Two functional but noncomplementing Drosophila tyrosine decarboxylase genes: distinct roles for neural tyramine and octopamine in female fertility

Cholinergic and Glutamatergic Axons Differentially Require Glial Support in the Drosophila PNS

In vertebrates, there is a differential interaction between peripheral axons and their associated glial cells. While large-caliber axons are covered by a myelin sheath, small-diameter axons are simply wrapped in Remak fibers. In peripheral nerves of Drosophila larvae, axons are covered by wrapping glial cell processes similar to vertebrate Remak fibers. Whether differences in axonal diameter influence the interaction with glial processes in Drosophila has not yet been analyzed. Likewise, it is not understood whether the modality of the neuron affects the interaction with the wrapping glia. To start to decipher the mechanisms underlying glial wrapping, we employed APEX2 labeling in larval filet preparations. This allowed us to follow individual axons of defined segmental nerves at ultrastructural resolution in the presence or absence of wrapping glia. Using these tools, we first demonstrate that motor axons are larger compared to sensory axons. Sensory axons fasciculate in larger groups than motor axons, suggesting that they do not require direct contact with wrapping glia. However, unlike motor axons, sensory axons show length-dependent degeneration upon ablation of wrapping glia. These data suggest that Drosophila may help to understand peripheral neuropathies caused by defects in Schwann cell function, in which a similar degeneration of sensory axons is observed.

The gut microbiome promotes locomotion of Drosophila larvae via octopamine signaling

The gut microbiome is a key partner of animals, influencing various aspects of their physiology and behaviors. Among the diverse behaviors regulated by the gut microbiome, locomotion is vital for survival and reproduction, although the underlying mechanisms remain unclear. Here, we reveal that the gut microbiome modulates the locomotor behavior of Drosophila larvae via a specific neuronal type in the brain. The crawling speed of germ-free (GF) larvae was significantly reduced compared to the conventionally reared larvae, while feeding and excretion behaviors were unaffected. Recolonization with Acetobacter and Lactobacillus can fully and partially rescue the locomotor defects in GF larvae, respectively, probably due to the highest abundance of Acetobacter as a symbiotic bacterium in the larval gut, followed by Lactobacillus. Moreover, the gut microbiome promoted larval locomotion, not by nutrition, but rather by enhancing the brain levels of tyrosine decarboxylase 2 (Tdc2), which is an enzyme that synthesizes octopamine (OA). Overexpression of Tdc2 rescued locomotion ability in GF larvae. These findings together demonstrate that the gut microbiome specifically modulates larval locomotor behavior through the OA signaling pathway, revealing a new mechanism underlying larval locomotion regulated by the gut microbiome.

Actomyosin contraction in the follicular epithelium provides the major mechanical force for follicle rupture during Drosophila ovulation

Ovulation is critical for sexual reproduction and consists of the process of liberating fertilizable oocytes from their somatic follicle capsules, also known as follicle rupture. The mechanical force for oocyte expulsion is largely unknown in many species. Our previous work demonstrated that Drosophila ovulation, as in mammals, requires the proteolytic degradation of the posterior follicle wall and follicle rupture to release the mature oocyte from a layer of somatic follicle cells. Here, we identified actomyosin contraction in somatic follicle cells as the major mechanical force for follicle rupture. Filamentous actin (F-actin) and nonmuscle myosin II (NMII) are highly enriched in the cortex of follicle cells upon stimulation with octopamine (OA), a monoamine critical for Drosophila ovulation. Pharmacological disruption of F-actin polymerization prevented follicle rupture without interfering with the follicle wall breakdown. In addition, we demonstrated that OA induces Rho1 guanosine triphosphate (GTP)ase activation in the follicle cell cortex, which activates Ras homolog (Rho) kinase to promote actomyosin contraction and follicle rupture. All these results led us to conclude that OA signaling induces actomyosin cortex enrichment and contractility, which generates the mechanical force for follicle rupture during Drosophila ovulation. Due to the conserved nature of actomyosin contraction, this work could shed light on the mechanical force required for follicle rupture in other species including humans.

