A nutrient-responsive hormonal circuit mediates an inter-tissue program regulating metabolic homeostasis in adult Drosophila

CAPA Neuropeptide and Its Receptor in Insects: A Mini Review

A neuropeptide, the CAPA, and its cognate receptor have been diversely characterized in different orders of class Insecta. CAPA peptides are synthesized in the abdominal neurohemal system and activate their corresponding receptor, CAPA receptor (CAPA-R), a type of G protein-coupled receptor (GPCR), to initiate cellular signals for diverse physiological functions in insects. Activation of the CAPA-R in Malpighian tubules results in ion-water homeostasis via antidiuresis in the majority of insect species; however, diuresis and myotropic activities are also known to result. Antidiuretic activity of CAPA peptides has been reported from mosquitoes, assassin bugs, spotted wing drosophila, and more; hence, this group of peptides also holds importance as potential targets when it comes to medical and agricultural entomology. GPCRs form a diverse family of cell membrane receptors responsible for signal transduction across the cell membrane in humans as well as in insects. With the advances in knowledge of human GPCRs, their physiological functions in agriculturally important insects have offered an opportunity for designing and implementing GPCR-targeting compounds in integrated pest management programs. In this review, we present a comprehensive view on physiological factors and peptides responsible for the diuresis/anti-diuresis in insects with special reference to the CAPA peptide-receptor interaction. The major focus is on the role of CAPA peptides in fluid and energy homeostasis, stress tolerance, muscle functioning, regulation of reproduction, and diapause-related processes. We end by outlining the significance of insect excretion with respect to the capa-r gene silencing and pest management.

The Integrative Physiology of Hormone Signaling: Insights from Insect Models

Hormones orchestrate virtually all physiological processes in animals and enable them to adjust internal responses to meet diverse physiological demands. Studies in both vertebrates and insects have uncovered many novel hormones and dissected the physiological mechanisms they regulate, demonstrating a remarkable conservation in endocrine signaling across the tree of life. In this review, we focus on recent advances in insect research, which have provided a more integrative view of the conserved interorgan communication networks that control physiology. These new insights have been driven by experimental advantages inherent to insects, which over the past decades have aligned with new technologies and sophisticated genetic tools, to transform insect genetic models into a powerful testbed for posing new questions and exploring longstanding issues in endocrine research. Here, we illustrate how insect studies have addressed classic questions in three main areas, hormonal control of growth and development, neuroendocrine regulation of ion and water balance, and hormonal regulation of behavior and metabolism, and how these discoveries have illuminated our fundamental understanding of endocrine signaling in animals. The application of integrative physiology in insect systems to questions in endocrinology and physiology is expanding and is poised to be a crucible of discovery, revealing fundamental mechanisms of hormonal regulation that underlie animal adaptations to their environments.

Protein-responsive gut hormone tachykinin directs food choice and impacts lifespan

Animals select food based on hungers that reflect dynamic macronutrient needs, but the hormonal mechanisms underlying nutrient-specific appetite regulation remain poorly defined. Here, we identify tachykinin (Tk) as a protein-responsive gut hormone in Drosophila and female mice, regulated by conserved environmental and nutrient-sensing mechanisms. Protein intake activates Tk-expressing enteroendocrine cells (EECs), driving the release of gut Tk through mechanisms involving target of rapamycin (TOR) and transient receptor potential A1 (TrpA1). In flies, we delineate a pathway by which gut Tk controls selective appetite and sleep after protein ingestion, mediated by glucagon-like adipokinetic hormone (AKH) signalling to neurons and adipose tissue. This mechanism suppresses protein appetite, promotes sugar hunger and modulates wakefulness to align behaviour with nutritional needs. Inhibiting protein-responsive gut Tk prolongs lifespan through AKH, revealing a role for nutrient-dependent gut hormone signalling in longevity. Our results provide a framework for understanding EEC-derived nutrient-specific satiety signals and the role of gut hormones in regulating food choice, sleep and lifespan.

