Differential circadian and light-driven rhythmicity of clock gene expression and behaviour in the turbot, Scophthalmus maximus

Integration of photoperiod and time-restricted feeding on the circadian gene rhythms in juvenile salmon

The circadian clock has evolved to synchronize animal behaviour and physiology with the external environment. Present in almost all cells, the clock is made up of a transcription-translation feedback loop that is responsive to cues such as light/dark cycles (photoperiod) and the time of feeding. Chinook salmon (Oncorhynchus tshawytscha) is a fish species whose clock is thought to be adapted in natural populations according to their latitude, where photoperiod variation can be extreme in northern spring/summer conditions. Here, we probed for the expression of circadian clock genes in four tissues of juvenile Chinook salmon under different environmental conditions. We find that the circadian clock is optimal when photoperiod is coupled with regular feeding during daylight hours. We further tested the effects of constant light and time-restricted feeding, environmental factors that are known to affect daily gene expression rhythms, on the expression of clock genes, appetite-regulating hormones, and metabolic regulators in the intestine of juvenile Chinook. We find that overall constant light is chrono-disruptive irrespective of the timing of food. The resulting disruption in gene expression produces aberrant rhythms, and affects glucose homeostasis, despite an increase in growth. Our data suggests photoperiod and time-restricted feeding could be optimized in Chinook aquaculture and raise the question of whether and how photoperiod changes are compensated in northern-adapted populations.

Clock Gene Expression in Eel Retina and Hypothalamus: Response to Photoperiod and Moonlight

Assessment of the clock genes, Period (Per) 1, Per2, Per3, and Cryptochrome (Cry) 2, Cry3, and Cry4, can help better understand eel spawning ecology. In this study, the circadian rhythm and moonlight effects of these clock genes in the eel retina and hypothalamus were analyzed. We examined clock gene expression patterns under 12 h light:12 h darkness (12L12D), constant darkness (DD), and constant light (LL) conditions; under short photoperiod (SP; 9L15D) and long photoperiod (LP; 15L9D), and during the new moon (NM) and full moon in male eels. Per2 expression increased after sunrise, Cry2, and Cry4 expression increased around sunset, and Per1, Per3, and Cry3 expression increased before sunrise. Under SP conditions, oscillations of retinal Per3 and Cry4, which did not occur under LP conditions, were generated. In addition, retinal Cry4 oscillation was generated under NM conditions. These results suggest that the retina of the eel may play an important role in regulating circadian rhythm, and migration is initiated by the synchronization of clock genes by moonlight, suggesting that photic signals are closely related to the migratory activity of the eel.

Circadian rhythm in turbot (Scophthalmus maximus): daily variation of blood metabolites in recirculating aquaculture systems

INTRODUCTION

Animal welfare in aquaculture is becoming increasingly important, and detailed knowledge of the species concerned is essential for further optimization on farms. Every organism is controlled by an internal clock, the circadian rhythm, which is crucial for metabolic processes and is partially influenced by abiotic factors, making it important for aquaculture practices.

OBJECTIVE

In order to determine the circadian rhythm of adult turbot (Scophthalmus maximus), blood samples were collected over a 24-h period and plasma metabolite profiles were analyzed by 1H-NMR spectroscopy.

METHODS

The fish were habituated to feeding times at 9 am and 3 pm and with the NMR spectroscopy 46 metabolites could be identified, eight of which appeared to shift throughout the day.

RESULTS

We noted exceptionally high values around 3 pm for the amino acids isoleucine, leucine, valine, phenylalanine, lysine, and the stress indicator lactate. These metabolic peaks were interpreted as either habituation to the usual feeding time or as natural peak levels in turbot in a 24-h circle because other indicators for stress (glucose, cortisol and lysozymes) showed a stable baseline, indicating that the animals had no or very little stress during the experimental period.

CONCLUSION

This study provides initial insights into the diurnal variation of metabolites in adult turbot; however, further studies are needed to confirm present findings of possible fluctuations in amino acids and sugars. Implementing optimized feeding times (with high levels of sugars and low levels of stress metabolites) could lead to less stress, fewer disease outbreaks and overall improved fish welfare in aquaculture facilities.