Heterogeneity in the projections and excitability of tyraminergic/octopaminergic neurons that innervate the Drosophila reproductive tract

Aminergic nuclei in mammals are generally composed of relatively small numbers of cells with broad projection patterns. Despite the gross similarity of many individual neurons, recent transcriptomic, anatomic and behavioral studies suggest previously unsuspected diversity. Smaller clusters of aminergic neurons in the model organism Drosophila melanogaster provide an opportunity to explore the ramifications of neuronal diversity at the level of individual cells. A group of approximately 10 tyraminergic/octopaminergic neurons innervates the female reproductive tract in flies and has been proposed to regulate multiple activities required for fertility. The projection patterns of individual neurons within the cluster are not known and it remains unclear whether they are functionally heterogenous. Using a single cell labeling technique, we show that each region of the reproductive tract is innervated by a distinct subset of tyraminergic/octopaminergic cells. Optogenetic activation of one subset stimulates oviduct contractions, indicating that the cluster as a whole is not required for this activity, and underscoring the potential for functional diversity across individual cells. Using whole cell patch clamp, we show that two adjacent and morphologically similar cells are tonically inhibited, but each responds differently to injection of current or activation of the inhibitory GluCl receptor. GluCl appears to be expressed at relatively low levels in tyraminergic/octopaminergic neurons within the cluster, suggesting that it may regulate their excitability via indirect pathways. Together, our data indicate that specific tyraminergic/octopaminergic cells within a relatively homogenous cluster have heterogenous properties and provide a platform for further studies to determine the function of each cell.

Gut microbiota metabolite tyramine ameliorates high-fat diet-induced insulin resistance via increased Ca2+ signaling

The gut microbiota and their metabolites are closely linked to obesity-related diseases, such as type 2 diabetes, but their causal relationship and underlying mechanisms remain largely elusive. Here, we found that dysbiosis-induced tyramine (TA) suppresses high-fat diet (HFD)-mediated insulin resistance in both Drosophila and mice. In Drosophila, HFD increases cytosolic Ca2+ signaling in enterocytes, which, in turn, suppresses intestinal lipid levels. 16 S rRNA sequencing and metabolomics revealed that HFD leads to increased prevalence of tyrosine decarboxylase (Tdc)-expressing bacteria and resulting tyramine production. Tyramine acts on the tyramine receptor, TyrR1, to promote cytosolic Ca2+ signaling and activation of the CRTC-CREB complex to transcriptionally suppress dietary lipid digestion and lipogenesis in enterocytes, while promoting mitochondrial biogenesis. Furthermore, the tyramine-induced cytosolic Ca2+ signaling is sufficient to suppress HFD-induced obesity and insulin resistance in Drosophila. In mice, tyramine intake also improves glucose tolerance and insulin sensitivity under HFD. These results indicate that dysbiosis-induced tyramine suppresses insulin resistance in both flies and mice under HFD, suggesting a potential therapeutic strategy for related metabolic disorders, such as diabetes.

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.

Octopaminergic descending neurons in Drosophila: Connectivity, tonic activity and relation to locomotion

