On the Molecular Evolution of Leptin, Leptin Receptor, and Endospanin

History and future of leptin: Discovery, regulation and signaling

The cloning of leptin 30 years ago in 1994 was an important milestone in obesity research. Prior to the discovery of leptin, obesity was stigmatized as a condition caused by lack of character and self-control. Mutations in either leptin or its receptor were the first single gene mutations found to cause severe obesity, and it is now recognized that obesity is caused mostly by a dysregulation of central neuronal circuits. Since the discovery of the leptin-deficient obese mouse (ob/ob) the cloning of leptin (ob aka lep) and leptin receptor (db aka lepr) genes, we have learned much about leptin and its action in the central nervous system. The first hope that leptin would cure obesity was quickly dampened because humans with obesity have increased leptin levels and develop leptin resistance. Nevertheless, leptin target sites in the brain represent an excellent blueprint to understand how neuronal circuits control energy homeostasis. Our expanding understanding of leptin function, interconnection of leptin signaling with other systems and impact on distinct physiological functions continues to guide and improve the development of safe and effective interventions to treat metabolic illnesses. This review highlights past concepts and current emerging concepts of the hormone leptin, leptin receptor signaling pathways and central targets to mediate distinct physiological functions.

Leptin- and cytokine-like unpaired signaling in Drosophila

Animals have evolved a multitude of signaling pathways that enable them to orchestrate diverse physiological processes to tightly regulate systemic homeostasis. This signaling is mediated by various families of peptide hormones and cytokines that are conserved across the animal kingdom. In this review, we primarily focus on the unpaired (Upd) family of proteins in Drosophila which are evolutionarily related to mammalian leptin and the cytokine interleukin 6. We summarize expression patterns of Upd in Drosophila and discuss the parallels in structure, signaling pathway, and functions between Upd and their mammalian counterparts. In particular, we focus on the roles of Upd in governing metabolic homeostasis, growth and development, and immune responses. We aim to stimulate future studies on leptin-like signaling in other phyla which can help bridge the evolutionary gap between insect Upd and vertebrate leptin and cytokines like interleukin 6.

Whole-body deletion of Endospanin 1 protects from obesity-associated deleterious metabolic alterations

The importance of the proper localization of most receptors at the cell surface is often underestimated, although this feature is essential for optimal receptor response. Endospanin 1 (Endo1) (also known as OBRGRP or LEPROT) is a protein generated from the same gene as the human leptin receptor and regulates the trafficking of proteins to the surface, including the leptin receptor. The systemic role of Endo1 on whole-body metabolism has not been studied so far. Here, we report that general Endo1-KO mice fed a high-fat diet develop metabolically healthy obesity with lipid repartitioning in organs and preferential accumulation of fat in adipose tissue, limited systematic inflammation, and better controlled glucose homeostasis. Mechanistically, Endo1 interacts with the lipid translocase CD36, thus regulating its surface abundance and lipid uptake in adipocytes. In humans, the level of Endo1 transcripts is increased in the adipose tissue of patients with obesity, but low levels rather correlate with a profile of metabolically healthy obesity. We suggest here that Endo1, most likely by controlling CD36 cell surface abundance and lipid uptake in adipocytes, dissociates obesity from diabetes and that its absence participates in metabolically healthy obesity.

Sequence identification and expression characterization of leptin in the spotted scat, Scatophagus argus

Scatophagus argus is an important marine culture fish in South and South-East Asia, including Southeast coastal areas of China. Artificial propagation technology for S. argus is not optimum; thus further studies on its reproduction biology are required. Although previous studies have shown that leptin (Lep) can regulate fish reproduction, the role of lep genes in S. argus is unknown. Herein, in silico analysis showed that S. argus has two lep genes (lepa and lepb). Protein 3D-structure prediction showed that Lepa has four α-helices (similar to mammals), while Lepb only has three. Tissue distribution analysis showed that lepa is highly expressed in the liver, whereas lepb was not detected in any tissue. Notably, lepr was expressed in all tissues. Lepa mRNA expression levels in the liver and serum Lep, estradiol (E2) and vitellogenin (Vtg) levels of female fish were significantly higher in ovaries at stage IV than in ovaries at stage II. Serum E2 levels were significantly positively correlated with Vtg levels in female fish at different development stages, while serum E2 was not correlated with Lep levels. Consistently, in vitro incubation of the liver with E2 significantly up-regulated vtga, while it did not affect lepa expression. Recombinant Lep (10 nM) significantly up-regulated chicken gonadotropin-releasing hormone (cGnRH/GnRH-II) in the hypothalamus and GnRH receptor (GnRHR) and luteinizing hormone beta (Lhb) in the pituitary. These results suggest that lepa regulates female reproduction in S. argus.

Leptin Resistance Does Not Facilitate Migratory Fattening in Ruby-Throated Hummingbirds (Archilochus Colubris)

In mammals, leptin is an important energy homeostasis hormone produced by adipose tissue. Circulating leptin concentrations correlate positively with fat mass and act in a negative feedback fashion to inhibit food intake and increase energy expenditure, thereby preventing fat gain. For some species, leptin resistance is advantageous during times of year where fat gain is necessary (e.g., prior to hibernation). While the function of leptin in birds remains controversial, seasonal leptin resistance may similarly benefit migratory species. Here, we used the ruby-throated hummingbird (Archilochus colubris) to test the hypothesis that leptin resistance promotes fattening prior to migration. We predicted that during the migratory fattening period, leptin levels should correlate positively with fat mass but should not inhibit food intake or increase energy expenditure, resulting in fattening. We tracked the body (fat) mass, the concentration of leptin-like protein in the urine, and the food intake of 12 captive hummingbirds from August 2021 to January 2022. In a subset of hummingbirds, we also quantified voluntary physical activity as a proxy for energy expenditure. We found remarkable age-related variation in fattening strategies, with juveniles doubling their body fat by mid-September and adults exhibiting only a 50% increase. Changes in fat mass were strongly associated with increased food intake and reduced voluntary activity. However, we found no correlation between leptin-like protein concentration and fat mass, food intake, or voluntary activity. Since increased torpor use has been shown to accelerate migratory fattening in ruby-throated hummingbirds, we also hypothesized that leptin is a mediator of torpor use. In an experimental manipulation of circulating leptin, however, we found no change in torpor use, body fat, or food intake. Overall, our findings suggest that leptin may not act as an adipostat in hummingbirds, nor does leptin resistance regulate how hummingbirds fatten prior to migration.

The Role of Cdc42 in the Insulin and Leptin Pathways Contributing to the Development of Age-Related Obesity

Age-related obesity significantly increases the risk of chronic diseases such as type 2 diabetes, cardiovascular diseases, hypertension, and certain cancers. The insulin-leptin axis is crucial in understanding metabolic disturbances associated with age-related obesity. Rho GTPase Cdc42 is a member of the Rho family of GTPases that participates in many cellular processes including, but not limited to, regulation of actin cytoskeleton, vesicle trafficking, cell polarity, morphology, proliferation, motility, and migration. Cdc42 functions as an integral part of regulating insulin secretion and aging. Some novel roles for Cdc42 have also been recently identified in maintaining glucose metabolism, where Cdc42 is involved in controlling blood glucose levels in metabolically active tissues, including skeletal muscle, adipose tissue, pancreas, etc., which puts this protein in line with other critical regulators of glucose metabolism. Importantly, Cdc42 plays a vital role in cellular processes associated with the insulin and leptin signaling pathways, which are integral elements involved in obesity development if misregulated. Additionally, a change in Cdc42 activity may affect senescence, thus contributing to disorders associated with aging. This review explores the complex relationships among age-associated obesity, the insulin-leptin axis, and the Cdc42 signaling pathway. This article sheds light on the vast molecular web that supports metabolic dysregulation in aging people. In addition, it also discusses the potential therapeutic implications of the Cdc42 pathway to mitigate obesity since some new data suggest that inhibition of Cdc42 using antidiabetic drugs or antioxidants may promote weight loss in overweight or obese patients.

