Light-dark Cycle Research Articles

Melatonin Induces per1a Expression in Zebrafish Brain

In vertebrates, the circadian mechanism regulates many physiological and behavioral activities. The major key output of the circadian clock is the secretion of melatonin in the pineal gland. Melatonin secretion remains low during the daytime and increases significantly at night. The rise and fall of melatonin level is a key factor that conveys rhythmic information to the organism to carry out daily and annual physiological rhythms. It also affects the rhythmic oscillation of clock genes in the suprachiasmatic nucleus (SCN) as well as in peripheral tissues. In this study, we have shown that zebrafish brain rhythmically expresses per1a and cry1a in different photoperiodic regimes: light-dark cycle (LD) and continuous light (LL). We have also demonstrated that an acute injection of melatonin in the middle of the subjective day induces per1a expression in zebrafish brain. Furthermore, we have also shown that an acute injection of melatonin affects circadian regulation of locomotor activity in zebrafish under LD conditions. These results provide insight into understanding the underlying mechanism of melatonin in regulation of clock genes and locomotor activity in zebrafish.

First report of Stenocarpella macrospora causing Diplodia leaf streak disease of maize in Yunnan Province, China.

Maize (Zea mays. L) is cultivated globally as a staple food crop, animal feed, and biofuel. However, persistent diseases in maize have led significant yield losses and a decline in grain quality (Yang et al., 2017). In August 2024, long and narrow lesions were observed on the leaves of maize growing in a field in Luoping County, Qujing City, Yunnan Province, China (24° 94' 87" N, 101° 32' 24" E). The incidence of the disease was investigated to be about 15-30% in different varieties of maize planting areas in seven townships. Initial symptoms appeared as yellow to tan stripes, with the lesions measuring 3 to 48 mm in width and 45 to 560 mm in length. In severe cases, the lesions expanded, leading to complete leaf necrosis, which caused significant damage to maize production. Dark brown sub-epidermal pycnidia and conidia were observed on the necrotic leaf tissue. The pycnidia were globose or sac-like structures, with short and narrow conidiophores. The newly formed conidia are narrow, non-septate, and have transparent cytoplasm. The conidia are subcylindrical to narrowly ellipsoid, straight, curved, or occasionally irregular, measuring 38 to 86 × 7.2 to 12.3 µm. They are 0-3-septate, smooth-walled, pale brown, apex obtuse, base truncate. Therefore, 80 individual conidia were picked under a dissecting microscope, transferred to PDA plates containing antibiotics (10 mg/L rifampicin and ampicillin) followed by incubation at 28°C for 7 days (Fei et al., 2019). After seven days, the colonies of all isolates were turned grey and downy. Based on the maize leaf symptoms and the morphological characteristics of the pycnidia and conidia, the fungus was tentatively identified as Stenocarpella spp. (Luna et al., 2016). To confirm the identity of all isolates, DNA was extracted from 10 randomly selected isolates using the cetyl trimethyl ammonium bromide (CTAB) method. The internal transcribed spacer (ITS) region and the translation elongation factor 1α (TEF-1α) gene were amplified using the primer pairs ITS-1/ITS-4 and EF-1/EF-2, respectively, and then sequenced (Lamprecht et al., 2011). After comparison, the two target sequences of 10 isolates were consistent. BLASTn analysis revealed 99.27% and 100.00% homology with the two target sequences of Stenocarpella macrospora (syn. = Diplodia macrospora) (GQ259128.1, MG934504.1). Based on phylogenetic analysis of two targets, the isolate MS01 was clustered on the same evolutionary branch with S. macrospora. The two target sequences of isolate MS01 was submitted to GenBank under the accession numbers PQ241617.1 and PQ243292.1. To confirm the pathogenicity, a suspension (1 × 106 spores /mL) of isolate MS01 conidial was sprayed onto nine healthy leaves of maize plants in vitro and three pots cultivated with the plants (five plants per pot) in vivo. Plant treated with sterilized water served as control group. The treated plants were incubated at 28°C, 90% relative humidity with alternating light-dark cycles (i.e. 12 h shifts) for 3-10 days. At the same time, the conidial suspension was injected and inoculated onto maize ears, with water used as a blank control. Each treatment contained 3ears, 10 µL of the suspension was applied to each seed treatment. Inoculated leaves developed brown spots that gradually expanded into streak lesions extending toward the ends of the leaves, similar to those observed in the field. Additionally, the maize seeds become also moldy, whereas the control leaves and ears remained symptomless. The same pathogen was re-isolated from the infected leaves and ears, confirming Koch's postulates. Previously, S. macrospora and S. maydis have been reported in many countries across North, Central and South America, Africa, Asia, and Oceania, where maize is grown commercially. These pathogens are known to infect maize ears, stalks, and leaves of maize and also can produce mycotoxins (Romero et al., 2015; Snyman et al., 2011). To our knowledge, S. macrospora causing dry rot and ear rot of maize has been reported in China, but it is mostly found in quarantine at the time of importation (Tai et al., 1979; Shan et al., 2024). This is the first report of S. macrospora causing Diplodia leaf streak disease of maize in Yunnan Province, China. Since Stenocarpella spp. is one of the most destructive diseases of maize globally, the results of this study provide a foundation for developing effective prevention, control, and quarantine strategies for managing this disease.