Projection neurons that communicate between different brain regions and local neurons that shape computation within a brain region form the majority of all neurons in the brain. Another important class of neurons is neuromodulatory neurons; these neurons are in much smaller numbers than projection/local neurons but have a large influence on computations in the brain. Neuromodulatory neurons are classified by the neurotransmitters they carry, such as dopamine and serotonin. Much of our knowledge of the effect of neuromodulators comes from experiments in which either a large population of neuromodulatory neurons or the entire population is perturbed. Alternatively, a given neuromodulator is exogenously applied. While these experiments are informative of the general role of the neurotransmitter, one limitation of these experiments is that the role of individual neuromodulatory neurons remains unknown. In this study, we investigate the role of a class of octopaminergic (octopamine is the invertebrate equivalent of norepinephrine) neurons in Drosophila or fruit fly. Neuromodulation in Drosophila work along similar principles as humans; and the smaller number of neuromodulatory neurons allow us to assess the role of individual neurons. This study focuses on a subpopulation of octopaminergic descending neurons (OA-DNs) whose cell bodies are in the brain and project to the thoracic ganglia. Using in-vivo whole-cell patch-clamp recordings and anatomical analyses that allow us to compare light microscopy data to the electron microscopic volumes available in the fly, we find that neurons within each cluster have similar physiological properties, including their relation to locomotion. However, neurons in the same cluster with similar anatomy have very different connectivity. Our data is consistent with the hypothesis that each OA-DN is recruited individually and has a unique function within the fly's brain.

Octopamine in the mushroom body circuitry for learning and memory

Octopamine, the functional analog of noradrenaline, modulates many different behaviors and physiological processes in invertebrates. In the central nervous system, a few octopaminergic neurons project throughout the brain and innervate almost all neuropils. The center of memory formation in insects, the mushroom bodies, receive octopaminergic innervations in all insects investigated so far. Different octopamine receptors, either increasing or decreasing cAMP or calcium levels in the cell, are localized in Kenyon cells, further supporting the release of octopamine in the mushroom bodies. In addition, different mushroom body (MB) output neurons, projection neurons, and dopaminergic PAM cells are targets of octopaminergic neurons, enabling the modulation of learning circuits at different neural sites. For some years, the theory persisted that octopamine mediates rewarding stimuli, whereas dopamine (DA) represents aversive stimuli. This simple picture has been challenged by the finding that DA is required for both appetitive and aversive learning. Furthermore, octopamine is also involved in aversive learning and a rather complex interaction between these biogenic amines seems to modulate learning and memory. This review summarizes the role of octopamine in MB function, focusing on the anatomical principles and the role of the biogenic amine in learning and memory.

Octopamine integrates the status of internal energy supply into the formation of food-related memories

The brain regulates food intake in response to internal energy demands and food availability. However, can internal energy storage influence the type of memory that is formed? We show that the duration of starvation determines whether Drosophila melanogaster forms appetitive short-term or longer-lasting intermediate memories. The internal glycogen storage in the muscles and adipose tissue influences how intensely sucrose-associated information is stored. Insulin-like signaling in octopaminergic reward neurons integrates internal energy storage into memory formation. Octopamine, in turn, suppresses the formation of long-term memory. Octopamine is not required for short-term memory because octopamine-deficient mutants can form appetitive short-term memory for sucrose and to other nutrients depending on the internal energy status. The reduced positive reinforcing effect of sucrose at high internal glycogen levels, combined with the increased stability of food-related memories due to prolonged periods of starvation, could lead to increased food intake.

A small-molecule approach to restore female sterility phenotype targeted by a homing suppression gene drive in the fruit pest Drosophila suzukii

CRISPR-based gene drives offer promising prospects for controlling disease-transmitting vectors and agricultural pests. A significant challenge for successful suppression-type drive is the rapid evolution of resistance alleles. One approach to mitigate the development of resistance involves targeting functionally constrained regions using multiple gRNAs. In this study, we constructed a 3-gRNA homing gene drive system targeting the recessive female fertility gene Tyrosine decarboxylase 2 (Tdc2) in Drosophila suzukii, a notorious fruit pest. Our investigation revealed only a low level of homing in the germline, but feeding octopamine restored the egg-laying defects in Tdc2 mutant females, allowing easier line maintenance than for other suppression drive targets. We tested the effectiveness of a similar system in Drosophila melanogaster and constructed additional split drive systems by introducing promoter-Cas9 transgenes to improve homing efficiency. Our findings show that genetic polymorphisms in wild populations may limit the spread of gene drive alleles, and the position effect profoundly influences Cas9 activity. Furthermore, this study highlights the potential of conditionally rescuing the female infertility caused by the gene drive, offering a valuable tool for the industrial-scale production of gene drive transgenic insects.