Reproductive phase-dependent and sexually dimorphic expression of leptin and its receptor in different parts of brain of spotted snakehead Channa punctata

The reproductive phase-wise leptin (lep) and its receptor (lepr) expression in different parts of the brain of adult male and female spotted snakehead Channa punctata reveals sexual dimorphism in the brain leptin system. In anterior, middle and posterior parts of the brain of males, a maximum lep was observed in resting, spawning and postspawning reproductive phases, respectively. In females, a high level of lep was seen during the preparatory phase in the anterior brain, preparatory and postspawning phases in the middle brain and resting and postspawning phases in the posterior brain. Nonetheless, the transcript level of lepr was recorded highest during the spawning phase, irrespective of sex and region of the brain. Regardless of the reproductive state of fishes, lep and lepr were seen considerably high in middle and posterior parts of male brain than that of female, implying the involvement of factors other than sex steroids for sex-related variation in the leptin system in these regions of the brain. Nonetheless, no sex difference was evidenced in the expression of either ligand or its receptor in the anterior brain. In summary, the presence of lep and lepr in different regions of the brain and variation in their expression depending on sex and reproductive phases raise the possibility of pivotal actions of leptin in influencing neuronal circuitry and thereby reproductive functions.

Mechanism of receptor assembly via the pleiotropic adipokine Leptin

The adipokine Leptin activates its receptor LEP-R in the hypothalamus to regulate body weight and exerts additional pleiotropic functions in immunity, fertility and cancer. However, the structure and mechanism of Leptin-mediated LEP-R assemblies has remained unclear. Intriguingly, the signaling-competent isoform of LEP-R is only lowly abundant amid several inactive short LEP-R isoforms contributing to a mechanistic conundrum. Here we show by X-ray crystallography and cryo-EM that, in contrast to long-standing paradigms, Leptin induces type I cytokine receptor assemblies featuring 3:3 stoichiometry and demonstrate such Leptin-induced trimerization of LEP-R on living cells via single-molecule microscopy. In mediating these assemblies, Leptin undergoes drastic restructuring that activates its site III for binding to the Ig domain of an adjacent LEP-R. These interactions are abolished by mutations linked to obesity. Collectively, our study provides the structural and mechanistic framework for how evolutionarily conserved Leptin:LEP-R assemblies with 3:3 stoichiometry can engage distinct LEP-R isoforms to achieve signaling.

Intestinal gluconeogenesis: metabolic benefits make sense in the light of evolution

The intestine, like the liver and kidney, in various vertebrates and humans is able to carry out gluconeogenesis and release glucose into the blood. In the fed post-absorptive state, intestinal glucose is sensed by the gastrointestinal nervous system. The latter initiates a signal to the brain regions controlling energy homeostasis and stress-related behaviour. Intestinal gluconeogenesis (IGN) is activated by several complementary mechanisms, in particular nutritional situations (for example, when food is enriched in protein or fermentable fibre and after gastric bypass surgery in obesity). In these situations, IGN has several metabolic and behavioural benefits. As IGN is activated by nutrients capable of fuelling systemic gluconeogenesis, IGN could be a signal to the brain that food previously ingested is suitable for maintaining plasma glucose for a while. This process might account for the benefits observed. Finally, in this Perspective, we discuss how the benefits of IGN in fasting and fed states could explain why IGN emerged and was maintained in vertebrates by natural selection.

Understanding Insulin in the Age of Precision Medicine and Big Data: Under-Explored Nature of Genomics

Insulin is amongst the human genome's most well-studied genes/proteins due to its connection to metabolic health. Within this article, we review literature and data to build a knowledge base of Insulin (INS) genetics that influence transcription, transcript processing, translation, hormone maturation, secretion, receptor binding, and metabolism while highlighting the future needs of insulin research. The INS gene region has 2076 unique variants from population genetics. Several variants are found near the transcriptional start site, enhancers, and following the INS transcripts that might influence the readthrough fusion transcript INS-IGF2. This INS-IGF2 transcript splice site was confirmed within hundreds of pancreatic RNAseq samples, lacks drift based on human genome sequencing, and has possible elevated expression due to viral regulation within the liver. Moreover, a rare, poorly characterized African population-enriched variant of INS-IGF2 results in a loss of the stop codon. INS transcript UTR variants rs689 and rs3842753, associated with type 1 diabetes, are found in many pancreatic RNAseq datasets with an elevation of the 3'UTR alternatively spliced INS transcript. Finally, by combining literature, evolutionary profiling, and structural biology, we map rare missense variants that influence preproinsulin translation, proinsulin processing, dimer/hexamer secretory storage, receptor activation, and C-peptide detection for quasi-insulin blood measurements.

In silico analyses of leptin and leptin receptor of spotted snakehead Channa punctata

The present study, in addition to molecular characterization of leptin (lepa) and its receptor (lepr) of spotted snakehead Channa punctata, is focussed on physicochemical, structural, evolutionary and selection pressure analyses which are poorly elucidated in teleosts in spite of that existence of these genes is well reported in several fish species. The putative full-length Lep and Lepr of C. punctata showed conserved structural and functional domains, especially the residues responsible for structural integrity and signal transduction. Conversely, residues predicted essential for Lep-Lepr interaction displayed divergence between teleosts and tetrapods. Impact of substitutions/deletions predicted using protein variation effect analyser tool highlighted species specificity in ligand-receptor interaction. Physicochemical properties of ligand and receptor predicted for the first time in vertebrates revealed high aliphatic and instability indices for both Lepa and Lepr, indicating thermostability of proteins but their instability under ex vivo conditions. Positive grand average of hydropathy score of Lepa suggests its hydrophobic nature conjecturing existence of leptin binding proteins in C. punctata. In addition to disulphide bonding, a novel posttranslational modification (S-126 phosphorylation) was predicted in Lepa of C. punctata. In Lepr, disulphide bond formation and N-linked glycosylation near WSXWS motif in ECD, and phosphorylation at tyrosine residues in ICD were predicted. Leptin and its receptor sequence of C. punctata cladded with its homolog from C. striata and C. argus of order Anabantiformes. Leptin system of Anabantiformes was phylogenetically closer to that of Pleuronectiformes, Scombriformes and Perciformes. Selection pressure analysis showed higher incidence of negative selection in teleostean leptin genes indicating limited adaptation in their structure and function. However, evidence of pervasive and episodic diversifying selection laid a foundation of co-evolution of Lepa and Lepr in teleosts.

Impaired leptin signaling causes subfertility in female zebrafish

Reproduction is an energetically costly event across vertebrates and tightly linked to nutritional status and energy reserves. In mammals, the hormone leptin is considered as a link between energy homeostasis and reproduction. However, its role in fish reproduction is still unclear. In this study, we investigated the possible role of leptin in the regulation of reproduction in zebrafish, using a loss of function leptin receptor (lepr) strain. Impaired leptin signaling resulted in severe reproductive deficiencies in female zebrafish. lepr mutant females laid significantly fewer eggs, with low fertilization rates compared to wild-type females. Folliculogenesis was not affected, but oocyte maturation and ovulation were disrupted in lepr mutants. Interestingly, the expression of luteinizing hormone beta (lhb) in the pituitary was significantly lower in mutant females. Analysis of candidate genes in the ovaries and isolated fully grown follicles revealed differential expression of genes involved in steroidogenesis, oocyte maturation and ovulation in the mutants, which are known to be regulated by LH signaling. Moreover, subfertility in lepr mutants could be partially restored by administration of human chorionic gonadotropin. In conclusion, our results show that leptin deficiency does not affect early stages of follicular development, but leptin might be essential in later steps, such as in oocyte maturation and ovulation. To our knowledge, this is the first time that leptin is associated to reproductive deficiencies in zebrafish.

