Search Results (148)

Dopamine is one of the most important neurotransmitters for regulating retinal function and adjusting vision to the diurnal cycle. It exerts its regulatory effects, in part, through the cAMP pathway. Previous studies have demonstrated that dopamine affects phototransduction in amphibian rods, and that elevated intracellular levels of cAMP modulate the function of vertebrate rods and cones. Lamprey, the most primitive vertebrate, could be valuable for studying the evolution of dopamine regulatory loops in the retina. We examined whether the photoresponse properties of long (cone-like) and short (rod-like) photoreceptors in the river lamprey could be regulated by dopamine via the cAMP pathway. Using suction pipette recording, we demonstrated that forskolin-induced elevation of cAMP has no effect on long or short photoreceptors. At the same time, dopamine modifies the photoresponse properties of long, but not short, photoreceptors at high, potentially non-physiological concentrations. Immunohistochemical analysis of the lamprey retina revealed the expression of both D1 and D2 dopamine receptors in lamprey photoreceptors; however, their distribution differs from jawed vertebrates. Taken together, our results suggest that, in lampreys, dopamine does not regulate photoreceptor sensitivity to light in the circadian rhythm, but, rather, adjusts other retinal functions based on widespread distribution of its receptors. Full article

Background: White adipose tissue (WAT) exhibits diurnal oscillations regulated by clock genes, which autonomously control its functionality. These rhythms are modulated by the central clock and external factors, such as light exposure and diet. Flavanols, phenolic compounds known for their beneficial metabolic effects, have been shown to modulate the expression of clock genes. This study explored the impact of flavanols on clock gene expression in WAT explants from lean and obese rats under changes in light/dark cycles. Methods: WAT explants were obtained from 24 Fischer rats fed a standard diet (STD) or cafeteria diet (CAF) for seven weeks. During the final week, rats were changed to short (6 h of light, L6) or long (18 h of light, L18) photoperiods. CAF-fed rats were also administered a grape seed (poly)phenol-rich extract (GSPE) (25 mg/kg) or vehicle (VH). After sacrifice, WAT explants were collected every 6 h starting at 8 a.m. the following day (CT0, CT6, CT12, CT18, and CT24). Results: The results showed that under L18 conditions, STD-fed rats displayed oscillations in Bmal1, Cry1, Per1, and Rev-erbα clock gene expression, whereas many of these rhythms were disrupted under L6 conditions. Moreover, the administration of the CAF diet also resulted in the loss of clock gene circadian oscillations in the WAT explants. GSPE administration restored the oscillation of these clock genes under L18 and L6 conditions. Conclusions: These findings highlight the potential zeitgeber role of flavanols in modulating WAT peripheral clocks and their capacity to improve metabolic and circadian regulation under conditions of diet- and photoperiod-induced disruption. Full article

Nest defense is a key component of avian reproductive success, yet its intensity and expression often depend on ecological and social contexts. We investigated the nest defense behaviors of Saunders’s Gulls (Saundersilarus saundersi) breeding in Incheon Bay of South Korea in 2022 in relation to nest density and perceived threats. Using decoy presentations of three heterospecifics, Oriental Magpie (Pica serica; diurnal avian nest predator), common raccoon dog (Nyctereutes procyonoides; nocturnal mammalian nest predator), and Little Tern (Sternula albifrons; neutral co-nester), we quantified latency to respond, bombing attack rate, and the number of mobbing individuals at high- and low-density nesting sites within a breeding colony. Mixed models revealed that latency to respond and attack rates varied strongly with stimulus type, with diurnal predator magpies eliciting the fastest and most intense responses, followed by nocturnal predator raccoon dogs and co-nester terns. Nest density influenced the number of mobbing individuals, which was significantly greater at high-density sites. Principal Component Analysis reduced the three behavioral metrics into a composite score, which correlated negatively with latency and positively with bombing attack rate and mobbing intensity. This score varied with both nest density and stimulus type. Our findings demonstrate that Saunders’s Gulls adjust their nest defense strategies according to both the social context and predator type, highlighting the importance of density-dependent collective nest defense in colonial breeders. Full article