Finishing the egg

Gamete development is a fundamental process that is highly conserved from early eukaryotes to mammals. As germ cells develop, they must coordinate a dynamic series of cellular processes that support growth, cell specification, patterning, the loading of maternal factors (RNAs, proteins, and nutrients), differentiation of structures to enable fertilization and ensure embryonic survival, and other processes that make a functional oocyte. To achieve these goals, germ cells integrate a complex milieu of environmental and developmental signals to produce fertilizable eggs. Over the past 50 years, Drosophila oogenesis has risen to the forefront as a system to interrogate the sophisticated mechanisms that drive oocyte development. Studies in Drosophila have defined mechanisms in germ cells that control meiosis, protect genome integrity, facilitate mRNA trafficking, and support the maternal loading of nutrients. Work in this system has provided key insights into the mechanisms that establish egg chamber polarity and patterning as well as the mechanisms that drive ovulation and egg activation. Using the power of Drosophila genetics, the field has begun to define the molecular mechanisms that coordinate environmental stresses and nutrient availability with oocyte development. Importantly, the majority of these reproductive mechanisms are highly conserved throughout evolution, and many play critical roles in the development of somatic tissues as well. In this chapter, we summarize the recent progress in several key areas that impact egg chamber development and ovulation. First, we discuss the mechanisms that drive nutrient storage and trafficking during oocyte maturation and vitellogenesis. Second, we examine the processes that regulate follicle cell patterning and how that patterning impacts the construction of the egg shell and the establishment of embryonic polarity. Finally, we examine regulatory factors that control ovulation, egg activation, and successful fertilization.

The octopamine receptor OAα1 influences oogenesis and reproductive performance in Rhodnius prolixus

The control of reproductive processes in Rhodnius prolixus involves a variety of neuroactive chemicals. Among these, several studies have suggested that the biogenic amine octopamine (OA), might play an active role in these processes. Here, we investigate the molecular profile of the R. prolixus α adrenergic-like OA receptor 1 (RpOAα1-R) and its role in egg production. Comparative molecular analyses confirm that the RpOAα1-R gene codes for a true OAα1 receptor. The RpOAα1-R transcript is highly expressed in tissues associated with egg production, and after a blood meal, which is the stimulus for full egg production in R. prolixus, the RpOAα1-R transcript is upregulated in the ovaries and spermatheca. After RNAi-mediated RpOAα1-R knockdown, an ovarian phenotype characterized by slow egg development is observed. Furthermore, an altered egg phenotype has been characterized with eggs that are deformed. Interestingly, there is no evidence of disruption in vitellogenin (Vg) synthesis by the fat body or uptake by the oocytes. On the other hand, RpOAα1-R downregulation is correlated with defective choriogenesis in the eggs. These results provide critical information concerning the role of OAα1-R in oogenesis in R. prolixus.

Post-Mating Responses in Insects Induced by Seminal Fluid Proteins and Octopamine

Following insect mating, females often exhibit a series of physiological, behavioral, and gene expression changes. These post-mating responses (PMRs) are induced by seminal fluid components other than sperm, which not only form network proteins to assist sperm localization, supplement female-specific protein requirements, and facilitate the formation of specialized functional structures, but also activate neuronal signaling pathways in insects. This review primarily discusses the roles of seminal fluid proteins (SFPs) and octopamine (OA) in various PMRs in insects. It explores the regulatory mechanisms and mediation conditions by which they trigger PMRs, along with the series of gene expression differences they induce. Insect PMRs involve a transition from protein signaling to neuronal signaling, ultimately manifested through neural regulation and gene expression. The intricate signaling network formed as a result significantly influences female behavior and organ function, contributing to both successful reproduction and the outcomes of sexual conflict.

