Endogenous Circadian Clock Research Articles

Regulation of the Cyanobacterial Circadian Clock by Electrochemically Controlled Extracellular Electron Transfer

AbstractThere is growing awareness that circadian clocks are closely related to the intracellular redox state across a range of species. As the redox state is determined by the exchange of the redox species, electrochemically controlled extracellular electron transfer (EC‐EET), a process in which intracellular electrons are exchanged with extracellular electrodes, is a promising approach for the external regulation of circadian clocks. Herein, we discuss whether the circadian clock can be regulated by EC‐EET using the cyanobacterium Synechococcus elongatus PCC7942 as a model system. In vivo monitoring of chlorophyll fluorescence revealed that the redox state of the plastoquionone pool could be controlled with EC‐EET by simply changing the electrode potential. As a result, the endogenous circadian clock of S. elongatus cells was successfully entrained through periodically modulated EC‐EET by emulating the natural light/dark cycle, even under constant illumination conditions. This is the first example of regulating the biological clock by electrochemistry.

Diurnal Oscillations of Soybean Circadian Clock and Drought Responsive Genes

Rhythms produced by the endogenous circadian clock play a critical role in allowing plants to respond and adapt to the environment. While there is a well-established regulatory link between the circadian clock and responses to abiotic stress in model plants, little is known of the circadian system in crop species like soybean. This study examines how drought impacts diurnal oscillation of both drought responsive and circadian clock genes in soybean. Drought stress induced marked changes in gene expression of several circadian clock-like components, such as LCL1-, GmELF4- and PRR-like genes, which had reduced expression in stressed plants. The same conditions produced a phase advance of expression for the GmTOC1-like, GmLUX-like and GmPRR7-like genes. Similarly, the rhythmic expression pattern of the soybean drought-responsive genes DREB-, bZIP-, GOLS-, RAB18- and Remorin-like changed significantly after plant exposure to drought. In silico analysis of promoter regions of these genes revealed the presence of cis-elements associated both with stress and circadian clock regulation. Furthermore, some soybean genes with upstream ABRE elements were responsive to abscisic acid treatment. Our results indicate that some connection between the drought response and the circadian clock may exist in soybean since (i) drought stress affects gene expression of circadian clock components and (ii) several stress responsive genes display diurnal oscillation in soybeans.

The light-induced transcriptome of the zebrafish pineal gland reveals complex regulation of the circadian clockwork by light

Light constitutes a primary signal whereby endogenous circadian clocks are synchronized (‘entrained’) with the day/night cycle. The molecular mechanisms underlying this vital process are known to require gene activation, yet are incompletely understood. Here, the light-induced transcriptome in the zebrafish central clock organ, the pineal gland, was characterized by messenger RNA (mRNA) sequencing (mRNA-seq) and microarray analyses, resulting in the identification of multiple light-induced mRNAs. Interestingly, a considerable portion of the molecular clock (14 genes) is light-induced in the pineal gland. Four of these genes, encoding the transcription factors dec1, reverbb1, e4bp4-5 and e4bp4-6, differentially affected clock- and light-regulated promoter activation, suggesting that light-input is conveyed to the core clock machinery via diverse mechanisms. Moreover, we show that dec1, as well as the core clock gene per2, is essential for light-entrainment of rhythmic locomotor activity in zebrafish larvae. Additionally, we used microRNA (miRNA) sequencing (miR-seq) and identified pineal-enhanced and light-induced miRNAs. One such miRNA, miR-183, is shown to downregulate e4bp4-6 mRNA through a 3′UTR target site, and importantly, to regulate the rhythmic mRNA levels of aanat2, the key enzyme in melatonin synthesis. Together, this genome-wide approach and functional characterization of light-induced factors indicate a multi-level regulation of the circadian clockwork by light.