Mammalian tumor-like organs. 2. Mammalian adipose has many tumor features and obesity is a tumor-like process

BACKGROUND

In previous publications, the author developed the theory of carcino-evo-devo, which predicts that evolutionarily novel organs should recapitulate some features of tumors in their development.

MAIN TEXT

Mammalian adipose is currently recognized as a multi-depot metabolic and endocrine organ consisting of several adipose tissues. Although lipid-storing cells and proteins are ancient, the adipose organ as a whole is evolutionarily novel to mammals. The adipose expansion has remarkable similarities with the growth of solid tumors. These similarities are the following: (1) The capability to unlimited expansion; (2) Reversible plasticity; (3) Induction of angiogenesis; (4) Chronic inflammation; (5) Remodeling and disfunction; (6) Systemic influence on the organism; (7) Hormone production; (8) Production of miRNAs that influence other tissues; (9) Immunosuppression; (10) DNA damage and resistance to apoptosis; (11) Destructive infiltration in other organs and tissues. These similarities include the majority of "hallmarks of cancer". In addition, lipomas are the most frequent soft tissue tumors, and similar drugs may be used for the treatment of obesity and cancer by preventing infiltration. This raises the possibility that obesity, at least in part, may represent an oncological problem. The existing similarities between adipose and tumors suggest the possible evolutionary origin of mammalian adipose from some ancestral benign mesenchymal hereditary tumors. Indeed, using a transgenic inducible zebrafish tumor model, we described many genes, which originated in fish and were expressed in fish tumors. Their human orthologs LEP, NOTCH1, SPRY1, PPARG, ID2, and CIDEA acquired functions connected with the adipose organ. They are also involved in tumor development in humans.

CONCLUSION

If the hypothesis of the evolutionary origin of the adipose organ from the ancestral hereditary tumor is correct, it may open new opportunities to resolve the oncological problem and the problem of the obesity epidemic. New interventions targeting LEP, NOTCH1, SPRY1, PPARG, ID2, and CIDEA gene network, in addition to what already is going on, can be designed for treatment and prevention of both obesity and tumors.

Leptin Receptor Deficiency Results in Hyperphagia and Increased Fatty Acid Mobilization during Fasting in Rainbow Trout (Oncorhynchus mykiss)

Leptin is a pleiotropic hormone known for regulating appetite and metabolism. To characterize the role of leptin signaling in rainbow trout, we used CRISPR/Cas9 genome editing to disrupt the leptin receptor (LepR) genes, lepra1 and lepra2. We compared wildtype (WT) and mutant fish that were either fed to satiation or feed deprived for six weeks. The LepR mutants exhibited a hyperphagic phenotype, which led to heavier body weight, faster specific growth rate, increased viscero- and hepatosomatic indices, and greater condition factor. Muscle glycogen, plasma leptin, and leptin transcripts (lepa1) were also elevated in fed LepR mutant fish. Expression levels of several hypothalamic genes involved in feed regulation were analyzed (agrp, npy, orexin, cart-1, cart-2, pomc-a1, pomc-b). No differences were detected between fed WT and mutants except for pomc-b (proopiomelanocortin-b), where levels were 7.5-fold higher in LepR fed mutants, suggesting that pomc-b expression is regulated by leptin signaling. Fatty acid (FA) content did not statistically differ in muscle of fed mutant fish compared to WT. However, fasted mutants exhibited significantly lower muscle FA concentrations, suggesting that LepR mutants exhibit increased FA mobilization during fasting. These data demonstrate a key role for leptin signaling in lipid and energy mobilization in a teleost fish.

Roles of leptin in initiation of acquired growth hormone resistance and control of metabolism in rainbow trout

Catabolic conditions often induce concomitant changes in plasma leptin (Lep), growth hormone (GH) and insulin growth factor I (IGF-I) levels in teleost fish, but it is unclear whether these parts of the endocrine system are responding independently or functionally linked. In this study, fasted rainbow trout was used to study the effects of Lep on the GH-IGF-I system and metabolism. Fish were implanted intraperitoneally with recombinant rainbow trout Lep pellets and remained unfed. After 4 days, plasma GH levels were elevated in the Lep-treated fish in a dose-dependent manner; the expression of hepatic igf1 and plasma IGF-I levels were suppressed accordingly. In vitro Lep treatment reversed ovine GH (oGH)-stimulated expression of igf1 and igf2 in hepatocytes isolated from fasted fish, similar to the inhibitory effects of the MEK1/2 inhibitor U0126 treatment. However, Lep treatment alone had no effect on the expression of igfs or oGH-stimulated ghr2a expression in the hepatocytes. These results demonstrate an additive effect of Lep on suppression of IGF-I under catabolic conditions, indicating that Lep is likely involved in initiation of acquired GH resistance. Although the Lep-implant treatment had no effect on standard metabolic rate, it significantly suppressed gene expression of hepatic hydroxyacyl-CoA dehydrogenase, phosphoenolpyruvate carboxykinase and glucose 6-phosphatase, which are key enzymes in lipid utilization and gluconeogenesis, in different patterns. Overall, this study indicates that the Lep increase in fasting salmonids is an important regulatory component for physiological adaptation during periods of food deprivation, involved in suppressing growth and hepatic metabolism to spare energy expenditure.

Leptin regulates glucose homeostasis via the canonical Wnt pathway in the zebrafish

Leptin is best known for its role in adipostasis, but it also regulates blood glucose levels. The molecular mechanism by which leptin controls glucose homeostasis remains largely unknown. Here, we use a zebrafish model to show that Wnt signaling mediates the glucoregulatory effects of leptin. Under normal feeding conditions, leptin regulates glucose homeostasis but not adipostasis in zebrafish. In times of nutrient excess, however, we found that leptin also regulates body weight and size. Using a Wnt signaling reporter fish, we show that leptin activates the canonical Wnt pathway in vivo. Utilizing two paradigms for hyperglycemia, it is revealed that leptin regulates glucose homeostasis via the Wnt pathway, as pharmacological inhibition of this pathway impairs the glucoregulatory actions of leptin. Our results may shed new light on the evolution of the physiological function of leptin.

Epiregulin as an Alternative Ligand for Leptin Receptor Alleviates Glucose Intolerance without Change in Obesity

The leptin receptor (LepR) acts as a signaling nexus for the regulation of glucose uptake and obesity, among other metabolic responses. The functional role of LepR under leptin-deficient conditions remains unclear. This study reports that epiregulin (EREG) governed glucose uptake in vitro and in vivo in Lep^ob mice by activating LepR under leptin-deficient conditions. Single and long-term treatment with EREG effectively rescued glucose intolerance in comparative insulin and EREG tolerance tests in Lep^ob mice. The immunoprecipitation study revealed binding between EREG and LepR in adipose tissue of Lep^ob mice. EREG/LepR regulated glucose uptake without changes in obesity in Lep^ob mice via mechanisms, including ERK activation and translocation of GLUT4 to the cell surface. EREG-dependent glucose uptake was abolished in Lepr^db mice which supports a key role of LepR in this process. In contrast, inhibition of the canonical epidermal growth factor receptor (EGFR) pathway implicated in other EREG responses, increased glucose uptake. Our data provide a basis for understanding glycemic responses of EREG that are dependent on LepR unlike functions mediated by EGFR, including leptin secretion, thermogenesis, pain, growth, and other responses. The computational analysis identified a conserved amino acid sequence, supporting an evolutionary role of EREG as an alternative LepR ligand.

