Circadian clock regulates photoperiodic responses governed by distinct output pathways in the bean bug,Riptortus pedestris

Effects of RNA interference (RNAi) targeted against circadian clock genes on two distinct types of photoperiodic responses – ovarian development and lipid accumulation – were investigated in a bean bug Riptortus pedestris, to explore which physiological process in the photoperiodic response involved the circadian clock. Ovarian development and lipid accumulation are known to be regulated by distinct output pathways. Control insects showed clear photoperiodic responses; i.e. induction of ovarian development and suppression of lipid accumulation under long-day conditions, whereas opposite characteristics under short-day conditions. We found that RNAi directed against period, a negative element of the circadian clock, produced a long-day effect for both the ovarian development and lipid accumulation, while RNAi directed against Clock, a positive element of the circadian clock, produced a short-day effect for both, irrespective of photoperiod. These results indicate that the circadian clock comprised of these genes regulates a process governing both distinct photoperiodic responses.     

The effect of artificial photoperiod on growth and reproduction in the land snail Cepaea nemoralis

Summary

Specimens of Cepaea nemoralis were raised from egg to adult in the laboratory for 15.5 months in two artificial photoperiods: short-day (LD 8:16) and long-day (LD 16:8). Over 20% of the snails in each photoperiod were functional adults by the end of the experiment and had fully developed male and female reproductive systems as determined both by dissection and by oviposition. A total of 925 eggs were laid by animals reared in a long-day photoperiod, whereas animals in a short-day photoperiod laid 677 eggs. Animals reared in a long-day photoperiod grew slightly faster (2.04 mg/day compared to 1.73 mg/day), began laying eggs about 18 days sooner, and suffered higher mortality (19% compared to 11%) than animals reared in a short-day photoperiod. These results clearly establish for C. nemoralis that gametogenesis and the development of a functional hermaphroditic reproductive system are neither prevented nor significantly retarded by exposing the animals to a short-day photoperiod for their entire pre-reproductive life.     

Control of diapause induction by a change in photoperiod in Melanoplus sanguinipes

The effect of photoperiod on diapause induction, developmental time and body size was examined in Melanoplus sanguinipes, the lesser migratory grasshopper. Contrary to what is found in most insects, facultative diapause-egg production is found to be controlled by changing rather than constant photoperiods. In addition, developmental time is shown to be faster under short-day photoperiods than long-day photoperiods. And finally, body size is larger under long-day photoperiods and smaller under short-day photoperiods. Implications of these results for the regulation of the seasonal life cycle of M. sanguinipes in the field are discussed.     

Effect of photoperiod on clock gene expression and subcellular distribution of PERIOD in the circadian clock neurons of the blow fly Protophormia terraenovae

We examined the effect of photoperiod on the expression of circadian clock genes period (per) and timeless (tim), using quantitative real-time polymerase chain reaction (PCR), and the effect of photoperiod on subcellular distribution of PERIOD (PER), using immunocytochemistry, in the blow fly, Protophormia terraenovae. Under both short-day and long-day conditions, the mRNA levels of per and tim in the brain oscillated, and their peaks and troughs occurred around lights-off and lights-on, respectively. The oscillations persisted even under constant darkness. In the large ventral lateral neurons (l-LN_vs), small ventral lateral neurons (s-LN_vs), dorsal lateral neurons (LN_ds), and medial dorsal neurons (DN_ms), the subcellular distribution of PER-immunoreactivity changed with time. The number of cells with PER-immunoreactivity in the nucleus was highest 12 h after lights-off and lowest 12 h after lights-on, regardless of photoperiod, suggesting that PER nuclear translocation entrains to photoperiod. When temporal changes in the nuclear localization of PER were compared, the neurons could be classified into 2 groups: the l-LN_vs were similar to the s-LN_vs, and the LN_ds were similar to DN_ms. In LN_ds and DN_ms, decreasing rates of the number of cells with PER immunoreactivity in the nucleus per brain from the maximum were large as compared with those in l-LN_vs and s-LN_vs under short-day conditions. These results suggest that photoperiodic information is reflected in the expression patterns of circadian clock genes per and tim and in the subcellular distribution of PER. This observation suggests that the 2 different groups of clock neurons respond to photoperiod in slightly different manners.     

