scholarly journals Photic Entrainment of the Circadian System

2022 ◽  
Vol 23 (2) ◽  
pp. 729
Author(s):  
Anna Ashton ◽  
Russell G. Foster ◽  
Aarti Jagannath
Keyword(s):  
Circadian Clock ◽  
Molecular Basis ◽  
Feedback Loop ◽  
Molecular Mechanisms ◽  
External World ◽  
Circadian System ◽  
Suprachiasmatic Nuclei ◽  
Photic Entrainment ◽  
External Time ◽  
Daily Changes

Circadian rhythms are essential for the survival of all organisms, enabling them to predict daily changes in the environment and time their behaviour appropriately. The molecular basis of such rhythms is the circadian clock, a self-sustaining molecular oscillator comprising a transcriptional–translational feedback loop. This must be continually readjusted to remain in alignment with the external world through a process termed entrainment, in which the phase of the master circadian clock in the suprachiasmatic nuclei (SCN) is adjusted in response to external time cues. In mammals, the primary time cue, or “zeitgeber”, is light, which inputs directly to the SCN where it is integrated with additional non-photic zeitgebers. The molecular mechanisms underlying photic entrainment are complex, comprising a number of regulatory factors. This review will outline the photoreception pathways mediating photic entrainment, and our current understanding of the molecular pathways that drive it in the SCN.

Evolution Analysis of the Circadian Clock Protein KaiB

2013 ◽  
Vol 647 ◽  
pp. 391-395
Author(s):  
Liu Sen ◽  
Song Liu
Keyword(s):  
Circadian Rhythms ◽  
Circadian Clock ◽  
Feedback Loop ◽  
Circadian System ◽  
Circadian Rhythmicity ◽  
Physiological Functions ◽  
Clock System ◽  
Evolution Analysis ◽  
Clock Protein

Regulation of daily physiological functions with approximate a 24-hour periodicity, or circadian rhythms, is a characteristic of eukaryotes. So far, cyanobacteria are only known prokaryotes reported to possess circadian rhythmicity. The circadian system in cyanobacteria comprises both a post-translational oscillator (PTO) and a transcriptional/translational feedback loop (TTFL). The PTO can be reconstituted in vitro with three purified proteins (KaiA, KaiB, and KaiC) with the existence of ATP. Phase of the nanoclockwork has been associated with the phosphorylation states of KaiC, with KaiA promoting the phosphorylation of KaiC, and KaiB de-phosphorylating KaiC. Here we studied the evolution of the KaiB protein. The result will be helpful in understanding the evolution of the circadian clock system.

Analysis of the Sequence Conservation of the Circadian Clock Protein KaiC

2013 ◽  
Vol 699 ◽  
pp. 184-188
Author(s):  
Liu Sen ◽  
Song Liu ◽  
Fei Yun Chen
Keyword(s):  
Circadian Rhythms ◽  
Circadian Clock ◽  
Feedback Loop ◽  
Sequence Variation ◽  
Protein Sequences ◽  
Circadian System ◽  
Site Variation ◽  
Key Residues ◽  
Clock Protein

Regulation of daily physiological functions with approximate a 24-hour periodicity, or circadian rhythms, is a characteristic of eukaryotes. So far, cyanobacteria are only known prokaryotes reported to possess circadian rhythmicity. The circadian system in cyanobacteria comprises both a post-translational oscillator (PTO) and a transcriptional/translational feedback loop (TTFL). The PTO can be reconstituted in vitro with three purified proteins (KaiA, KaiB, and KaiC) with the existence of ATP. Phase of the nanoclockwork has been associated with the phosphorylation states of KaiC, with KaiA promoting the phosphorylation of KaiC, and KaiB de-phosphorylating KaiC. Here we studied the sequence variation of 65 KaiC proteins in evolution, and determined some key residues in KaiC by analyzing the site variation rates of the protein sequences. These key residues could be used to study the key interactions of KaiC with KaiA and KaiB.

Entrainment of circadian clocks in mammals by arousal and food

2011 ◽  
Vol 49 ◽  
pp. 119-136 ◽  
Author(s):  
Ralph E Mistlberger ◽  
Michael C Antle
Keyword(s):  
Clock Gene ◽  
Gene Mutations ◽  
Circadian System ◽  
Neural Pathways ◽  
Suprachiasmatic Nuclei ◽  
Social Stimuli ◽  
Clock Gene Expression ◽  
Circadian Oscillators ◽  
External Time ◽  
The Brain