Skeletal muscle plays vital roles in locomotion, metabolic regulation and endocrine signalling. Critically, it undergoes structural and functional decline with age, leading to a progressive loss of muscle mass and strength (sarcopenia) and contributing to a systemic loss of tissue resilience to stressors of multiple tissue systems (frailty). Emerging evidence implicates misalignments in both the circadian molecular clock and redox homeostasis as major drivers of age-related skeletal muscle deterioration. The circadian molecular clock, through core clock components such as BMAL1 and CLOCK, orchestrates rhythmic gene, protein and myokine expression impacting diurnal regulation of skeletal muscle structure and metabolism, mitochondrial function, antioxidant defence, extracellular matrix organisation and systemic inter-tissue communication. In parallel, the master redox regulator, NRF2, maintains cellular antioxidant defence, tissue stress resistance and mitochondrial health. Disruption of either system impairs skeletal muscle contractility, metabolism, and regenerative capacity as well as systemic homeostasis. Notably, NRF2-mediated redox signalling is clock-regulated and, in turn, affects circadian clock regulation. Both systems are responsive to external cues such as exercise and hormones, yet studies do not consistently include circadian timing or biological sex as key methodological variables. Given that circadian regulation shifts with age and differs between sexes, aligning exercise interventions with one’s own chronotype may enhance health benefits, reduce adverse side effects, and overcome anabolic resistance with ageing. This review highlights the essential interplay between circadian and redox systems in skeletal muscle homeostasis and systemic health and argues for incorporating personalised chrono-redox approaches and sex-specific considerations into future experimental research and clinical studies, aiming to improve functional outcomes in age-related sarcopenia and broader age-related metabolic and musculoskeletal conditions. Full article

Background/Objectives: Patients with epilepsy commonly experience patterns of seizures that change with sleep/wake behavior or diurnal rhythms. The cellular and molecular mechanisms that underlie these patterns in seizure activity are not well understood but may involve non-neuronal cells, such as astrocytes. Our previous studies show the critical importance of one specific astrocyte factor, the brain-type fatty acid binding protein Fabp7, in the regulation of time-of-day-dependent electroshock seizure threshold and neural activity-dependent gene expression in mice. Here, we examined whether Fabp7 influences differential seizure activity-dependent protein expression, by comparing Fabp7 knockout (KO) to wild-type (WT) mice under control conditions and after reaching the maximal electroshock seizure threshold (MEST). Methods: We analyzed the proteome in cortical–hippocampal extracts from MEST and SHAM groups of WT and KO mice using mass spectrometry (MS), followed by Gene Ontology (GO) and pathway analyses. GO and pathway analyses of all groups revealed a diverse set of up- and downregulated differentially expressed proteins (DEPs). Results: We identified 65 significant DEPs in the comparison of KO SHAM versus WT SHAM; 33 proteins were upregulated and 32 were downregulated. We found downregulation in mitochondrial-associated proteins in WT MEST compared to WT SHAM controls, including Slc1a4, Slc25a27, Cox7a2, Cox8a, Micos10, and Atp5mk. Several upregulated DEPs in the KO SHAM versus WT SHAM comparison were associated with the 20S proteasomal subunit, suggesting proteasomal activity is elevated in the absence of Fabp7 expression. We also observed 92 DEPs significantly altered in the KO MEST versus WT MEST, with 49 proteins upregulated and 43 downregulated. Conclusions: Together, these data suggest that the astrocyte Fabp7 regulation of time-of-day-mediated neural excitability is modulated by multiple cellular mechanisms, which include proteasomal pathways, independent of its role in activity-dependent gene expression. Full article

Thiamine is a vitamin essential for the function of central metabolic enzymes, of which pyruvate dehydrogenase (PDH) possesses one of the broadest regulations. Diurnal effects of thiamine supplementation on energy metabolism have previously been shown for the rat brain. Here, we report data on the diurnal changes and the effects of thiamine administration to rats on the function of thiamine-dependent enzymes in the cerebral cortex, heart, and liver. The most pronounced diurnal differences were found at the level of cerebral PDH activity. Analysis of PDH phosphorylation in five rat tissues revealed diurnal and thiamine-dependent differences in the cerebral cortex and heart. The expression of tissue-specific PDH kinases PDK3 and PDK4 showed a daytime-dependent response to thiamine administration in the cerebral cortex and heart, respectively. In addition, cardiac PDK4 expression was doubled in the evening, compared to morning. Furthermore, cerebral cortex demonstrated tissue-specific diurnal changes in thiamine diphosphate (ThDP) and monophosphate levels. Elevation of blood, cardiac, and cerebral ThDP was more effective upon the evening thiamine administration. Importantly, only ThDP was elevated in the rat cerebral cortex exclusively after evening thiamine supplementation. Coenzyme role of ThDP and/or other thiamine functions in nerve tissue reduced the existing daytime changes in animal behavior and ECG parameters. The reported data on diurnal regulation of central energy metabolism as well as the diurnal difference in thiamine accumulation in the cerebral cortex, heart, and other tissues are of clinical importance, as high doses of thiamine are used for the treatment of acute thiamine deficiencies and many other mostly neurological diseases in patients. Full article