Association of clock gene variants with Autism Spectrum Disorder in South Indian population

Background Autism Spectrum disorder is a group of neurodevelopmental disorders that manifests in the first three years of life. Social impairments, communication difficulties and repetitive/stereotyped behaviour are the common symptoms of the spectrum. One of the major endophenotype associated with the disease is circadian and sensory dysfunction. Circadian dysfunction is mainly observed by difficulties in sleeping. Around 56-83% of patients with ASD suffer from sleep problems. There is an endogenous circadian clock that regulates the sleep and wakefulness, cognitive function, systematic hormonal release and body temperature. We hypothesize that the genes functioning to maintain this molecular clock may be associated with ASD either directly or by its transcriptional regulation of other genes. Materials and methods The study population was from the Malayalam speaking population of Kerala. The patients were diagnosed and characterized based on DSM-IV criteria. We selected 2 genes which are core clock components, hCLOCK and PER3 due to its functional relevance. The CLOCK gene is the first essential component of the mammalian clock and was found to be associated with circadian rhythm sleep disorders. PER3 gene is implicated in delayed sleep phase syndrome and extreme diurnal preference. Single Nucleotide Polymorphisms in both genes were studied for association with the disease. Genotyping was done by sequencing and PCR RFLP. Results and conclusion Genotypic and allelic frequencies of the SNPs studied were analyzed to understand if there exists an association with the disease. We could not find any association with the 8 polymorphisms screened in hCLOCK gene in our population. However we were able to get an association with a VNTR in PER3 gene, with the 5 repeat allele being the risk allele. This is also the first report of PER3 gene being associated with ASD.

Chapter Ten - DEC1/STRA13/SHARP2 and DEC2/SHARP1 Coordinate Physiological Processes, Including Circadian Rhythms in Response to Environmental Stimuli

Daily physiological and behavioral rhythms are regulated by endogenous circadian molecular clocks. Clock proteins DEC1 (BHLHe40) and DEC2 (BHLHe41) belong to the basic helix-loop-helix protein superfamily, which contains other clock proteins CLOCK and BMAL1. DEC1 and DEC2 are induced by CLOCK:BMAL1 heterodimer via the CACGTG E-box in the promoter and, thereafter, suppress their own expression by competing with CLOCK:BMAL1 for the DNA binding. This negative feedback DEC loop together with the PER loop involving PER and CRY, the other negative clock regulators, maintains the circadian rhythm of Dec1 and Dec2 expression. DEC1 is induced by light pulse and adjusts the circadian phase of the central clock in the suprachiasmatic nucleus, whereas DEC1 upregulation by TGF-β resets the circadian phase of the peripheral clocks in tissues. Furthermore, DEC1 and DEC2 modulate the clock output signals to control circadian rhythms in behavior and metabolism. In addition to the functions in the clocks, DEC1 and DEC2 are involved in hypoxia responses, immunological reactions, and carcinogenesis. These DEC actions are mediated by the direct binding to the E-box elements in target genes or by protein-protein interactions with transcription factors such as HIF-1α, RXRα, MyoD, and STAT. Notably, numerous growth factors, hormones, and cytokines, along with ionizing radiation and DNA-damaging agents, induce Dec1 and/or Dec2 in a tissue-specific manner. These findings suggest that DEC1 and DEC2 play a critical role in animal adaptation to various environmental stimuli.

Sex differences in circadian timing systems: Implications for disease

Virtually every eukaryotic cell has an endogenous circadian clock and a biological sex. These cell-based clocks have been conceptualized as oscillators whose phase can be reset by internal signals such as hormones, and external cues such as light. The present review highlights the inter-relationship between circadian clocks and sex differences. In mammals, the suprachiasmatic nucleus (SCN) serves as a master clock synchronizing the phase of clocks throughout the body. Gonadal steroid receptors are expressed in almost every site that receives direct SCN input. Here we review sex differences in the circadian timing system in the hypothalamic-pituitary-gonadal axis (HPG), the hypothalamic-adrenal-pituitary (HPA) axis, and sleep-arousal systems. We also point to ways in which disruption of circadian rhythms within these systems differs in the sexes and is associated with dysfunction and disease. Understanding sex differentiated circadian timing systems can lead to improved treatment strategies for these conditions.