Circadian rhythms in mammals are regulated by a system of endogenous circadian oscillators (clock cells) in the brain and in most peripheral organs and tissues. One group of clock cells in the hypothalamic SCN (suprachiasmatic nuclei) functions as a pacemaker for co-ordinating the timing of oscillators elsewhere in the brain and body. This master clock can be reset and entrained by daily LD (light–dark) cycles and thereby also serves to interface internal with external time, ensuring an appropriate alignment of behavioural and physiological rhythms with the solar day. Two features of the mammalian circadian system provide flexibility in circadian programming to exploit temporal regularities of social stimuli or food availability. One feature is the sensitivity of the SCN pacemaker to behavioural arousal stimulated during the usual sleep period, which can reset its phase and modulate its response to LD stimuli. Neural pathways from the brainstem and thalamus mediate these effects by releasing neurochemicals that inhibit retinal inputs to the SCN clock or that alter clock-gene expression in SCN clock cells. A second feature is the sensitivity of circadian oscillators outside of the SCN to stimuli associated with food intake, which enables animals to uncouple rhythms of behaviour and physiology from LD cycles and align these with predictable daily mealtimes. The location of oscillators necessary for food-entrained behavioural rhythms is not yet certain. Persistence of these rhythms in mice with clock-gene mutations that disable the SCN pacemaker suggests diversity in the molecular basis of light- and food-entrainable clocks.

Out of breath, out of time: interactions between HIF and circadian rhythms

2020 ◽  
Vol 319 (3) ◽  
pp. C533-C540
Author(s):  
Emma J. O’Connell ◽  
Chloe-Anne Martinez ◽  
Yichuan G. Liang ◽  
Peter A. Cistulli ◽  
Kristina M. Cook
Keyword(s):  
Circadian Clock ◽  
Feedback Loop ◽  
Molecular Mechanisms ◽  
Hypoxia Inducible Factor ◽  
Cellular Level ◽  
The Body ◽  
Circadian Clocks ◽  
Molecular Clocks ◽  
Circadian Transcription ◽  
New Strategies

Humans have internal circadian clocks that ensure that important physiological functions occur at specific times of the day. These molecular clocks are regulated at the genomic level and exist in most cells of the body. Multiple circadian resetting cues have been identified, including light, temperature, and food. Recently, oxygen has been identified as a resetting cue, and emerging science indicates that this occurs through interactions at the cellular level between the circadian transcription-translation feedback loop and the hypoxia-inducible pathway (hypoxia-inducible factor; subject of the 2019 Nobel Prize in Physiology or Medicine). This review will cover recently identified relationships between HIF and proteins of the circadian clock. Interactions between the circadian clock and hypoxia could have wide-reaching implications for human diseases, and understanding the molecular mechanisms regulating these overlapping pathways may open up new strategies for drug discovery.

scholarly journals Targeted Disruption of the Inhibitor of DNA Binding 4 (Id4) Gene Alters Photic Entrainment of the Circadian Clock

2021 ◽  
Vol 22 (17) ◽  
pp. 9632
Author(s):  
Giles E. Duffield ◽  
Maricela Robles-Murguia ◽  
Tim Y. Hou ◽  
Kathleen A. McDonald
Keyword(s):  
Dna Binding ◽  
Circadian Clock ◽  
Time Of Day ◽  
Circadian System ◽  
Targeted Disruption ◽  
Photic Entrainment ◽  
Helix Loop Helix ◽  
Advanced Phase ◽  
Id Genes ◽  
Inhibitor Of Dna Binding

Inhibitor of DNA binding (Id) genes comprise a family of four helix–loop–helix (HLH) transcriptional inhibitors. Our earlier studies revealed a role for ID2 within the circadian system, contributing to input, output, and core clock function through its interaction with CLOCK and BMAL1. Here, we explore the contribution of ID4 to the circadian system using a targeted disruption of the Id4 gene. Attributes of the circadian clock were assessed by monitoring the locomotor activity of Id4−/− mice, and they revealed disturbances in its operation. Id4-mutant mice expressed a shorter circadian period length, attenuated phase shifts in responses to continuous and discrete photic cues, and an advanced phase angle of entrainment under a 12:12 light:dark cycle and under short and long photoperiods. To understand the basis for these properties, suprachiasmatic nucleus (SCN) and retinal structures were examined. Anatomical analysis reveals a smaller Id4−/− SCN in the width dimension, which is a finding consistent with its smaller brain. As a result of this feature, anterograde tracing in Id4−/− mice revealed retinal afferents innovate a disproportionally larger SCN area. The Id4−/− photic entrainment responses are unlikely to be due to an impaired function of the retinal pathways since Id4−/− retinal anatomy and function tested by pupillometry were similar to wild-type mice. Furthermore, these circadian characteristics are opposite to those exhibited by the Id2−/− mouse, suggesting an opposing influence of the ID4 protein within the circadian system; or, the absence of ID4 results in changes in the expression or activity of other members of the Id gene family. Expression analysis of the Id genes within the Id4−/− SCN revealed a time-of-day specific elevated Id1. It is plausible that the increased Id1 and/or absence of ID4 result in changes in interactions with bHLH canonical clock components or with targets upstream and/or downstream of the clock, thereby resulting in abnormal properties of the circadian clock and its entrainment.