Influence of extreme light/dark cycles on monoamine levels, physiological indices, and emotional behaviors in rats

ABSTRACT Aberrant light/dark (LD) cycles are prevalent in modern society due to electric light usage, leading to mood disorders from circadian disruption or misalignment. However, research on the physiological and behavioral effects of LD variations on brain neurotransmitters is limited. We investigated the effects of extreme LD cycles on body weight (BW), core body temperature (Tcore), locomotor activity (ACT), emotional behaviors, and monoamine levels (noradrenaline [NA], dopamine [DA], and serotonin [5-HT]) in male Wistar rats that were exposed to 1 month of either long light phase (20 L:4D), long dark phase (4 L:20D), or normal (12 L:12D) LD cycles. The 20 L:4D rats exhibited blunted rhythms, with decreased amplitude and advanced/delayed acrophase in Tcore and ACT, alongside increased BW. The 4 L:20D rats showed circadian misalignment, with increased/decreased amplitude in Tcore or ACT and delayed acrophase in Tcore and ACT, also gaining BW. In the 20 L:4D group, NA and 5-HT levels decreased in the suprachiasmatic nucleus and amygdala, respectively, while the 4 L:20D group had increased DA and 5-HT levels in the caudate putamen and dorsomedial hypothalamus, respectively. Open field and social interaction tests indicated anxiety-like behaviors in both test groups. Overall, each extreme LD cycle affected Tcore, ACT amplitude, acrophase, and monoamine levels differently, inducing anxiogenic responses.

Circadian modulation of behavioural stress indicators varies between diurnal and nocturnal fish species

In the wild, most animals experience daily fluctuations in threats and resources that are synchronised with environmental time cues such as the light-dark cycle. Consequently, animals have evolved daily behavioural patterns (i.e., diurnal or nocturnal) that enhance their fitness by, for example, reducing the temporal overlapping with predators. In fish, previous studies revealed stronger physiological stress responses during the resting period of the species. However, little is known about the circadian modulation of stress indicators and how they are influenced by daily behavioural patterns. In this research, we investigated the behavioural stress responses of two farmed fish species with different activity patterns: the diurnal Nile tilapia (Oreochromis niloticus) and the nocturnal tench (Tinca tinca). To this end, we examined the behavioural response of individuals exposed to the diving test every 4 h over a 24 h cycle (n = 12 fish/species/time point). Results indicated that most behavioural indicators varied according to the time of day, aligning with the daily rhythmic pattern of the two species. Tilapia exhibited stronger stress responses to novelty during the dark phase, while tench displayed higher stress during the light phase. This was supported by stress-related behaviours such as freezing and erratic movements (in both tilapia and tench) and bottom-dwelling (in tench only). These results indicated that stress responses peaked during the resting phase of each species, although behavioural indicators exhibiting this daily variation did not completely coincide between the studied species. Overall, these findings suggest interspecific differences in the daily modulation of behavioural stress indicators in farmed fish, an effect with potential relevance for welfare. Understanding the activity rhythmic patterns, resting periods, and associated daily variation in stress for each fish species of interest can precisely help tailor farming procedures to minimise suffering.

Interaction Between Early Meals (Big-Breakfast Diet), Clock Gene mRNA Expression, and Gut Microbiome to Regulate Weight Loss and Glucose Metabolism in Obesity and Type 2 Diabetes.