There is evidence that bone health is closely linked to a functioning circadian rhythm. Most of the evidence comes from mice, which may exhibit some species-specific differences from humans due to their nocturnal lifestyle. To address the current lack of human model systems, the present study aimed to develop an in vitro model system that can represent diurnal changes in bone metabolism. The model is based on co-cultured SCP-1 and THP-1 cells that serve as osteoblast and osteoclast precursors, respectively. Diurnal effects were induced by replacing the FCS in the differentiation medium with human serum pools (HSPs) obtained in the morning, noon, or evening. The model system was tested for cell viability, gene expression, and osteoblast and osteoclast function. The replacement of the FCS with the HSPs increased viability and induced expression changes in circadian clock genes in the model system. Resulting alterations in osteoblast and osteoclast function led to a gradual increase in mineral density and stiffness when 3D co-cultures were differentiated in the presence of the HSPs collected in the morning, noon, or evening, respectively. Here, we present for the first time an in vitro model that can present diurnal changes in bone metabolism in the form of a snapshot. With the simple use of HSPs, this model can be used as a platform technique to investigate bone function in various situations, taking into account the time of day. Full article

Fructose-1,6-bisphosphatase (FBP) is a crucial regulatory enzyme in sucrose synthesis and photosynthetic carbon assimilation, functioning through two distinct isoforms: cytosolic FBP (cyFBP) and chloroplastic FBP (cpFBP). However, the identification and functional characterization of FBP genes in Saccharum remains limited. In this study, we conducted a systematic identification and comparative genomics analyses of FBPs in three Saccharum species. We further examined their expression patterns across leaf developmental zones, spatiotemporal profiles, and responses to diurnal rhythms and hormonal treatments. Our analysis identified 95 FBP genes, including 44 cyFBPs and 51 cpFBPs. Comparative analyses revealed significant divergence in physicochemical properties, gene structures, and motif compositions between the two isoforms. Expression profiling indicated that both cyFBPs and cpFBPs were predominantly expressed in leaves, particularly in maturing and mature zones. During diurnal cycles, their expression peaked around the night–day transition, with cpFBPs exhibiting earlier peaks than cyFBPs. FBP genes in Saccharum spontaneum displayed greater diurnal sensitivity than those in Saccharum officinarum. Hormonal treatments further revealed significant regulatory divergence in FBP genes, both between isoforms and across species. Notably, cyFBP_2 and cpFBP_2 members consistently exhibited higher expression levels across all datasets, suggesting their pivotal roles in sugarcane physiology. These findings not only identify potential target genes for enhancing sucrose accumulation, but also highlight the breeding value of S. spontaneum and S. officinarum in sugarcane breeding. Full article

Hemerocallis spp. exhibit distinct flower opening times, categorized into nocturnal and diurnal types. Previous studies have demonstrated that the circadian clock and CONSTANS (CO) genes play crucial roles in regulating flowering in Hemerocallis. However, the key genes that integrate flowering pathways remain largely unknown. To address this gap, we identified potential homologs of the FLOWERING LOCUS T (FT) gene in Hemerocallis. A yeast one-hybrid assay revealed that HfCOL2 and HfLHY directly bind to the HfFT1 and HfFT2 promoters, thereby activating FT transcription. The expression analysis reveals that HfCOL2 expression rhythms not only display opposing patterns between nocturnal and diurnal opening types of Hemerocallis but also between leaf and flower tissues. The peak expression of HfCOL2 in flowers aligns closely with the respective opening times of diurnally and nocturnally flowering Hemerocallis. The overexpression of HfCOL2 in tobacco plants led to early flowering and prolonged flower longevity. In Hemerocallis, the HfCOL2 gene plays a pivotal role not only in photoperiod-induced flowering but also in the circadian rhythm-mediated regulation of flower opening time. Due to the limited availability of plant materials exhibiting distinct flower opening rhythms, research in this area has been constrained. Identifying the key genes in the flowering pathway of Hemerocallis can facilitate a better understanding of the mechanisms by which plants respond to circadian rhythms. Full article

