A model for the regulation of the timing of cell division by the circadian clock in the cyanobacterium Synechococcus elongatus

1SummaryCells of the cyanobacterium Synechococcus elongatus possess a circadian clock in the form of three core clock proteins (the Kai proteins) whose concentrations and phosphorylation states oscillate with daily periodicity under constant conditions [1]. The circadian clock regulates the cell cycle such that the timing of cell divisions is biased towards certain times during the circadian period [2, 3, 4, 5], but the mechanism underlying how the clock regulates division timing remains unclear. Here, we propose a mechanism in which a protein limiting for division accumulates at a rate proportional to cell volume growth and modulated by the clock. This “modulated rates” model, in which the clock signal is integrated over time to affect division timing, differs fundamentally from the previously proposed “gating” concept, in which the clock is assumed to suppress divisions during a specific time window [2, 3]. We found that while both models can capture the single-cell statistics of division timing in S. elongatus, only the modulated rates model robustly places divisions away from darkness during changes in the environment. Moreover, within the framework of the modulated rates model, existing experiments on S. elongatus are consistent with the simple mechanism that division timing is regulated by the accumulation of a division limiting protein in phase with genes whose activity peak at dusk.

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Synechocystis KaiC3 Displays Temperature- and KaiB-Dependent ATPase Activity and Is Important for Growth in Darkness

Journal of Bacteriology ◽

10.1128/jb.00478-19 ◽

2019 ◽

Vol 202 (4) ◽

Author(s):

Anika Wiegard ◽

Christin Köbler ◽

Katsuaki Oyama ◽

Anja K. Dörrich ◽

Chihiro Azai ◽

...

Keyword(s):

Atpase Activity ◽

Circadian Clock ◽

Atp Hydrolysis ◽

Synechococcus Elongatus ◽

Constant Darkness ◽

Content Type ◽

Clock Proteins ◽

Pcc 7942 ◽

Pcc 6803

ABSTRACT Cyanobacteria form a heterogeneous bacterial group with diverse lifestyles, acclimation strategies, and differences in the presence of circadian clock proteins. In Synechococcus elongatus PCC 7942, a unique posttranslational KaiABC oscillator drives circadian rhythms. ATPase activity of KaiC correlates with the period of the clock and mediates temperature compensation. Synechocystis sp. strain PCC 6803 expresses additional Kai proteins, of which KaiB3 and KaiC3 proteins were suggested to fine-tune the standard KaiAB1C1 oscillator. In the present study, we therefore characterized the enzymatic activity of KaiC3 as a representative of nonstandard KaiC homologs in vitro. KaiC3 displayed ATPase activity lower than that of the Synechococcus elongatus PCC 7942 KaiC protein. ATP hydrolysis was temperature dependent. Hence, KaiC3 is missing a defining feature of the model cyanobacterial circadian oscillator. Yeast two-hybrid analysis showed that KaiC3 interacts with KaiB3, KaiC1, and KaiB1. Further, KaiB3 and KaiB1 reduced in vitro ATP hydrolysis by KaiC3. Spot assays showed that chemoheterotrophic growth in constant darkness is completely abolished after deletion of ΔkaiAB1C1 and reduced in the absence of kaiC3. We therefore suggest a role for adaptation to darkness for KaiC3 as well as a cross talk between the KaiC1- and KaiC3-based systems. IMPORTANCE The circadian clock influences the cyanobacterial metabolism, and deeper understanding of its regulation will be important for metabolic optimizations in the context of industrial applications. Due to the heterogeneity of cyanobacteria, characterization of clock systems in organisms apart from the circadian model Synechococcus elongatus PCC 7942 is required. Synechocystis sp. strain PCC 6803 represents a major cyanobacterial model organism and harbors phylogenetically diverged homologs of the clock proteins, which are present in various other noncyanobacterial prokaryotes. By our in vitro studies we unravel the interplay of the multiple Synechocystis Kai proteins and characterize enzymatic activities of the nonstandard clock homolog KaiC3. We show that the deletion of kaiC3 affects growth in constant darkness, suggesting its involvement in the regulation of nonphotosynthetic metabolic pathways.

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Cell-permeable Circadian Clock Proteins

10.21236/ada405529 ◽

2002 ◽

Author(s):

Carl H. Johnson

Keyword(s):

Circadian Clock ◽

Clock Proteins ◽

Circadian Clock Proteins

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Cell-based screen identifies a new potent and highly selective CK2 inhibitor for modulation of circadian rhythms and cancer cell growth

Science Advances ◽

10.1126/sciadv.aau9060 ◽

2019 ◽

Vol 5 (1) ◽

pp. eaau9060 ◽

Cited By ~ 33

Author(s):

Tsuyoshi Oshima ◽

Yoshimi Niwa ◽

Keiko Kuwata ◽

Ashutosh Srivastava ◽

Tomoko Hyoda ◽

...