Circadian adaptation to seasons: effects on activity behavior in subtropical House Sparrow, Passer domesticus

Birds use endogenous circadian clocks to regulate the wide array of functions. In the natural environment synchronized with day–night cycle, they exhibit these as daily rhythms in physiology and behavior. It is less understood, however, whether these daily rhythms have a seasonal perspective. We investigated this by measuring circadian clock governed activity behavior in House Sparrows (Passer domesticus) exposed to natural and artificial light–dark (LD) cycles at 27°N (Lucknow, India). Daily activity of Sparrows was recorded under natural daylight and temperature conditions (NDL) for ~11 months, beginning in late March. With more precise onsets than ends, Sparrows had varied daily activity pattern and duration between seasons. Further experiments investigated effect of seasons on circadian rhythm characteristics in Sparrows exposed to constant dim light (<1 lux) at different times of the year. The circadian rhythm period, activity pattern, and duration, but not the sensitivity of endogenous clock as shown by light-induced phase shifts, significantly varied over seasons. Also, resynchronization time (days) did not differ between seasons; although it was significantly longer to delay than to advance 6 h LD zeitgeber shifts. Thus, endogenous clock seems to closely correspond with environmental photoperiod in determining the daily activity behavior in House Sparrows.

Chronopharmacology: New Insights and Therapeutic Implications

Most facets of mammalian physiology and behavior vary according to time of day, thanks to endogenous circadian clocks. Therefore, it is not surprising that many aspects of pharmacology and toxicology also oscillate according to the same 24-h clocks. Daily oscillations in abundance of proteins necessary for either drug absorption or metabolism result in circadian pharmacokinetics, and oscillations in the physiological systems targeted by these drugs result in circadian pharmacodynamics. These clocks are present in most cells of the body, organized in a hierarchical fashion. Interestingly, some aspects of physiology and behavior are controlled directly via a "master clock" in the suprachiasmatic nuclei of the hypothalamus, whereas others are controlled by "slave" oscillators in separate brain regions or body tissues. Recent research shows that these clocks can respond to different cues and thereby show different phase relationships. Therefore, full prediction of chronopharmacology in pathological contexts will likely require a systems biology approach that considers chronointeractions among different clock-regulated systems.

Circadian and Circalunar Clock Interactions in a Marine Annelid

SummaryLife is controlled by multiple rhythms. Although the interaction of the daily (circadian) clock with environmental stimuli, such as light, is well documented, its relationship to endogenous clocks with other periods is little understood. We establish that the marine worm Platynereis dumerilii possesses endogenous circadian and circalunar (monthly) clocks and characterize their interactions. The RNAs of likely core circadian oscillator genes localize to a distinct nucleus of the worm’s forebrain. The worm’s forebrain also harbors a circalunar clock entrained by nocturnal light. This monthly clock regulates maturation and persists even when circadian clock oscillations are disrupted by the inhibition of casein kinase 1δ/ε. Both circadian and circalunar clocks converge on the regulation of transcript levels. Furthermore, the circalunar clock changes the period and power of circadian behavior, although the period length of the daily transcriptional oscillations remains unaltered. We conclude that a second endogenous noncircadian clock can influence circadian clock function.