Regulation of feeding and defecation in Drosophila by trpγ, piezo, and DH44R2

Normal gastrointestinal (GI) motility, including defecation, is crucial for nutrient absorption, energy balance, and overall health in species ranging from insects to humans. Disruptions in GI motility can lead to conditions like constipation or severe diseases. Mechanosensors, including TRP channels and Piezo, are known to play key roles in regulating gut physiology in Drosophila melanogaster, but their precise involvement in defecation is not fully understood. Additionally, neuropeptides like DH44 have been implicated in gut regulation. This study explores the roles of Trpγ, Diuretic hormone 44 Receptor 2 (DH44R2), and Piezo in controlling feeding amount, gut motility, and defecation using genetic mutants and RNAi techniques. Mutants for these genes exhibited increased excreta production and size, whereas Dh44 and Dh44R1 mutants had a reduced number of excreta, but with increased size. Co-expression and rescue experiments further confirmed the critical roles of these genes in the same gut cells. The findings reveal that local gut-specific mechanisms are the primary drivers of defecation. The results highlight the collaboration between Trpγ, Piezo, and DH44R2 in regulating gut motility and defecation. By uncovering how these mechanosensory proteins and cells work together, this research may offer insights into human GI disorders like Irritable Bowel Syndrome (IBS) and Hirschsprung's disease, shedding light on the complex regulatory network underlying defecation.

Neuropeptides from a praying mantis: what the loss of pyrokinins and tryptopyrokinins suggests about the endocrine functions of these peptides

Background

Neuropeptides play important roles in insects, but in many cases their functions remain obscure. Comparative neuropeptidome analyses may provide clues to what these functions might be. Praying mantises are predators and close relatives of cockroaches that are scavengers. Cockroach neuropeptidomes are well established, but little is known about mantis neuropeptides. The recently published genome assembly of the praying mantis Tenodera sinensis makes it Possible to change that.

Methods

The genome assembly from T. sinensis was analyzed for the presence of genes coding neuropeptides. For comparison, publicly available short read archives from this and other mantis species were also examined for the presence and expression of neuropeptides.

Results

As a rule, the neuropeptidomes of the Mantodea and Blattodea are almost identical; praying mantises and cockroaches use very similar neuropeptides. However, there is one surprising exception. Praying mantises lack the receptors for pyrokinins, including those for the tryptopyrokinins. No typical pyrokinin genes were found, but some species do have a tryptopyrokinin gene, in others this has also been lost and, in one species it is a speudogene. For most praying mantises there is no information where tryptopyrokinin is expressed, but in Deroplatys truncata it is in the thorax and thus not in the suboesophageal ganglion, as in other insects. In the genomic short read archives of two species-out of 52-sequences were found for a tryptopyrokinin specific receptor. The phylogenetic position of those two species implies that the receptor gene was independently lost on multiple occasions. The loss of the tryptopyrokinin gene also happened more than once.

Discussion

The multiple independent losses of the pyrokinin receptors in mantises suggests that these receptors are irrelevant in praying mantises. This is very surprising, since expression of tryptopyrokinin is very strongly conserved in two neuroendocrine cells in the suboeosphageal ganglion. In those species for which this is known, the expression of its receptor is in the salivary gland. As a neuroendocrine, tryptopyrokinin is unlikely to acutely regulate salivation, which in other insects is regulated by well characterized neurons. If the action of tryptopyrokinin were to prime the salivary gland for subsequent salivation, it would make perfect sense for a praying mantis to lose this capacity, as they can not anticipate when they will catch their next prey. Priming the salivary gland days before it is actually needed would be energetically costly. The other pyrokinins are known to facilitate feeding and may in a similar fashion prime muscles needed for moving to the food source and digesting it. This hypothesis provides a good explanation as to why praying mantises do not need pyrokinins, and also what the function of these ubiquitous arthropod neuropeptides may be.