The circadian clock gene system plays a pivotal role in coordinating the daily rhythms of most metabolic processes. It is synchronized with the light-dark cycle and the eating-fasting schedule. Notably, the interaction between meal timing and circadian clock genes (CGs) allows for optimizing metabolic processes at specific times of the day. Breakfast has a powerful resetting effect on the CG network. A misaligned meal pattern, such as skipping breakfast, can lead to a discordance between meal timing and the endogenous CGs, and is associated with obesity and T2D. Conversely, concentrating most calories and carbohydrates (CH) in the early hours of the day upregulates metabolic CG expression, thus promoting improved weight loss and glycemic control. Recently, it was revealed that microorganisms in the gastrointestinal tract, known as the gut microbiome (GM), and its derived metabolites display daily oscillation, and play a critical role in energy and glucose metabolism. The timing of meal intake coordinates the oscillation of GM and GM-derived metabolites, which in turn influences CG expression, playing a crucial role in the metabolic response to food intake. An imbalance in the gut microbiota (dysbiosis) can also reciprocally disrupt CG rhythms. Evidence suggests that misaligned meal timing may cause such disruptions and can lead to obesity and hyperglycemia. This manuscript focuses on the reciprocal interaction between meal timing, GM oscillation, and circadian CG rhythms. It will also review studies demonstrating how aligning meal timing with the circadian clock can reset and synchronize CG rhythms and GM oscillations. This synchronization can facilitate weight loss and improve glycemic control in obesity and those with T2D.

Effects of chronodisruption and alcohol consumption on gene expression in reward-related brain areas in female rats.

Circadian dysfunction caused by exposure to aberrant light-dark conditions is associated with abnormal alcohol consumption in humans and animal models. Changes in drinking behavior have been linked to alterations in clock gene expression in reward-related brain areas, which could be attributed to either the effect of chronodisruption or alcohol. To date, however, the combinatory effect of circadian disruption and alcohol on brain functions is less understood. Moreover, despite known sex differences in alcohol drinking behavior, most research has been carried out on male subjects only, and therefore implications for females remain unclear. To address this gap, adult female rats housed under an 11 h/11 h light-dark cycle (LD22) or standard light conditions (LD24, 12 h/12 h light-dark) were given access to an intermittent alcohol drinking protocol (IA20%) to assess the impact on gene expression in brain areas implicated in alcohol consumption and reward: the prefrontal cortex (PFC), nucleus accumbens (NAc), and dorsal striatum (DS). mRNA expression of core clock genes (Bmal1, Clock, Per2), sex hormone receptors (ERβ, PR), glutamate receptors (mGluR5, GluN2B), a calcium-activated channel (Kcnn2), and an inflammatory cytokine (TNF-α) were measured at two-time points relative to the locomotor activity cycle. Housing under LD22 did not affect alcohol intake but significantly disrupted circadian activity rhythms and reduced locomotion. Significant changes in the expression of Bmal1, ERβ, and TNF-α were primarily related to the aberrant light conditions, whereas changes in Per2 and PR expression were associated with the effect of alcohol. Collectively, these results indicate that disruption of circadian rhythms and/or intermittent alcohol exposure have distinct effects on gene expression in the female brain, which may have implications for the regulation of alcohol drinking, addiction, and, ultimately, brain health.

Bilateral Correlational Behavior of Pyroglutamate Aminopeptidase I Activity in Rat Photoneuroendocrine Locations During a Standard 12:12 h Light–Dark Cycle

We previously described the circadian variation and bilateral distribution of pyroglutamate aminopeptidase I (pGluPI) activity levels in photoneuroendocrine locations of adult male rats during a standard 12:12 h light–dark cycle. However, the correlational analysis between such locations has not yet been studied. This may provide new data about the unilateral and bilateral functional interaction between photoneuroendocrine locations under light and dark conditions. We analyzed the correlations between locations of a photoneuroendocrine circuit consisting of retina, anterior hypothalamus, superior cervical ganglion, and pineal gland, as well as other related photoneuroendocrine locations: posterior hypothalamus, anterior pituitary, posterior pituitary, occipital cortex, and serum. In particular, we analyzed the correlations between the left retina or the right retina versus the rest of the locations, as well as the correlations between the left and right sides of paired structures at the different time points selected from 12 h light and 12 h dark periods. Also, the profiles of correlational results were compared with the corresponding mean levels. The results demonstrate the complexity of asymmetrical brain behavior. The correlation profile did not always parallel the profile observed with the mean activity values. The diurnal behavior of correlations with the left or right retina differed from one location to another. Likewise, the diurnal variation of correlations between the left and right sides of the paired structures differed between them. Particularly, while most correlations between the left versus right sides of paired structures showed positive values, that of the posterior hypothalamus showed a negative value at 13 h of light period. In addition, except the posterior hypothalamus, most paired locations only correlated significantly with right retina at 07 h of the light period. The results demonstrate the dynamic complexity of brain asymmetry, which represents a challenge for understanding its functional meaning.

