Structural and Functional Evolution of the Pineal Melatonin System in Vertebrates

Adaptive Evolution of the Greater Horseshoe Bat AANAT: Insights into the Link between AANAT and Hibernation Rhythms

Arylalkylamine N-acetyltransferase (AANAT) is a crucial rate-limiting enzyme in the synthesis of melatonin. AANAT has been confirmed to be independently duplicated and inactivated in different animal taxa in order to adapt to the environment. However, the evolutionary forces associated with having a single copy of AANAT remain unclear. The greater horseshoe bat has a single copy of AANAT but exhibits different hibernation rhythms in various populations. We analyzed the adaptive evolution at the gene and protein levels of AANAT from three distinct genetic lineages in China: northeast (NE), central east (CE), and southwest (SW). The results revealed greater genetic diversity in the AANAT loci of the NE and CE lineage populations that have longer hibernation times, and there were two positive selection loci. The catalytic capacity of AANAT in the Liaoning population that underwent positive selection was significantly higher than that of the Yunnan population (p < 0.05). This difference may be related to the lower proportion of α helix and the variation in two interface residues. The adaptive evolution of AANAT was significantly correlated with climate and environment (p < 0.05). After controlling for geographical factors (latitude and altitude), the evolution of AANAT by the negative temperature factor was represented by the monthly mean temperature (r = -0.6, p < 0.05). The results identified the gene level variation, functional adaptation, and evolutionary driving factors of AANAT, provide an important foundation for further understanding the adaptive evolution of the single copy of AANAT in pteropods, and may offer evidence for adaptive hibernation rhythms in bats.

Effects of dopamine and melatonin treatment on the expression of the genes associated with artificially induced sexual maturation in Japanese eel, Anguilla japonica

Japanese eel (Anguilla japonica) is a commercially important fish species in Asia. Understanding factors like photoperiod, temperature, and lunar cycles is crucial for successful aquaculture and managing its reproduction. Melatonin and dopamine (DA) are essential for regulating reproduction in vertebrates, including fish. This study investigated the effects of melatonin and DA on the reproductive system of mature male Japanese eels to better understand reproductive regulation in fish. To clarify the effects of these hormones on sexual maturation in eels, a critical stage in the reproductive process, sexual maturation was induced by injecting human chorionic gonadotropin, which stimulates the production of sex hormones. To check the effect of melatonin and DA on sexual maturation, DA, melatonin, and DA + domperidone were intraperitoneally injected into fish from each group (six per treatment) at a dose of 1 mg/kg body weight. The fish were then examined using quantitative RT-PCR by comparing the messenger RNA level of reproduction-related genes (gonadotropin releasing hormone 1; gnrh1, gonadotropin releasing hormone 2; gnrh2, follicle stimulating hormone; fshβ, luteinizing hormone; lhβ and DA receptor 2b; d2b), involved in the gonadotropic axis in eels, to those that received a control injection. The results indicate significant differences in the expression levels of gnrh1, gnrh2 and d2b in the brain and d2b, fshβ, lhβ in the pituitary at different stages of sexual maturation. Melatonin appears to enhance the production of sex gonadotropins, whereas DA inhibits them. These findings suggest an interaction between melatonin and DA in regulating reproduction in Japanese eels.

Recent Advances in Nanomaterials Based Optical Sensors for the Detection of Melatonin and Serotonin

In this review paper we discussed the detection of melatonin and serotonin by using various optical methods. Melatonin and serotonin are very necessary body hormones these are also called neuroregulatory hormones secreted by pineal gland in brain by pinealocytes and shape of pineal gland is cone like. Sensitive detection of melatonin and serotonin in pharmacological samples and human serum is crucial for human beings, lots of research publications available in literature for melatonin and serotonin and we overviewed these papers. We have deeply reviewed many research papers where sensitively sensing of melatonin and serotonin occurs, by using of various interfering agents and nanomaterials. This review aims presenting colorimetry, fluorometry and spectrophotometric detection of melatonin (MEL) and serotonin (SER) by using different metal oxides, carbon nanomaterials (nanosheets, nanorods, nanofibers) and many other agents. Nanomaterials typically possess favourable optical, electrical and mechanical characteristics, they provide up new avenues for enhancing the efficacy of sensors. It is crucial to provide an optical sensors platform that is dependable, sensitive and low price. The development of sensors and biosensors to use nanomaterials for neurotransmitters has advanced significantly in recent years. There are currently many developing biomarkers in biological fluids, and bionanomaterial-based biosensor systems, as well as clinical and pharmacological settings, have garnered significant interest. Biomarkers have been found using optical devices in a quick, selective and sensitive manner. Our aim is to compile all the data that already published on MEL, SER sensing and comparison of each method, we mainly focused on principle, observations, sensitivity, selectivity, limit of detection, mechanism behind the reaction, effect of temperature, pH and concentration. In the last of this paper, we discuss some challenges of these methods and future projects.

Circadian patterns and photoperiodic modulation of clock gene expression and neuroendocrine hormone secretion in the marine teleost Larimichthys crocea

The light/dark cycle, known as the photoperiod, plays a crucial role in influencing various physiological activities in fish, such as growth, feeding and reproduction. However, the underlying mechanisms of this influence are not fully understood. This study focuses on exploring the impact of different light regimes (LD: 12 h of light and 12 h of darkness; LL: 24 h of light and 0 h of darkness; DD: 0 h of light and 24 h of darkness) on the expression of clock genes (LcClocka, LcClockb, LcBmal, LcPer1, LcPer2) and the secretion of hormones (melatonin, GnRH, NPY) in the large yellow croaker, Larimichthys crocea. Real-time quantitative PCR (RT-qPCR) and enzyme-linked immunosorbent assays were utilized to assess how photoperiod variations affect clock gene expression and hormone secretion. The results indicate that changes in photoperiod can disrupt the rhythmic patterns of clock genes, leading to phase shifts and decreased expression. Particularly under LL conditions, the pineal LcClocka, LcBmal and LcPer1 genes lose their rhythmicity, while LcClockb and LcPer2 genes exhibit phase shifts, highlighting the importance of dark phase entrainment for maintaining rhythmicity. Additionally, altered photoperiod affects the neuroendocrine system of L. crocea. In comparison to the LD condition, LL and DD treatments showed a phase delay of GnRH secretion and an acceleration of NPY synthesis. These findings provide valuable insights into the regulatory patterns of circadian rhythms in fish and may contribute to optimizing the light environment in the L. crocea farming industry.