A tumor-secreted protein utilizes glucagon release to cause host wasting

Tumor‒host interaction plays a critical role in malignant tumor-induced organ wasting across multiple species. Despite known regulation of regional wasting of individual peripheral organs by tumors, whether and how tumors utilize critical host catabolic hormone(s) to simultaneously induce systemic host wasting, is largely unknown. Using the conserved yki3SA-tumor model in Drosophila, we discovered that tumors increase the production of adipokinetic hormone (Akh), a glucagon-like catabolic hormone, to cause systemic host wasting, including muscle dysfunction, lipid loss, hyperglycemia, and ovary atrophy. We next integrated RNAi screening and Gal4-LexA dual expression system to show that yki3SA-gut tumors secrete Pvf1 to remotely activate its receptor Pvr in Akh-producing cells (APCs), ultimately promoting Akh production. The underlying molecular mechanisms involved the Pvf1-Pvr axis that triggers Mmp2-dependent ECM remodeling of APCs and enhances innervation from the excitatory cholinergic neurons. Interestingly, we also confirmed the similar mechanisms governing tumor-induced glucagon release and organ wasting in mammals. Blockade of either glucagon or PDGFR (homolog of Pvr) action efficiently ameliorated organ wasting in the presence of malignant tumors. Therefore, our results demonstrate that tumors remotely promote neural-associated Akh/glucagon production via Pvf1-Pvr axis to cause systemic host wasting.

A brief history of insect neuropeptide and peptide hormone research

This review briefly summarizes 50 years of research on insect neuropeptide and peptide hormone (collectively abbreviated NPH) signaling, starting with the sequencing of proctolin in 1975. The first 25 years, before the sequencing of the Drosophila genome, were characterized by efforts to identify novel NPHs by biochemical means, mapping of their distribution in neurons, neurosecretory cells, and endocrine cells of the intestine. Functional studies of NPHs were predominantly dealing with hormonal aspects of peptides and many employed ex vivo assays. With the annotation of the Drosophila genome, and more specifically of the NPHs and their receptors in Drosophila and other insects, a new era followed. This started with matching of NPH ligands to orphan receptors, and studies to localize NPHs with improved detection methods. Important advances were made with introduction of a rich repertoire of innovative molecular genetic approaches to localize and interfere with expression or function of NPHs and their receptors. These methods enabled cell- or circuit-specific interference with NPH signaling for in vivo assays to determine roles in behavior and physiology, imaging of neuronal activity, and analysis of connectivity in peptidergic circuits. Recent years have seen a dramatic increase in reports on the multiple functions of NPHs in development, physiology and behavior. Importantly, we can now appreciate the pleiotropic functions of NPHs, as well as the functional peptidergic "networks" where state dependent NPH signaling ensures behavioral plasticity and systemic homeostasis.

Allatotropin, DH31, and proctolin reduce chill tolerance in the two-spotted cricket, Gryllus bimaculatus

The ability of insects to tolerate low temperatures, known as chill tolerance, contributes to their global distribution. However, the mechanisms underlying insect chill tolerance remain poorly understood. At low temperatures, insects enter chill coma, a reversible state of paralysis, owing to disrupted ion and water homeostasis. Upon returning to normal temperatures, insects reestablish ion and water homeostasis and recover the ability to move. In this study, we used the two-spotted cricket, Gryllus bimaculatus, as an experimental model and unveiled the roles of neuropeptides in regulating chill tolerance, typically evaluated by the time taken to recover from chill coma. Screening of 37 neuropeptides revealed that Allatotropin, DH31, and Proctolin inhibited chill coma recovery and decreased the survival rate under cold stress. RT-qPCR analyses revealed that the receptors for Allatotropin and DH31 were predominantly expressed in the hindgut. Injection of the three neuropeptides decreased both hemolymph mass and gut water content at low temperatures, most likely by increasing water excretion from the hindgut due to their effects on the rectum contraction. Additionally, Allatotropin and DH31 were produced by the terminal abdominal ganglion (TAG) innervating the hindgut since they were partly co-localized in the TAG, and their mature peptides were detected in the TAG-hindgut nerves. Moreover, the transcriptional levels of the neuropeptides in the TAG and receptors in the hindgut changed with cold exposure and rewarming. Based on these findings, we propose that Allatotropin, DH31, and Proctolin affect the physiological activities of the gut, probably the hindgut, to disrupt water homeostasis at low temperatures, thereby reducing chill tolerance in crickets.