Endospanin Is a Candidate for Regulating Leptin Sensitivity

The hypothesis advanced is that endospanin, a highly conserved vesicle traffic protein in vertebrates, regulates leptin sensitivity in bone signaling. The effects of leptin on bones are well-studied but without consensus on whether the increases in leptin signaling stimulate bone gain or loss. The bone response may depend on leptin sensitivity, and endospanin is an established modulator of leptin sensitivity. An argument is advanced to develop zebrafish models for specific leptin signaling pathways. Zebrafish have well-developed molecular tools (e.g., CRISPR) and the advantage of non-destructive sampling of bones in the form of scales. Using these tools, experiments are described to substantiate the role of endospanin in zebrafish bone dynamics.

Thermal stress induces tissue damage and a broad shift in regenerative signaling pathways in the honey bee digestive tract

Honey bee colonies in the USA have suffered from increased die-off in the last few years with a complex set of interacting stresses playing a key role. With changing climate, an increase in the frequency of severe weather events, such as heat waves, is anticipated. Understanding how these changes may contribute to stress in honey bees is crucial. Individual honey bees appear to have a high capacity to endure thermal stress. One reason for this high-level endurance is likely their robust heat shock response (HSR), which contributes to thermotolerance at the cellular level. However, less is known about other mechanisms of thermotolerance, especially those operating at the tissue level. To elucidate other determinants of resilience in this species, we used thermal stress coupled with RNAseq and identified broad transcriptional remodeling of a number of key signaling pathways in the honey bee, including those pathways known to be involved in digestive tract regeneration in the fruit fly such as the Hippo and JAK/STAT pathways. We also observed cell death and shedding of epithelial cells, which likely leads to induction of this regenerative transcriptional program. We found that thermal stress affects many of these pathways in other tissues, suggesting a shared program of damage response. This study provides important foundational characterization of the tissue damage response program in this key pollinating species. In addition, our data suggest that a robust regeneration program may also be a critical contributor to thermotolerance at the tissue level, a possibility which warrants further exploration in this and other species.

Trajectory of leptin and leptin receptor in vertebrates: Structure, function and their regulation

The present review provides a comparative insight into structure, function and control of leptin system in fishes, herptiles, birds and mammals. In general, leptin acts as an anorexigenic hormone since its administration results in decrease of food intake in vertebrates. Nonetheless, functional paradox arises in fishes from contradictory observations on level of leptin during fasting and re-feeding. In addition, leptin is shown to modulate metabolic functions in fishes, reptiles, birds and mammals. Leptin also regulates reproductive and immune functions though more studies are warranted in non-mammalian vertebrates. The expression of leptin and its receptor is influenced by numerous factors including sex steroids, stress and stress-induced catecholamines and glucocorticoids though their effect in non-mammalian vertebrates is hard to be generalized due to limited studies.

Leptinergic Regulation of Vertebrate Communication Signals

Animal communication signals are regulated by multiple hormonal axes that ensure appropriate signal targeting, timing, and information content. The regulatory roles of steroid hormones and many peptide hormones are well understood and documented across a wide range of vertebrate taxa. Two recent studies have reported a novel function for leptin, a peptide hormone central to energy balance regulation: regulating communication signals of weakly electric fish and singing mice. With only limited evidence available at this time, a key question is just how widespread leptinergic regulation of communication signals is within and across taxa. A second important question is what features of communication signals are subject to leptinergic regulation. Here we consider the functional significance of leptinergic regulation of animal communication signals in the context of both direct and indirect signal metabolic costs. Direct costs arise from metabolic investment in signal production, while indirect costs arise from the predation and social conflict consequences of the signal's information content. We propose a preliminary conceptual framework for predicting which species will exhibit leptinergic regulation of their communication signals and which signal features leptin will regulate. This framework suggests a number of directly testable predictions within and across taxa. Accounting for additional factors such as life history and the potential co-regulation of communication signals by leptin and glucocorticoids will likely require modification or elaboration of this model.

Characterization of a Leptin Receptor Paralog and Its Response to Fasting in Rainbow Trout (Oncorhynchus mykiss)

Leptin is a cytokine that regulates appetite and energy expenditure, where in fishes it is primarily produced in the liver and acts to mobilize carbohydrates. Most fishes have only one leptin receptor (LepR/LepRA1), however, paralogs have recently been documented in a few species. Here we reveal a second leptin receptor (LepRA2) in rainbow trout that is 77% similar to trout LepRA1. Phylogenetic analyses show a salmonid specific genome duplication event as the probable origin of the second LepR in trout. Tissues distributions showed tissue specific expression of these receptors, with lepra1 highest in the ovaries, nearly 50-fold higher than lepra2. Interestingly, lepra2 was most highly expressed in the liver while hepatic lepra1 levels were low. Feed deprivation elicited a decline in plasma leptin, an increase in hepatic lepra2 by one week and remained elevated at two weeks, while liver expression of lepra1 remained low. By contrast, muscle lepra1 mRNA increased at one and two weeks of fasting, while adipose lepra1 was concordantly lower in fasted fish. lepra2 transcript levels were not affected in muscle and fat. These data show lepra1 and lepra2 are differentially expressed across tissues and during feed deprivation, suggesting paralog- and tissue-specific functions for these leptin receptors.

Leptin signalling in teleost fish with emphasis in food intake regulation

Leptin, the product of the obese (ob or Lep) gene, was first cloned in teleost fish in 2005, more than a decade after its identification in mammals. This was because bony fish and mammalian leptins share a very low amino acid sequence identity, which suggests different functionality of the leptin system in fish compared to that of mammals. Indeed, major differences are evident between the mammalian and fish leptin system. Thus, for instance, mammalian leptin is synthesized and released by the adipose tissue in response to the amount of fat depots, while several tissues (mainly the liver) are the main sources of leptin in fish, whose determining factors of production are still unclear. In mammals, the main physiological role for leptin is its involvement in the maintenance of energy balance by decreasing food intake and increasing energy expenditure, although a wide variety of actions have been attributed to this hormone (e.g., regulation of lipid and carbohydrate metabolism, reproduction and immune functions). In fish, available literature also points towards a multifunctional nature for leptin, although knowledge on its functions is limited. In this review, we offer an overview of teleostean leptin structure and mechanism of action, and discuss the available knowledge on the role of this hormone in food intake regulation in teleost fish, aiming to provide a comparative overview between the functioning of the teleostean and mammalian leptin systems.

Single nucleotide polymorphisms of leptin gene in five Ethiopian indigenous cattle breeds and the Korean Hanwoo breed

Considering the escalating number of scientific reports on the association between the leptin gene and diverse physiological traits and performance of cattle populations, this study was directed towards identifying SNPs in the leptin gene among five indigenous cattle breeds of Ethiopia. DNA samples were extracted from the nasal swabs of the Ethiopian indigenous cattle breeds: Arsi (n = 18), Horro (n = 20), Begait (n = 21), Boran (n = 19), and Fogera (n = 17) and the Korean Hanwoo (a representative taurine breed) (n = 20), followed by PCR amplification of exon 2 and exon 3 regions of the leptin gene and sequence analysis of the PCR products. Five SNPs, two (generating missense mutations) on exon 2 and three (generating silent mutations) on exon 3 regions, were explicated in this study. Allele frequency and genotype frequency distribution pertaining to the SNPs were recorded for the studied cattle breeds besides the minor allele frequency and deviation from the Hardy-Weinberg equilibrium. Positive F_IS index values were recorded for all the markers except SNP2, illustrative of heterozygote deficiency. MEGA X software-based evolutionary divergence analysis of the phylogenetic tree based on the SNP data revealed that the large-sized breeds, Hanwoo, Begait, Boran, and Fogera, were more closely clustered compared to the small-sized Arsi breed. Among the seven haplotypes documented from the various breeds, sequence analysis was suggestive of haplotypes 1 and 2 to be ancestral haplotypes for the leptin gene. This study is envisaged to accelerate molecular breeding programs for the genetic improvement of the Ethiopian cattle breeds.

