Circadian changes in cyclic AMP levels in synchronously dividing and stationary-phase cultures of the achlorophyllous ZC mutant of Euglena gracilis

1989 ◽  
Vol 94 (2) ◽  
pp. 267-272
Author(s):  
ISABELLE A. CARRÉ ◽  
DANIELLE L. LAVAL-MARTIN ◽  
LELAND N. EDMUNDS
Keyword(s):  
Cell Division ◽  
Cyclic Amp ◽  
Euglena Gracilis ◽  
Phase Response Curve ◽  
Circadian Variation ◽  
Light Signal ◽  
Circadian Oscillator ◽  
Circadian Oscillation ◽  
Continuous Darkness ◽  
Free Running

Oscillations in adenosine 3′,5′-cyclic monophosphate (cyclic AMP) level have been proposed to be part of the biochemical feed-back loop(s), or ‘clock(8)’, believed to underlie circadian rhythmicity. This possibility has been examined for a cellular circadian oscillator in synchronously dividing (or nondividing) cultures of the photosynthesis- deficient ZC mutant of the alga Euglena gracilis Klebs (Z). We have demonstrated a bimodal, autonomously oscillating, circadian variation of cyclic AMP content in this unicell. Rhythmic changes of the cyclic AMP level, which may reflect the transition of the cell population through the different phases of the cell division cycle (CDC) in division-phased cultures, also persisted after the culture medium had become limiting and the cells had stopped dividing. We have also shown that the free-running, circadian oscillation of cyclic AMP content displayed by nondividing cells in continuous darkness could be phase-shifted by a light signal (a property inherent to most circadian systems), in a manner that could be predicted from the phase-response curve previously obtained for the cell division rhythm in the ZC mutant. These results suggest a possible role for cyclic AMP, either as an element of the coupling pathway for the control of the CDC by the circadian oscillator, or as a ‘gear’ of the clock itself.

scholarly journals The Cell Division Cycle of Euglena gracilis Indicates That the Level of Circadian Plasticity to the External Light Regime Changes in Prolonged-Stationary Cultures

Plants ◽  
2021 ◽  
Vol 10 (7) ◽  
pp. 1475
Author(s):  
Shota Kato ◽  
Hong Gil Nam
Keyword(s):  
Cell Division ◽  
Circadian Rhythms ◽  
Euglena Gracilis ◽  
Cell Cycle Progression ◽  
Light Signal ◽  
Cell Division Cycle ◽  
Regime Changes ◽  
Fitness Advantage ◽  
Subjective Night ◽  
Free Running

In unicellular photosynthetic organisms, circadian rhythm is tightly linked to gating of cell cycle progression, and is entrained by light signal. As several organisms obtain a fitness advantage when the external light/dark cycle matches their endogenous period, and aging alters circadian rhythms, senescence phenotypes of the microalga Euglena gracilis of different culture ages were characterized with respect to the cell division cycle. We report here the effects of prolonged-stationary-phase conditions on the cell division cycles of E. gracilis under non-24-h light/dark cycles (T-cycles). Under T-cycles, cells established from 1-month-old and 2-month-old cultures produced lower cell concentrations after cultivation in the fresh medium than cells from 1-week-old culture. This decrease was not due to higher concentrations of dead cells in the populations, suggesting that cells of different culture ages differ in their capacity for cell division. Cells from 1-week-old cultures had a shorter circadian period of their cell division cycle under shortened T-cycles than aged cells. When algae were transferred to free-running conditions after entrainment to shortened T-cycles, the young cells showed the peak growth rate at a time corresponding to the first subjective night, but the aged cells did not. This suggests that circadian rhythms are more plastic in younger E. gracilis cells.

Circadian rhythmicity in the activities of adenylate cyclase and phosphodiesterase in synchronously dividing and stationary-phase cultures of the achlorophyllous ZC mutant of Euglena gracilis

1991 ◽  
Vol 100 (2) ◽  
pp. 365-369 ◽  
Author(s):  
J. Tong ◽  
I.A. Carre ◽  
L.N. Edmunds
Keyword(s):  
Cyclic Amp ◽  
Adenylate Cyclase ◽  
Euglena Gracilis ◽  
Circadian Variation ◽  
Constant Darkness ◽  
Key Factors ◽  
Peak Phase ◽  
Methyl Xanthine ◽  
Daily Oscillation

Key factors in the adenosine 3′,5′-cyclic monophosphate (cyclic AMP) metabolic pathway are two enzymes responsible for its generation and degradation, namely, adenylate cyclase (AC) and phosphodiesterase (PDE). In LD: 12,12 (12 h light, 12 h dark), these enzymes were found to undergo bimodal, circadian variation of activity in both dividing and nondividing cultures of the photosynthesis-deficient, achlorophyllous ZC mutant of Euglena gracilis Klebs (Z). Maximal AC activity occurred 2 h after the onset of the light interval (CT 02) and at the beginning of darkness (CT 12–14); these times corresponded to the acrophase profile for the rhythmic changes in cyclic AMP content that have been previously reported. The activity of PDE also exhibited a daily oscillation, but with an inverse phase pattern. Both the AC and PDE activity rhythms persisted after the cultures were transferred from LD: 12,12 to constant darkness. The activity of AC was activated significantly in vivo by forskolin at the trough phase (CT 20), while that of PDE was inhibited by 3-isobutyl-1-methyl-xanthine (IBMX) at its peak phase. These results indicate that the rhythms of both AC and PDE may be the main factors generating the circadian oscillations of cyclic AMP content in Euglena, which appear to be under control of an endogenous pacemaker.

