Analysis of the circadian transcriptome of the Antarctic krill Euphausia superba
Ontology highlight
ABSTRACT: Antarctic krill (Euphausia superba) is a high latitude pelagic organism which plays a central role in the Southern Ocean ecosystem. E. superba shows daily and seasonal rhythms in physiology and behaviour, which are synchronized with the environmental cycles of its habitat. Recently, the main components of the krill circadian machinery have been identified and characterized. However, the exact mechanisms through which the endogenous timing system operates the control and regulation of the overt rhythms remains only partially understood. Here we investigate the involvement of the circadian clock in the temporal orchestration of gene expression by using a newly developed version of a krill microarray platform. The analysis of transcriptome data from krill exposed to both light-dark cycles (LD 18:6) and constant darkness (DD), has led to the identification of 1,564 putative clock-controlled genes. A remarkably large proportion of such genes, including several clock components (clock, period, cry2, vrille, and slimb), show oscillatory expression patterns in DD, with a periodicity shorter than 24 hours. Energy-storage pathways appear to be regulated by the endogenous clock in accordance with their ecological relevance in daily energy managing and overwintering. Our results provide the first representation of the krill circadian transcriptome under laboratory, free-running conditions. This SuperSeries is composed of the SubSeries listed below.
Project description:Circadian clocks are cell-autonomous oscillators regulating daily rhythms in a wide range of physiological, metabolic and behavioral processes. Conversely, metabolic signals such as redox state, NAD+/NADH and AMP/ADP ratios or heme feed back to and modulate circadian mechanisms to optimize energy utilization across the 24-hour cycle. We show that the signaling molecule carbon monoxide (CO) generated by rhythmic heme degradation is required for normal circadian rhythms as well as circadian metabolic outputs. CO suppresses circadian transcription by attenuating CLOCK/BMAL1 binding to target promoters. Pharmacological inhibition or genetic depletion of CO-producing heme oxygenases abrogate normal daily cycles in mammalian cells and Drosophila. In mouse hepatocytes, suppression of CO production leads to a global upregulation of CLOCK/BMAL1-dependent circadian gene expression and thereby misregulation of many metabolic processes including gluconeogenesis.
Project description:This work represents the first characterization of the krill circadian transcriptome under laboratory conditions and provides a first insight into the genetic regulation of physiological changes, which occur around the clock in light-dark (LD) and in constant darkness (DD) condition.
Project description:This work represents the first characterization of the krill circadian transcriptome under laboratory conditions and provides a first insight into the genetic regulation of physiological changes, which occur around the clock in light-dark (LD) and in constant darkness (DD) condition.
Project description:The daily pattern of temporal gene expression is regulated by the circadian clock system. Under constant environmental conditions, aging is associated with a shortening of the endogenous period of circadian rhythms in Arabidopsis. This study investigated to investigate how aging influences the waveforms of rhythmic patterns of gene expression under light/dark cycles. The waveforms of the daily cycling circadian clock showed significant warping in aged leaves, which shifted their expression pattern. Transcriptomic analysis revealed that the number of daily cycling genes in aged leaves was reduced by more than half. Furthermore, in aged plants, the expression schedule of cycling genes in both young and old leaves warped. Circadian clock mutants, including toc1, which did not exhibit age-dependent warping, had significantly altered warping patterns.
Project description:Circadian clocks are endogenous oscillators that drive organismal metabolism and physiology. Here, we report the first global in vivo quantification of circadian phosphorylation rhythms in mammals. Of more than 20,000 in vivo phosphosites, 25% significantly oscillate in the mouse liver, including novel sites on core clock proteins. Analyzing kinase substrate motifs, we find that the EGF/RAS/ERK pathway is predominantly activated during the day and the AKT/mTOR/p70S6K at night. The extent and amplitude of phosphorylation cycles dominate the rhythms of transcript and protein abundance. A dominant regulatory role for phosphorylation-dependent circadian tuning of signaling pathways allows the organism to rapidly and economically respond to daily changes in nutrient availability and integrate different signaling triggers.
Project description:The circadian clock drives daily changes of physiology, including sleep-wake cycles, by regulating transcription, protein abundance and function. Circadian phosphorylation controls cellular processes in peripheral organs, but little is known about its role in brain function and synaptic activity. We applied advanced quantitative phosphoproteomics to mouse forebrain synaptoneurosomes isolated across 24h, accurately quantifying almost 8,000 phosphopeptides. Remarkably, half of the synaptic phosphoproteins, including numerous kinases, had large-amplitude rhythms peaking at rest-activity and activity-rest transitions. Bioinformatic analyses revealed global temporal control of synaptic function via phosphorylation, including synaptic transmission, cytoskeleton reorganization and excitatory/inhibitory balance. Remarkably, sleep deprivation abolished 98% of all phosphorylation cycles in synaptoneurosomes, indicating that sleep-wake cycles rather than circadian signals are main drivers of synaptic phosphorylation, responding to both sleep and wake pressures.