Protein Stores Regulate When Reproductive Displays Begin in the Male Caribbean Fruit Fly

Many animals exhibit reproductive behavior that requires expenditure of valuable nutrients. In males of many species, competitive energetically demanding displays and the development of sexual ornaments require prior accumulation of nutrient stores. Males must coordinate nutrient stores with ornament development and reproductive displays or they risk depleting their resources mid-development or mid-display, reducing their chance of mating. Males may use nutrient stores to regulate their reproductive behavior. Amino acid reserves may be important for reproduction, but the roles of amino acid stores in initiating maturation and reproductive behavior are less studied than fat stores. Insects store amino acids as hexamerin storage proteins. Many fly species use a specific hexamerin, larval serum protein 2 (LSP-2), as both a juvenile storage medium and to store protein consumed after adult eclosion. Protein stored as LSP-2 has previously been suggested to regulate reproduction in females, but no role has been proposed for LSP-2 in regulating male maturation. We use males of the Caribbean fruit fly, Anastrepha suspensa, a species with nutrient-intensive male sexual displays to test whether LSP-2 stores regulate male reproductive displays. We fed adult A. suspensa males a diet with or without protein, then assayed these males for lsp-2 transcript abundance via qRT-PCR, LSP-2 protein abundance via Western blot, and reproductive display behavior via observation. We found that adult males with ad libitum dietary protein had greater lsp-2 transcript and protein abundance, earlier sexual display behavior, and were more likely to exhibit sexual display behavior than protein-deprived adult males. We show that lsp-2 knockdown via RNAi decreases the proportion of males exhibiting reproductive displays, particularly early in the onset of reproductive behavior. Our results suggest circulating LSP-2 protein stores regulate reproductive behavior in A. suspensa males, consistent with protein stores modulating reproduction in males with expensive reproductive strategies. Our results are consistent with hexamerin storage proteins performing dual roles of protein storage and protein signaling. Our work also has substantial practical applications because tephritid flies are a pest group and the timing and expression of male reproductive displays in this group are important for control efforts using the sterile insect technique.

Down-regulation of a cytokine secreted from peripheral fat bodies improves visual attention while reducing sleep in Drosophila

Sleep is vital for survival. Yet under environmentally challenging conditions, such as starvation, animals suppress their need for sleep. Interestingly, starvation-induced sleep loss does not evoke a subsequent sleep rebound. Little is known about how starvation-induced sleep deprivation differs from other types of sleep loss, or why some sleep functions become dispensable during starvation. Here, we demonstrate that down-regulation of the secreted cytokine unpaired 2 (upd2) in Drosophila flies may mimic a starved-like state. We used a genetic knockdown strategy to investigate the consequences of upd2 on visual attention and sleep in otherwise well-fed flies, thereby sidestepping the negative side effects of undernourishment. We find that knockdown of upd2 in the fat body (FB) is sufficient to suppress sleep and promote feeding-related behaviors while also improving selective visual attention. Furthermore, we show that this peripheral signal is integrated in the fly brain via insulin-expressing cells. Together, these findings identify a role for peripheral tissue-to-brain interactions in the simultaneous regulation of sleep quality and attention, to potentially promote adaptive behaviors necessary for survival in hungry animals.

Modulation of angiogenesis by topical application of leptin and high and low molecular heparin using the Japanese quail chorioallantoic membrane model

Pathological angiogenesis characterized by uncontrollable vessel growth is an accompanying feature of many diseases. The avian embryo chorioallantoic membrane (CAM) is an excellent model for angiogenesis research. In our study we used a less common Japanese quail CAM model for the testing of angiogenic potential of leptin, high-molecular (heparin sodium) andlow-molecular (nadroparin calcium) heparins. Heparins play a significant role in vascular endothelial cell function, and they are able to modulate the activities of angiogenic growth factors. On embryonic day 7 leptin (5 μg per CAM), heparin sodium (75 IU per CAM) and nadroparin calcium (47.5 IU per CAM) in 500 μl PBS were applied on the CAM surface. After 24 h the fractal dimension (Df) of the vasculature was evaluated. Samples from each group were histologically analyzed and VEGF-A and Quek1 expression were detected by qPCR. Df was significantly increased in the leptin group. A moderate stimulatory effect of heparin sodium and an inhibitory effect of nadroparin calcium were observed. Both leptin and heparin sodium caused a noticeable increase in the CAM thickness compared to the control and nadroparin calcium groups. We observed an increased number of blood vessels and accumulation of fibroblasts. There was no significant impact on gene expression of VEGF-A and Quek1 24 h after treatment, however, trends similar to the changes in Df and CAM thickness were present. The resulting effect of nadroparin administration on Quek1 levels was exactly the opposite to that of leptin (p < 0.05).

Delayed access to feed alters gene expression associated with hormonal signaling, cellular differentiation, and protein metabolism in muscle of newly hatch chicks

Birds rely solely on utilization of the yolk sac as a means of nutritional support throughout embryogenesis and early post-hatch, before first feeding occurs. Newly hatched broiler (meat-type) chickens are frequently not given immediate access to feed, and this can result in numerous alterations to developmental processes, including those that occur in muscle. The objective of this study was to characterize the gene expression profile of newly hatched chicks' breast muscle with regards to hormonal regulation of growth and metabolism and development and differentiation of muscle tissue, and determine impacts of delayed access to feed on these profiles. Within 3 h of hatch, birds were placed in battery pens and given immediate access to feed (Fed) or delayed access to feed for 48 h (Delayed Fed). Breast muscle collected from male birds at hatch, or 4 h, 1 day (D), 2D, 4D, and 8D after hatch was used for analysis of mRNA expression by reverse transcription-quantitative PCR. Under fully fed conditions, insulin-like growth factor receptor and leptin receptor mRNA expression decreased as birds aged; however, delayed access to feed resulted in prolonged upregulation of these genes so their mRNA levels were higher in Delayed Fed birds at 2D. These expression profiles suggest that delayed feed access alters sensitivity to hormones that may regulate muscle development. Myogenin, a muscle differentiation factor, showed increasing mRNA expression in Fed birds through 2D, after which expression decreased. A similar expression pattern in Delayed Fed birds was deferred until 4D. Levels of myostatin, a negative regulator of muscle growth, increased in Fed birds starting at 2D, while levels in Delayed Fed birds began to increase at 4D. In Fed birds, levels of transcripts for two genes associated with protein catabolism, F-box protein 32 and forkhead box O3, were lower at 2D, while Delayed Fed mRNA levels did not decrease until 4D. Mechanistic target of rapamycin mRNA levels decreased from 1D through 8D in both treatments, except for a transient increase in the Delayed Fed birds between 1D and 2D. These data suggest that within breast muscle, delayed feeding alters hormonal signaling, interrupts tissue differentiation, postpones onset of growth, and may lead to increased protein catabolism. Together, these processes could ultimately contribute to a reduction in proper growth and development of birds not given feed immediately after hatch, and ultimately hinder the long-term potential of muscle accretion in meat type birds.