Effect of aminergic signaling on the humoral innate immunity response of Drosophila

Biogenic amines are crucial signaling molecules that modulate various physiological life functions both in vertebrates and invertebrates. In humans, these neurotransmitters influence the innate and adaptive immunity systems. In this work, we analyzed whether the aminergic neurotransmission of dopamine, serotonin, and octopamine could have an impact on the humoral innate immune response of Drosophila melanogaster. This is a powerful model system widely used to uncover the insect innate immunity mechanisms which are also conserved in mammals. We found that the neurotransmission of all these amines positively modulates the Toll-responsive antimicrobial peptide (AMP) drosomycin (drs) gene in adult flies infected with the Micrococcus luteus bacterium. Indeed, we showed that either blocking the neurotransmission in their specific aminergic neurons by expressing shibirets (Shits) or silencing the vesicular monoamine transporter gene (dVMAT) by RNAi caused a significantly reduced expression of the Toll-responsive drs gene. However, upon M. luteus infection, the block of aminergic transmission did not alter the expression of AMP attacin genes responding to the immune deficiency (Imd) and Toll pathways. Overall, our results not only reveal a neuroimmune function for biogenic amines in humoral immunity but also further highlight the complexity of the network controlling AMP gene regulation.

Characterization and functional analysis of an α-adrenergic-like octopamine receptor in the small brown planthopper Laodelphax striatellus

As an important biogenic amine in invertebrates and corresponding to the neurotransmitter norepinephrine in vertebrates, octopamine (OA) regulates diverse physiological and behavioral processes by binding to specific octopamine receptors (OARs) in invertebrates. At present, OARs have been identified and characterized in several insects. However, less is known about the OARs of Laodelphax striatellus, one of the most destructive pests in East Asian rice fields. In the present study, an α1-adrenergic-like OAR (LsOA1) from L. striatellus was cloned. LsOA1 has the typical characteristics of G-protein coupled receptors and is clustered with other insect homologs. The transcript level of LsOA1 varied in various stages and tissues, and was highly expressed at the egg stage and in the brain. Silencing of LsOA1 causes a reduction in vitellogenin (LsVg) and vitellogenin receptor (LsVgR) expression. Although LsOA1 interference did not affect the fecundity and survival of L. striatellus, the hatching rate of L. striatellus was significantly reduced, and the hatching period was prolonged. The decrease in the amount of honeydew excreted after silencing LsOA1 indicates that LsOA1 may be involved in regulating the feeding behavior of L. striatellus. In addition, the interference of LsOA1 significantly reduced the expression of capsid protein (CP) and viral RNA3 segment (RNA3) in rice stripe virus (RSV)-viruliferous L. striatellus, but did not affect the vertical transmission rate of RSV. The present study demonstrated that LsOA1 played a crucial role in the physiological and behavioral processes of L. striatellus, which will provide the basis for developing a new target gene for pest control.

Precise CRISPR-Cas9-mediated mutation of a membrane trafficking domain in the Drosophila vesicular monoamine transporter gene

Monoamine neurotransmitters such as noradrenalin are released from both synaptic vesicles (SVs) and large dense-core vesicles (LDCVs), the latter mediating extrasynaptic signaling. The contribution of synaptic versus extrasynaptic signaling to circuit function and behavior remains poorly understood. To address this question, we have previously used transgenes encoding a mutation in the Drosophila Vesicular Monoamine Transporter (dVMAT) that shifts amine release from SVs to LDCVs. To circumvent the use of transgenes with non-endogenous patterns of expression, we have now used CRISPR-Cas9 to generate a trafficking mutant in the endogenous dVMAT gene. To minimize disruption of the dVMAT coding sequence and a nearby RNA splice site, we precisely introduced a point mutation using single-stranded oligonucleotide repair. A predicted decrease in fertility was used as a phenotypic screen to identify founders in lieu of a visible marker. Phenotypic analysis revealed a defect in the ovulation of mature follicles and egg retention in the ovaries. We did not detect defects in the contraction of lateral oviducts following optogenetic stimulation of octopaminergic neurons. Our findings suggest that release of mature eggs from the ovary is disrupted by changing the balance of VMAT trafficking between SVs and LDCVs. Further experiments using this model will help determine the mechanisms that sensitize specific circuits to changes in synaptic versus extrasynaptic signaling.