Oscillator control of cell division in Euglena: cyclic AMP oscillations mediate the phasing of the cell division cycle by the circadian clock

1993 ◽  
Vol 104 (4) ◽  
pp. 1163-1173 ◽  
Author(s):  
I.A. Carre ◽  
L.N. Edmunds
Keyword(s):  
Cell Division ◽  
Cyclic Amp ◽  
Cell Division Cycle ◽  
Circadian Oscillator ◽  
Constant Darkness ◽  
Rapid Loss ◽  
Subjective Night ◽  
Circadian Time ◽  
Pharmacological Studies

The achlorophyllous ZC strain of Euglena gracilis exhibits a circadian rhythm of cell division in constant darkness (DD). Mitosis occurs during a restricted part of the circadian cycle, corresponding to the dark intervals in a light-dark cycle comprising 12 h of light and 12 h of darkness. We have demonstrated that division-phased cultures also exhibit bimodal, circadian changes of cyclic AMP level. Maximum cyclic AMP levels occurred at the beginning of the light period (CT (circadian time) 00–02), and at the beginning of darkness (CT 12–14). These variations persisted in cultures that had been transferred into DD and appeared to be under the control of the circadian oscillator rather than to be cell division cycle (CDC)-dependent, since they continued in cultures that had reached the stationary phase of growth. In the experiments reported in this paper, we tested for the possible role of this periodic cyclic AMP signal in the generation of cell division rhythmicity by examining the effects of exogenous cyclic AMP signals and of forskolin, which permanently increased the cyclic AMP level, on the cell division rhythm. Perturbations of the cyclic AMP oscillation by exogenous cyclic AMP resulted in the temporary uncoupling of the CDC from the circadian timer. The addition of cyclic AMP during the subjective day resulted in delays (up to 9 h) of the next synchronous division step. In contrast, mitosis was stimulated when cyclic AMP was administered in the middle of the subjective night. Measurement of the DNA content of cells by flow cytometry indicated that cyclic AMP injected at CT 06–08 delayed progression through S phase, and perhaps also through mitosis. When added at CT 18–20, cyclic AMP accelerated the G2/M transition. The circadian oscillator was not perturbed by the addition of exogenous cyclic AMP: the division rhythm soon returned to its original phase. On the other hand, the permanent elevation of cyclic AMP levels in the presence of forskolin induced a rapid loss of cell division rhythmicity. These findings are consistent with the hypothesis that cyclic AMP acts downstream from the oscillator and that the cyclic AMP oscillation is an essential component of the signaling pathway for the control of the CDC by the circadian oscillator. The receptors for cyclic AMP in Euglena have been shown to be two cyclic AMP-dependent kinases (cPKA and cPKB). Pharmacological studies using cyclic AMP analogs suggested that cPKA mediates cyclic AMP effects during the subjective day, and cPKB during the subjective night.(ABSTRACT TRUNCATED AT 400 WORDS)

Circadian Variation of Cyclic AMP in the Rat Pineal Gland

1981 ◽  
Vol 36 (3) ◽  
pp. 1295-1297 ◽  
Author(s):  
Masahiko Mikuni ◽  
Yoshiro Saito ◽  
Tsukasa Koyama ◽  
Itaru Yamashita
Keyword(s):  
Cyclic Amp ◽  
Pineal Gland ◽  
Circadian Variation ◽  
Rat Pineal Gland

Organization of rat circadian rhythms during daily infusion of melatonin or S20098, a melatonin agonist

1999 ◽  
Vol 277 (3) ◽  
pp. R812-R828 ◽  
Author(s):  
B. Pitrosky ◽  
R. Kirsch ◽  
A. Malan ◽  
E. Mocaer ◽  
P. Pevet
Keyword(s):  
Body Temperature ◽  
Circadian Rhythms ◽  
Phase Response Curve ◽  
Constant Darkness ◽  
Time Interval ◽  
General Activity ◽  
Activity Peak ◽  
Free Running ◽  
Wheel Activity ◽  
Free Running Period