Droplet-Based Microfluidic Photobioreactor as a Growth Optimization Tool for Cyanobacteria and Microalgae

Microalgae and cyanobacteria are photosynthetic microorganisms with significant biotechnological potential for the production of bioactive compounds, making them a promising resource for diverse industrial applications. This study presents the development and validation of a modular, droplet-based microfluidic photobioreactor (µPBR) designed for high-throughput screening and cultivation under controlled light conditions. The µPBR, based on polytetrafluoroethylene (PTFE) tubing and a 4-channel LED illumination system, enables precise modulation of light intensity, wavelength, and photoperiod, facilitating dose–response experiments. Synechococcus elongatus UTEX 2973 and Chlorella vulgaris were used to demonstrate the system’s capacity to support photosynthetic growth under various conditions. The results indicate that continuous illumination, particularly under blue and mixed blue-red light, promotes higher autofluorescence and chlorophyll a content in cyanobacteria Synechococcus elongatus UTEX2973, while Chlorella vulgaris achieved optimal growth under a 16:8 light-dark cycle with moderate light intensity. This µPBR offers not only a flexible, scalable platform for optimizing growth parameters but also allows for the investigation of highly resolved dose response screenings of environmental stressors such as salinity. The presented findings highlight its potential for advancing microalgal biotechnology research and applications.

1,8-Dihydroxynaphthalene (DHN) melanin provides unequal protection to black fungi Knufia petricola and Cryomyces antarcticus from UV-B radiation.

Black fungi on rock surfaces endure a spectrum of abiotic stresses, including UV radiation. Their ability to tolerate extreme conditions is attributed to the convergent evolution of adaptive traits, primarily highly melanized cell walls. However, studies on fungal melanins have not provided univocal results on their photoprotective functions. Here, we investigated whether the black fungi Knufia petricola and Cryomyces antarcticus only use DHN melanin or may employ alternative mechanisms to counteract UV-induced damage. For this, melanized wild types and non-melanized Δpks1 mutants were exposed to different doses of UV-B (312 nm) followed by incubation in constant darkness or in light-dark cycles to allow light-dependent DNA repair by photolyases (photoreactivation). C. antarcticus could tolerate higher UV-B doses but was sensitive to white light, whereas K. petricola showed the opposite trend. DHN melanin provided UV-B protection in C. antarcticus, whereas the same pigment or even carotenoids proved ineffective in K. petricola. Both fungi demonstrated functional photoreactivation in agreement with the presence of photolyase-encoding genes. Our findings reveal that although the adaptive trait of DHN melanization commonly occurs across black fungi, it is not equally functional and that there are species-specific adaptations towards either UV-induced lesion avoidance or repair strategies.

Circadian desynchrony in early life leads to enduring autistic-like behavioral changes in adulthood

Circadian rhythm regulates a variety of biological processes in almost all living organisms. Modern lifestyles, e.g. transmeridian travel, night shift, light at night, etc., frequently disrupt people’s regular sleep-wake cycles and create a misalignment (circadian desynchrony) between the natural environment and the endogenous body clock, and between different circadian oscillators within the body. The long-term consequences of circadian desynchrony on neurodevelopment and adult behavior remain elusive. Increasing clinical evidence supports a correlation between the disruption of the circadian system and neurodevelopmental disorders, such as autism spectrum disorders. Despite clinical correlations, experimental evidence is yet to establish a link between circadian disturbance in early life and adult behavioral changes. Here, using a “short day” (SD) mouse model, in which mice were exposed to an 8 h/8 h light/dark (LD) cycle mimicking a “shift work” schedule from gestation day 1 to postnatal day 21, we performed a battery of behavioral tests to assess changes in adult behaviors, including sociability, affective behaviors, stereotypy, cognition and locomotor functions. In contrast to the control mice kept in a 12 h/12 h LD cycle, the adult SD mice entrained to the 8 h/8 h LD cycle, but their free running rhythms remained normal in constant darkness. Interestingly, however, the SD mice displayed diminished sociability, a reduced preference for social novelty, excessive repetitive behaviors, and compromised cognitive functions, all of which resemble characteristics of autism-like behavioral alterations. In addition, the SD mice exhibited significant anxiety- and depressive-like behaviors and impaired motor functions. By western blotting and immunostaining analyses, hyperactivation of the mTORC1/S6K1 pathway was detected in multiple forebrain regions of SD mice. These findings underscore the enduring impact of early-life circadian disruption on neurochemical signaling and behavioral patterns into adulthood, highlighting a pivotal role for circadian regulation in neurodevelopment.