Cloning, tissue distribution, and effects of different circadian rhythms on the mRNA expression levels of circadian clock genes Per1a and Per1b in Phoxinus lagowskii

This study describes the cloning and characterization of Period 1a and Period 1b genes and the analysis of their mRNA and protein expression in Amur minnow (Phoxinus lagowskii) after exposure to different light cycles. The full-length P. lagowskii Per1a and Per1b genes encode proteins consisting of 1393 and 1409 amino acids, and share high homology with the per1 genes of other freshwater fish species. The Per1a and Per1b genes were widely expressed within the brain, eye, and peripheral tissues. The acrophase of the Per1a gene in the pituitary gland occurred during the dark phase at ZT15 (zeitgeber time 15, 12 L: 12 D) and ZT18 (8 L, 16 D), whereas the acrophase of the Per1b gene in the pituitary gland was observed during the light phase. Our study suggests that the expression of Per1a and Per1b in P. lagowskii varied depending on differences in circadian rhythm patterns. The results of our dual-luciferase reporter assays demonstrated that the P. lagowskii Per1b gene enhances the activation of NF-κB. This study is the first to examine the circadian clock gene Per1a and Per1b in the high-latitude fish P. lagowskii, offering valuable insights into the effects of different light periods on this fish species.

Time of the day of exercise impact on cardiovascular disease risk factors in adults: a systematic review and meta-analysis

OBJECTIVES

To compare the effect of a single bout of morning vs. evening exercise on cardiovascular risk factors in adults.

DESIGN

Systematic review and meta-analysis.

METHODS

A systematic search of studies was conducted using PubMed and Web of Science from inception to June 2022. Selected studies accomplished the following criteria: crossover design, acute effect of exercise, blood pressure, blood glucose, and/or blood lipids as the study's endpoint, a washout period of at least 24 h, and adults. Meta-analysis was performed by analyzing: 1) separated effect of morning and evening exercise (pre vs. post); and 2) comparison between morning and evening exercise.

RESULTS

A total of 11 studies were included for systolic and diastolic blood pressure and 10 studies for blood glucose. Meta-analysis revealed no significant difference between morning vs. evening exercise for systolic blood pressure (g ∆ = 0.02), diastolic blood pressure (g ∆ = 0.01), or blood glucose (g ∆ = 0.15). Analysis of moderator variables (age, BMI, sex, health status, intensity and duration of exercise, and hour within the morning or evening) showed no significant morning vs. evening effect.

CONCLUSIONS

Overall, we found no influence of the time of the day on the acute effect of exercise on blood pressure neither on blood glucose.

Non-synonymous variation and protein structure of candidate genes associated with selection in farm and wild populations of turbot (Scophthalmus maximus)

Non-synonymous variation (NSV) of protein coding genes represents raw material for selection to improve adaptation to the diverse environmental scenarios in wild and livestock populations. Many aquatic species face variations in temperature, salinity and biological factors throughout their distribution range that is reflected by the presence of allelic clines or local adaptation. The turbot (Scophthalmus maximus) is a flatfish of great commercial value with a flourishing aquaculture which has promoted the development of genomic resources. In this study, we developed the first atlas of NSVs in the turbot genome by resequencing 10 individuals from Northeast Atlantic Ocean. More than 50,000 NSVs where detected in the ~ 21,500 coding genes of the turbot genome, and we selected 18 NSVs to be genotyped using a single Mass ARRAY multiplex on 13 wild populations and three turbot farms. We detected signals of divergent selection on several genes related to growth, circadian rhythms, osmoregulation and oxygen binding in the different scenarios evaluated. Furthermore, we explored the impact of NSVs identified on the 3D structure and functional relationship of the correspondent proteins. In summary, our study provides a strategy to identify NSVs in species with consistently annotated and assembled genomes to ascertain their role in adaptation.