The Circadian Clock in Oral Health and Diseases

Most physiological processes in mammals display circadian rhythms that are driven by the endogenous circadian clock. This clock is comprised of a central component located in the hypothalamic suprachiasmatic nucleus and subordinate clocks in peripheral tissues. Circadian rhythms sustain 24-hour oscillations of a large number of master genes controlling the correct timing and synchronization of diverse physiological and metabolic processes within our bodies. This complex regulatory network provides an important communication link between our brain and several peripheral organs and tissues. At the molecular level, circadian oscillations of gene expression are regulated by a family of transcription factors called “clock genes”. Dysregulation of clock gene expression results in diverse human pathological conditions, including autoimmune diseases and cancer. There is increasing evidence that the circadian clock affects tooth development, salivary gland and oral epithelium homeostasis, and saliva production. This review summarizes current knowledge of the roles of clock genes in the formation and maintenance of oral tissues, and discusses potential links between “oral clocks” and diseases such as head and neck cancer and Sjögren’s syndrome.

Interactions between endocrine and circadian systems

In most species, endogenous circadian clocks regulate 24-h rhythms of behavior and physiology. Clock disruption has been associated with decreased cognitive performance and increased propensity to develop obesity, diabetes, and cancer. Many hormonal factors show robust diurnal secretion rhythms, some of which are involved in mediating clock output from the brain to peripheral tissues. In this review, we describe the mechanisms of clock-hormone interaction in mammals, the contribution of different tissue oscillators to hormonal regulation, and how changes in circadian timing impinge on endocrine signalling and downstream processes. We further summarize recent findings suggesting that hormonal signals may feed back on circadian regulation and how this crosstalk interferes with physiological and metabolic homeostasis.

Sensory control of clutch size in the Common Swift Apus apus

Clutch size varies among individuals in most bird species. A widespread assumption is that such variation results from variable timing in the disruption of ovarian follicular growth that brings, with a few days' lag, egg‐laying to an end. Currently, there is empirical evidence that this is the case in Blue Tits Cyanistes caeruleus but not in Zebra Finches Taeniopygia guttata, in which the timing of follicular disruption has been shown to be invariant. Here, I investigate clutch size regulation of Common Swifts Apus apus. Using experimental egg removal, I show that, assuming the female gets enough egg contact, the determination of clutch size occurs at noon solar time on the day the first egg of a clutch is laid. In spite of individual variation in clutch size, there was no hint of any variability in the timing of clutch‐size determination. In this species therefore, the timing of the signal disrupting follicular growth appears invariant. The physiological mechanism that controls clutch size is discussed, including the existence of an endogenous circadian clock and potential zeitgeber, the developmental range of clutch size for the species, the sensory nature of the input that triggers follicular disruption, and the stress of laying extra eggs.

Patterns of activity expressed by juvenile horseshoe crabs.

Adult American horseshoe crabs, Limulus polyphemus, possess endogenous circadian and circatidal clocks controlling visual sensitivity and locomotion, respectively. The goal of this study was to determine the types of activity rhythms expressed by juvenile horseshoe crabs (n = 24) when exposed to a 14:10 light/dark cycle (LD) for 10 days, followed by 10 days of constant darkness (DD). Horseshoe crab activity was recorded with a digital time-lapse video system that used an infrared-sensitive camera so animals could be monitored at night. In LD, 15 animals expressed daily patterns of activity, 6 displayed a circatidal pattern, and the remaining 3 were arrhythmic. Of the 15 animals with daily patterns of locomotion, 7 had a significant preference (P < 0.05) for diurnal activity and 3 for nocturnal activity; the remainder did not express a significant preference for day or night activity. In DD, 13 horseshoe crabs expressed circatidal rhythms and 8 maintained a pattern of about 24 h. Although these results suggest the presence of a circadian clock influencing circatidal patterns of locomotion, these apparent circadian rhythms may actually represent the expression of just one of the two bouts of activity driven by the putative circalunidian clocks that control their tidal rhythms. Overall, these results indicate that, like adults, juvenile horseshoe crabs express both daily and tidal patterns of activity and that at least one, and maybe both, of these patterns is driven by endogenous clocks.