Keyword(s):

Cell Growth ◽

Circadian Clock ◽

Cancer Cell ◽

Direct Interaction ◽

Cancer Cell Growth ◽

X Ray ◽

Clock Proteins ◽

Target Deconvolution ◽

Phenotypic Screen ◽

Dependent Inhibition

Compounds targeting the circadian clock have been identified as potential treatments for clock-related diseases, including cancer. Our cell-based phenotypic screen revealed uncharacterized clock-modulating compounds. Through affinity-based target deconvolution, we identified GO289, which strongly lengthened circadian period, as a potent and selective inhibitor of CK2. Phosphoproteomics identified multiple phosphorylation sites inhibited by GO289 on clock proteins, including PER2 S693. Furthermore, GO289 exhibited cell type–dependent inhibition of cancer cell growth that correlated with cellular clock function. The x-ray crystal structure of the CK2α-GO289 complex revealed critical interactions between GO289 and CK2-specific residues and no direct interaction of GO289 with the hinge region that is highly conserved among kinases. The discovery of GO289 provides a direct link between the circadian clock and cancer regulation and reveals unique design principles underlying kinase selectivity.

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How is the inner circadian clock controlled by interactive clock proteins?

FEBS Letters ◽

10.1016/j.febslet.2015.05.024 ◽

2015 ◽

Vol 589 (14) ◽

pp. 1516-1529 ◽

Cited By ~ 24

Author(s):

Torsten Merbitz-Zahradnik ◽

Eva Wolf

Keyword(s):

Circadian Clock ◽

Clock Proteins

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Stability of the Synechococcus elongatus PCC 7942 circadian clock under directed anti-phase expression of the kai genes

Microbiology ◽

10.1099/mic.0.28030-0 ◽

2005 ◽

Vol 151 (8) ◽

pp. 2605-2613 ◽

Cited By ~ 33

Author(s):

Jayna L. Ditty ◽

Shannon R. Canales ◽

Breanne E. Anderson ◽

Stanly B. Williams ◽

Susan S. Golden

Keyword(s):

Circadian Clock ◽

Expression Patterns ◽

Phase Relationship ◽

Synechococcus Elongatus ◽

Cycle Period ◽

Rhythmic Expression ◽

Core Components ◽

Synechococcus Elongatus Pcc 7942 ◽

Time Required ◽

Pcc 7942

The kaiA, kaiB and kaiC genes encode the core components of the cyanobacterial circadian clock in Synechococcus elongatus PCC 7942. Rhythmic expression patterns of kaiA and of the kaiBC operon normally peak in synchrony. In some mutants the relative timing of peaks (phase relationship) between these transcription units is altered, but circadian rhythms persist robustly. In this study, the importance of the transcriptional timing of kai genes was examined. Expressing either kaiA or kaiBC from a heterologous promoter whose peak expression occurs 12 h out of phase from the norm, and thus 12 h out of phase from the other kai locus, did not affect the time required for one cycle (period) or phase of the circadian rhythm, as measured by bioluminescence reporters. Furthermore, the data confirm that specific cis elements within the promoters of the kai genes are not necessary to sustain clock function.

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Circadian Clock Proteins in Prokaryotes: Hidden Rhythms?

Frontiers in Microbiology ◽

10.3389/fmicb.2010.00130 ◽

2010 ◽

Vol 1 ◽

Cited By ~ 21

Author(s):

Maria Loza-Correa ◽

Laura Gomez-Valero ◽

Carmen Buchrieser

Keyword(s):

Circadian Clock ◽

Clock Proteins ◽

Circadian Clock Proteins

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Attenuated SIRT1 Activity Leads to PER2 Cytoplasmic Localization and Dampens the Amplitude of Bmal1 Promoter-Driven Circadian Oscillation

Frontiers in Neuroscience ◽

10.3389/fnins.2021.647589 ◽

2021 ◽

Vol 15 ◽

Author(s):

Atsushige Ashimori ◽

Yasukazu Nakahata ◽

Toshiya Sato ◽

Yuichiro Fukamizu ◽

Takaaki Matsui ◽

...

Keyword(s):

Subcellular Localization ◽

Circadian Clock ◽

Posttranslational Modifications ◽

Cultured Cells ◽

Circadian Oscillation ◽

Clock Proteins ◽

Circadian Clock Proteins ◽

Circadian Physiology ◽

And Behavior ◽

Robust Systems

The circadian clock possesses robust systems to maintain the rhythm approximately 24 h, from cellular to organismal levels, whereas aging is known to be one of the risk factors linked to the alternation of circadian physiology and behavior. The amount of many metabolites in the cells/body is altered with the aging process, and the most prominent metabolite among them is the oxidized form of nicotinamide adenine dinucleotide (NAD+), which is associated with posttranslational modifications of acetylation and poly-ADP-ribosylation status of circadian clock proteins and decreases with aging. However, how low NAD+ condition in cells, which mimics aged or pathophysiological conditions, affects the circadian clock is largely unknown. Here, we show that low NAD+ in cultured cells promotes PER2 to be retained in the cytoplasm through the NAD+/SIRT1 axis, which leads to the attenuated amplitude of Bmal1 promoter-driven luciferase oscillation. We found that, among the core clock proteins, PER2 is mainly affected in its subcellular localization by NAD+ amount, and a higher cytoplasmic PER2 localization was observed under low NAD+ condition. We further found that NAD+-dependent deacetylase SIRT1 is the regulator of PER2 subcellular localization. Thus, we anticipate that the altered PER2 subcellular localization by low NAD+ is one of the complex changes that occurs in the aged circadian clock.