Animal models in biomedical research: Relevance of Drosophila melanogaster

Animal models have become veritable tools in gaining insight into the pathogenesis and progression of several human diseases. These models could range in complexity from Caenorhabditis elegans to non-human primates. With the aid of these animal models, a lot of new knowledge has been gained about several diseases which otherwise would not have been possible. Most times, the utilization of these animal models is predicated on the level of homology they share with humans, which suggests that outcomes of studies using them could be extrapolated to humans. However, this has not always been the case. Drosophila melanogaster is becoming increasingly relevant as preferred model for understanding the biochemical basis of several human diseases. Apart from its relatively short lifespan, high fecundity and ease of rearing, the simplicity of its genome and lower redundancy of its genes when compared with vertebrate models, as well as availability of genetic tool kit for easy manipulation of its genome, have all contributed to its emergence as a valid animal model of human diseases. This review aimed at highlighting the contributions of selected animal models in biomedical research with a focus on the relevance of Drosophila melanogaster in understanding the biochemical basis of some diseases that have continued to plague mankind.

Neuropeptides specify and reprogram division of labor in the leafcutter ant Atta cephalotes

Social insects offer powerful models to investigate the mechanistic foundation of elaborate individual behaviors comprising a cooperative community. Workers of the leafcutter ant genus Atta provide an extreme example of behavioral segregation among many phenotypically distinct worker types. We utilize the complex worker system of Atta cephalotes to test the molecular underpinnings of behavioral programming and, in particular, the extent of plasticity to reprogramming. We identify specific neuropeptides as mediators of worker division of labor in A. cephalotes , finding two neuropeptides associated with characteristic behaviors of leafcutting and of brood care. Manipulation via genetic knockdown or by injection of these neuropeptides led to stark loss or gain of each behavior and to transcriptomic shifts in the predicted direction, that is, towards gene pathways expressed in the natural caste. We also compare specific A. cephalotes worker transcriptomes with those of orthologous workers of the eusocial mammal, the naked mole rat H. gaber , revealing global similarities between caste-biased expression and link to specific roles of our studied neuropeptides in ants. This work underscores the essential function of neuropeptides in establishing complex social behavior and a remarkable plasticity among individual behavioral types.

Synaptic connectome of a neurosecretory network in the Drosophila brain

Hormones mediate inter-organ signaling which is crucial in orchestrating diverse behaviors and physiological processes including sleep and activity, feeding, growth, metabolism and reproduction. The pars intercerebralis and pars lateralis in insects represent major hubs which contain neurosecretory cells (NSC) that produce various hormones. To obtain insight into how hormonal signaling is regulated, we have characterized the synaptic connectome of NSC in the adult Drosophila brain. Identification of neurons providing inputs to multiple NSC subtypes implicates diuretic hormone 44-expressing NSC as a major coordinator of physiology and behavior. Surprisingly, despite most NSC having dendrites in the subesophageal zone (primary taste processing center), gustatory inputs to NSC are largely indirect. We also deciphered pathways via which diverse olfactory inputs are relayed to NSC. Further, our analyses revealed substantial inputs from descending neurons to NSC, suggesting that descending neurons regulate both endocrine and motor output to synchronize physiological changes with appropriate behaviors. In contrast to NSC inputs, synaptic output from NSC is sparse and mostly mediated by corazonin NSC. Therefore, we additionally determine putative paracrine interconnectivity between NSC subtypes and hormonal pathways from NSC to peripheral tissues by analyzing single-cell transcriptomic datasets. Our comprehensive characterization of the Drosophila neurosecretory network connectome provides a platform to understand complex hormonal networks and how they orchestrate animal behaviors and physiology.

LGR signaling mediates muscle-adipose tissue crosstalk and protects against diet-induced insulin resistance