Effects of circadian phase and melatonin injection on anxiety-like behavior in nocturnal and diurnal rodents

Animals show daily rhythms in most bodily functions, resulting from the integration of information from an endogenous circadian clock and external stimuli. These rhythms are adaptive and are expected to be related to activity patterns, i.e., to be opposite in diurnal and nocturnal species. Melatonin is secreted during the night in all mammalian species, regardless of their activity patterns. Consequently, in diurnal species the nocturnal secretion of melatonin is concurrent with the resting phase, whereas in nocturnal species it is related to an increase in activity. In this research, we examined in three diurnal and three nocturnal rodent species whether a daily rhythm in anxiety-like behavior exists; whether it differs between nocturnal and diurnal species; and how melatonin affects anxiety-like behavior in species with different activity patterns. Anxiety-like behavior levels were analyzed using the elevated plus-maze. We found a daily rhythm in anxiety-like behavior and a significant response to daytime melatonin administration in all three nocturnal species, which showed significantly lower levels of anxiety during the dark phase, and after melatonin administration. The diurnal species showed either an inverse pattern to that of the nocturnal species in anxiety-like behavior rhythm and in response to daytime melatonin injection, or no rhythm and, accordingly, no response to melatonin.

Eating at the right time of day

aily cycles of light and dark due to the rotation ofthe earth around its axis have dictated how life hasevolved on Earth. Organisms have thus developedthe ability to predict these 24-h cycles by developing anendogenous circadian clock, which is entrained to externalcues. In mammals, circadian rhythms are controlled andgeneratedbythecentralormastercircadianclocklocatedinthe suprachiasmatic nuclei (SCN)of the anterior hypothala-mus in the brain [1]. This master clock consists of multiplesingle-cellcircadianoscillatorsthataresynchronizedto24hby environmental factors, primarily dark/light and alsotemperature and food. The retina perceives the dark/lightcycleinformationandtransmitsthissignaltotheSCNviatheretinohypothalamic tract. The SCN then transmits theseinputs to peripheral oscillators located outside the SCN.Such peripheral oscillators exist in nearly all peripheraltissues such as liver, adipose, pancreas, muscle and blood.Therefore, circadian rhythms have been described for vir-tually all physiological and biochemical processes, includ-ing behavioural ones [2].The SCN may influence the cardiovascular systemprimarily through multisynaptic neural projections to theheart,adrenalcortex,kidneysandvasculatureandresultantneural or endocrine effects, and secondarily by circadianinfluences on behaviours such as sleep and activity andfeeding patterns [3]. Thus, the master SCN clock sendsperiodic signals to the peripheral oscillators in order toprevent dampening of circadian rhythms, but a complexreciprocal relationship seems also to exist. Indeed, alteredbehaviours, for example when sleeping or food intake isdesynchronized from normal circadian patterns, seem toaffect the peripheral oscillators or clocks in particular,resulting in metabolic processes that are decoupled fromthe primarily light-driven SCN [4,5]. In addition, the multi-plicityofperipheralclocksinthehumanorganismhasbeenfound to comprise networks that both control circadianprocessesandaretightlyconnectedtometabolicandneuralcontrol networks, such that disturbance of one affects theother. Hence, misalignment of circadian rhythms in theSCN and peripheral tissues may constitute an importantunderling factor for a variety of metabolic and vasculardisorders such as obesity, metabolic syndrome, diabetesand hypertension [4,6,7]. Adverse cardiometabolic end-points including higher glucose, insulin, leptin, ghrelin,glucagon-like peptide-1, cortisol, blood pressure (BP)and catecholamines have been reported as results ofmisalignments invoked by food intake/irregular meal fre-quency (for comprehensive reviews see, for instance[1,2,4]). This new evidence illustrates how knowledge onchronobiology, that is the circadian influences on mech-anisms involved in metabolic and cardiovascular disease,and their interaction with behavioural influences, may beimportant for optimizing preventive lifestyle measures orpharmacological therapy [8,9]. For instance, preventingadversebehaviouraltriggersatspecificvulnerablecircadiantimes [4] or prescribing ingestion of medicines at specifictimes in anticipation of vulnerable periods [9,10] maymaximize their beneficial effects. Currently, such timedmeasures or chronotherapy constitute new avenues ofresearchforthepreventionandtreatmentofmanydiseases,including asthma, arthritis, cancer and seasonal affectivedisorder [11].Chronotherapy has been recommended for the treat-ment of major cardiovascular risk factors such as hyperten-sion [11] and dyslipidaemia [10], though typically in thecontext of pharmacotherapy. Timing of meals may con-stitute one such lifestyle therapeutical tool as well. In fact,some form of dietary chronotherapy is already imple-mented in metabolic diseases such as diabetes, whereinthe timing of meals is particularly important, as patientsneed to coordinate insulin administration with calorieintake. Interestingly, in recognition of the chronobiologicalaspects of nutrition, Franz Halberg [12] called for researchon the ‘when to eat’ question more than two decades ago.Currently, the beneficial chronobiological effects of foodintake (e.g. meal time, frequency and regularity) are beingsubject of intensive research as a potential additional or

