling of SCN cells, it does not affect coupling of molecular clock gene rhythms. Thus, electrical coupling of neurons and coupling of circadian clock gene oscillations can be regulated independently in the SCN.

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“…Regulated Protein [96]). One may thus hypothesise that some of the reported effects of cell density on circadian rhythmicity [97,98] operate through this mechanism (Figure 3). due to the levels of reinitiation factors such as DENR) and/or tissue-specific uORF usage could regulate the levels of core clock proteins and thus complex stoichiometry, altering clock parameters in a way that is dependent on organ, physiological condition, or other cues.…”

Section: Specific Roles Of the Mtor Pathway In The Scnmentioning

confidence: 99%

Emerging Roles of Translational Control in Circadian Timekeeping

Castelo-Szekely

Gatfield

2020

Journal of Molecular Biology

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A large part of mammalian physiology and behaviour shows regular daily variations. This temporal organisation is driven by the activity of an endogenous circadian clock, whose molecular basis consists of diurnal waves in gene expression. Circadian transcription is the major driver of these rhythms, yet post-transcriptional mechanisms, some of which occur in response to systemic cues and in a tissue-specific fashion, have central roles in ultimately establishing the oscillatory gene expression programme as well. Regulatory control that occurs at the level of translation is emerging as an important player in the generation and modulation of protein accumulation rhythms. As a mechanism, translation lies at a privileged position to integrate genetically encoded rhythmic signals with other, external and internal stimuli, including nutrient-derived cues. In this review, we summarise our current knowledge of how diurnal control of translation affects both bulk protein levels and gene-specific protein biosynthesis. We discuss mechanisms of regulation, in particular with regard to the complex interplay between circadian cycles and feeding/fasting cycles, as well as emerging roles for upstream open reading frames (uORFs) in clock control. cyanobacterial clocks can operate in the absence of any transcription at all and that self-sustained rhythmic phosphorylation of the essential clock component KaiC even occurs in vitro using recom-2 binant clock proteins and ATP [4]. Transcription-independent molecular rhythms have also been observed in human erythrocytes. In these naturally nucleus-free cells, antioxidant proteins known as peroxiredoxins undergo changes in their redox status, which show self-sustained, entrainable, and 35 temperature-compensated 24-hour periodicity in the absence of transcription and translation [5]. In the wake of such surprising discoveries (and as a consequence of the technical advances made in the fields of high-throughput nucleic acid sequencing and proteomics), the longstanding concept which places daily changes in transcriptional activity at the heart of rhythmic gene expression was revisited as well. A more nuanced picture has arisen that accords a significant role to post-transcriptional 40 mechanisms in the generation of rhythmic clock outputs in mammals. Furthermore, it has become clear that a significant proportion of RNA and protein oscillations is not necessarily a direct output of the local, cellular clock, but rather driven by systemic cues, in particular by signals related to feeding.This review aims at presenting and discussing our current knowledge of how one of the implicated 45 post-transcriptional mechanism, i.e. translation, can generate, modulate, and sustain circadian rhythms. Our main focus will lie on the mammalian circadian system. Before we delve into the details, however, we shall take this opportunity for a brief digression into findings from two of the more exotic organisms that have been used in circadian clock research, namely green algae and marine dinoflagellates. It i...

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Fibroblast PER2 Circadian Rhythmicity Depends on Cell Density

Cited by 50 publications

References 53 publications

Circadian Rhythms of PER2::LUC in Individual Primary Mouse Hepatocytes and Cultures

Circadian Rhythms of PER2::LUC in Individual Primary Mouse Hepatocytes and Cultures

Cellular circadian oscillators in the suprachiasmatic nucleus remain coupled in the absence of connexin-36

Emerging Roles of Translational Control in Circadian Timekeeping

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