Two-Sex Life Table Analysis of Phenacoccus solenopsis (Hemiptera: Pseudococcidae) on Lettuce, Parsley, and Rocket

Phenacoccus solenopsis Tinsley (Hemiptera: Pseudococcidae), commonly known as the cotton mealybug, is a polyphagous pest causes significant economic losses worldwide. This study aimed to determine two-sex life table analysis of P. solenopsis on lettuce (Lactuca sativa), parsley (Petroselinum crispum), and rocket (Eruca sativa). Experiments were conducted under controlled conditions 26°C, 65 ± 10% relative humidity, and a 16:8 light-dark cycle. The results indicated that lettuce was more suitable for P. solenopsis development comparted to parsley and rocket. Total fecundity of P. solenopsis was recorded as 221.45, 158.00, and 121.64, on lettuce, parsley, and rocket respectively. In addition, ovipositon period of P. solenopsis was 14.00, 9.73, and 8.45 days on lettuce, parsley, and rocket respectively. The highest values of net reproductive rate (R0), intrinsic rate of increase (r), and finite rate of increase (λ) were obtained as 97.44 offspring female-1, 0.14 day-1, 1.16 day-1, respectively from lettuce in this present research. The results showed that lettuce was the better host plant for P. soleneopsis than parsley and rocket. However, further studies should be done about host plant pest interactions to provide successful control measures against P. solenopsis.

THE EFFECT OF NF-ΚB ON THE INTENSITY OF OXIDATIVE STRESS IN THE CEREBRAL CORTEX OF RATS UNDER THE COMBINED INFLUENCE OF THE LIGHT-DARK CYCLE, SYSTEMIC INFLAMMATORY RESPONSE, AND SODIUM GLUTAMATE ADMINISTRATION

To date, scientists have confirmed the link between the development of oxidative stress and disruptions in the light regime, as well as the systemic inflammatory response. The impact of monosodium glutamate on increasing oxidative damage to rat brain tissue has also been identified. The aim of this study was to investigate the role of the transcription factor NF-κB by examining the effect of its inhibitor, ammonium pyrrolidinedithiocarbamate, on the development of oxidative stress in the cerebral hemispheres of rats, in combination with acute desynchronosis, systemic inflammatory response, and monosodium glutamate administration. The study was conducted on 45 white Wistar rats weighing 150-200 g, divided into three groups: control (n=15), a group subjected to a combination of acute desynchronosis, systemic inflammatory response, and sodium glutamate administration (n=15), and a group exposed to the combination of acute desynchronosis, systemic inflammatory response, and received sodium glutamate and pyrrolidinedithiocarbamate (n=15). To induce acute desynchronosis, the rats were initially kept under a regular light-dark cycle (12 hours of light, 12 hours of darkness) for 3 weeks, followed by a shift in the light-dark phases by 6 hours back over the next 3 days. The systemic inflammatory response was modeled through intraperitoneal administration of Salmonella typhi lipopolysaccharide. During the first week, lipopolysaccharide was administered three times at a dose of 0.4 μg per 1 kg of body weight, and during the following seven weeks, it was given once a week. Sodium glutamate, at a dose of 30 mg/kg, dissolved in 0.5 ml of distilled water, was administered intragastrically for 20 days. The NF-kB activation inhibitor ammonium pyrrolidinedithiocarbamate (Sigma-Aldrich, Inc., USA) was administered at a dose of 76 mg/kg three times a week for 20 days. In a 10% homogenate of the cerebral hemispheres, the following were measured: the rate of superoxide anion radical production, the content of thiobarbituric acid-reactive substances (TBARS), the increase in these parameters, as well as the activity of catalase and superoxide dismutase. Administration of pyrrolidinedithiocarbamate in combination with acute desynchronosis, systemic inflammatory response, and sodium glutamate reduced the rate of basic superoxide anion radical production by 10%, NADPH-induced production by 17.6%, NADH-induced production by 13%, reduced the concentration and growth of TBC-active products by 6.6% and 14.6%, respectively, increased the activity of superoxide dismutase by 35.2%, catalase by 10.5% compared to the group exposed to the combination of acute desynchronosis, systemic inflammatory response, and sodium glutamate administration. Conclusion. The administration of pyrrolidinedithiocarbamate in combination with a systemic inflammatory response, acute desynchronosis and the action of sodium glutamate reduces the production of the superoxide anion radical, the concentration and increase in TBC-active products, enhances antioxidant protection that indicates the possible influence of the nuclear factor NF-κB on the development of oxidative processes in the cerebral hemispheres of rats.