Cross-species single-cell landscape of vertebrate pineal gland

The pineal gland has evolved from a photoreceptive organ in fish to a neuroendocrine organ in mammals. This study integrated multiple daytime single-cell RNA-seq datasets from the pineal glands of zebrafish, rats, and monkeys, providing a detailed examination of the evolutionary transition at single-cell resolution. We identified key factors responsible for the anatomical and functional transformation of the pineal gland. We retrieved and integrated daytime single-cell transcriptomic datasets from the pineal glands of zebrafish, rats, and monkeys, resulting in a total of 22 431 cells after rigorous quality filtering. Comparative analysis was then conducted to elucidate the evolution of pineal cells, their photosensitivity, their role in melatonin production, and the signaling processes within the glands of these species. Our analysis identified distinct cellular compositions of the pineal gland in zebrafish, rats, and monkeys. Zebrafish photoreceptors exhibited comprehensive phototransduction gene expression, while specific genes, including transducin (Gngt1, Gnb3, and Gngt2) and phosducin (Pdc), were consistently present in mammalian pinealocytes. We found transcriptional similarities between the pineal gland and retina, underscoring shared evolutionary and functional pathways. Zebrafish displayed unique light-responsive circadian gene activity compared to rats and monkeys. Key ligand-receptor interactions were identified, especially involving MDK and PTN, influencing melatonin synthesis across species. Furthermore, we observed species-specific GPCR (G protein-coupled receptors) expressions related to melatonin synthesis and their alignment with retinal expressions. Our findings also highlighted specific transcription factors (TFs) and regulatory networks associated with pineal gland evolution and function. Our study provides a detailed analysis of the pineal gland's evolution from fish to mammals. We identified key transcriptional changes and controls that highlight the gland's functional diversity. Notably, we found significant ligand-receptor interactions influencing melatonin synthesis and demonstrated parallels between pineal and retinal expressions. These insights enhance our understanding of the pineal gland's role in phototransduction, melatonin production, and circadian rhythms in vertebrates.

Role of melanocortin system in the locomotor activity rhythms and melatonin secretion as revealed by agouti-signalling protein (asip1) overexpression in zebrafish

Temporal signals such as light and temperature cycles profoundly modulate animal physiology and behaviour. Via endogenous timing mechanisms which are regulated by these signals, organisms can anticipate cyclic environmental changes and thereby enhance their fitness. The pineal gland in fish, through the secretion of melatonin, appears to play a critical role in the circadian system, most likely acting as an element of the circadian clock system. An important output of this circadian clock is the locomotor activity circadian rhythm which is adapted to the photoperiod and thus determines whether animals are diurnal or nocturnal. By using a genetically modified zebrafish strain known as Tg (Xla.Eef1a1:Cau.asip1)iim04, which expresses a higher level of the agouti signalling protein 1 (Asip1), an endogenous antagonist of the melanocortin system, we observed a complete disruption of locomotor activity patterns, which correlates with the ablation of the melatonin daily rhythm. Consistent with this, in vitro experiments also demonstrated that Asip1 inhibits melatonin secretion from the zebrafish pineal gland, most likely through the melanocortin receptors expressed in this gland. Asip1 overexpression also disrupted the expression of core clock genes, including per1a and clock1a, thus blunting circadian oscillation. Collectively, these results implicate the melanocortin system as playing an important role in modulating pineal physiology and, therefore, circadian organisation in zebrafish.

Age-related changes in the gut melatonin levels and its possible role in the regulation of feeding and digestibility, with the development of the gut from fingerling to adult stages of carp, Catla catla

The present study aims to understand the feeding-related age-bound changes in gut histoarchitecture and its response to gut melatonin (GM) titer regulating major digestive enzymes in carp, Catla catla. Therefore, gut samples were collected from different growth stages of carp, viz. (i) fingerling (FL), body weight (BW) ≥ 3 g to ≤ 20 g; (ii) advanced fingerling (AFL), BW > 20 g to ≤ 40 g; (iii) early juvenile (EJv), BW > 40 g to ≤ 70 g; (iv) juvenile (Jv), BW > 70 g to ≤ 200 g; (v) late juvenile (LJv), BW > 200 g to ≤ 300 g; (vi) preadult (PA), BW > 300 g to ≤ 500 g; (vii) subadult (SA), BW > 500 g to ≤ 1.00 kg; and (viii) adult (AD), BW > 1 kg to ≤ 2.5 kg. Data analysis revealed that the highest titer of GM was noted in FL, moderate in AFL, Jv, and PA, lower in EJv, SA, and AD, and lowest in LJv. Results depicted a negative correlation between the development of the gut and its melatonin content. Moreover, GM was positively associated with feeding intensity and gastro-somatic index (GaSI) and negatively related to ovarian onset and development. Following correlation and principal component analysis, several pieces of evidence were recorded on the role of gut melatonin in regulating digestive physiology. Finally, it indicates that gut melatonin has a progressively influential role in improving digestion, particularly protein and microbial digestion, with the development of an adult gut from the fingerling stage.

Biosynthesis of neuroprotective melatonin is dysregulated in Huntington's disease

Huntington's disease (HD) is a progressive neurodegenerative brain disorder associated with uncontrolled body movements, cognitive decline, and reduced circulating melatonin levels. Melatonin is a potent antioxidant and exogenous melatonin treatment is neuroprotective in experimental HD models. In neurons, melatonin is exclusively synthesized in the mitochondrial matrix. Thus, we investigated the integrity of melatonin biosynthesis pathways in pineal and extrapineal brain areas in human HD brain samples, in the R6/2 mouse model of HD and in full-length mutant huntingtin knock-in cells. Aralkylamine N-acetyltransferase (AANAT) is the rate-limiting step enzyme in the melatonin biosynthetic pathway. We found that AANAT expression is significantly decreased in the pineal gland and the striatum of HD patients compared to normal controls. In the R6/2 mouse forebrain, AANAT protein expression was decreased in synaptosomal, but not nonsynaptosomal, mitochondria and was associated with decreased synaptosomal melatonin levels compared to wild type mice. We also demonstrate sequestration of AANAT in mutant-huntingtin protein aggregates likely resulting in decreased AANAT bioavailability. Paradoxically, AANAT mRNA expression is increased in tissues where AANAT protein expression is decreased, suggesting a potential feedback loop that is, ultimately unsuccessful. In conclusion, we demonstrate that pineal, extrapineal, and synaptosomal melatonin levels are compromised in the brains of HD patients and R6/2 mice due, at least in part, to protein aggregation.