Photoperiodic responses during larval development and diapause of two geographic ecotypes of the rice stem maggot, Chlorops oryzae

Chlorops oryzae is bivoltine in northern Japan but trivoltine in the southern part of the country. In the bivoltine strain, both the egg and larval stages were found to be sensitive to photoperiod. When the egg stage was exposed to a long-day photoperiod (16L:8D), larval development showed a short-day type response, and mature third-instar larvae entered a summer diapause under a long-day photoperiod (15L:9D). When eggs experienced short days, the first-instar larvae entered a winter diapause under short-day conditions, and the critical photoperiod in the larval stage ranged from about 14L:10D to about 12L:12D as the photoperiod experienced by the eggs increased from 12L:12D to 14L:10D. However, the development of the larvae after overwintering was not influenced by the photoperiod. In the trivoltine strain, larval development was retarded under a 14L:10D photoperiod but not under either shorter or longer photoperiods, when larvae had spent the egg stage under a 16L:8D photoperiod. The critical photoperiod of the larval stage for the induction of a winter diapause in the first instar was about 12L:12D, though it varied to some extent with the photoperiod during the egg stage. Thus, Chlorops oryzae was able to adapt itself to the local climatic conditions by the development of variable and complicated photoperiodic responses.     

Day-length perception and the photoperiodic regulation of flowering in Arabidopsis

The flowering of Arabidopsis plants is accelerated by long-day photoperiods, and recent genetic studies have identified elements of the photoperiodic timing mechanism. These elements comprise genes that regulate the function of the circadian clock, photoreceptors, and downstream components of light signaling pathways. These results provide evidence for the role of the circadian clock in photoperiodic time measurement and suggest that photoperiod perception may follow Pittendrigh's external coincidence model. T-cycle experiments indicated that changes in the timing of circadian rhythms, relative to dawn and dusk, correlated with altered flowering time. Thus, the perception of photoperiod maybe mediated by adjustments in the phase of the circadian cycle that arise upon re-entrainment to a different light-dark cycle. The nature of the rhythm underlying the floral response is not known, but candidate molecules have been identified.     

Photoperiod sensitivity of the Arabidopsis circadian clock is tissue-specific

Tissue-specific functions of the circadian clock in Arabidopsis have recently been revealed. The vasculature clock shows distinctive gene expression profiles compared to the clock in other tissues under light-dark cycles. However, it has not yet been established whether the vasculature clock also shows unique gene expression patterns that correlate with temperature cycles, another important environmental cue. Here, we detected diel phase of TIMING OF CAB EXPRESSION 1 (TOC1) expression in the vasculature and whole leaf under long-day light-dark cycles and temperature cycles. We found that the vasculature clock had advanced TOC1 phase under light-dark cycles but not under temperature cycles, suggesting that the vasculature clock has lower sensitivity against temperature signals. Furthermore, the phase advancement of TOC1 was seen only under long-day condition but not under short-day condition. These results support our previous conclusion that the circadian clock in vasculature preferentially senses photoperiodic signals.     

Lipoic acid entrains the hepatic circadian clock and lipid metabolic proteins that have been desynchronized with advanced age

It is well established that lipid metabolism is controlled, in part, by circadian clocks. However, circadian clocks lose temporal precision with age and correlates with elevated incidence in dyslipidemia and metabolic syndrome in older adults. Because our lab has shown that lipoic acid (LA) improves lipid homeostasis in aged animals, we hypothesized that LA affects the circadian clock to achieve these results. We fed 24 month old male F344 rats a diet supplemented with 0.2% (w/w) LA for 2 weeks prior to sacrifice and quantified hepatic circadian clock protein levels and clock-controlled lipid metabolic enzymes. LA treatment caused a significant phase-shift in the expression patterns of the circadian clock proteins Period (Per) 2, Brain and Muscle Arnt-Like1 (BMAL1), and Reverse Erythroblastosis virus (Rev-erb) β without altering the amplitude of protein levels during the light phase of the day. LA also significantly altered the oscillatory patterns of clock-controlled proteins associated with lipid metabolism. The level of peroxisome proliferator-activated receptor (PPAR) α was significantly increased and acetyl-CoA carboxylase (ACC) and fatty acid synthase (FAS) were both significantly reduced, suggesting that the LA-supplemented aged animals are in a catabolic state. We conclude that LA remediates some of the dyslipidemic processes associated with advanced age, and this mechanism may be at least partially through entrainment of circadian clocks.     

Effect of photoperiod and temperature on diapause in a Florida strain of the tropical warehouse moth Ephestia cautella

A photoperiodically-controlled diapause of the long-day, short-day type was identified in a brown-winged, yellow-eyed strain of Ephestia cautella (Walker). The proportion of larvae diapausing in very long photoperiods was less than in short photoperiods. The mean critical photoperiod, here defined as that photoperiod giving half the maximum percentage of insects that diapause in response to photoperiod at a given temperature, was between 12 and 13 hr for the long-day reaction at both 20 and 25°C. The principal sensitive phase occurred near the time of the last larval moult. The mean duration of diapause was 2–3 months at 20°C and slightly longer at 25°C. The optimum temperature for diapause development was near 15°C, all larvae pupating within 24 days after a 45-day exposure at this temperature. Diapause could be terminated whenever larvae diapausing at 20°C were exposed to as few as five long (15 hr) photoperiods at 25°C. Long photoperiods at 20°C, or short photoperiods (9 hr) at 25°C were less effective in terminating diapause.     