Background: Renal ischemia–reperfusion injury (IRI) is a frequent cause of kidney transplant failure. Recent studies have shown that the extent of injury is closely linked to ferroptosis, and the process of cellular ferroptosis is diurnal and regulated by circadian genes. NRF2, involved in iron–heme metabolism, may be related to ferroptosis. We hypothesize that the pathway plays a role in circadian regulation in ferroptosis in renal IRI. Methods: Using hematoxylin and eosin (H&E) staining, enzyme-linked immunosorbent assay (ELISA), Cell Counting Kit-8 (CCK8), flow cytometry, real-time quantitative reverse transcription PCR (qRT-PCR), and Western blotting, we analyzed renal tubular tissues in vivo and in vitro and compared the groups with IR injury treatment, inhibition of ferroptosis, and inhibition of BMAL1 gene expression at the ZT0 (zeitgeber time 0) and ZT12 (zeitgeber time 12) time points. Results: IR injury treatments caused exacerbation of injury, both in vivo and in vitro, and were more pronounced at the ZT12 time point, which correlates with circadian rhythms. The use of the ferroptosis inhibitor (Fer-I) attenuated IR injury, suggesting that IRI is associated with ferroptosis. In contrast, reduced BMAL1-gene expression exacerbated injury, and NRF2, which is elevated in IR injury, was suppressed. Conclusions: The circadian gene BMAL1 affects the circadian rhythm of ferroptosis in renal IRI through the regulation of NRF2 and its downstream pathway. In this study, renal injury is well ameliorated by the ferroptosis inhibitor, exhibiting potential as a therapeutic agent for use in renal transplantation. Full article

Daytime-restricted feeding (TRF) exerts outstanding effects on circadian physiology, nutrient utilization, and energy metabolism. Limiting feeding access to two hours during the daytime (12:00–14:00 h) for three weeks promotes food-anticipatory activity (FAA). FAA encompasses not only behaviors related to meal expectations but also includes diurnal fluctuations in liver metabolic responses, including distinct redox handling. Hepatic microarray profiles of genes associated with redox response processes were analyzed at three crucial time points: at the beginning of the light period or before FAA (08:00 h), during the expression of FAA (11:00 h), and after feeding (14:00 h). Data on fasting and nutrient processing were integrated, whereas circadian implications were extrapolated by comparing the TRF transcriptional output with a one-day fasting group. Transcripts of redox reactions, such as reactive oxygen species (ROS) generation, antioxidant defenses, NAD⁺/NADH equilibrium, and glutathione, hydrogen peroxide (H₂O₂), arginine, nitric oxide (NO), and hydrogen sulfide (H₂S) metabolism, were analyzed. Results showed a decline in antioxidant defenses at 08:00 h, followed by a burst of pro-oxidant reactions, preparation of glutathione metabolism factors, and a tendency to decrease H₂O₂ and increase NO and H₂S during the FAA. Most of the findings observed during the FAA were absent in response to one-day fasting. Hence, TRF involves concerted and sequential responses in liver pro-oxidant and antioxidant reactions, facilitating a redox-related circadian control that optimizes the metabolic utilization of nutrients, which differs from a response to a simple fast-feed cycle. Full article

In mammals, the core molecular clock genes and the overall circadian system are established during early development; during this critical period of development, maternal metabolic condition plays a major role in programming temporal metabolic regulation. Therefore, this study aimed to evaluate the effects of the chronic maternal intake of a high-fat and high-carbohydrate diet (HFCD) before and during pregnancy, in addition to a challenge with HFCD during adulthood, on offspring diurnal metabolic profile and on clock gene expression in central and peripheral circadian oscillators. The HFCD offspring and/or those exposed to the metabolic challenge exhibited alterations in the temporal profiles of analytes associated with both the carbohydrate and lipid metabolisms, as well as markers associated with liver and kidney damage, ranging from phase changes in rhythmicity or, in some cases, to the complete loss of 24 h variations. At the molecular level, the expression of clock genes (Per1, Cry1, Bmal1, and Clock) in the central and peripheral oscillators showed differential susceptibility to undergoing changes in their abundance. Our data indicate that maternal HFCD during pregnancy, a second exposure in adulthood, or both result in the long-term misalignment of the diurnal rhythm’s metabolic and damage markers; these changes are possibly associated with alterations in the core molecular circadian clockwork. Full article