scholarly journals The Arabidopsis Circadian Clock and Metabolic Energy: A Question of Time

2021 ◽  
Vol 12 ◽  
Author(s):  
Luis Cervela-Cardona ◽  
Benjamin Alary ◽  
Paloma Mas
Keyword(s):  
Circadian Clock ◽  
Molecular Mechanisms ◽  
Environmental Changes ◽  
Building Blocks ◽  
Fundamental Principle ◽  
Metabolic Energy ◽  
Mitochondrial Activity ◽  
Cellular Processes ◽  
Control Growth ◽  
External Time

A fundamental principle shared by all organisms is the metabolic conversion of nutrients into energy for cellular processes and structural building blocks. A highly precise spatiotemporal programming is required to couple metabolic capacity with energy allocation. Cellular metabolism is also able to adapt to the external time, and the mechanisms governing such an adaptation rely on the circadian clock. Virtually all photosensitive organisms have evolved a self-sustained timekeeping mechanism or circadian clock that anticipates and responds to the 24-h environmental changes that occur during the day and night cycle. This endogenous timing mechanism works in resonance with the environment to control growth, development, responses to stress, and also metabolism. Here, we briefly describe the prevalent role for the circadian clock controlling the timing of mitochondrial activity and cellular energy in Arabidopsis thaliana. Evidence that metabolic signals can in turn feedback to the clock place the spotlight onto the molecular mechanisms and components linking the circadian function with metabolic homeostasis and energy.

scholarly journals Smith-Magenis Syndrome: Molecular Basis of a Genetic-Driven Melatonin Circadian Secretion Disorder

2019 ◽  
Vol 20 (14) ◽  
pp. 3533 ◽  
Author(s):  
Alice Poisson ◽  
Alain Nicolas ◽  
Idriss Bousquet ◽  
Véronique Raverot ◽  
Claude Gronfier ◽  
...  
Keyword(s):  
Molecular Basis ◽  
Circadian System ◽  
Light Signal ◽  
Suprachiasmatic Nuclei ◽  
Melatonin Secretion ◽  
Secretion Pathway ◽  
Sleep Maintenance ◽  
Unique Model ◽  
Cycle Disorders

Smith-Magenis syndrome (SMS), linked to Retinoic Acid Induced (RAI1) haploinsufficiency, is a unique model of the inversion of circadian melatonin secretion. In this regard, this model is a formidable approach to better understand circadian melatonin secretion cycle disorders and the role of the RAI1 gene in this cycle. Sleep-wake cycle disorders in SMS include sleep maintenance disorders with a phase advance and intense sleepiness around noon. These disorders have been linked to a general disturbance of sleep-wake rhythm and coexist with inverted secretion of melatonin. The exact mechanism underlying the inversion of circadian melatonin secretion in SMS has rarely been discussed. We suggest three hypotheses that could account for the inversion of circadian melatonin secretion and discuss them. First, inversion of the circadian melatonin secretion rhythm could be linked to alterations in light signal transduction. Second, this inversion could imply global misalignment of the circadian system. Third, the inversion is not linked to a global circadian clock shift but rather to a specific impairment in the melatonin secretion pathway between the suprachiasmatic nuclei (SCN) and pinealocytes. The development of diurnal SMS animal models that produce melatonin appears to be an indispensable step to further understand the molecular basis of the circadian melatonin secretion rhythm.

The circadian clock and metabolism

2010 ◽  
Vol 120 (2) ◽  
pp. 65-72 ◽  
Author(s):  
Oren Froy
Keyword(s):  
Circadian Clock ◽  
Clock Genes ◽  
The Body ◽  
Suprachiasmatic Nuclei ◽  
Peripheral Tissues ◽  
Environmental Light ◽  
Activity Of Enzymes ◽  
Transcription Activators ◽  
The Relationship ◽  
Daily Changes

Mammals have developed an endogenous circadian clock located in the SCN (suprachiasmatic nuclei) of the anterior hypothalamus that responds to the environmental light–dark cycle. Human homoeostatic systems have adapted to daily changes in a way that the body anticipates the sleep and activity periods. Similar clocks have been found in peripheral tissues, such as the liver, intestine and adipose tissue. Recently it has been found that the circadian clock regulates cellular and physiological functions in addition to the expression and/or activity of enzymes and hormones involved in metabolism. In turn, key metabolic enzymes and transcription activators interact with and affect the core clock mechanism. Animals with mutations in clock genes that disrupt cellular rhythmicity have provided evidence to the relationship between the circadian clock and metabolic homoeostasis. The present review will summarize recent findings concerning the relationship between metabolism and circadian rhythms.

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