The perspective of ceRNA regulation of circadian rhythm on choroidal neovascularization

Abnormal growth of blood vessels (choroidal neovascularization) can lead to age-related macular degeneration (AMD) and eventually cause vision loss due to detachment of the retinal pigmented epithelium. This indicates that choroidal neovascularization is important for the treatment of AMD. The circadian clock in the mammalian retina is responsible for controlling various functions of the retina, enabling it to adjust to changes in light and darkness. Recent studies have revealed a potential connection between the circadian clock and eye diseases, although a cause-and-effect relationship has not been definitively established. C57BL/6J male mice (aged 6 weeks) were randomly divided into two groups (Control group: 9:00–21:00 light period (300 lx); Jet lag group: 8-hour phase advance once every 4 days). A laser-induced CNV model was created after 2 weeks of feeding in a controlled or jet-lagged environment. Then, full transcriptome sequencing was performed. The pathways regulated by differentially expressed mRNAs were identified by GO analysis and GSEA. Further protein networks were constructed with the STRING database and Cytoscape software. WGCNA was used to further explore the co-expression modules of these differential genes and the correlation between these differential genes and phenotypes. ceRNA networks were constructed with miRanda and TargetScan. The pathways associated with the overlapping differentially expressed mRNAs in the ceRNA network were identified, and the hub genes were validated by qPCR. A total of 661 important DEGs, 31 differentially expressed miRNAs, 106 differentially expressed lncRNAs and 87 differentially expressed circRNAs were identified. GO and GSEA showed that the upregulated DEGs were mainly involved in reproductive structure development and reproductive system development. The STRING database and Cytoscape were used to determine the protein interaction relationships of these DEGs. WGCNA divided the expression of these genes into several modules and screened the hub genes of each module separately. Furthermore, a ceRNA network was constructed. GO analysis and GSEA showed that these target DEmRNAs mainly function in wound healing, cell spreading, epiboly involved in wound healing, epiboly, and morphogenesis of an epithelial sheet. Finally, ten key genes were identified, and their expression patterns were confirmed by real-time qPCR. In this study, we investigated the regulatory mechanism of ceRNAs in choroidal neovascularization according to different light-dark cycles in the eyeball.

Light–dark cycles improve the 3HV molar fraction in PHBV produced by photoheterotrophic bacteria from odd‐chain fatty acids and cheese whey

Light–dark cycles improve the <scp>3HV</scp> molar fraction in <scp>PHBV</scp> produced by photoheterotrophic bacteria from odd‐chain fatty acids and cheese whey

Light exposure induces phenotypic plasticity of the upside-down jellyfish Cassiopea sp. and its endosymbiotic dinoflagellates

The upside-down jellyfish, Cassiopea, is an increasingly popular model organism gaining prominence for both its endosymbiotic dinoflagellates from the family Symbiodiniaceae and its behavioral changes of bell pulsations associated with environmental cues. Pulsation provides a unique window into the host's response to environmental conditions, a typically difficult to access component of other symbiotic cnidarians. Pulsation has also been hypothesized to play a regulatory role on the endosymbiotic assemblage, but the magnitude of this regulatory effect is not well understood. Here, we used two light-acclimation experiments to help disentangle the complex phenotypic responses of the cnidarian host and its endosymbiotic dinoflagellates. The first experiment examined the phenotypic plasticity (size, behavior, color) of Cassiopea sp. in response to repeated ambient light acclimation trials to determine the rate and magnitude of phenotypic plasticity. The second experiment compared the acclimation response of jellyfish across three experimental groups to test whether a short acclimation time destabilized the host-endosymbiont relationship. Our goal was to identify covarying host-endosymbiont phenotypes to gain new insights into the dynamics of this relationship. We employed flow cytometric phenotypic profiling for high-throughput phenotypic characterization of endosymbiotic dinoflagellates in addition to pulse-amplitude modulated (PAM) fluorometry to characterize photosynthetic efficiency (Fv/Fm). Host phenotypes responded predictably to light-dark cycles and stabilized after nine to twelve days of exposure to consistent light conditions. However, disruption of this acclimation period affected the holobiont's phenotypic profile. We also found evidence that phenotypic responses of the host and endosymbionts were generally decoupled, indicating a stronger regulatory response of light conditions on phenotypes than possible host-regulatory strategies on the endosymbiotic assemblage. This study provides unique insights into the acclimation strategies of upside-down jellyfish, an emerging model for the study of cnidarian-dinoflagellate symbiosis.