Project description:In the chronobiology field, a fundamental dichotomy exists to explain daily rhythmicity of biological processes: these can be elicited in response to cyclic extrinsic/environmental signals such as light, or driven endogenously by the circadian clock. In mammals, the circadian clock ticks in almost every cell of the body, and functions based on a network of transcription-translation feedback loops. The PI3K-AKT signaling pathway relays environmental information of nutritional/metabolic state to regulate cell size and proliferation. AKT, a Serine/Threonine protein kinase, is activated by phosphorylation, where phospho-serine 473 (pAKT) serves as a hallmark for its activation. Following activation, it proceeds to phosphorylate dozens of target proteins that convey the signal to regulate gene expression and other key cellular functions. Overall, this pathway is widely known to be activated in response to feeding related signals, and previous studies in mice found elevated pAKT levels in correspondence with food ingestion. However, it is still unknown whether this can (also) be driven through intrinsic mechanisms, such as the circadian clock. Here, we inspected daily activation of AKT both in cultured cells and animal models. Unexpectedly, we found, that neither environmental cues nor the circadian clock were necessary for pAKT rhythms, which exhibited ultradian, rather than circadian, cycles of phosphorylation. In addition, hepatic gene expression also exhibited short rhythms in clock disrupted mice, corresponding with AKT related genes/functions. Reciprocally, inhibition of AKT phosphorylation did not affect the rhythmicity of the circadian clock. Overall, our findings uncover temporal regulation of AKT activation and reveal ultradian molecular rhythmicity that cycles independently of the canonical circadian clock.
Project description:Most higher organisms, including plants and animals, have developed a time-keeping mechanism that allows them to anticipate daily fluctuations of environmental parameters such as light and temperature. This circadian clock efficiently coordinates plant growth and metabolism with respect to time-of-day by producing self-sustained rhythms of gene expression with an approximately 24-hour period. The importance of these rhythms has in fact been demonstrated in both phytoplankton and higher plants: organisms that have an internal clock period matched to the external environment possess a competitive advantage over those that do not. We used microarrays to identify circadian-regulated genes of Arabidopsis thaliana to elucidate how the clock provides an adaptive advantage by understanding how the clock regulates outputs and determining which pathways and processes may be under circadian control. Experiment Overall Design: Groups of Arabidopsis seedlings were grown in light/dark cycles for 7 d before, transferred to constant light, and after 24 h in constant light 12 samples were harvested at 4-h intervals over the next 44 h for RNA extraction and hybridization on Affymetrix microarrays.
Project description:Circadian (~24 hour) clocks exist in almost all types of living organism and play a fundamental role in regulating daily physiological and behavioural processes. The transcription factor BMAL1 (ARNTL) is thought to be one of the principal drivers of the molecular clock in mammals since its deletion abolishes 24-hour activity patterning, an important physiological output of the clockwork. However, whether or not Bmal1-/- mice can nevertheless display molecular 24-hour rhythms is unknown. Here, we determined whether Bmal1 function is necessary for daily molecular oscillations in two tissues – skin fibroblasts and liver. Unexpectedly, both tissues exhibited robust 24-hour oscillations over 2-3 days in the absence of any exogenous synchronizers such as daily light or temperature cycles. This demonstrates a competent 24-hour molecular pacemaker in Bmal1 knockouts. Indeed, molecular oscillations were pervasive throughout the transcriptome, proteome and phosphoproteome of Bmal1-/- mice. In particular, several proteins exhibited rhythmic phosphorylation in both Bmal1-proficient and -deficient cells, highlighting an unanticipated role for post-translational regulators in 24-hour rhythms in the absence of any known clock mechanisms.
Project description:The circadian clock generates daily rhythms in mammalian liver processes, such as glucose and lipid homeostasis, xenobiotic metabolism, and regeneration. The mechanisms governing these rhythms are not well understood, particularly the distinct contributions of the cell-autonomous clock and central pacemaker to rhythmic liver physiology. Through microarray expression profiling in MMH-D3 hepatocytes, we identified over 1,000 transcripts that exhibit circadian oscillations, demonstrating that many rhythms can be driven by the cell-autonomous clock and that MMH-D3 is a valid circadian model system. The genes represented by these circadian transcripts displayed both co-phasic and anti-phasic organization within a protein-protein interaction network, suggesting the existence of competition for binding sites or partners by genes of disparate transcriptional phases. Multiple pathways displayed enrichment in MMH-D3 circadian transcripts, including the polyamine synthesis module of the glutathione metabolic pathway. The polyamine synthesis module, which is highly associated with cell proliferation and whose products are required for initiation of liver regeneration, includes enzymes whose transcripts exhibit circadian oscillations, such as ornithine decarboxylase (Odc1) and spermidine synthase (Srm). Metabolic profiling revealed that the enzymatic product of SRM, spermidine, cycles as well. Thus, the cell-autonomous hepatocyte clock can drive a significant amount of transcriptional rhythms and orchestrate physiologically relevant modules such as polyamine synthesis.