Indispensable role of melatonin, a scavenger of reactive oxygen species (ROS), in the protective effect of Akkermansia muciniphila in cadmium-induced intestinal mucosal damage

The gastrointestinal tract is the main target of cadmium toxicity. However, whether Akkermansia muciniphila (A. muciniphila), which has been reported to be the next generation of promising probiotics, can alleviate cadmium-induced intestinal damage has not been investigated. In this study, we found that compared to the cadmium exposure group, mice gavaged with A. muciniphila showed less severe intestinal mucosal damage, with improved bodyweight, colon length, a decline in inflammation, and significantly increased glutathione and goblet cell numbers. Meanwhile, melatonin was interestingly found to be strikingly increased after A. muciniphila treatment. We then demonstrated that melatonin also could ameliorate the intestinal mucosal damage caused by cadmium through scavenging reactive oxygen species (ROS) and increasing the number of goblet cells. Furthermore, mice treated with inhibitors had a low level of melatonin and could not reproduce the beneficial effects of the A. muciniphila. Our results implied that the regulation of melatonin production by A. muciniphila is associated with an increase in enterochromaffin cells number, which determine melatonin secretion. This study indicated that the A. muciniphila-melatonin axis reduces cadmium-induced damage by increasing the goblet cells and scavenging the ROS, which may guide the prevention of the toxic effects of heavy metals.

Microglia in Circumventricular Organs: The Pineal Gland Example

The circumventricular organs (CVOs) are unique areas within the central nervous system. They serve as a portal for the rest of the body and, as such, lack a blood-brain barrier. Microglia are the primary resident immune cells of the brain parenchyma. Within the CVOs, microglial cells find themselves continuously challenged and stimulated by local and systemic stimuli, even under steady-state conditions. Therefore, CVO microglia in their typical state often resemble the activated microglial forms found elsewhere in the brain as they are responding to pathological conditions or other stressors. In this review, I focus on the dynamics of CVO microglia, using the pineal gland as a specific CVO example. Data related to microglia heterogeneity in both homeostatic and unhealthy environments are presented and discussed, including those recently generated by using advanced single-cell and single-nucleus technology. Finally, perspectives in the CVO microglia field are also included.Summary StatementMicroglia in circumventricular organs (CVOs) continuously adapt to react differentially to the diverse challenges they face. Herein, I discuss microglia heterogeneity in CVOs, including pineal gland. Further studies are needed to better understand microglia dynamics in these unique brain areas. .

Harbours as unique environmental sites of multiple anthropogenic stressors on fish hormonal systems

Fish development and acclimation to environmental conditions are strongly mediated by the hormonal endocrine system. In environments contaminated by anthropogenic stressors, hormonal pathway alterations can be detrimental for growth, survival, fitness, and at a larger scale for population maintenance. In the context of increasingly contaminated marine environments worldwide, numerous laboratory studies have confirmed the effect of one or a combination of pollutants on fish hormonal systems. However, this has not been confirmed in situ. In this review, we explore the body of knowledge related to the influence of anthropogenic stressors disrupting fish endocrine systems, recent advances (focusing on thyroid hormones and stress hormones such as cortisol), and potential research perspectives. Through this review, we highlight how harbours can be used as "in situ laboratories" given the variety of anthropogenic stressors (such as plastic, chemical, sound, light pollution, and invasive species) that can be simultaneously investigated in harbours over long periods of time.

Morphological study of the pineal gland of Alouatta belzebul

ABSTRACT The pineal is a neuroendocrine gland responsible for the synthesis and release of melatonin. It is present in the brain of vertebrates, but its morphology and location vary considerably among species. For the species Alouatta belzebul, although some anatomical aspects of the nervous system have been described, there is no information on the morphology and histological composition of this gland. Thus, the present study aimed to describe the morphological, morphometric, and histological aspects of the pineal of Alouatta belzebul. Seven adult specimens were dissected from which the location of the gland in relation to the surrounding brain structures was described, and its length and width were measured. Histological slides were then prepared and stained using hematoxylin-eosin and PAS techniques. It was observed that the pineal of Alouatta belzebul is located superior and cranial to the cerebellum, superior to the superior colliculi and below the splenium of the corpus callosum and was classified as sub-callosal. It had an average length of 2.6mm and an average width of 1.14mm. Histologically the gland is composed of irregular strands of pinealocytes and gliocytes. The pinealocytes showed pigments similar to melanin.

A Zebrafish Model for a Rare Genetic Disease Reveals a Conserved Role for FBXL3 in the Circadian Clock System

The circadian clock, which drives a wide range of bodily rhythms in synchrony with the day–night cycle, is based on a molecular oscillator that ticks with a period of approximately 24 h. Timed proteasomal degradation of clock components is central to the fine-tuning of the oscillator’s period. FBXL3 is a protein that functions as a substrate-recognition factor in the E3 ubiquitin ligase complex, and was originally shown in mice to mediate degradation of CRY proteins and thus contribute to the mammalian circadian clock mechanism. By exome sequencing, we have identified a FBXL3 mutation in patients with syndromic developmental delay accompanied by morphological abnormalities and intellectual disability, albeit with a normal sleep pattern. We have investigated the function of FBXL3 in the zebrafish, an excellent model to study both vertebrate development and circadian clock function and, like humans, a diurnal species. Loss of fbxl3a function in zebrafish led to disruption of circadian rhythms of promoter activity and mRNA expression as well as locomotor activity and sleep–wake cycles. However, unlike humans, no morphological effects were evident. These findings point to an evolutionary conserved role for FBXL3 in the circadian clock system across vertebrates and to the acquisition of developmental roles in humans.

Type II Opsins in the Eye, the Pineal Complex and the Skin of Xenopus laevis: Using Changes in Skin Pigmentation as a Readout of Visual and Circadian Activity

The eye, the pineal complex and the skin are important photosensitive organs. The African clawed frog, Xenopus laevis, senses light from the environment and adjusts skin color accordingly. For example, light reflected from the surface induces camouflage through background adaptation while light from above produces circadian variation in skin pigmentation. During embryogenesis, background adaptation, and circadian skin variation are segregated responses regulated by the secretion of α-melanocyte-stimulating hormone (α-MSH) and melatonin through the photosensitivity of the eye and pineal complex, respectively. Changes in the color of skin pigmentation have been used as a readout of biochemical and physiological processes since the initial purification of pineal melatonin from pigs, and more recently have been employed to better understand the neuroendocrine circuit that regulates background adaptation. The identification of 37 type II opsin genes in the genome of the allotetraploid X. laevis, combined with analysis of their expression in the eye, pineal complex and skin, is contributing to the elucidation of the role of opsins in the different photosensitive organs, but also brings new questions and challenges. In this review, we analyze new findings regarding the anatomical localization and functions of type II opsins in sensing light. The contribution of X. laevis in revealing the neuroendocrine circuits that regulate background adaptation and circadian light variation through changes in skin pigmentation is discussed. Finally, the presence of opsins in X. laevis skin melanophores is presented and compared with the secretory melanocytes of birds and mammals.