The Pierced Lasso Topology Leptin has a Bolt on Dynamic Domain Composed by the Disordered Loops I and III

Leptin is an important signaling hormone, mostly known for its role in energy expenditure and satiety. Furthermore, leptin plays a major role in other proteinopathies, such as cancer, marked hyperphagia, impaired immune function, and inflammation. In spite of its biological relevance in human health, there are no NMR resonance assignments of the human protein available, obscuring high-resolution characterization of the soluble protein and/or its conformational dynamics, suggested as being important for receptor interaction and biological activity. Here, we report the nearly complete backbone resonance assignments of human leptin. Chemical shift-based secondary structure prediction confirms that in solution leptin forms a four-helix bundle including a pierced lasso topology. The conformational dynamics, determined on several timescales, show that leptin is monomeric, has a rigid four-helix scaffold, and a dynamic domain, including a transiently formed helix. The dynamic domain is anchored to the helical scaffold by a secondary hydrophobic core, pinning down the long loops of leptin to the protein body, inducing motional restriction without a well-defined secondary or tertiary hydrogen bond stabilized structure. This dynamic region is well suited for and may be involved in functional allosteric dynamics upon receptor binding.

A cross-talk between leptin and 17β-estradiol in vitellogenin synthesis in rainbow trout Oncorhynchus mykiss liver

The existence of nutritional and energy reserves is fundamental for fish female fertility, so that the existence of a correlation between metabolic reserves and reproductive capacity is suggested. Leptin regulates body weight and energy homeostasis. Estradiol induces the synthesis of vitellogenin, a phospholipoglycoprotein produced by the liver and taken up by the growing oocytes. The objective of this study was to investigate the possible existence of a crosstalk between 17β-estradiol (E₂) and leptin in the modulation of E₂-induced vtg in the rainbow trout Oncorhynchus mykiss. Liver slices were incubated with recombinant trout leptin (rt-lep) at three different concentrations (1-10-100 ng/ml). rt-lep brought about the decrease of E₂-induced vtg secretion in the medium and the down-regulation of vtg mRNA expression. Moreover, rt-lep stimulated the lipase activity and diminished the liver fatty acid content. The combined employment of signal transduction inhibitors and the analysis of signal transduction phosphorylated factors revealed that rt-lep effect on E₂-induced vtg occurred through the activation of phosphodiesterase, protein kinase C, MAP kinases, and protein kinase A. In conclusion, our study suggests that leptin influences E₂-induced vtg synthesis in the rainbow trout Oncorhynchus mykiss by modifying both the protein and the lipid components.

Molecular characterization of two leptin genes and their transcriptional changes in response to fasting and refeeding in Northern snakehead (Channa argus)

Leptin has been proved to play critical roles in energy metabolism, body weight regulation, food intake, reproduction and immunity in mammals. However, its roles are still largely unclear in fish. Here, we report two leptin genes (lepA and lepB) from the Northern snakehead (Channa argus) and their transcriptions in response to different feeding status. The snakehead lepA is 781 bp in length and contains a 480 bp open reading frame (ORF) encoding a 159-aa protein, while the snakehead lepB is 553 bp in length and contains a 477 bp ORF encoding a 158-aa protein. Multi-sequences alignment, three-dimensional (3D) model prediction, syntenic and genomic comparison, and phylogenetic analysis confirm two leptin genes are widely existing in teleost. Tissue distribution revealed that the two leptin genes exhibit different patterns. In a post-prandial experiment, the hepatic lepA and brain lepB showed a similar transcription pattern. In a long-term (2-week) fasting and refeeding experiment, the hepatic lepA and brain lepB showed a similar transcription change pattern induced by food deprivation stimulation but differential changes after refeeding. These findings suggest snakehead lepA and lepB are differential both in tissue distribution and molecular functions, and they might play as an important regulator in energy metabolism and food intake in fish, respectively.

Acyl-CoA-binding protein (ACBP): a phylogenetically conserved appetite stimulator

Recently, we reported that, in mice, hunger causes the autophagy-dependent release of a protein called "acyl-CoA-binding protein" or "diazepam binding inhibitor" (ACBP/DBI) from cells, resulting in an increase in plasma ACBP concentrations. Administration of extra ACBP is orexigenic and obesogenic, while its neutralization is anorexigenic in mice, suggesting that ACBP is a major stimulator of appetite and lipo-anabolism. Accordingly, obese persons have higher circulating ACBP levels than lean individuals, and anorexia nervosa is associated with subnormal ACBP plasma concentrations. Here, we investigated whether ACBP might play a phylogenetically conserved role in appetite stimulation. We found that extracellular ACBP favors sporulation in Saccharomyces cerevisiae, knowing that sporulation is a strategy for yeast to seek new food sources. Moreover, in the nematode Caenorhabditis elegans, ACBP increased the ingestion of bacteria as well as the frequency pharyngeal pumping. These observations indicate that ACBP has a phylogenetically ancient role as a 'hunger factor' that favors food intake.

D76V, L161R, and C117S are the most pathogenic amino acid substitutions with several dangerous consequences on leptin structure, function, and stability

Background

Leptin is a versatile hormone with a variety of functions, including regulation of food intake by inhibiting hunger. Any deleterious mutation in this protein can lead to serious consequences for the body. This study was conducted to identify the most deleterious non-synonymous single-nucleotide polymorphisms (nsSNPs) of human LEP gene and their impact on its encoded protein.

Methods

To predict the possible impact of nsSNPs on leptin, a total of 90 nsSNPs were retrieved from dbSNP and investigated using many in silico tools which specially designed to analyze nsSNPs’ consequences on the protein structure, function, and stability.

Results

Three nsSNPs, namely D76V, L161R, and C117S, were found to be completely deleterious by all utilized nsSNPs prediction tools, thus affecting leptin protein structure, biological activity, and stability. Evolutionary information indicated L161R and C117S mutations to be located in extremely high conserved positions. Furthermore, several deleterious mechanisms controlled by both L161R and C117S mutations which alter several motifs in the secondary structure of leptin were detected. However, all D76V, L161R, and C117S mutations exhibited alteration in polar interactions in their representative positions. Further in-depth analyses proved several harmful structural effects of the three nsSNPs on leptin, which may lead to multiple intrinsic disorders in the altered protein forms.

Conclusions

This study provides the first comprehensive computation of the effect of the most damaging nsSNPs on leptin. The exploration of these missense mutations may present novel perspectives for various deleterious consequences originated from such amino acids substitutions. The dynamics of leptin performance, therefore, in many biological pathways, may be changed to create a variety of disorders, such as obesity and diabetes. These findings will help in detecting the most harmful variations needed to be screened for clinically diagnosed patients with leptin disorders.

Trial registration

ISRCTN73824458

Sex-dependent dominance maintains migration supergene in rainbow trout

Males and females often differ in their fitness optima for shared traits that have a shared genetic basis, leading to sexual conflict. Morphologically differentiated sex chromosomes can resolve this conflict and protect sexually antagonistic variation, but they accumulate deleterious mutations. However, how sexual conflict is resolved in species that lack differentiated sex chromosomes is largely unknown. Here we present a chromosome-anchored genome assembly for rainbow trout (Oncorhynchus mykiss) and characterize a 55-Mb double-inversion supergene that mediates sex-specific migratory tendency through sex-dependent dominance reversal, an alternative mechanism for resolving sexual conflict. The double inversion contains key photosensory, circadian rhythm, adiposity and sex-related genes and displays a latitudinal frequency cline, indicating environmentally dependent selection. Our results show sex-dependent dominance reversal across a large autosomal supergene, a mechanism for sexual conflict resolution capable of protecting sexually antagonistic variation while avoiding the homozygous lethality and deleterious mutations associated with typical heteromorphic sex chromosomes.