The circadian clock influences heart performance

Circadian clocks are believed to provide the selective advantage of anticipation, thus allowing organisms to respond efficiently to stimuli at the appropriate moment. Disrupted circadian rhythms have been found to affect a variety of basic physiological processes. However, the importance of the circadian clock in regulating heart performance remains undetermined. We hypothesized that the circadian clock plays a crucial role in heart performance through the anticipation of daily workload. Echocardiography was employed to monitor heart function and structure in mice in a noninvasive, real-time manner. In wild-type mice, both the ejection fraction (EF) and the shortening fraction (FS), two important markers of cardiac function, show diurnal variation. In addition, the amplitude of the EF and the FS enlarges in response to forced exercise in a time-dependent manner. The diurnal variations in EF and FS are altered in mice with disruptions in circadian clock genes and are significantly attenuated under an imposed light regimen. Furthermore, it shows that the overexpression of peroxisome proliferator-activated receptor gamma coactivator 1 alpha (Pgc1α) under control of the muscle creatine kinase (MCK) promoter inhibited clock gene expression in the heart and muscle and decreased the expression of peroxisome proliferator-activated receptor alpha (Pparα), metabolic genes glucose transporter (Glut4), and acetyl-coA synthetase (Acs1). Pgc1α overexpression abolished the diurnal variation of EF. We thus propose that PGC1α might play an important role in circadian-mediated, impaired cardiac function by regulating the circadian rhythm of metabolic genes.     

Seasonal Variations in Clock‐Gene Expression in Atlantic Salmon (Salmo salar)

In homeothermic vertebrates inhabiting temperate latitudes, it is clear that the seasonal changes in daylength are decoded by the master circadian clock, which through secondary messengers (like pineal melatonin secretion) entrains rhythmic physiology to local conditions. In contrast, the entrainment and neuroendocrine regulation of rhythmic physiology in temperate teleosts is not as clear, primarily due to the lack of understanding of the clock gene system in these species. In this study, we analyzed the diel expression of the clock‐genes in brains of Atlantic salmon, a species that is both highly photoperiodic and displays robust clock‐controlled behavior. Atlantic salmon parr were acclimated to either long‐day (LD) or short‐day (SD) photoperiods for one month and thereafter sampled at 4 h intervals over a 24 h cycle. Clock, Bmal1, Per2, and Cry2 were all actively expressed in salmon brain homogenates and, with the exception of Per2, all displayed rhythmic expression under SD photoperiods that parallels that reported in zebrafish. Interestingly, daylength significantly altered the mRNA expression of all clock genes studied, with Clock, Bmal1, and Per2 all becoming arrhythmic under the LD compared to SD photoperiod, while Cry2 expression was phase delayed under LD. It is thus proposed that the clock‐gene system is actively expressed in Atlantic salmon, and, furthermore, as has been reported in homeothermic vertebrates, it appears that clock expression is daylength‐dependent.     

The role of photoperiod on the initiation of the breeding season of the brushtail possum (Trichosurus vulpecula).

The role of photoperiod on the initiation of the breeding season of brushtail possums was investigated in possums housed in three light regimens: a short-day, a natural and a long-day photoperiod. Seven possums were housed in a natural photoperiod. Four possums were transferred to a short-day photoperiod (10 h light, 14 h dark) and eight possums to a long-day photoperiod (14 h light, 10 h dark) on 22 November, when the daylength was 13.34 h. The first rises in plasma progesterone concentrations were observed on 9 January +/- 9 days (n = 4), 11 March +/- 6 days (n = 7) and 6 May +/- 6 days (n = 8), for possums held in short-day, natural or long-day photoperiods respectively. Similarly, births were observed on 12 January and 14 February in the short-day group, from 3 March to 8 May for the natural photoperiod group, and from 5 May to 8 August for the long-day group. These results suggest that photoperiod is important in the timing of the breeding season. However, annual breeding will commence in a nonstimulatory long-day photoperiod. Thus a long-day photoperiod does not prevent breeding activity.     