Interlinks between sleep and metabolism

Interlinks between sleep and metabolism

Abstract 5303: Biomarker development for the evaluation of molecular circadian desynchrony in a single measurement.

Abstract Most organisms possess an endogenous circadian clock which is responsible for the temporal organization of rhythmic biochemical and metabolic processes. At the molecular level, rhythmicity in peripheral tissues is maintained by a core set of circadian genes, which in turn influence the expression programs of a large number of additional genes. Disruption in circadian rhythms has been implicated in a variety of human diseases, including cancer. However, the dynamic nature of the circadian system complicates study of molecular rhythms, and this is compounded by the inherent tissue-specificity of biological rhythms, which preclude the use of surrogate tissue. Since serial sampling of target peripheral tissue is unrealistic in human studies, our goal is to produce a model that will allow single-measurement evaluation of molecular desynchrony in archived tissue by identifying in-phase gene expression signatures in circadian gene pairs that vary over time on an absolute scale, but do not vary relative to one another. Using next-generation sequencing technologies, we have annotated the complete circadian transcriptome in primary, pre-stasis human mammary epithelial cells (HMECs) with sampling every 4-hours over a 24-hour time period. Cycling transcripts were identified using the non-parametric JTK_CYCLE algorithm, with further stratification according to circadian phase. In-phase transcript pairs were identified by calculating the standard error of the mean difference (SEM) in normalized gene expression across all time points for all pairwise comparisons among genes within each phase. Candidate pairs were then selected for further investigation, both in vitro and in normal and tumor tissue profiling experiments extracted from publicly available datasets, in order to evaluate their utility as biomarkers of tumor-associated desynchrony. Here we present the example of one such pair: IFNGR2 and PER1. In our primary HMEC model, IFNGR2 expression varies in a circadian manner over time, but maintains a consistent relationship with the core circadian gene PER1 with an approximately two-fold difference at each time-point (mean ratio = 2.29, SEM = 0.2280). In array data from single time point measurements of human mammary tissue (Array Express accession number E-TABM-276), the relationship between IFNGR2 and PER1 expression is similar to the tissue culture model in normal tissue, but becomes increasingly desynchronous in tissue with cystic changes (mean ratio = 3.83, SEM = 0.5717, P = 0.0422), and invasive carcinoma tissue (mean ratio=9.12, SEM = 0.9367, P = 0.0002). This data provides proof of principle that objective, quantitative biomarkers of molecular circadian disruption can be identified. In addition, these biomarkers can be useful for single measurement analysis, and are shown to correlate with the progression from normal tissue to invasive carcinoma. Citation Format: Tracy L. Mandichak, Joseph C. Combs, Elizabeth J. Ferree, Aaron E. Hoffman. Biomarker development for the evaluation of molecular circadian desynchrony in a single measurement. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 5303. doi:10.1158/1538-7445.AM2013-5303