Avian Leptin: Bird's-Eye View of the Evolution of Vertebrate Energy-Balance Control

Discovery of the satiety hormone leptin in 1994 and its characterization in mammals provided a key tool to deciphering the complex mechanism governing adipose tissue regulation of appetite and energy expenditure. Surprisingly, despite the perfectly logical notion of an energy-storing tissue announcing the amount of fat stores using leptin signaling, alternate mechanisms were chosen in bird evolution. This conclusion emerged based on the recent discovery and characterization of genuine avian leptin - after it had been assumed missing by some, and erroneously identified by others. Critical evaluation of the past and present indications of the role of leptin in Aves provides a new perspective on the evolution of energy-balance control in vertebrates; proposing a regulation strategy alternative to the adipostat mechanism.

Effects of quercetin on the neuromotor function and behavioral responses of Wistar and Zucker rats fed a high-fat and high-carbohydrate diet

Quercetin can affect some pathological manifestations in obesity. The mechanism underlying the presumed therapeutic effect of quercetin is probably related to the influence on the central processes regulating energy homeostasis. Thus, the purpose of this study was to examine the effect of quercetin on the neuromotor and behavioral functions in Zucker (Z) and Wistar (W) rats with genetically and/or diet-induced obesity. Rats of both strains received balanced or high fat and fructose diet (HFCD) in a 62-day experiment or the same diets supplemented with quercetin at the dose of 50 mg/kg body weight per day. The neuromotor function and behavioral responses were examined using the grip strength test, open field test, elevated plus maze test and conditioned passive avoidance response (CPAR) test. The quercetin potentiated a decrease in anxiety in W rats consumed HFCD and this effect was absent in Z rats with a defect in the leptin receptor gene. In contrast, quercetin increased locomotor activity and impaired short-term memory in the CPAR test only in Z rats with the absence of normal leptin reception. Against the background of the identified changes quercetin exerted significant effects on the lipid and nitrogen metabolism indices such as HDL cholesterol, AsAT/AlAT activities ratio, urea level as well as body and fat mass that were different in Z and W rats. The data obtained show that the effects of quercetin on behavior vary significantly between two strains of rat and consequently are mediated by processes of leptin reception.

Leptin-a mediates transcription of genes that participate in central endocrine and phosphatidylinositol signaling pathways in 72-hour embryonic zebrafish (Danio rerio)

We analyzed microarray expression data to highlight biological pathways that respond to embryonic zebrafish Leptin-a (lepa) signaling. Microarray expression measures for 26,046 genes were evaluated from lepa morpholino oligonucleotide "knockdown", recombinant Leptin-a "rescue", and uninjected control zebrafish at 72-hours post fertilization. In addition to KEGG pathway enrichment for phosphatidylinositol signaling and neuroactive ligand-receptor interactions, Gene Ontology (GO) data from lepa rescue zebrafish include JAK/STAT cascade, sensory perception, nervous system processes, and synaptic signaling. In the zebrafish lepa rescue treatment, we found changes in the expression of homologous genes that align with mammalian leptin signaling cascades including AMPK (prkaa2), ACC (acacb), Ca²⁺/calmodulin-dependent kinase (camkk2), PI3K (pik3r1), Ser/Thr protein kinase B (akt3), neuropeptides (agrp2, cart1), mitogen-activated protein kinase (MAPK), and insulin receptor substrate (LOC794738, LOC100537326). Notch signaling pathway and ribosome biogenesis genes respond to knockdown of Leptin-a. Differentially expressed transcription factors in lepa knockdown zebrafish regulate neurogenesis, neural differentiation, and cell fate commitment. This study presents a role for zebrafish Leptin-a in influencing expression of genes that mediate phosphatidylinositol and central endocrine signaling.

Zebrafish Mutants Carrying Leptin a (lepa) Gene Deficiency Display Obesity, Anxiety, Less Aggression and Fear, and Circadian Rhythm and Color Preference Dysregulation

Leptin, a hormone secreted by peripheral adipose tissues, regulates the appetite in animals. Recently, evidence has shown that leptin also plays roles in behavioral response in addition to controlling appetite. In this study, we examined the potential function of leptin on non-appetite behaviors in zebrafish model. By using genome editing tool of Transcription activator-like effector nuclease (TALEN), we successfully knocked out leptin a (lepa) gene by deleting 4 bp within coding region to create a premature-translation stop. Morphological and appetite analysis showed the lepa KO fish display a phenotype with obese, good appetite and elevation of Agouti-related peptide (AgRP) and Ghrelin hormones, consistent with the canonical function of leptin in controlling food intake. By multiple behavior endpoint analyses, including novel tank, mirror biting, predator avoidance, social interaction, shoaling, circadian rhythm, and color preference assay, we found the lepa KO fish display an anxiogenic phenotype showing hyperactivity with rapid swimming, less freezing time, less fear to predator, loose shoaling area forming, and circadian rhythm and color preference dysregulations. Using biochemical assays, melatonin, norepinephrine, acetylcholine and serotonin levels in the brain were found to be significantly reduced in lepa KO fish, while the levels of dopamine, glycine and cortisol in the brain were significantly elevated. In addition, the brain ROS level was elevated, and the anti-oxidative enzyme catalase level was reduced. Taken together, by performing loss-of-function multiple behavior endpoint testing and biochemical analysis, we provide strong evidence for a critical role of lepa gene in modulating anxiety, aggression, fear, and circadian rhythm behaviors in zebrafish for the first time.

Perspectives and applications of machine learning for evolutionary developmental biology

Evolutionary Developmental Biology (Evo-Devo) is an ever-expanding field that aims to understand how development was modulated by the evolutionary process. In this sense, "omic" studies emerged as a powerful ally to unravel the molecular mechanisms underlying development. In this scenario, bioinformatics tools become necessary to analyze the growing amount of information. Among computational approaches, machine learning stands out as a promising field to generate knowledge and trace new research perspectives for bioinformatics. In this review, we aim to expose the current advances of machine learning applied to evolution and development. We draw clear perspectives and argue how evolution impacted machine learning techniques.

Adipocytes spectrum - From homeostasia to obesity and its associated pathology

Firstly identified by anatomists, the fat tissue is nowadays an area of intense research due to increased global prevalence of obesity and its associated diseases. Histologically, there are four types of fat tissue cells which are currently recognized (white, brown, beige, and perivascular adipocytes). Therefore, in this study we are reviewing the most recent data regarding the origin, structure, and molecular mechanisms involved in the development of adipocytes. White adipocytes can store triglycerides as a consequence of lipogenesis, under the regulation of growth hormone or leptin and adiponectin, and release fatty acids resulted from lipolysis, under the regulation of the sympathetic nervous system, glucocorticoids, TNF-α, insulin, and natriuretic peptides. Brown adipocytes possess a mitochondrial transmembrane protein thermogenin or UCP1 which allows heat generation. Recently, thermogenic, UCP positive adipocytes have been identified in the subcutaneous white adipose tissue and have been named beige adipocytes. The nature of these cells is still controversial, as current theories are suggesting their origin either by transdifferentiation of white adipocytes, or by differentiation from an own precursor cell. Perivascular adipocytes surround most of the arteries, exhibiting a supportive role and being involved in the maintenance of intravascular temperature. Thoracic perivascular adipocytes resemble brown adipocytes, while abdominal ones are more similar to white adipocytes and, consequently, are involved in obesity-induced inflammatory reactions. The factors involved in the regulation of adipose stem cells differentiation may represent potential pathways to inhibit or to divert adipogenesis. Several molecules, such as pro-adipogenic factors (FGF21, BMP7, BMP8b, and Cox-2), cell surface proteins or receptors (Asc-1, PAT2, P2RX5), and hypothalamic receptors (MC4R) have been identified as the most promising targets for the development of future therapies. Further investigations are necessary to complete the knowledge about adipose tissue and the development of a new generation of therapeutic tools based on molecular targets.