Diabetes mellitus and melatonin: Where are we?

Diabetes mellitus (DM) and diabetes-related complications are amongst the leading causes of mortality worldwide. The international diabetes federation (IDF) has estimated 592 million people to suffer from DM by 2035. Hence, finding a novel biomolecule that can effectively aid diabetes management is vital, as other existing drugs have numerous side effects. Melatonin, a pineal hormone having antioxidative and anti-inflammatory properties, has been implicated in circadian dysrhythmia-linked DM. Reduced levels of melatonin and a functional link between melatonin and insulin are implicated in the pathogenesis of type 2 diabetes (T2D) Additionally, genomic studies revealed that rare variants in melatonin receptor 1b (MTNR1B) are also associated with impaired glucose tolerance and increased risk of T2D. Moreover, exogenous melatonin treatment in cell lines, rodent models, and diabetic patients has shown a potent effect in alleviating diabetes and other related complications. This highlights the role of melatonin in glucose homeostasis. However, there are also contradictory reports on the effects of melatonin supplementation. Thus, it is essential to explore if melatonin can be taken from bench to bedside for diabetes management. This review summarizes the therapeutic potential of melatonin in various diabetic models and whether it can be considered a safe drug for managing diabetic complications and diabetic manifestations like oxidative stress, inflammation, ER stress, mitochondrial dysfunction, metabolic dysregulation, etc.

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.

Low Temperature Effect on the Endocrine and Circadian Systems of Adult Danio rerio

The control of the biological rhythms begins with the activation of photo- and thermosensitive cells located in various organs of the fish such as brain, eye, and skin, but a central clock is still to be identified in teleosts. Thermal changes are stressors which increase cortisol and affect the rhythm of other hormones such as melatonin and growth hormone (GH), in both endo- and ectothermic organisms. Our aim was to investigate how temperature (23°C for 6 days) lower than the optimal (28°C) modulates expression of several gene pathways including growth hormone (gh1) and its receptors (ghra, ghrb), insulin-like growth factor1 (igf1a, igf1b) and its receptors (igf1ra, igf1rb), cortisol and its receptor (gr), the limiting enzyme of melatonin synthesis (arylalkylamine N-acetyltransferase, aanat) and melatonin receptors (mtnr1aa, mtnr1bb), as well as their relationship with clock genes in Danio rerio in early light and early dark phases of the day. Lower temperature reduced the expression of the hormone gene gh1, and of the related receptors ghra, ghrb, igf1ra, and igf1rb. Cortisol levels were higher at the lower temperature, with a decrease of its receptor (gr) transcripts in the liver. Interestingly, we found higher levels of aanat transcripts in the brain at 23°C. Overall, lower temperature downregulated the transcription of hormone related genes and clock genes. The results suggest a strong correlation of temperature challenge with the clock molecular mechanism and the endocrine systems analyzed, especially the growth hormone and melatonin axes, in D. rerio tissues.

Recent Advances in Electrochemical and Optical Sensors for Detecting Tryptophan and Melatonin

Tryptophan and melatonin are pleiotropic molecules, each capable of influencing several cellular, biochemical, and physiological responses. Therefore, sensitive detection of tryptophan and melatonin in pharmaceutical and human samples is crucial for human well-being. Mass spectrometry, high-performance liquid chromatography, and capillary electrophoresis are common methods for both tryptophan and melatonin analysis; however, these methods require copious amounts of time, money, and manpower. Novel electrochemical and optical detection tools have been subjects of intensive research due to their ability to offer a better signal-to-noise ratio, high specificity, ultra-sensitivity, and wide dynamic range. Recently, researchers have designed sensitive and selective electrochemical and optical platforms by using new surface modifications, microfabrication techniques, and the decoration of diverse nanomaterials with unique properties for the detection of tryptophan and melatonin. However, there is a scarcity of review articles addressing the recent developments in the electrochemical and optical detection of tryptophan and melatonin. Here, we provide a critical and objective review of high-sensitivity tryptophan and melatonin sensors that have been developed over the past six years (2015 onwards). We review the principles, performance, and limitations of these sensors. We also address critical aspects of sensitivity and selectivity, limit and range of detection, fabrication process and time, durability, and biocompatibility. Finally, we discuss challenges related to tryptophan and melatonin detection and present future outlooks.

Melatonin in plants: what we know and what we don’t

Melatonin is an endogenous micromolecular compound of indoleamine with multiple physiological functions in various organisms. In plants, melatonin is involved in growth and development, as well as in responses to biotic and abiotic stresses. Furthermore, melatonin functions in phytohormone-mediated signal transduction pathways. There are multiple melatonin biosynthesis pathways, and the melatonin content in plants is greatly affected by intrinsic genetic characteristics and external environmental factors. Although melatonin biosynthesis has been extensively studied in model plants, it remains uncharacterized in most plants. This article focuses on current knowledge on the biosynthesis, regulation and application of melatonin, particularly for fruit quality and preservation. In addition, it highlights the links between melatonin and other hormones, as well as future research directions.

Phytomelatonin: An overview of the importance and mediating functions of melatonin against environmental stresses

Recently, melatonin has gained significant importance in plant research. The presence of melatonin in the plant kingdom has been known since 1995. It is a molecule that is conserved in a wide array of evolutionary distant organisms. Its functions and characteristics have been found to be similar in both plants and animals. The review focuses on the role of melatonin pertaining to physiological functions in higher plants. Melatonin regulates physiological functions regarding auxin activity, root, shoot, and explant growth, activates germination of seeds, promotes rhizogenesis (growth of adventitious and lateral roots), and holds up impelled leaf senescence. Melatonin is a natural bio-stimulant that creates resistance in field crops against various abiotic stress, including heat, chemical pollutants, cold, drought, salinity, and harmful ultra-violet radiation. The full potential of melatonin in regulating physiological functions in higher plants still needs to be explored by further research.