Obesity impairs tissue insulin sensitivity and signaling, promoting type-2 diabetes. Although improving insulin signaling is key to reversing diabetes, the multi-organ mechanisms regulating this process are poorly defined. Here, we screen the secretome and receptome in Drosophila to identify the hormonal crosstalk affecting diet-induced insulin resistance and obesity. We discover a complex interplay between muscle, neuronal, and adipose tissues, mediated by Bone Morphogenetic Protein (BMP) signaling and the hormone Bursicon, that enhances insulin signaling and sugar tolerance. Muscle-derived BMP signaling, induced by sugar, governs neuronal Bursicon signaling. Bursicon, through its receptor Rickets, a Leucine-rich-repeat-containing G-protein coupled receptor (LGR), improves insulin secretion and insulin sensitivity in adipose tissue, mitigating hyperglycemia. In mouse adipocytes, loss of the Rickets ortholog LGR4 blunts insulin responses, showing an essential role of LGR4 in adipocyte insulin sensitivity. Our findings reveal a muscle-neuronal-fat-tissue axis driving metabolic adaptation to high-sugar conditions, identifying LGR4 as a critical mediator in this regulatory network.

Compensatory enhancement of input maintains aversive dopaminergic reinforcement in hungry Drosophila

Hungry animals need compensatory mechanisms to maintain flexible brain function, while modulation reconfigures circuits to prioritize resource seeking. In Drosophila, hunger inhibits aversively reinforcing dopaminergic neurons (DANs) to permit the expression of food-seeking memories. Multitasking the reinforcement system for motivation potentially undermines aversive learning. We find that chronic hunger mildly enhances aversive learning and that satiated-baseline and hunger-enhanced learning require endocrine adipokinetic hormone (AKH) signaling. Circulating AKH influences aversive learning via its receptor in four neurons in the ventral brain, two of which are octopaminergic. Connectomics revealed AKH receptor-expressing neurons to be upstream of several classes of ascending neurons, many of which are presynaptic to aversively reinforcing DANs. Octopaminergic modulation of and output from at least one of these ascending pathways is required for shock- and bitter-taste-reinforced aversive learning. We propose that coordinated enhancement of input compensates for hunger-directed inhibition of aversive DANs to preserve reinforcement when required.

A nutrient responsive lipase mediates gut-brain communication to regulate insulin secretion in Drosophila

Pancreatic β cells secrete insulin in response to glucose elevation to maintain glucose homeostasis. A complex network of inter-organ communication operates to modulate insulin secretion and regulate glucose levels after a meal. Lipids obtained from diet or generated intracellularly are known to amplify glucose-stimulated insulin secretion, however, the underlying mechanisms are not completely understood. Here, we show that a Drosophila secretory lipase, Vaha (CG8093), is synthesized in the midgut and moves to the brain where it concentrates in the insulin-producing cells in a process requiring Lipid Transfer Particle, a lipoprotein originating in the fat body. In response to dietary fat, Vaha stimulates insulin-like peptide release (ILP), and Vaha deficiency results in reduced circulatory ILP and diabetic features including hyperglycemia and hyperlipidemia. Our findings suggest Vaha functions as a diacylglycerol lipase physiologically, by being a molecular link between dietary fat and lipid amplified insulin secretion in a gut-brain axis.

The functional assay identified authentic interactions between CAPA peptides and the CAPA receptor isoforms in Bemisia tabaci (Gennadius)

CAPA neuropeptides regulate the diuresis/ antidiuresis process in insects by activating specific cognate receptor, CAPAr. In this study, we characterized the CAPAr gene (BtabCAPAr) in the whitefly, Bemisia tabaci Asia II 1. The two alternatively spliced isoforms of BtabCAPAr gene, BtabCAPAr-1 and BtabCAPAr-2, having six and five exons, respectively, were identified. The BtabCAPAr gene expression was highest in adult whitefly as compared to gene expression in egg, nymphal and pupal stages. Among the three putative CAPA peptides, CAPA-PVK1 and CAPA-PVK2 strongly activated the BtabCAPAr-1 with very low EC50 values of 0.067 nM and 0.053 nM, respectively, in heterologous calcium mobilization assays. None of the peptide activated the alternatively spliced isoform BtabCAPAr-2 that has lost the transmembrane segments 3 and 4. Significant levels of mortality were observed when whiteflies were fed with CAPA-PVK1 at 1.0 μM (50.0%), CAPA-PVK2 at 100.0 nM (43.8%) and CAPA-tryptoPK 1.0 μM (40.0%) at the 96 h after the treatment. This study provides valuable information to design biostable peptides to develop a class of insecticides.