Daily rhythms of locomotor activity and transcript levels of non-visual opsins in the brain of the blind Mexican cavefish (Astyanax mexicanus)

Most organisms possess endogenous circadian clocks that synchronise their physiology and behaviour with environmental cycles, with the light-dark (LD) cycle being the most potent synchronising signal. Consequently, it can be hypothesised that animals that have evolved in the dark, as in caves or deep sea, may no longer possess a functional light-entrained biological clock. In this research, the blind cavefish Astyanax mexicanus was selected as a model organism to investigate the potential effects of daily light conditions on the circadian timekeeping mechanisms. First, we focused on describing behavioural photic entrainment and the presence of a circadian endogenous rhythmicity by recording locomotor activity rhythms under different lighting regimes: LD 12:12, after a 6-h shift of LD, constant darkness (DD), and constant dim light (LLdim). Secondly, we aimed at characterising the mechanisms of photodetection by analysing the daily rhythms of expression of selected non-visual extraocular opsins (exo-rhod, opn3, rgra, rgrb, tmt1a and tmt1b) in the brain of this blind species using real-time quantitative PCR. Our results revealed that blind Mexican cavefish activity rhythms were entrained to the LD cycle, with a diurnal activity pattern that persisted in a circadian fashion under constant lighting conditions. Additionally, statistically significant daily variations and/or rhythms were observed in three out of the six non-visual opsin genes analysed (opn3, rgra and tmt1b), all of them displaying nocturnal acrophases. These findings suggest that daily rhythms in extraretinal non-visual opsins may be transducing daily photic cycles and contributing to the entrainment of locomotor activity and other light-synchronised rhythms in blind cavefish species.

Fresh insights into the light‐induced pineal gland circadian rhythm transmission mechanism derived from mRNA and miRNA profiling

AbstractThe circadian clock significantly impacts animal health and productivity, with light playing a crucial role in regulating circadian rhythms. However, the mechanisms behind light‐induced circadian transmission remain unclear, particularly in light‐sensitive avian species. The pineal gland is a key component acting as the photosensitive master oscillator in the avian clock system. Using transcriptome sequencing and small RNA sequencing technologies, we identified circadian genes and miRNAs in the chick pineal gland under light–dark and sudden constant‐light conditions. We observed rhythmic oscillations in up to 1299 genes during the light–dark cycle, with 400 genes maintaining rhythms under constant light. Our findings highlight the light‐sensitive temporal organization in birds as the phase distribution of circadian genes in the pineal gland correlates with light exposure changes. A novel regulatory mechanism involving light, cyclic adenosine monophosphate, cyclic guanosine monophosphate, light‐sensitive miRNAs, such as gga‐miR‐34b‐5p, and light‐sensitive circadian genes, such as CRY2, was discovered to participate in the light input system of the chick pineal clock, through which light regulates the oscillators and outputs of the circadian clock system. Additionally, transcriptomic analysis, liquid chromatography–mass spectrometry, and Oil Red O staining revealed cyclic changes in lipid synthesis and metabolism throughout the circadian day, which may be a key mechanism through which the circadian clock influences pineal physiology. Our results enhance the understanding of light‐induced circadian transmission mechanisms and identify potential targets for optimizing the circadian clock through light.

Chronic mistimed feeding results in renal fibrosis and disrupted circadian blood pressure rhythms.

Circadian disruption is a disturbance in biological timing, which can occur within or between different organizational levels, ranging from molecular rhythms within specific cells to the misalignment of behavioral and environmental cycles. Previous work from our group showed that less than 1 wk of food restriction to the light (inactive) period is sufficient to invert diurnal blood pressure rhythms in mice. However, kidney excretory rhythms and functions remained aligned with the light-dark cycle. Shift workers have an increased risk of cardiovascular disease that may different between sexes and often have irregular mealtimes, making the possibility of mistimed feeding as a potential contributor to the development of kidney disease. Thus, we hypothesized that chronic mistimed food intake would result in adverse cardiorenal effects, with sex differences in severity. Here, we show that chronic circadian disruption via mistimed feeding results in renal fibrosis and aortic stiffness in a sex-dependent manner. Our results indicate the importance of meal timing for the maintenance of blood pressure rhythms and kidney function, particularly in males. Our results also demonstrate that females are better able to acclimate to circadian-related behavioral change. NEW & NOTEWORTHY Circadian disruption through mistimed feeding resulted in nondipping blood pressure, renal fibrosis, and arterial stiffness that were less severe in females versus males. Mice fed exclusively during the daytime maintain their circadian rhythms of locomotor activity regardless of their loss of blood pressure rhythms. Although these mice ate less food, they maintained body weight, suggesting inefficiencies in overall metabolism. These findings demonstrate the importance of maintaining optimal food intake patterns to prevent cardiorenal pathophysiology.