The bHLH-PAS transcriptional complex Sim:Tgo plays active roles in late oogenesis to promote follicle maturation and ovulation

Across species, ovulation is a process induced by a myriad of signaling cascades that ultimately leads to the release of encapsulated oocytes from follicles. Follicles first need to mature and gain ovulatory competency before ovulation; however, the signaling pathways regulating follicle maturation are incompletely understood in Drosophila and other species. Our previous work has shown that the bHLH-PAS transcription factor Single-minded (Sim) plays important roles in follicle maturation downstream of the nuclear receptor Ftz-f1 in Drosophila. Here, we demonstrate that Tango (Tgo), another bHLH-PAS protein, acts as a co-factor of Sim to promote follicle cell differentiation from stages 10 to 12. In addition, we discover that re-upregulation of Sim in stage-14 follicle cells is also essential to promote ovulatory competency by upregulating octopamine receptor in mushroom body (OAMB), matrix metalloproteinase 2 (Mmp2) and NADPH oxidase (NOX), either independently of or in conjunction with the zinc-finger protein Hindsight (Hnt). All these factors are crucial for successful ovulation. Together, our work indicates that the transcriptional complex Sim:Tgo plays multiple roles in late-stage follicle cells to promote follicle maturation and ovulation.

The monoaminergic system is a bilaterian innovation

Monoamines like serotonin, dopamine, and adrenaline/noradrenaline (epinephrine/norepinephrine) act as neuromodulators in the nervous system. They play a role in complex behaviours, cognitive functions such as learning and memory formation, as well as fundamental homeostatic processes such as sleep and feeding. However, the evolutionary origin of the genes required for monoaminergic modulation is uncertain. Using a phylogenomic approach, in this study, we show that most of the genes involved in monoamine production, modulation, and reception originated in the bilaterian stem group. This suggests that the monoaminergic system is a bilaterian novelty and that its evolution may have contributed to the Cambrian diversification.

Drosophila cells that express octopamine receptors can either inhibit or promote oviposition

Adrenergic signaling is known to play a critical role in regulating female reproductive processes in both mammals and insects. In Drosophila , the ortholog of noradrenaline, octopamine (Oa), is required for ovulation as well as several other female reproductive processes. Loss of function studies using mutant alleles of receptors, transporters, and biosynthetic enzymes for Oa have led to a model in which disruption of octopaminergic pathways reduces egg laying. However, neither the complete expression pattern in the reproductive tract nor the role of most octopamine receptors in oviposition is known. We show that all six known Oa receptors are expressed in peripheral neurons at multiple sites within in the female fly reproductive tract as well as in non-neuronal cells within the sperm storage organs. The complex pattern of Oa receptor expression in the reproductive tract suggests the potential for influencing multiple regulatory pathways, including those known to inhibit egg-laying in unmated flies. Indeed, activation of some neurons that express Oa receptors inhibits oviposition, and neurons that express different subtypes of Oa receptor can affect different stages of egg laying. Stimulation of some Oa receptor expressing neurons (OaRNs) also induces contractions in lateral oviduct muscle and activation of non-neuronal cells in the sperm storage organs by Oa generates OAMB-dependent intracellular calcium release. Our results are consistent with a model in which adrenergic pathways play a variety of complex roles in the fly reproductive tract that includes both the stimulation and inhibition of oviposition.