Mechanisms of Systemic Osmoregulation in Insects

Water is essential to life. Terrestrial insects lose water by evaporation from the body surface and respiratory surfaces, as well as in the excretory products, posing a challenge made more acute by their high surface-to-volume ratio. These losses must be kept to a minimum and be offset by water gained from other sources. By contrast, insects such as the blood-sucking bug Rhodnius prolixus consume up to 10 times their body weight in a single blood meal, necessitating rapid expulsion of excess water and ions. How do insects manage their ion and water budgets? A century of study has revealed a great deal about the organ systems that insects use to maintain their ion and water balance and their regulation. Traditionally, a taxonomically wide range of species were studied, whereas more recent research has focused on model organisms to leverage the power of the molecular genetic approach. Key advances in new technologies have become available for a wider range of species in the past decade. We document how these approaches have already begun to inform our understanding of the diversity and conservation of insect systemic osmoregulation. We advocate that these technologies be combined with traditional approaches to study a broader range of nonmodel species to gain a comprehensive overview of the mechanism underpinning systemic osmoregulation in the most species-rich group of animals on earth, the insects.

Self-DNA Inhibition in Drosophila melanogaster Development: Metabolomic Evidence of the Molecular Determinants

We investigated the effects of dietary delivered self-DNA in the model insect Drosophila melanogaster. Self-DNA administration resulted in low but significant lethality in Drosophila larvae and considerably extended the fly developmental time. This was characterized by the abnormal persistence of the larvae in the L2 and L3 stages, which largely accounted for the average 72 h delay observed in pupariation, as compared to controls. In addition, self-DNA exposure affected adult reproduction by markedly reducing both female fecundity and fertility, further demonstrating its impact on Drosophila developmental processes. The effects on the metabolites of D. melanogaster larvae after exposure to self-DNA were studied by NMR, LC-MS, and molecular networking. The results showed that self-DNA feeding reduces the amounts of all metabolites, particularly amino acids and N-acyl amino acids, which are known to act as lipid signal mediators. An increasing amount of phloroglucinol was found after self-DNA exposure and correlated to developmental delay and egg-laying suppression. Pidolate, a known intermediate in the γ-glutamyl cycle, also increased after exposure to self-DNA and correlated to the block of insect oogenesis.

Managing fuels and fluids: Network integration of osmoregulatory and metabolic hormonal circuits in the polymodal control of homeostasis in insects

Osmoregulation in insects is an essential process whereby changes in hemolymph osmotic pressure induce the release of diuretic or antidiuretic hormones to recruit individual osmoregulatory responses in a manner that optimizes overall homeostasis. However, the mechanisms by which different osmoregulatory circuits interact with other homeostatic networks to implement the correct homeostatic program remain largely unexplored. Surprisingly, recent advances in insect genetics have revealed several important metabolic functions are regulated by classic osmoregulatory pathways, suggesting that internal cues related to osmotic and metabolic perturbations are integrated by the same hormonal networks. Here, we review our current knowledge on the network mechanisms that underpin systemic osmoregulation and discuss the remarkable parallels between the hormonal networks that regulate body fluid balance and those involved in energy homeostasis to provide a framework for understanding the polymodal optimization of homeostasis in insects.

Post-feeding transcriptomics reveals essential genes expressed in the midgut of the desert locust

The digestive tract constitutes an important interface between an animal's internal and external environment. In insects, available gut transcriptome studies are mostly exploratory or look at changes upon infection or upon exposure to xenobiotics, mainly performed in species belonging to holometabolan orders, such as Diptera, Lepidoptera or Coleoptera. By contrast, studies focusing on gene expression changes after food uptake and during digestion are underrepresented. We have therefore compared the gene expression profiles in the midgut of the desert locust, Schistocerca gregaria, between three different time points after feeding, i.e., 24 h (no active digestion), 10 min (the initial stage of feeding), and 2 h (active food digestion). The observed gene expression profiles were consistent with the polyphagous herbivorous lifestyle of this hemimetabolan (orthopteran) species. Our study reveals the upregulation of 576 genes 2 h post-feeding. These are mostly predicted to be associated with digestive physiology, such as genes encoding putative digestive enzymes or nutrient transporters, as well as genes putatively involved in immunity or in xenobiotic metabolism. The 10 min time point represented an intermediate condition, suggesting that the S. gregaria midgut can react rapidly at the transcriptional level to the presence of food. Additionally, our study demonstrated the critical importance of two transcripts that exhibited a significant upregulation 2 h post-feeding: the vacuolar-type H(+)-ATPase and the sterol transporter Niemann-Pick 1b protein, which upon RNAi-induced knockdown resulted in a marked increase in mortality. Their vital role and accessibility via the midgut lumen may make the encoded proteins promising insecticidal target candidates, considering that the desert locust is infamous for its huge migrating swarms that can devastate the agricultural production in large areas of Northern Africa, the Middle East, and South Asia. In conclusion, the transcriptome datasets presented here will provide a useful and promising resource for studying the midgut physiology of S. gregaria, a socio-economically important pest species.