Gene duplication and loss of AANAT in mammals driven by rhythmic adaptations

Arylalkylamine N-acetyltransferase (AANAT) plays a crucial role in synchronizing internal biological functions to circadian and circannual changes. Generally speaking, only one copy of AANAT gene has been found in mammals, however, three independent duplications of this gene were detected in several cetartiodactyl lineages (i.e., Suidae, Hippopotamidae, and Pecora), which originated in the middle Eocene, a geological period characterized with the increased climate seasonality. Lineage-specific expansions of AANAT and the associated functional enhancement in these lineages strongly suggest an improvement in regulating photoperiodic response to adapt to seasonal climate changes. In contrast, independent inactivating mutations or deletions of the AANAT locus were identified in the four pineal-deficient clades (cetaceans, sirenians, xenarthrans, and pangolins). Loss of AANAT function in cetaceans and sirenians could disrupt the sleep-promoting effects of pineal melatonin, which might contribute to increasing wakefulness, adapting these clades to underwater sleep. The absence of AANAT and pineal glands in xenarthrans and pangolins may be associated with their body temperature maintenance. The present work demonstrates a far more complex and intriguing evolutionary pattern and functional diversity of mammalian AANAT genes than previously thought and provides further evidence for understanding AANAT evolution as driven by rhythmic adaptations in mammals.

Integrated Metabolomics and Lipidomics Analysis Reveal Remodeling of Lipid Metabolism and Amino Acid Metabolism in Glucagon Receptor-Deficient Zebrafish

The glucagon receptor (GCGR) is activated by glucagon and is essential for glucose, amino acid, and lipid metabolism of animals. GCGR blockade has been demonstrated to induce hypoglycemia, hyperaminoacidemia, hyperglucagonemia, decreased adiposity, hepatosteatosis, and pancreatic α cells hyperplasia in organisms. However, the mechanism of how GCGR regulates these physiological functions is not yet very clear. In our previous study, we revealed that GCGR regulated metabolic network at transcriptional level by RNA-seq using GCGR mutant zebrafish (gcgr ^-/-). Here, we further performed whole-organism metabolomics and lipidomics profiling on wild-type and gcgr ^-/- zebrafish to study the changes of metabolites. We found 107 significantly different metabolites from metabolomics analysis and 87 significantly different lipids from lipidomics analysis. Chemical substance classification and pathway analysis integrated with transcriptomics data both revealed that amino acid metabolism and lipid metabolism were remodeled in gcgr-deficient zebrafish. Similar to other studies, our study showed that gcgr ^-/- zebrafish exhibited decreased ureagenesis and impaired cholesterol metabolism. More interestingly, we found that the glycerophospholipid metabolism was disrupted, the arachidonic acid metabolism was up-regulated, and the tryptophan metabolism pathway was down-regulated in gcgr ^-/- zebrafish. Based on the omics data, we further validated our findings by revealing that gcgr ^-/- zebrafish exhibited dampened melatonin diel rhythmicity and increased locomotor activity. These global omics data provide us a better understanding about the role of GCGR in regulating metabolic network and new insight into GCGR physiological functions.

Melatonin and Its Homologs Induce Immune Responses via Receptors trP47363-trP13076 in Nicotiana benthamiana

Melatonin (N-acetyl-5-methoxytryptamine), a naturally occurring small molecule, can protect plants against abiotic stress after exogenous treatmenting with it. It is not known if melatonin homologs, such as 5-methoxytryptamine and 5-methoxyindole, that are easy and more cost-effective to synthesize can stimulate the plant immune system in the same manner as melatonin. In the present study, we assessed the biological activity of the melatonin homologs, 5-methoxytryptamin and 5-methoxyindole. The results showed that melatonin and its homologs all induced disease resistance against Phytophthora nicotianae in Nicotiana benthamiana plants. The application of all three compounds also induced stomatal closure and the production of reactive oxygen species. Gene expression analysis indicated that the expression of genes involved in hydrogen peroxide (H₂O₂), nitric oxide (NO) production, and salicylic acid (SA) biosynthesis was significantly upregulated by all three compounds. Four homologs of the melatonin receptors were identified by blasting search with the phytomelatonin receptor in Arabidopsis. Molecular docking studies were also used to identify four putative melatonin receptors in N. benthamiana. Further experimentation revealed that silencing of the melatonin receptors trP47363 and trP13076 in N. benthamiana compromised the induction of stomatal closure, PR-1a gene expression and SA accumulation by all three compounds. Collectively, our data indicate that the induction of defense responses in N. benthamiana by melatonin, 5-methoxytryptamine, and 5-methoxyindole involves the melatonin receptors trP47363 and trP13076.

Melatonin in business with abiotic stresses in plants

Melatonin (MEL) is the potential biostimulator molecule, governing multiple range of growth and developmental processes in plants, particularly under different environmental constrains. Mainly, its role is considered as an antioxidant molecule that copes with oxidative stress through scavenging of reactive oxygen species and modulation of stress related genes. It also enhances the antioxidant enzyme activities and thus helps in regulating the redox hemostasis in plants. Apart from its broad range of antioxidant functions, it is involved in the regulation of various physiological processes such as germination, lateral root growth and senescence in plants. Moreover this multifunctional molecule takes much interest due to its recent identification and characterization of receptorCandidate G-protein-Coupled Receptor 2/Phytomelatonin receptor(CAND2/PMTR1) in Arabidopsis thaliana. In this compiled work, different aspects of melatonin in plants such as melatonin biosynthesis and detection in plants, signaling pathway, modulation of stress related genes and physiological role of melatonin under different environmental stresses have been dissected in detail.

Can skyglow reduce nocturnal melatonin concentrations in Eurasian perch?

Artificial light at night (ALAN) changes the natural rhythm of light and darkness and can impair the biorhythms of animals, for example the nocturnal melatonin production of vertebrates, which serves as a proxy for daily physiological rhythms. Freshwater fish are exposed to ALAN in large urban and suburban areas in the form of direct light or in the form of skyglow, a diffuse brightening of the night sky through the scattered light reflected by clouds, atmospheric molecules, and particles in the air. However, investigations on the sensitivity of melatonin production of fish towards low intensities of ALAN in the range of typical skyglow are rare. Therefore, we exposed Eurasian perch (Perca fluviatilis) to nocturnal illumination levels of 0.01 lx, 0.1 lx and 1 lx and a control group with dark nights and daylight intensities of 2900 lx in all groups. After ten days of exposure to the experimental conditions, tank water was non-invasively sampled every 3 h over a 24 h period and melatonin was measured by ELISA. Melatonin was gradually reduced in all treatments with increasing intensity of ALAN whereas rhythmicity was maintained in all treatment groups although at 1 lx not all evaluated parameters confirmed rhythmicity. These results show a high sensitivity of Eurasian perch towards ALAN indicating that low light intensities of 0.01 lx and 0.1 lx as they occur in urban and suburban areas in the form of skyglow can affect the physiology of Eurasian perch. Furthermore, we highlight how this may impact perch in their sensitivity towards lunar rhythms and the role of skyglow for biorhythms of temperate freshwater fish.