Leptin and leptin receptor genes in tongue sole (Cynoglossus semilaevis): Molecular cloning, tissue distribution and differential regulation of these genes by sex steroids

Leptin (Lep) is a key factor for the regulation of food intake and energy homeostasis in mammals. To date, a number of studies have provided evidence for the existence of multiple leptin genes in teleosts, but not much information is available in fish regarding the regulation of leptin genes by sex steriods. As a first step, two leptin genes (lepa and lepb) and a leptin receptor (lepr) gene were cloned from the half-smooth tongue sole (Cynoglossus semilaevis), a representative species of the order Pleuronectiformes. The full-length cDNAs of tongue sole lepa and lepb were 1265 bp and 1157 bp in length, encoding for proteins of 160 aa and 158 aa, respectively. The three-dimensional structures modeling of tongue sole LepA and LepB showed strong conservation of tertiary structure with other vertebrates. The full-length cDNA of tongue sole lepr was 4576 bp, encoding a protein of 1133 aa which contained all functionally important domains conserved among vertebrate LepRs. Tissue distribution analysis showed that tongue sole lepa mRNA was highly detectable in the ovary and brain, while lepb mRNA was ubiquitously expressed in various tissues. Notably, the tongue sole lepr mRNA was most abundant in the ovary. Using a primary hepatocyte culture system, we evaluated the effects of sex steroids on lep/lepr gene expression. Both 17β-estradiol (E2) and testosterone (T) inhibited hepatic lepa and lepr mRNAs without affecting lepb mRNA levels. In addition, T also suppressed growth hormone receptor 1 (ghr1), ghr2, and insulin-like growth factor 2 (igf-2) mRNA levels, and stimulated expression of igf-1 gene. On the other hand, none of these four genes were altered by E2. To the best of our knowledge, this is the first description of a direct and differential regulation of lep/lepr gene expression by sex steroids at the hepatocyte level of a flatfish, supporting that individual leptin peptide may possess different biological roles in teleosts.

The expression and distribution of a leptin receptor in the central nervous system, digestive organs, and gonads of the giant freshwater prawn, Macrobrachium rosenbergii

In the present study, the presence and distribution of leptin receptor (LEP-R) in central nervous system, digestive organs, gonads of giant freshwater prawn, Macrobrachium rosenbergii, were investigated with Western blot and immunohistochemistry. By Western blot a LEP-R with a molecular weight (MW) of 100 kDa was detected in the brain, thoracic ganglia, abdominal ganglia, hepatopancreas, all parts of the gastrointestinal tract, ovaries, and testes. In hepatopancreas and foregut, another intense positive band was detected at molecular weight of 30 kDa, which could be an isotype of LEP-R. By immunohistochemistry, LEP-R-ir was detected in the neurons, and neuropils in the brain, thoracic ganglia, and abdominal ganglia. In the gastrointestinal tract, there was intense LEP-R-ir in the apical part of the epithelial cells of the foregut, midgut, and hindgut. In addition, LEP-R-ir was found in the Restzellen(R)cells and Fibrillenzellen(F) cells in the hepatopancreas. In the ovary, LEP-R-ir was detected in early stage of oocytes and mature oocytes. Intense LEP-R-ir was observed in spermatogonia and spermatocytes of the small and orange claw male prawns. In addition, LEP-R was seen in the high epithelium of spermatic ducts from all male morphotypes. In summary, the detection of the LEP-R-ir suggests the existence of a LEP-R in several organs of M. rosenbergii. Through binding with leptin peptide, LEP-R may be an important signaling molecule that has critical functions in modulating and controlling food intake, energy expenditure, and reproduction in this prawn.

Adiposity signals predict vocal effort in Alston's singing mice

Advertisement displays often seem extravagant and expensive, and are thought to depend on the body condition of a signaller. Nevertheless, we know little about how signallers adjust effort based on condition, and few studies find a strong relationship between natural variation in condition and display. To examine the relationship between body condition and signal elaboration more fully, we characterized physiological condition and acoustic displays in a wild rodent with elaborate vocalizations, Alston's singing mouse, Scotinomys teguina We found two major axes of variation in condition-one defined by short-term fluctuations in caloric nutrients, and a second by longer-term variation in adiposity. Among acoustic parameters, song effort was characterized by high rates of display and longer songs. Song effort was highly correlated with measures of adiposity. We found that leptin was a particularly strong predictor of display effort. Leptin is known to influence investment in other costly traits, such as immune function and reproduction. Plasma hormone levels convey somatic state to a variety of tissues, and may govern trait investment across vertebrates. Such measures offer new insights into how animals translate body condition into behavioural and life-history decisions.

Leptin Stimulates Prolactin mRNA Expression in the Goldfish Pituitary through a Combination of the PI3K/Akt/mTOR, MKK3/6/p38MAPK and MEK1/2/ERK1/2 Signalling Pathways

Leptin actions at the pituitary level have been extensively investigated in mammalian species, but remain insufficiently characterized in lower vertebrates, especially in teleost fish. Prolactin (PRL) is a pituitary hormone of central importance to osmoregulation in fish. Using goldfish as a model, we examined the global and brain-pituitary distribution of a leptin receptor (lepR) and examined the relationship between expression of lepR and major pituitary hormones in different pituitary regions. The effects of recombinant goldfish leptin-AI and leptin-AII on PRL mRNA expression in the pituitary were further analysed, and the mechanisms underlying signal transduction for leptin-induced PRL expression were determined by pharmacological approaches. Our results showed that goldfish lepR is abundantly expressed in the brain-pituitary regions, with highly overlapping PRL transcripts within the pituitary. Recombinant goldfish leptin-AI and leptin-AII proteins could stimulate PRL mRNA expression in dose- and time-dependent manners in the goldfish pituitary, by both intraperitoneal injection and primary cell incubation approaches. Moreover, the PI3K/Akt/mTOR, MKK_3/6/p³⁸MAPK, and MEK_1/2/ERK_1/2—but not JAK2/STAT 1, 3 and 5 cascades—were involved in leptin-induced PRL mRNA expression in the goldfish pituitary.

The evolution of metabolic regulation in animals

Energy metabolism is determined by a suite of regulatory mechanism, and their increasing complexity over evolutionary time provides the key to understanding the emergence of different metabolic phenotypes. Energy metabolism is at the core of biological processes because all organisms must maintain energy balance against thermodynamic gradients. Energy metabolism is regulated by a bewildering array of interacting molecular mechanisms, and much of what is known about metabolic regulation comes from the medical literature. However, ecology and evolutionary research would gain considerably by incorporating regulatory mechanisms more explicitly in research on topics such as the evolution of endothermy, metabolic plasticity, and energy balance. The purpose of this brief review is to summarise the main regulatory pathways of energy metabolism in animals and their evolutionary origins to make these complex interactions more accessible to researchers from a broad range of backgrounds. Some of the principal regulators of energy balance, such as the AMP-stimulated protein kinase, have an ancient prokaryotic origin. Most regulatory pathways (e.g. thyroid hormone, insulin, adipokines), however, are eukaryotic in origin and diversified substantially in metazoans and vertebrates. Diversification in vertebrates is at least partly due to genome duplications early in this lineage. The interaction between regulatory mechanisms permitted an increasingly sophisticated fine-tuning of energy balance and metabolism. Hence, regulatory complexity increased over evolutionary time, and taxa differ in their potential range of metabolic phenotypes. Choice of model organism therefore becomes important, and bacteria or even invertebrates are not good models for more derived vertebrates. Different metabolic phenotypes and their evolution, such as endothermy and metabolic plasticity, should be interpreted against this regulatory background.