FoxO directly regulates the expression of odorant receptor genes to govern olfactory plasticity upon starvation in Bactrocera dorsalis

Under nutrient-poor conditions, animals must save energy by adjusting their behavior and physiology in order to survive. Although the impact of feeding state on olfactory sensory neuron activity has been well studied, the regulatory mechanisms underlying the transcriptional changes in odorant receptors (Ors) induced by feeding signals are seldom mentioned. Here, we showed that starvation could attenuate antennal responses of Bactrocera dorsalis toward multiple odorants, which could be reverted by sugar re-feeding, but not by a protein-rich diet. Using methyl eugenol (ME) as a paradigm, our study provided molecular evidence that Forkhead Box protein O (FoxO) can be expressed in antennal tissues to govern starvation-induced olfactory modifications by binding to the upstream regulatory regions of ME-responsive Ors and regulating their expressions. Since the consensus FoxO binding motif was also identified in other 17 Ors whose expression levels were also significantly altered upon FoxO knockdown and starvation, our data suggest that FoxO-dependent binding is likely a universal regulatory mechanism for Or genes during starvation and re-feeding cycles. Taken together, the FoxO-Ors axis elucidated in this study provides an improved understanding of how the insulin signaling pathway senses the feeding state and certain macronutrient composition to shape olfactory plasticity, allowing flies to dynamically alter chemosensory sensitivities toward different odors. Our study also highlights sugar as a satiety signal, which could increase ME-mediated trap efficiency in the field.

Insect PRXamides: Evolutionary Divergence, Novelty, and Loss in a Conserved Neuropeptide System

The PRXamide neuropeptides have been described in both protostome and deuterostome species, including all major groups of the Panarthropoda. Best studied are the insect PRXamides consisting of three genes: pk/pban, capa, and eth, each encoding multiple short peptides that are cleaved post-translationally. Comparisons of genome and transcriptome sequences reveal that while retaining its fundamental ancestral organization, the products of the pk/pban gene have undergone significant change in the insect Order Diptera. Basal dipteran pk/pban genes are much like those of other holometabolous insects, while more crown species have lost two peptide coding sequences including the otherwise ubiquitous pheromone biosynthesis activating neuropeptide (PBAN). In the genomic model species Drosophila melanogaster, one of the remaining peptides (hugin) plays a potentially novel role in feeding and locomotor regulation tied to circadian rhythms. Comparison of peptide coding sequences of pk/pban across the Diptera pinpoints the acquisition or loss of the hugin and PBAN peptide sequences respectively, and provides clues to associated changes in life history, physiology, and/or behavior. Interestingly, the neural circuitry underlying pk/pban function is highly conserved across the insects regardless of the composition of the pk/pban gene. The rapid evolution and diversification of the Diptera provide many instances of adaptive novelties from genes to behavior that can be placed in the context of emerging selective pressures at key points in their phylogeny; further study of changing functional roles of pk/pban may then be facilitated by the high-resolution genetic tools available in Drosophila melanogaster.