Frost hardening and photosynthetic performance of Scots pine (Pinus sylvestris L.) needles. I. Seasonal changes in the photosynthetic apparatus and its function

Photosynthetic CO₂ uptake, the photochemical efficiency of photosystem II, the contents of chlorophyll and chlorophyll-binding proteins, and the degree of frost hardiness were determined in three-year-old Scots pine (Pinus sylvestris L.) trees growing in the open air but under controlled daylength. The following conditions were compared: 9-h light period (short day), 16-h light period (long day), and natural daylength. Irrespective of induction by short-day photoperiods or by subfreezing temperatures, frost hardening of the trees was accompanied by a long-lasting pronounced decrease in the photosynthetic rates of one-year-old needles. Under moderate winter conditions, trees adapted to a long-day photoperiod, assimilated CO₂ with higher rates than the short-day-treated trees. In the absence of strong frost, photochemical efficiency was lower under short-day conditions than under a long-day photoperiod. Under the impact of strong frost, photochemical efficiency was strongly inhibited in both sets of plants. The reduction in photosynthetic performance during winter was accompanied by a pronounced decrease in the content of chlorophyll and of several chlorophyll-binding proteins [light-harvesting complex (LHC)IIb, LHC Ib, and a chlorophyll-binding protein with MW 43 kDa (CP 43)]. This observed seasonal decrease in photosynthetic pigments and in pigment-binding proteins was irrespective of the degree of frost hardiness and was apparantly under the control of the length of the daily photoperiod. Under a constant 9-h daily photoperiod the chlorophyll content of the needles was considerably lower than under long-day conditions. Transfer of the trees from short-day to long-day conditions resulted in a significantly increased chlorophyll content, whereas the chlorophyll content decreased when trees were transferred from a long-day to a short-day photoperiod. The observed changes in photosynthetic pigments and pigment-binding proteins in Scots pine needles are interpreted as a reduction in the number of photosynthetic units induced by shortening of the daily light period during autumn. This results in a reduction in the absorbing capacity during the frost-hardened state. Received: 3 March 1997 / Accepted: 16 July 1997     

Photoperiod regulates corticosterone rhythms by altered adrenal sensitivity via melatonin-independent mechanisms in Fischer 344 rats and C57BL/6J mice

Most species living in temperate zones adapt their physiology and behavior to seasonal changes in the environment by using the photoperiod as a primary cue. The mechanisms underlying photoperiodic regulation of stress-related functions are not well understood. In this study, we analyzed the effects of photoperiod on the hypothalamic-pituitary-adrenal axis in photoperiod-sensitive Fischer 344 rats. We first examined how photoperiod affects diurnal variations in plasma concentrations of adrenocorticotropic hormone (ACTH) and corticosterone. ACTH levels did not exhibit diurnal variations under long- and short-day conditions. On the other hand, corticosterone levels exhibited a clear rhythm under short-day condition with a peak during dark phase. This peak was not observed under long-day condition in which a significant rhythm was not detected. To analyze the mechanisms responsible for the photoperiodic regulation of corticosterone rhythms, ACTH was intraperitoneally injected at the onset of the light or dark phase in dexamethasone-treated rats maintained under long- and short-day conditions. ACTH induced higher corticosterone levels in rats examined at dark onset under short-day condition than those maintained under long-day condition. Next, we asked whether melatonin signals are involved in photoperiodic regulation of corticosterone rhythms, and rats were intraperitoneally injected with melatonin at late afternoon under long-day condition for 3 weeks. However, melatonin injections did not affect the corticosterone rhythms. In addition, photoperiodic changes in the amplitude of corticosterone rhythms were also observed in melatonin-deficient C57BL/6J mice, in which expression profiles of several clock genes and steroidgenesis genes in adrenal gland were modified by the photoperiod. Our data suggest that photoperiod regulates corticosterone rhythms by altered adrenal sensitivity through melatonin-independent mechanisms that may involve the adrenal clock.     

Endogenous timing mechanism controlling the circannual pupation rhythm of the varied carpet beetle Anthrenus verbasci

This paper describes the detailed characteristics of the circannual pupation rhythm in Anthrenus verbasci determined by laboratory experiments under various photoperiods and temperatures. The frequency distribution of larval duration showed a periodic pattern over 2-3 years and the period was 37-40 weeks under a constant short-day photoperiod (light:dark 12:12) at 20 degrees C. This rhythm showed temperature compensation to some extent under a short-day photoperiod between 17.5 degrees C and 27.5 degrees C. Under alternations of a long-day (light:dark 16:8) and a short-day photoperiod, pupation occurred 21-24.5 weeks after transfer from a long-day to a short-day photoperiod. Therefore, we concluded that the timing of pupation in A. verbasci is controlled by a circannual rhythm and its zeitgeber is a change in photoperiod. Furthermore, when larvae were transferred from a long-day to a short-day photoperiod at various ages, the larval duration after the photoperiodic transfer depended on the time of the transfer. This difference can be explained by phase-dependent phase shifts in the circannual rhythm.