An Arabidopsis Cell Culture With Weak Circadian Rhythms Under Constant Light Compared With Constant Dark Can Be Rescued by ELF3.

Callus and cell suspension culture techniques are valuable tools in plant biotechnology and are widely used in fundamental and applied research. For studies in callus and cell suspension cultures to be relevant, it is essential to know if the underlying biochemistry is similar to intact plants. This study examined the expression of core circadian genes in Arabidopsis callus from the cell suspension named AT2 and found that the circadian rhythms were impaired. The circadian waveforms were like intact plants in the light/dark cycles, but the circadian expression in the AT2 callus became weaker in the free-running, constant light conditions. Temperature cycles could drive the rhythmic expression in constant conditions, but there were novel peaks at the point of temperature transitions unique to each clock gene. We found that callus freshly induced from seedlings had normal oscillations, like intact plants, suggesting that the loss of the circadian oscillation in the AT2 callus was specific to this callus. We determined that neither the media composition nor the source of the AT2 callus caused this disruption. We observed that ELF3 expression was not differentially expressed between dawn and dusk in both entrained, light-dark cycles and constant light conditions. Overexpression of AtELF3 in the AT2 callus partially recovers the circadian oscillation in the AT2 callus. This work shows that while callus and cell suspension cultures can be valuable tools for investigating plant responses, careful evaluation of their phenotype is important. Moreover, the altered circadian rhythms under constant light and temperature cycles in the AT2 callus could be useful backgrounds to understand the connections driving circadian oscillators and light and temperature sensing at the cellular level.

Histomorphometric changes in pituitary gonadotropic endocrinocytes when exposed to dark deprivation

Aim. To assess the effect of 30-day dark deprivation on functional and histomorphometric changes in adenohypophysis gonadotropic endocrinocytes and their reversibility in mature male rats.Materials and methods. Mongrel white male rats (n = 36) weighing 365–375 g at 4 months of age were randomly divided into three groups (each n = 12). For 30 days the control group was in automatic light-dark mode 12/12, and the rats of experimental groups 1 and 2 were in round-the-clock artificial lighting (24/0, 300 Lux), then the rats of group 2 were returned to 12/12 mode for the next 14 days. In the animals of the control and group 1 during their lifetime on the 31st day, and in group 2 on the 45th day, blood was taken from the abdominal aorta and levels of follicle-stimulating (FSH) and luteinizing (LH) hormones, melatonin, and Klotho protein were determined an enzyme-linked immunosorbent assay and immunoassay and after which they were removed from the experiment by decapitation. Postmortem histological and immunohistochemical examination of the pituitary gland was done using rabbit polyclonal antibodies targeting caspase-3 and Klotho protein, as well as morphometry. Statistical data processing was performed using the Kruskal-Wallis test with post-hoc Dunn’s test.Results. Light desynchronization in the form of 30 days of dark deprivation increased FSH and LH levels and decreased melatonin and Klotho protein levels in the blood of male rats; increased gonadotropic endocrine cell area, volume, and perimeter by 23.1% (p &lt; 0.001), 48.7% (p &lt; 0.001), and 10.9% (p &lt; 0.001), respectively; and increased nucleus area, volume, and perimeter by 16%, 11.7%, and 2.5%, respectively. An immunohistochemical study showed an increase in the specific area of caspase-3-immunoreactive gonadotropic endocrinocytes by 25.2% without obvious morphological signs of apoptosis, and a decrease in the expression of Klotho protein by 25.7%. All indicators were reversible, the levels of FSH and Klotho protein in the blood of animals almost reached their initial values after 14 days of restoration of the light-dark cycle 12/12.Conclusion. Dark deprivation for 30 days in male rats induced reversible processes of accelerated aging and apoptosis in cells, as evidenced by changes in the expression of aging markers in gonadotropic endocrinocytes and levels of gonadotropic hormones in the blood. When the light-dark mode is restored, the levels of FSH and Klotho protein normalize as early as 14 days.