A gut-derived hormone suppresses sugar appetite and regulates food choice in Drosophila

Animals must adapt their dietary choices to meet their nutritional needs. How these needs are detected and translated into nutrient-specific appetites that drive food-choice behaviours is poorly understood. Here we show that enteroendocrine cells of the adult female Drosophila midgut sense nutrients and in response release neuropeptide F (NPF), which is an ortholog of mammalian neuropeptide Y-family gut-brain hormones. Gut-derived NPF acts on glucagon-like adipokinetic hormone (AKH) signalling to induce sugar satiety and increase consumption of protein-rich food, and on adipose tissue to promote storage of ingested nutrients. Suppression of NPF-mediated gut signalling leads to overconsumption of dietary sugar while simultaneously decreasing intake of protein-rich yeast. Furthermore, gut-derived NPF has a female-specific function in promoting consumption of protein-containing food in mated females. Together, our findings suggest that gut NPF-to-AKH signalling modulates specific appetites and regulates food choice to ensure homeostatic consumption of nutrients, providing insight into the hormonal mechanisms that underlie nutrient-specific hungers.

Dietary regulation in health and disease

Nutriments have been deemed to impact all physiopathologic processes. Recent evidences in molecular medicine and clinical trials have demonstrated that adequate nutrition treatments are the golden criterion for extending healthspan and delaying ageing in various species such as yeast, drosophila, rodent, primate and human. It emerges to develop the precision-nutrition therapeutics to slow age-related biological processes and treat diverse diseases. However, the nutritive advantages frequently diversify among individuals as well as organs and tissues, which brings challenges in this field. In this review, we summarize the different forms of dietary interventions extensively prescribed for healthspan improvement and disease treatment in pre-clinical or clinical. We discuss the nutrient-mediated mechanisms including metabolic regulators, nutritive metabolism pathways, epigenetic mechanisms and circadian clocks. Comparably, we describe diet-responsive effectors by which dietary interventions influence the endocrinic, immunological, microbial and neural states responsible for improving health and preventing multiple diseases in humans. Furthermore, we expatiate diverse patterns of dietotheroapies, including different fasting, calorie-restricted diet, ketogenic diet, high-fibre diet, plants-based diet, protein restriction diet or diet with specific reduction in amino acids or microelements, potentially affecting the health and morbid states. Altogether, we emphasize the profound nutritional therapy, and highlight the crosstalk among explored mechanisms and critical factors to develop individualized therapeutic approaches and predictors.

The gut hormone Allatostatin C/Somatostatin regulates food intake and metabolic homeostasis under nutrient stress

The intestine is a central regulator of metabolic homeostasis. Dietary inputs are absorbed through the gut, which senses their nutritional value and relays hormonal information to other organs to coordinate systemic energy balance. However, the gut-derived hormones affecting metabolic and behavioral responses are poorly defined. Here we show that the endocrine cells of the Drosophila gut sense nutrient stress through a mechanism that involves the TOR pathway and in response secrete the peptide hormone allatostatin C, a Drosophila somatostatin homolog. Gut-derived allatostatin C induces secretion of glucagon-like adipokinetic hormone to coordinate food intake and energy mobilization. Loss of gut Allatostatin C or its receptor in the adipokinetic-hormone-producing cells impairs lipid and sugar mobilization during fasting, leading to hypoglycemia. Our findings illustrate a nutrient-responsive endocrine mechanism that maintains energy homeostasis under nutrient-stress conditions, a function that is essential to health and whose failure can lead to metabolic disorders.

G protein-coupled receptors that influence lifespan of human and animal models

Humanity has always sought to live longer and for this, multiple strategies have been tried with varying results. In this sense, G protein-coupled receptors (GPCRs) may be a good option to try to prolong our life while maintaining good health since they have a substantial participation in a wide variety of processes of human pathophysiology and are one of the main therapeutic targets. In this way, we present the analysis of a series of GPCRs whose activity has been shown to affect the lifespan of animal and human models, and in which we put a special interest in describing the molecular mechanisms involved. Our compilation of data revealed that the mechanisms most involved in the role of GPCRs in lifespan are those that mimic dietary restriction, those related to insulin signaling and the AMPK and TOR pathways, and those that alter oxidative homeostasis and severe and/or chronic inflammation. We also discuss the possibility of using agonist or antagonist drugs, depending on the beneficial or harmful effects of each GPCR, in order to prolong people's lifespan and healthspan.