Daily administration of melatonin or S20098, a melatonin agonist, is known to entrain the free-running circadian rhythms of rats. The effects of the duration of administration on entrainment were studied. The animals demonstrated free-running circadian rhythms (running-wheel activity, body temperature, general activity) in constant darkness. Daily infusions of melatonin or S20098 for 1, 8, or 16 h entrained the circadian rhythms to 24 h. Two daily infusions of 1 h (separated by 8 h) entrained the activity peak within the shorter time interval. The entraining properties of melatonin and S20098 were similar and were affected neither by pinealectomy nor by infusion of 1- or 8-h duration. However, with 16-h infusion, less than half of the animals became entrained. Once entrained, the phase angle between the onset of infusion and the rhythms (onset of activity or acrophase of body temperature) increased with the duration of infusion. Before entrainment, the free-running period increased with the duration of infusion, an effect that was not predictable from the phase response curve.

scholarly journals The ultrastructure of cell division in Euglena gracilis

1978 ◽  
Vol 31 (1) ◽  
pp. 25-35
Author(s):  
M.A. Gillott ◽  
R.E. Triemer
Keyword(s):  
Cell Division ◽  
Nuclear Envelope ◽  
Basal Body ◽  
Euglena Gracilis ◽  
Equatorial Region ◽  
Basal Bodies ◽  
Cleavage Furrow ◽  
Free Zone ◽  
Prophase Nucleus

The ultrastructure of mitosis in Euglena gracilis was investigated. At preprophase the nucleus migrates anteriorly and associates with the basal bodies. Flagella and basal bodies replicate at preprophase. Cells retain motility throughout division. The reservoir and the prophase nucleus elongate perpendicular to the incipient cleavage furrow. One basal body pair surrounded by a ribosome-free zone is found at each of the nuclear poles. The spindle forms within the intact nuclear envelope- Polar fenestrae are absent. At metaphase, the endosome is elongated from pole to pole, and chromosomes are loosely arranged in the equatorial region. Distinct, trilayered kinetochores are present. Spindle elongates as chromosomes migrate to the poles forming a dumb-bell shaped nucleus by telophase. Daughter nuclei are formed by constriction of the nuclear envelope. Cytokinesis is accomplished by furrowing. Cell division in Euglena is compared with that of certain other algae.

Magnesium Regulates the Circadian Oscillator in Cyanobacteria

2019 ◽  
Vol 34 (4) ◽  
pp. 380-390 ◽  
Author(s):  
Young M. Jeong ◽  
Cristiano Dias ◽  
Casey Diekman ◽  
Helene Brochon ◽  
Pyonghwa Kim ◽  
...  
Keyword(s):  
Structural Analysis ◽  
Circadian Clock ◽  
Biological Rhythms ◽  
Circadian Oscillator ◽  
Magnesium Concentration ◽  
Circadian Oscillation ◽  
Magnesium Homeostasis ◽  
Low Magnesium

The circadian clock controls 24-h biological rhythms in our body, influencing many time-related activities such as sleep and wake. The simplest circadian clock is found in cyanobacteria, with the proteins KaiA, KaiB, and KaiC generating a self-sustained circadian oscillation of KaiC phosphorylation and dephosphorylation. KaiA activates KaiC phosphorylation by binding the A-loop of KaiC, while KaiB attenuates the phosphorylation by sequestering KaiA from the A-loop. Structural analysis revealed that magnesium regulates the phosphorylation and dephosphorylation of KaiC by dissociating from and associating with catalytic Glu residues that activate phosphorylation and dephosphorylation, respectively. High magnesium causes KaiC to dephosphorylate, whereas low magnesium causes KaiC to phosphorylate. KaiC alone behaves as an hourglass timekeeper when the magnesium concentration is alternated between low and high levels in vitro. We suggest that a magnesium-based hourglass timekeeping system may have been used by ancient cyanobacteria before magnesium homeostasis was established.

Biological alarm clock arouses hibernating big brown bats, Eptesicus fuscus

1987 ◽  
Vol 65 (7) ◽  
pp. 1668-1674 ◽  
Author(s):  
John W. Twente ◽  
Janet Twente
Keyword(s):  
Laboratory Study ◽  
Eptesicus Fuscus ◽  
Continuous Darkness ◽  
Exogenous Variables ◽  
Alarm Clock ◽  
Big Brown Bats ◽  
Free Running ◽  
The Times ◽  
The Individual

This laboratory study showed that the individual averages of the times of day of arousal from hibernation of 55 big brown bats, Eptesicus fuscus, maintained in darkness, ranged from 14:05 to 20:50 (2:05 p.m. to 8:50 p.m.). The data were interpreted as representing a persistent but inexact 24-h rhythm that functioned as a biological alarm clock. This rhythm was, according to the parameters measured, apparent only on the day of arousal. The rhythm was determined to be independent of the length of time the bat had hibernated; independent of temperature; persistent and did not drift and become free-running in continuous darkness; unapparent in daily cardiac patterns or themogenic activity; and independent of obvious exogenous variables.

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