Shedding light on the circadian clock of the threespine stickleback

The circadian clock is an internal timekeeping system shared by most organisms, and knowledge about its functional importance and evolution in natural environments is still needed. Here, we investigated the circadian clock of wild-caught threespine sticklebacks (Gasterosteus aculeatus) at the behavioural and molecular levels. Although their behaviour, ecology and evolution are well studied, information on their circadian rhythms are scarce. We quantified the daily locomotor activity rhythm under a light:dark cycle (LD) and under constant darkness (DD). Under LD, all fish exhibited significant daily rhythmicity, while under DD, only 18% of individuals remained rhythmic. This interindividual variation suggests that the circadian clock controls activity only in certain individuals. Moreover, under LD, some fish were almost exclusively nocturnal, while others were active around the clock. Furthermore, the most nocturnal fish were also the least active. These results suggest that light masks activity (i.e. suppresses activity without entraining the internal clock) more strongly in some individuals than others. Finally, we quantified the expression of five clock genes in the brain of sticklebacks under DD using qPCR. We did not detect circadian rhythmicity, which could indicate either that the clock molecular oscillator is highly light-dependent, or that there was an oscillation but that we were unable to detect it. Overall, our study suggests that a strong circadian control on behavioural rhythms may not necessarily be advantageous in a natural population of sticklebacks and that the daily phase of activity varies greatly between individuals because of a differential masking effect of light.

Feeding regimes affected the circadian rhythms of pancreatic digestive enzymes and somatic growth in flathead grey mullet (Mugil cephalus) fry

The effect of different feeding regimes on the circadian rhythms of pancreatic digestive enzyme activities was evaluated in Mugil cephalus fry weighting 0.34 ± 0.01 g. Feeding regimes (feeding ration = 3% stocked biomass) differed on the number of meals offered per day: one, two and ten meals per day (R1, R2 and R3, respectively). The number of meals per day affected somatic growth; in particular, fry from the R3 group (0.80 ± 0.01 g) grew better than their congeners from R2 (0.70 ± 0.01 g) and R1 (0.63 ± 0.01 g) groups (P < 0.05). Feeding behaviour was modulated by the feeding regime, being the maximal gut fullness values found just after meal distribution in R1 and R2 groups, whereas this trend was not observed when feed was offered continuously during light hours (R3). Fry from R1 and R2 groups showed hyperphagia as they tended to store in their gut as much as possible feed particles to be later digested due to the limited daily meals. This strategy negatively affected feed digestion due to inappropriate enzyme to substrate ratio, changes in digestive enzyme activities and chyme transit times, which ultimately impaired growth performance. Enzyme activities were modulated by the number of meals, the more frequent the meals offered, the lower enzyme activities, supporting the hypothesis that digestive function is adapted to obtain a maximum benefit of the ingested nutrients. Present results showed that feeding grey mullet fry continuously during day light hours optimized feed digestion and promoted fry growth.

The Lack of Light-Dark and Feeding-Fasting Cycles Alters Temporal Events in the Goldfish (Carassius auratus) Stress Axis

Vertebrates possess circadian clocks, driven by transcriptional-translational loops of clock genes, to orchestrate anticipatory physiological adaptations to cyclic environmental changes. This work aims to investigate how the absence of a light-dark cycle and a feeding schedule impacts the oscillators in the hypothalamus-pituitary-interrenal axis of goldfish. Fish were maintained under 12L:12D feeding at ZT 2; 12L:12D feeding at random times; and constant darkness feeding at ZT 2. After 30 days, fish were sampled to measure daily variations in plasma cortisol and clock gene expression in the hypothalamus-pituitary-interrenal (HPI) axis. Clock gene rhythms in the HPI were synchronic in the presence of a light-dark cycle but were lost in its absence, while in randomly fed fish, only the interrenal clock was disrupted. The highest cortisol levels were found in the randomly fed group, suggesting that uncertainty of food availability could be as stressful as the absence of a light-dark cycle. Cortisol daily rhythms seem to depend on central clocks, as a disruption in the adrenal clock did not impede rhythmic cortisol release, although it could sensitize the tissue to stress.