Protein Phosphatase-Dependent Circadian Regulation of Intermediate-Term Associative Memory

The endogenous circadian clock is a principal factor modulating memory across species. Determining the processes through which the circadian clock modulates memory formation is a key issue in understanding and identifying mechanisms to improve memory. We used the marine mollusk Aplysia californica to investigate circadian modulation of intermediate-term memory (ITM) and the mechanisms through which the circadian clock phase specifically suppresses memory using the operant learning paradigm, learning that food is inedible. We found that ITM, a temporally and mechanistically distinct form of memory, is rhythmically expressed under light-dark and constant conditions when induced by either massed or spaced training. Strong circadian regulation of ITM occurs with memory exhibited only by animals trained during the early subjective day; no apparent memory is expressed when training occurs during the late subjective day or night. Given the necessity of multiple persistent kinase cascades for ITM, we investigated whether protein phosphatase activity affected circadian modulation. Inhibition of protein phosphatases 1 and 2A blocked ITM when animals were trained during the early (subjective) day while resulting in phase-specific memory rescue when animals were trained late in the subjective day and early night. In contrast, inhibition of calcineurin did not block ITM when animals were trained during the early day and permitted ITM when animals were trained during the late subjective day, early evening, and throughout the night. These results demonstrate that levels of protein phosphatase activity are critical regulators of ITM and one mechanism through which the circadian clock regulates memory formation.

Daily Changes in Ultraviolet Light Levels Can Synchronize the Circadian Clock of Bumblebees (Bombus terrestris)

Endogenous circadian clocks are synchronized to the 24-h day by external zeitgebers such as daily light and temperature cycles. Bumblebee foragers show diurnal rhythms under daily light:dark cycles and short-period free-running circadian rhythms in constant light conditions in the laboratory. In contrast, during the continuous light conditions of the arctic summer, they show robust 24-h rhythms in their foraging patterns, meaning that some external zeitgeber must entrain their circadian clocks in the presence of constant light. Although the sun stays above the horizon for weeks during the arctic summer, the light quality, especially in the ultraviolet (UV) range, exhibits pronounced daily changes. Since the photoreceptors and photopigments that synchronize the circadian system of bees are not known, we tested if the circadian clocks of bumblebees (Bombus terrestris) can be entrained by daily cycles in UV light levels. Bumblebee colonies were set up in the laboratory and exposed to 12 h:12 h UV + :UV− cycles in otherwise continuous lighting conditions by placing UV filters on their foraging arenas for 12 h each day. The activity patterns of individual bees were recorded using fully automatic radiofrequency identification (RFID). We found that colonies manipulated in such a way showed synchronized 24-h rhythms, whereas simultaneously tested control colonies with no variation in UV light levels showed free-running rhythms instead. The results of our study show that bumblebee circadian rhythms can indeed be synchronized by daily cycles in ambient light spectral composition. (Author correspondence: r.stanewsky@qmul.ac.uk)

ROS signaling pathways and biological rhythms: perspectives in crustaceans

This work reviews concepts regarding the endogenous circadian clock and the relationship between oxidative stress (OS), light and entrainment in different organisms including crustaceans, particularly crayfish. In the first section, the molecular control of circadian rhythms in invertebrates, particularly in Drosophila, is reviewed, and this model is contrasted with recent reports on the circadian genes and proteins in crayfish. Second, the redox mechanisms and signaling pathways that participate in the entrainment of the circadian clock in different organisms are reviewed. Finally, the light signals and transduction pathways involved in the entrainment of the circadian clock, specifically in relation to cryptochromes (CRYs) and their dual role in the circadian clock of different animal groups and their possible relationship to the circadian clock and redox mechanisms in crustaceans is discussed. The relationship between metabolism, ROS signals and transcription factors, such as HIF-1 alpha in crayfish, as well as the possibility that HIF-1 alpha participates in the regulation of circadian control genes (ccgs) in crustaceans is discussed.