The SWEET (Sugar Will Eventually be Exported Transporters) protein family plays a key role in plant growth, adaptation, and stress responses by facilitating soluble sugar transport. However, their functions in Cymbidium remain poorly understood. This study identified 59 SWEET genes across four Cymbidium species, encoding conserved MtN3/saliva domains. Despite variations in exon-intron structures, gene motifs and domains were highly conserved. Phylogenetic analysis grouped 95 SWEET proteins from six species into four clades, with gene expansion driven by whole-genome, segmental, and tandem duplications. Cis-element analysis and expression profiling across 72 samples revealed diverse regulatory patterns. Notably, SWEET genes showed peak expression in floral development, leaf morph variations, and diurnal rhythms. qRT-PCR and transcription factor binding analysis further highlighted their regulatory roles in floral patterning, leaf variation, and metabolic rhythms. These findings provide a foundation for future studies on SWEET gene function and their potential molecular breeding value in orchids. Full article

Members of Agave L. utilize CAM. To date, research on the physiological and morphological adaptations of Agave has analyzed only a few species. With the aim of understanding basic aspects of the physiological responses of polyploid (2n = 2x = 60 to 2n = 6x = 180) Agave accessions in association with CO₂ fixation, we carried out genetic and physiological studies of A. tequilana Weber, A. fourcroydes Lem., and A. angustifolia Haw., which are adapted to two ecoregions in the Yucatán of Mexico: the Regional Roger Orellana-CICY Botanical Garden (RO-CICY) in the city of Merida and the Germplasm Bank of the Scientific-Technological Park of Yucatán (GB-PCTY) located in the Sierra Papacal. Differences in genetic variability in Agave spp. were assessed using AFLP markers. Monitoring of stomatal openings during the night showed differences in polyploid species of Agave. The highest expression levels of PEPC and PEPCK genes were observed at the largest suprastomatol cavity areas. All of the evaluated accessions showed a four-fold increase in internal CO₂ during the transition from 23:00 h to 3:00 h, indicating a larger diurnal fixation of internal CO₂. The results of PCA, including photosynthetic parameters during night–day, indicated differential physiological responses that suggest the occurrence of five groups within the two ecoregions. The physiological data we report here indicate thar polyploid accessions of Agave exhibited differences associated with CO₂ exchange, suggesting that these polyploid taxa may be better adapted to climates with high CO₂ concentrations and they could be used in atmospheric CO₂ sequestration. Full article

The western flower thrips, Frankliniella occidentalis, a worldwide insect pest with its polyphagous feeding behavior and capacity to transmit viruses, follows a diurnal rhythmicity driven by expression of the circadian clock genes. However, it remained unclear how the clock signal triggers the thrips behaviors. This study posed a hypothesis that the clock signal modulates cGMP-dependent protein kinase (PKG) activity to mediate the diurnal behaviors. A PKG gene is encoded in F. occidentalis and exhibits high sequence homologies with those of honeybee and fruit fly. Interestingly, its expression followed a diel pattern with high expression during photophase in larvae and adults of F. occidentalis. It is noteworthy that PKG expression was clearly observed in the midgut during photophase but not in scotophase from our fluorescence in situ hybridization analysis. A prediction of protein–protein interaction suggested its functional association with clock genes. To test this functional link, RNA interference (RNAi) of the PKG gene expression was performed by feeding a gene-specific double-stranded RNA, which led to significant alteration of the two clock genes (Clock and Period) in their expression levels. The RNAi treatment caused adverse effects on early-life development and adult fecundity. To further analyze the role of PKG in affecting diurnal behavior, the adult females were continuously observed for a 24 h period with an automatic digitization device to obtain movement parameters and durations (%) in different micro-areas in the observation arena. Diel difference was observed with speed in RNAi-control females at 0.16 mm/s and 0.08 mm/s, in photo- and scotophase, respectively, whereas diel difference was not observed for the PKG-specific RNAi-treated females, which showed 0.07 mm/s and 0.06 mm/s, respectively. The diel difference was also observed in durations (%) in the control females, more strongly in the intermediate area in the observation arena. Speed and durations in the different micro-areas in mid-scotophase were significantly different from most photophase in the control females, while speed was significantly different mainly during late photophase when comparing effects of control and RNAi treatments in each light phase. Three sequential stages consisting of high activity followed by feeding and visiting of micro-areas were observed for the control females. For RNAi-treated females, the three phases were disturbed with irregular speed and visits to micro-areas. These results suggest that PKG is associated with implementing the diurnal behavior of F. occidentalis by interacting with expressions of the circadian clock genes. Full article