The matricellular protein Drosophila Cellular Communication Network Factor is required for synaptic transmission and female fertility

Within the extracellular matrix, matricellular proteins are dynamically expressed nonstructural proteins that interact with cell surface receptors, growth factors, and proteases, as well as with structural matrix proteins. The cellular communication network factors family of matricellular proteins serve regulatory roles to regulate cell function and are defined by their conserved multimodular organization. Here, we characterize the expression and neuronal requirement for the Drosophila cellular communication network factor family member. Drosophila cellular communication network factor is expressed in the nervous system throughout development including in subsets of monoamine-expressing neurons. Drosophila cellular communication network factor-expressing abdominal ganglion neurons innervate the ovaries and uterus and the loss of Drosophila cellular communication network factor results in reduced female fertility. In addition, Drosophila cellular communication network factor accumulates at the synaptic cleft and is required for neurotransmission at the larval neuromuscular junction. Analyzing the function of the single Drosophila cellular communication network factor family member will enhance our potential to understand how the microenvironment impacts neurotransmitter release in distinct cellular contexts and in response to activity.

Assessing Ovulation in Drosophila melanogaster

Ovulation is a critical reproductive process by which a mature oocyte is released from the ovary for fertilization. This process requires the coordination of multiple cellular and molecular events including the spatiotemporal breakdown of the follicle wall. Recent work has shown that ovulation in Drosophila utilizes conserved cellular processes and molecular pathways as in mammals. Thus, Drosophila ovulation can serve as a good model to decipher the fundamental mechanisms of ovulation utilized across species. In past decades, several methods have been developed to study Drosophila ovulation, but all of them have drawbacks. This chapter offers a strategy and detailed protocols for performing and analyzing the necessary assays to evaluate the ovulation process in Drosophila.

Feeding Asian honeybee queens with European honeybee royal jelly alters body color and expression of related coding and non-coding RNAs

Background and aims: The Asian honeybee (Apis cerana) and the European honeybee (Apis mellifera) are reproductively isolated. Previous studies reported that exchanging the larval food between the two species, known as nutritional crossbreeding, resulted in obvious changes in morphology, physiology and behavior. This study explored the molecular mechanisms underlying the honeybee nutritional crossbreeding. Methods: This study used full nutritional crossbreeding technology to rear A. cerana queens by feeding them with an A. mellifera royal jelly-based diet in an incubator. The body color and the expression of certain genes, microRNA, lncRNA, and circRNA among nutritional crossbred A. cerana queens (NQ), and control A. cerana queens (CQ) were compared. The biological functions of two target genes, TPH1 and KMO, were verified using RNA interference. Results: Our results showed that the NQ's body color turned yellow compared to the black control queens. Whole transcriptome sequencing results showed that a total of 1484, 311, 92, and 169 DEGs, DElncRNAs, DEmiRNAs, and DEcircRNAs, respectively, were identified in NQ and CQ, in which seven DEGs were enriched for three key pathways (tryptophan, tyrosine, and dopamine) involved in melanin synthesis. Interestingly, eight DElncRNAs and three DEmiRNAs were enriched into the key pathways regulating the above key DEGs. No circRNAs were enriched into these key pathways. Knocking down two key genes (KMO and TPH1) resulted in altered body color, suggesting that feeding NQ's an RNAi-based diet significantly downregulated the expression of TPH1 and KMO in 4-day-old larvae, which confirmed the function of key DEGs in the regulation of honeybee body color. Conclusion: These findings reveal that the larval diets from A. mellifera could change the body color of A. cerana, perhaps by altering the expression of non-coding RNAs and related key genes. This study serves as a model of epigenetic regulation in insect body color induced by environmental factors.

