TIMELESS
Protein timeless homolog (hTIM) [TIM] [TIM1] [TIMELESS1]
Publications[править]
TIMELESS protein is known to be essential for normal circadian rhythms. Aging is a deleterious process which affects all the physiological functions of complex organisms including the circadian rhythms. The circadian aging may produce disorganization among the circadian rhythms, arrhythmicity and even, disconnection from the environment, resulting in a detrimental situation to the organism. However, the role of circadian genes on the aging process is poorly understood. In present study, we found TIMELESS was down-regulated in cellular senescence, and further research indicated E2F1 bound to the promotor of TIMELESS and regulated its expression in cellular senescence. Knockdown of TIMELESS accelerated cellular senescence induced by ectopic expression of RasV12, and overexpression of TIMELESS delayed this kind onset of senescence. Meanwhile, micrococcal nuclease assays proved depletion of TIMELESS exacerbated genomic instability at the onset of senescence. Together, our data reveal that TIMELESS plays a role in OIS, which is associated with genome stability changing.
MeSH Terms
- Cell Cycle Proteins
- Cell Line
- Cellular Senescence
- Circadian Rhythm
- E2F1 Transcription Factor
- Fibroblasts
- Gene Expression Regulation
- Genes, Reporter
- Genomic Instability
- HEK293 Cells
- Humans
- Hydrogen Peroxide
- Intracellular Signaling Peptides and Proteins
- Promoter Regions, Genetic
- Protein Binding
- RNA, Small Interfering
- Signal Transduction
- beta-Galactosidase
- ras Proteins
Keywords
- E2F1
- Senescence
- TIMELESS
The importance of the circadian clock for the regulation of behaviour and physiology, and the molecular control of these rhythms by a set of clock genes are well defined. The circadian clock deteriorates with advancing age but the mechanism underlying is unclear. Here we recorded the expression of two key clock genes in young, middle-aged and old Drosophila using transgenic luciferase lines reporting period and timeless in vivo. We report a novel marker of imminent death in the expression of TIMELESS. In the days immediately preceding death TIMELESS expression increased to at least 150% of previous acrophase values (88.0% of n = 217) and lost circadian rhythmicity, which predicted death equally well in flies of different ages and under light and temperature cycles. We suggest this transient aberrant clock-gene expression is central to the mechanism of the disturbance in circadian behaviour before death (82.7% of n = 342). We also find that PERIOD expression in central-clock neurons remained robust with age, however PERIOD and TIMELESS in peripheral clocks showed a reduction in both expression level and rhythmicity. In conclusion, as flies age the molecular clock gradually declines at the peripheral level but continues to function at the central until days before death.
MeSH Terms
- Aging
- Animals
- Animals, Genetically Modified
- CLOCK Proteins
- Circadian Clocks
- Circadian Rhythm
- Drosophila Proteins
- Drosophila melanogaster
- Gene Expression Regulation, Developmental
- Locomotion
- Longevity
- Period Circadian Proteins
- Photoperiod
- Survival Analysis
Most animals show rest/activity rhythms that are regulated by an endogenous timing mechanism, the so-called circadian system. The rhythm becomes weaker with age, but the mechanism underlying the age-associated rhythm change remains to be elucidated. Here we employed Drosophila melanogaster as a model organism to study the aging effects on the rhythm. We first investigated activity rhythms under light-dark (LD) cycles and constant darkness (DD) in young (1-day-old) and middle-aged (30-, 40-, and 50-day-old) wild-type male flies. The middle-aged flies showed a reduced activity level in comparison with young flies. Additionally, the free-running period significantly lengthened in DD, and the rhythm strength was diminished. Immunohistochemistry against pigment-dispersing factor (PDF), a principal neurotransmitter of the Drosophila clock, revealed that PDF levels declined with age. We also found an attenuation of TIMELESS (TIM) oscillation in the cerebral clock neurons in elder flies. Intriguingly, overexpression of PDF suppressed age-associated changes not only in the period and strength of free-running locomotor rhythms but also in the amplitude of TIM oscillations in many pacemaker neurons in the elder flies, suggesting that the age-dependent PDF decline is responsible for the rhythm attenuation. These results suggest that the age-associated reduction of PDF may cause attenuation of intercellular communication in the circadian neuronal network and of TIM cycling, which may result in the age-related rhythm decay.
MeSH Terms
- Activity Cycles
- Aging
- Animals
- CLOCK Proteins
- Drosophila Proteins
- Drosophila melanogaster
- Male
- Motor Activity
- Neurons
- Neuropeptides
- Period Circadian Proteins
- Phenotype