Article reviewed: Entrainment of free-running circadian rhythms by melatonin in blind people

Molecular models for the endogenous oscillators that drive circadian rhythms in eukaryotes center on rhythmic transcription/translation of a small number of “clock genes.” Although substantial evidence supports the concept that negative and positive transcription/translation feedback loops (TTFLs) are responsible for regulating the expression of these clock genes, certain rhythms in the filamentous fungus Neurospora crassa continue even when clock genes ( frq, wc-1, and wc-2) are not rhythmically expressed. Identification of the rhythmic processes operating outside of the TTFL has been a major unresolved area in circadian biology. Our lab previously identified a mutation ( vta) that abolishes FRQ-less rhythmicity of the conidiation rhythm and also affects rhythmicity when FRQ is functional. Further studies identified the vta gene product as a component of the TOR (Target of Rapamycin) nutrient-sensing pathway that is conserved in eukaryotes. We now report the discovery of TOR pathway components including GTR2 (homologous to the yeast protein Gtr2, and RAG C/D in mammals) as binding partners of VTA through co-immunoprecipitation (IP) and mass spectrometry analysis using a VTA-FLAG strain. Reciprocal IP with GTR2-FLAG found VTA as a binding partner. A Δ gtr2 strain was deficient in growth responses to amino acids. Free-running conidiation rhythms in a FRQ-less strain were abolished in Δ gtr2. Entrainment of a FRQ-less strain to cycles of heat pulses demonstrated that Δ gtr2 is defective in entrainment. In all of these assays, Δ gtr2 is similar to Δ vta. In addition, expression of GTR2 protein was found to be rhythmic across two circadian cycles, and functional VTA was required for GTR2 rhythmicity. FRQ protein exhibited the expected rhythm in the presence of GTR2 but the rhythmic level of FRQ dampened in the absence of GTR2. These results establish association of VTA with GTR2, and their role in maintaining functional circadian rhythms through the TOR pathway.

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Restricted food access and light-dark: impact of conflicting zeitgebers on circadian rhythms of the rabbit

AJP Regulatory Integrative and Comparative Physiology ◽

10.1152/ajpregu.1993.264.4.r708 ◽

1993 ◽

Vol 264 (4) ◽

pp. R708-R715 ◽

Cited By ~ 2

Author(s):

B. Jilge ◽

H. Stahle

Keyword(s):

Circadian Rhythms ◽

Phase Difference ◽

Food Access ◽

Activity Rhythm ◽

Light Period ◽

The Other ◽

Behavioral Rhythms ◽

Activity Component ◽

Common Control ◽

Free Running

Free-running circadian rhythms of rabbits were exposed to a 11:55-11:55-h light-dark (LD) schedule. After complete entrainment (63 +/- 22 days), the predominantly nocturnally active rabbits were exposed to an additional zeitgeber, restricted food access (RF), which was imposed during the light period. In five animals RF had the same period (T) as the LD cycle (23:50 h), and in five other animals TRF was 24:10 h. At a period of 23:50 h for both zeitgebers, the rhythms of four animals were stably entrained to RF, while in one animal a component of the rhythm broke away from RF and entrained to the LD zeitgeber. In animals exposed to zeitgebers of different periods most of the activity rhythm also entrained to RF, but 20 +/- 7% of the activity entrained to the LD zeitgeber. The light-entrained activity component merged with the RF component when the zeitgebers crossed, and decomposition occurred when the phase difference exceeded 4-6 h. The results indicate that two circadian oscillator systems exist in the rabbit, one entrained by light-dark cycles and the other by feeding-fasting cycles. Both exert common control over a number of overt behavioral rhythms.

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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 ◽

10.3390/plants10071475 ◽

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.

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

AJP Regulatory Integrative and Comparative Physiology ◽

10.1152/ajpregu.1999.277.3.r812 ◽

1999 ◽

Vol 277 (3) ◽

pp. R812-R828 ◽

Cited By ~ 14

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.

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Photoperiodic modulation of circadian rhythms in the silk gland protein profiles of Bombyx mori and its influence on the silk productivity and quality

Journal of Applied and Natural Science ◽

10.31018/jans.v2i1.94 ◽

2010 ◽

Vol 2 (1) ◽

pp. 48-56 ◽

Cited By ~ 1

Author(s):

B. Sailaja ◽

S. Sivaprasad

Keyword(s):

Circadian Rhythms ◽

Bombyx Mori ◽

Continuous Light ◽

Silk Gland ◽

Protein Profiles ◽

Dark Cycle ◽

Response Curves ◽

Silk Proteins ◽

Free Running ◽

Clock Shift

Circadian rhythms in the silk gland protein profiles of Bombyx mori were analyzed under 12 h light and 12 h dark cycle (LD), continuous light (LL) and continuous dark (DD) conditions. The phase response curves of protein rhythms indicate the prevalence of a series of silk cycles, each comprising three phases; transcription, translation and consolidation of silk proteins. In the 24h- protein rhythm, the silk cycle repeats every 3h, 42 m under LD, 2h, 36m under LL and 3h under DD. The light and dark conditions advanced the rhythm of each silk cycle by 48m and 24m respectively. As a result the silk gland completes 7 rounds of protein synthesis under LD, 9 rounds under LL and 8 rounds under DD during the 24h-free running time of the rhythm. The light-induced clock-shift in the protein rhythm caused significant gains in economic parameters of sericulture with positive signals for enhancing silk productivity and quality.

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