Structural characterization of melatonin as an inhibitor of the Wnt deacylase Notum

The hormone melatonin, secreted from the pineal gland, mediates multiple physiological effects including modulation of Wnt/β-catenin signalling. The Wnt palmitoleate lipid modification is essential for its signalling activity, while the carboxylesterase Notum can remove the lipid from Wnt and inactivate it. Notum enzyme inhibition can therefore upregulate Wnt signalling. While searching for Notum inhibitors by crystallographic fragment screening, a hit compound N-[2-(5-fluoro-1H-indol-3-yl)ethyl]acetamide that is structurally similar to melatonin came to our attention. We then soaked melatonin and its precursor N-acetylserotonin into Notum crystals and obtained high-resolution structures (≤1.5 Å) of their complexes. In each of the structures, two compound molecules bind with Notum: one at the enzyme's catalytic pocket, overlapping the space occupied by the acyl tail of the Wnt palmitoleate lipid, and the other at the edge of the pocket opposite the substrate entrance. Although the inhibitory activity of melatonin shown by in vitro enzyme assays is low (IC50 75 µmol/L), the structural information reported here provides a basis for the design of potent and brain accessible drugs for neurodegenerative diseases such as Alzheimer's disease, in which upregulation of Wnt signalling may be beneficial.

Light Pollution, Circadian Photoreception, and Melatonin in Vertebrates

Artificial light at night (ALAN) is increasing exponentially worldwide, accelerated by the transition to new efficient lighting technologies. However, ALAN and resulting light pollution can cause unintended physiological consequences. In vertebrates, production of melatonin—the “hormone of darkness” and a key player in circadian regulation—can be suppressed by ALAN. In this paper, we provide an overview of research on melatonin and ALAN in vertebrates. We discuss how ALAN disrupts natural photic environments, its effect on melatonin and circadian rhythms, and different photoreceptor systems across vertebrate taxa. We then present the results of a systematic review in which we identified studies on melatonin under typical light-polluted conditions in fishes, amphibians, reptiles, birds, and mammals, including humans. Melatonin is suppressed by extremely low light intensities in many vertebrates, ranging from 0.01–0.03 lx for fishes and rodents to 6 lx for sensitive humans. Even lower, wavelength-dependent intensities are implied by some studies and require rigorous testing in ecological contexts. In many studies, melatonin suppression occurs at the minimum light levels tested, and, in better-studied groups, melatonin suppression is reported to occur at lower light levels. We identify major research gaps and conclude that, for most groups, crucial information is lacking. No studies were identified for amphibians and reptiles and long-term impacts of low-level ALAN exposure are unknown. Given the high sensitivity of vertebrate melatonin production to ALAN and the paucity of available information, it is crucial to research impacts of ALAN further in order to inform effective mitigation strategies for human health and the wellbeing and fitness of vertebrates in natural ecosystems.

Dysregulation of circadian rhythm in zebrafish (Danio rerio) by thifluzamide: Involvement of positive and negative regulators

Thifluzamide as a fungicide is toxic to brain of zebrafish embryos. Brain can regulate biological rhythms. To clarify whether thifluzamide would influence circadian rhythms, zebrafish embryos were treated with thifluzamide (0, 0.19, 1.90 and 2.85 mg/L) for 4 days. Exposure to thifluzamide induced pronounced changes in embryo brain and melatonin levels. The mRNA levels of genes related to circadian rhythms were apparently altered. Among these, the transcripts of cry1ba and clock1 were extremely correlated with exposure concentrations. Importantly, the content of cry1 showed no apparent changes, but the clock level was dramatically increased. Moreover, consistent with the inhibition of development and behavior, the levels of GH and DA were significantly inhibited. In addition, the expression levels of genes related to development, behavior and reproduction were significantly changed by thifluzamide. Therefore, we speculated that circadian disruption due to thifluzamide exposure were primarily attributed to increases in expression of clock1a and contents of clock, which might be at least in part responsible for abnormal development and behavior of zebrafish. In addition, our research will provide important insights into the grouped assessment of SDHI pesticides in future.

Phylogenetic Reclassification of Vertebrate Melatonin Receptors To Include Mel1d

The circadian and seasonal actions of melatonin are mediated by high affinity G-protein coupled receptors (melatonin receptors, MTRs), classified into phylogenetically distinct subtypes based on sequence divergence and pharmacological characteristics. Three vertebrate MTR subtypes are currently described: MT1 (MTNR1A), MT2 (MTNR1B), and Mel1c (MTNR1C / GPR50), which exhibit distinct affinities, tissue distributions and signaling properties. We present phylogenetic and comparative genomic analyses supporting a revised classification of the vertebrate MTR family. We demonstrate four ancestral vertebrate MTRs, including a novel molecule hereafter named Mel1d. We reconstructed the evolution of each vertebrate MTR, detailing genetic losses in addition to gains resulting from whole genome duplication events in teleost fishes. We show that Mel1d was lost separately in mammals and birds and has been previously mistaken for an MT1 paralogue. The genetic and functional diversity of vertebrate MTRs is more complex than appreciated, with implications for our understanding of melatonin actions in different taxa. The significance of our findings, including the existence of Mel1d, are discussed in an evolutionary and functional context accommodating a robust phylogenetic assignment of MTR gene family structure.

Melatonin synthesis and clock gene regulation in the pineal organ of teleost fish compared to mammals: Similarities and differences

The pineal organ of all vertebrates synthesizes and secretes melatonin in a rhythmic manner due to the circadian rhythm in the activity of arylalkylamine N-acetyltransferase (AANAT) - the rate-limiting enzyme in melatonin synthesis pathway. Nighttime increase in AANAT activity and melatonin synthesis depends on increased expression of aanat gene (a clock-controlled gene) and/or post-translation modification of AANAT protein. In mammalian and avian species, only one aanat gene is expressed. However, three aanat genes (aanat1a, aanat1b, and aanat2) are reported in fish species. While aanat1a and aanat1b genes are expressed in the fish retina, the nervous system and other peripheral tissues, aanat2 gene is expressed exclusively in the fish pineal organ. Clock genes form molecular components of the clockwork, which regulates clock-controlled genes like aanat gene. All core clock genes (i.e., clock, bmal1, per1, per2, per3, cry1 and cry2) and aanat2 gene (a clock-controlled gene) are expressed in the pineal organ of several fish species. There is a large body of information on regulation of clock genes, aanat gene and melatonin synthesis in the mammalian pineal gland. However, the information available on clock genes, aanat genes and melatonin synthesis in photoreceptive pineal organ of teleosts is fragmentary and not well documented. Therefore, we have reviewed published information on rhythmic expression of clock genes, aanat genes as well as synthesis of melatonin, and their regulation by photoperiod and temperature in teleostean pineal organ as compared to mammalian pineal gland. A critical analysis of the literature suggests that in contrast to the mammalian pineal gland, the pineal organ of teleosts (except salmonids) possesses a well developed indigenous clock composed of clock genes for regulation of rhythmic expression of aanat2 gene and melatonin synthesis. Further, the fish pineal organ also possesses essential molecular components for responding to light and temperature directly. The fish pineal organ seems to act as a potential master biological clock in most of the teleosts.