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383. Feasibility of Specimen Self-collection in Young Children Undergoing SARS-CoV-2 Surveillance for In-person Learning

Open Forum Infectious Diseases ◽

10.1093/ofid/ofab466.584 ◽

2021 ◽

Vol 8 (Supplement_1) ◽

pp. S293-S293

Author(s):

Jonathan Altamirano ◽

Grace Tam ◽

Marcela Lopez ◽

India Robinson ◽

Leanne Chun ◽

...

Keyword(s):

Young Children ◽

Time Window ◽

School Administrators ◽

Error Rates ◽

Independent Observer ◽

Specimen Collection ◽

Timing Data ◽

Short Time Window ◽

Short Time ◽

Over Time

Abstract Background While pediatric cases of COVID-19 are at low risk for adverse events, schoolchildren should be considered for surveillance as they can become infected at school and serve as sources of household or community transmission. Our team assessed the feasibility of young children self-collecting SARS-CoV-2 samples for surveillance testing in an educational setting. Methods Students at a K-8 school were tested weekly for SARS-CoV-2 from September 2020 - June 2021. Error rates were collected from September 2020 - January 2021. Clinical staff provided all students with instructions for anterior nares specimen self-collection and then observed them to ensure proper technique. Instructions included holding the sterile swab while making sure not to touch the tip, inserting the swab into their nostril until they start to feel resistance, and rubbing the swab in four circles before repeating the process in their other nostril. An independent observer timed random sample self-collections from April - June 2021. Results 2,590 samples were collected from 209 students during the study period when data on error rates were collected. Errors occurred in 3.3% of all student encounters (n=87). Error rates over time are shown in Figure 1, with the highest rate occurring on the first day of testing (n=20/197, 10.2%) and the lowest in January 2021 (n=1/202, 0.5%). 2,574 visits for sample self-collection occurred during the study period when independent timing data was collected (April - June 2021). Of those visits, 7.5% (n=193) were timed. The average duration of each visit was 70 seconds. Figure 1. Swab Error Rates Over Time Conclusion Pediatric self-collected lower nasal swabs are a viable and easily tolerated specimen collection method for SARS-CoV-2 surveillance in school settings, as evidenced by the low error rate and short time window of sample self-collection during testing. School administrators should expect errors to drop quickly after implementing testing. Disclosures All Authors: No reported disclosures

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Early detection of daylengths with a feedforward circuit coregulated by circadian and diurnal cycles

10.1101/2020.04.23.057711 ◽

2020 ◽

Author(s):

Nicholas Panchy ◽

Albrecht G. von Arnim ◽

Tian Hong

Keyword(s):

Circadian Clock ◽

Ribosomal Protein ◽

Complex Dynamics ◽

Expression Profiles ◽

Small Subunit ◽

Control Circuit ◽

Clock Signal ◽

Post Translational Modification ◽

Diel Cycles ◽

Opposite Manner

AbstractLight-entrained circadian clocks confer rhythmic dynamics of cellular and molecular activities to animals and plants. These intrinsic clocks allow stable anticipations to light-dark (diel) cycles. Many genes in the model plant Arabidopsis thaliana are regulated by diel cycles via pathways independent of the clock, suggesting that the integration of circadian and light signals is important for the fitness of plants. Previous studies of light-clock signal integrations have focused on moderate phase adjustment of the two signals. However, dynamical features of integrations across a broad range of phases remain elusive. We recently found that phosphorylation of RIBOSOMAL PROTEIN OF THE SMALL SUBUNIT 6 (RPS6 or eS6), a ubiquitous post-translational modification across kingdoms, is influenced by the circadian clock and the light-dark (diel) cycle in an opposite manner. In order to understand this striking phenomenon and its underlying information processing capabilities, we built a mathematical model for the eS6-P control circuit. We found that the dynamics of eS6-P can be explained by a feedforward circuit with inputs from both circadian and diel cycles. Furthermore, the early-day response of this circuit with dual rhythmic inputs is sensitive to the changes in daylength, including both transient and gradual changes observed in realistic light intervals across a year, due to weather and seasons. By analyzing published gene expression data, we found that the dynamics produced by the eS6-P control circuit can be observed in the expression profiles of a large number of genes. Our work provides mechanistic insights into the complex dynamics of a ribosomal protein, and it proposes a previously underappreciated function of the circadian clock which not only prepares organisms for normal diel cycles but also helps to detect both transient and seasonal changes with a predictive power.

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