Agouti-Related Protein 2 Is a New Player in the Teleost Stress Response System

Agouti-related protein (AgRP) is a hypothalamic regulator of food consumption in mammals. However, AgRP has also been detected in circulation, but a possible endocrine role has not been examined. Zebrafish possess two agrp genes: hypothalamically expressed agrp1, considered functionally equivalent to the single mammalian agrp, and agrp2, which is expressed in pre-optic neurons and uncharacterized pineal gland cells and whose function is not well understood. By ablation of AgRP1-expressing neurons and knockout of the agrp1 gene, we show that AgRP1 stimulates food consumption in the zebrafish larvae. Single-cell sequencing of pineal agrp2-expressing cells revealed molecular resemblance to retinal-pigment epithelium cells, and anatomic analysis shows that these cells secrete peptides, possibly into the cerebrospinal fluid. Additionally, based on AgRP2 peptide localization and gene knockout analysis, we demonstrate that pre-optic AgRP2 is a neuroendocrine regulator of the stress axis that reduces cortisol secretion. We therefore suggest that the ancestral role of AgRP was functionally partitioned in zebrafish by the two AgRPs, with AgRP1 centrally regulating food consumption and AgRP2 acting as a neuroendocrine factor regulating the stress axis.

Environmental Cycles, Melatonin, and Circadian Control of Stress Response in Fish

Fish have evolved a biological clock to cope with environmental cycles, so they display circadian rhythms in most physiological functions including stress response. Photoperiodic information is transduced by the pineal organ into a rhythmic secretion of melatonin, which is released into the blood circulation with high concentrations at night and low during the day. The melatonin rhythmic profile is under the control of circadian clocks in most fish (except salmonids), and it is considered as an important output of the circadian system, thus modulating most daily behavioral and physiological rhythms. Lighting conditions (intensity and spectrum) change in the underwater environment and affect fish embryo and larvae development: constant light/darkness or red lights can lead to increased malformations and mortality, whereas blue light usually results in best hatching rates and growth performance in marine fish. Many factors display daily rhythms along the hypothalamus-pituitary-interrenal (HPI) axis that controls stress response in fish, including corticotropin-releasing hormone (Crh) and its binding protein (Crhbp), proopiomelanocortin A and B (Pomca and Pomcb), and plasma cortisol, glucose, and lactate. Many of these circadian rhythms are under the control of endogenous molecular clocks, which consist of self-sustained transcriptional-translational feedback loops involving the cyclic expression of circadian clock genes (clock, bmal, per, and cry) which persists under constant light or darkness. Exposing fish to a stressor can result in altered rhythms of most stress indicators, such as cortisol, glucose, and lactate among others, as well as daily rhythms of most behavioral and physiological functions. In addition, crh and pomca expression profiles can be affected by other factors such as light spectrum, which strongly influence the expression profile of growth-related (igf1a, igf2a) genes. Additionally, the daily cycle of water temperature (warmer at day and cooler at night) is another factor that has to be considered. The response to any acute stressor is not only species dependent, but also depends on the time of the day when the stress occurs: nocturnal species show higher responses when stressed during day time, whereas diurnal fish respond stronger at night. Melatonin administration in fish has sedative effects with a reduction in locomotor activity and cortisol levels, as well as reduced liver glycogen and dopaminergic and serotonergic activities within the hypothalamus. In this paper, we are reviewing the role of environmental cycles and biological clocks on the entrainment of daily rhythms in the HPI axis and stress responses in fish.

Signaling within the pineal gland: A parallelism with the central nervous system

The pineal gland (PG) derives from the neural tube, like the rest of the central nervous system (CNS). The PG is specialized in synthesizing and secreting melatonin in a circadian fashion. The nocturnal elevation of melatonin is a highly conserved feature among species which proves its importance in nature. Here, we review a limited set of intrinsic and extrinsic regulatory elements that have been shown or proposed to influence the PG's melatonin production, as well as pineal ontogeny and homeostasis. Intrinsic regulators include the transcription factors CREB, Pax6 and NeuroD1. In addition, microglia within the PG participate as extrinsic regulators of these functions. We further discuss how these same elements work in other parts of the CNS, and note similarities and differences to their roles in the PG. Since the PG is a relatively well-defined and highly specialized organ within the CNS, we suggest that applying this comparative approach to additional PG regulators may be a useful tool for understanding complex areas of the brain, as well as the influence of the PG in both health and disease, including circadian functions and disorders.

Melatonin as a Hormone: New Physiological and Clinical Insights

Melatonin is a ubiquitous molecule present in almost every live being from bacteria to humans. In vertebrates, besides being produced in peripheral tissues and acting as an autocrine and paracrine signal, melatonin is centrally synthetized by a neuroendocrine organ, the pineal gland. Independently of the considered species, pineal hormone melatonin is always produced during the night and its production and secretory episode duration are directly dependent on the length of the night. As its production is tightly linked to the light/dark cycle, melatonin main hormonal systemic integrative action is to coordinate behavioral and physiological adaptations to the environmental geophysical day and season. The circadian signal is dependent on its daily production regularity, on the contrast between day and night concentrations, and on specially developed ways of action. During its daily secretory episode, melatonin coordinates the night adaptive physiology through immediate effects and primes the day adaptive responses through prospective effects that will only appear at daytime, when melatonin is absent. Similarly, the annual history of the daily melatonin secretory episode duration primes the central nervous/endocrine system to the seasons to come. Remarkably, maternal melatonin programs the fetuses' behavior and physiology to cope with the environmental light/dark cycle and season after birth. These unique ways of action turn melatonin into a biological time-domain-acting molecule. The present review focuses on the above considerations, proposes a putative classification of clinical melatonin dysfunctions, and discusses general guidelines to the therapeutic use of melatonin.

Effect of Monochromatic Light on Circadian Rhythm of Clock Genes in Chick Pinealocytes

The avian circadian system is a complex of mutually coupled pacemakers residing in pineal gland, retina and suprachiasmatic nucleus. In this study, the self-regulation mechanism of pineal circadian rhythm was investigated by culturing chick primary pinealocytes exposed to red light (RL), green light (GL), blue light (BL), white light (WL) and constant darkness (DD), respectively. All illuminations were set up with a photoperiod of 12 light: 12 dark. The 24-h expression profiles of seven core clock genes (cBmal1/2, cClock, cCry1/2 and cPer2/3), cAanat and melatonin showed significant circadian oscillation in all groups, except for the loss of cCry1 rhythm in BL. Compared to WL, GL increased the amplitudes and mesors of positive elements (cClock and cBmal1/2) and reduced those of negative elements (cCry1/2 and cPer2/3), in contrast to RL. The temporal patterns of cAanatmRNA and melatonin secretion have always been consistent with the positive genes. Besides, GL advanced the acrophases of the positive elements, cAanat and melatonin, but RL and BL showed the opposite effect. Thereby, GL could promote the secretion of melatonin by enhancing the expressions of positive clock genes and repressing the expressions of negative clock genes.

Cold temperature represses daily rhythms in the liver transcriptome of a stenothermal teleost under decreasing day length

The climate-change-driven increase in temperature is occurring rapidly and decreasing the predictability of seasonal rhythms at high latitudes. It is therefore urgent to understand how a change in the relationship between photoperiod and temperature can affect ectotherms in these environments. We tested whether temperature affects daily rhythms of transcription in a cold-adapted salmonid using high-throughput RNA sequencing. Arctic char (Salvelinus alpinus) from a subarctic population were reared at a high and a low temperature (15 and 8°C) for 1 month under natural, decreasing day length during late summer. Liver transcriptomes were compared between samples collected in the middle and towards the end of the light period and in the middle of the dark period. Daily variation in transcription was lower in fish from the low temperature compared with strong daily variation in warm-acclimated fish, suggesting that cold temperatures dampen the cycling of transcriptional rhythms under a simultaneously decreasing day length. Different circadian clock genes had divergent expression patterns, responding either by decreased expression or by increased rhythmicity at 15°C compared with 8°C. The results point out mechanisms that can affect the ability of fish to adapt to increasing temperatures caused by climate change.

Influence of light intensity and spectral composition of artificial light at night on melatonin rhythm and mRNA expression of gonadotropins in roach Rutilus rutilus

In this study we investigated the influence of artificial light at night (ALAN) of different intensities (0, 1, 10, 100 lx) and different colours (blue, green, red) on the daily melatonin rhythm and mRNA expression of gonadotropins in roach Rutilus rutilus, a ubiquitous cyprinid, which occur in standing and moderately flowing freshwater habitats of central Europe. Melatonin concentrations were significantly lowered under nocturnal white light already at 1 lx. Low intensity blue, green and red ALAN lowered the melatonin levels significantly in comparison to a dark control. We conclude that ALAN can disturb melatonin rhythms in roach at very low intensities and at different wavelengths and thus light pollution in urban waters has the potential to impact biological rhythms in fish. However, mRNA expression of gonadotropins was not affected by ALAN during the period of the experiments. Thus, suspected implications of ALAN on reproduction of roach could not be substantiated.

Melatonin as a treatment for mood disorders: a systematic review

OBJECTIVE

Melatonin has been widely studied in the treatment of sleep disorders and evidence is accumulating on a possible role for melatonin influencing mood. Our aim was to determine the efficacy and acceptability of melatonin for mood disorders.

METHOD

We conducted a comprehensive systematic review of randomized clinical trials on patients with mood disorders, comparing melatonin to placebo.

RESULTS

Eight clinical trials were included; one study in bipolar, three in unipolar depression and four in seasonal affective disorder. We have only a small study on patients with bipolar disorder, while we have more studies testing melatonin as an augmentation strategy for depressive episodes in major depressive disorder and seasonal affective disorder. The acceptability and tolerability were good. We analyzed data from three trials on depressive episodes and found that the evidence for an effect of melatonin in improving mood symptoms is not significant (SMD = 0.37; 95% CI [-0.05, 0.37]; P = 0.09). The small sample size and the differences in methodology of the trials suggest that our results are based on data deriving from investigations occurring early in this field of study.

CONCLUSION

There is no evidence for an effect of melatonin on mood disorders, but the results are not conclusive and justify further research.

Northern Spotted Owl (Strix occidentalis caurina) Genome: Divergence with the Barred Owl (Strix varia) and Characterization of Light-Associated Genes

We report here the assembly of a northern spotted owl (Strix occidentalis caurina) genome. We generated Illumina paired-end sequence data at 90× coverage using nine libraries with insert lengths ranging from ∼250 to 9,600 nt and read lengths from 100 to 375 nt. The genome assembly is comprised of 8,108 scaffolds totaling 1.26 × 109 nt in length with an N50 length of 3.98 × 106 nt. We calculated the genome-wide fixation index (FST) of S. o. caurina with the closely related barred owl (Strix varia) as 0.819. We examined 19 genes that encode proteins with light-dependent functions in our genome assembly as well as in that of the barn owl (Tyto alba). We present genomic evidence for loss of three of these in S. o. caurina and four in T. alba. We suggest that most light-associated gene functions have been maintained in owls and their loss has not proceeded to the same extent as in other dim-light-adapted vertebrates.

Dual role of mitochondria in producing melatonin and driving GPCR signaling to block cytochrome c release

G protein-coupled receptors (GPCRs) are classically characterized as cell-surface receptors transmitting extracellular signals into cells. Here we show that central components of a GPCR signaling system comprised of the melatonin type 1 receptor (MT₁), its associated G protein, and β-arrestins are on and within neuronal mitochondria. We discovered that the ligand melatonin is exclusively synthesized in the mitochondrial matrix and released by the organelle activating the mitochondrial MT₁ signal-transduction pathway inhibiting stress-mediated cytochrome c release and caspase activation. These findings coupled with our observation that mitochondrial MT₁ overexpression reduces ischemic brain injury in mice delineate a mitochondrial GPCR mechanism contributing to the neuroprotective action of melatonin. We propose a new term, "automitocrine," analogous to "autocrine" when a similar phenomenon occurs at the cellular level, to describe this unexpected intracellular organelle ligand-receptor pathway that opens a new research avenue investigating mitochondrial GPCR biology.