Regulation and modulation of biogenic amine neurotransmission in Drosophila and Caenorhabditis elegans

Neurotransmitters are crucial for the relay of signals between neurons and their target. Monoamine neurotransmitters dopamine (DA), serotonin (5-HT), and histamine are found in both invertebrates and mammals and are known to control key physiological aspects in health and disease. Others, such as octopamine (OA) and tyramine (TA), are abundant in invertebrates. TA is expressed in both Caenorhabditis elegans and Drosophila melanogaster and plays important roles in the regulation of essential life functions in each organism. OA and TA are thought to act as the mammalian homologs of epinephrine and norepinephrine respectively, and when triggered, they act in response to the various stressors in the fight-or-flight response. 5-HT regulates a wide range of behaviors in C. elegans including egg-laying, male mating, locomotion, and pharyngeal pumping. 5-HT acts predominantly through its receptors, of which various classes have been described in both flies and worms. The adult brain of Drosophila is composed of approximately 80 serotonergic neurons, which are involved in modulation of circadian rhythm, feeding, aggression, and long-term memory formation. DA is a major monoamine neurotransmitter that mediates a variety of critical organismal functions and is essential for synaptic transmission in invertebrates as it is in mammals, in which it is also a precursor for the synthesis of adrenaline and noradrenaline. In C. elegans and Drosophila as in mammals, DA receptors play critical roles and are generally grouped into two classes, D1-like and D2-like based on their predicted coupling to downstream G proteins. Drosophila uses histamine as a neurotransmitter in photoreceptors as well as a small number of neurons in the CNS. C. elegans does not use histamine as a neurotransmitter. Here, we review the comprehensive set of known amine neurotransmitters found in invertebrates, and discuss their biological and modulatory functions using the vast literature on both Drosophila and C. elegans. We also suggest the potential interactions between aminergic neurotransmitters systems in the modulation of neurophysiological activity and behavior.

Gliotransmission of D-serine promotes thirst-directed behaviors in Drosophila

Thirst emerges from a range of cellular changes that ultimately motivate an animal to consume water. Although thirst-responsive neuronal signals have been reported, the full complement of brain responses is unclear. Here, we identify molecular and cellular adaptations in the brain using single-cell sequencing of water-deprived Drosophila. Water deficiency primarily altered the glial transcriptome. Screening the regulated genes revealed astrocytic expression of the astray-encoded phosphoserine phosphatase to bi-directionally regulate water consumption. Astray synthesizes the gliotransmitter D-serine, and vesicular release from astrocytes is required for drinking. Moreover, dietary D-serine rescues aay-dependent drinking deficits while facilitating water consumption and expression of water-seeking memory. D-serine action requires binding to neuronal NMDA-type glutamate receptors. Fly astrocytes contribute processes to tripartite synapses, and the proportion of astrocytes that are themselves activated by glutamate increases with water deprivation. We propose that thirst elevates astrocytic D-serine release, which awakens quiescent glutamatergic circuits to enhance water procurement.

A neurogenetic mechanism of experience-dependent suppression of aggression

Aggression is an ethologically important social behavior, but excessive aggression can be detrimental to fitness. Social experiences among conspecific individuals reduce aggression in many species, the mechanism of which is largely unknown. We found that loss-of-function mutation of nervy (nvy), a Drosophila homolog of vertebrate myeloid translocation genes (MTGs), increased aggressiveness only in socially experienced flies and that this could be reversed by neuronal expression of human MTGs. A subpopulation of octopaminergic/tyraminergic neurons labeled by nvy was specifically required for such social experience-dependent suppression of aggression, in both males and females. Cell type-specific transcriptomic analysis of these neurons revealed aggression-controlling genes that are likely downstream of nvy. Our results illustrate both genetic and neuronal mechanisms by which the nervous system suppresses aggression in a social experience-dependent manner, a poorly understood process that is considered important for maintaining the fitness of animals.

A single-cell transcriptomic atlas of complete insect nervous systems across multiple life stages

Molecular profiles of neurons influence neural development and function but bridging the gap between genes, circuits, and behavior has been very difficult. Here we used single cell RNAseq to generate a complete gene expression atlas of the Drosophila larval central nervous system composed of 131,077 single cells across three developmental stages (1 h, 24 h and 48 h after hatching). We identify 67 distinct cell clusters based on the patterns of gene expression. These include 31 functional mature larval neuron clusters, 1 ring gland cluster, 8 glial clusters, 6 neural precursor clusters, and 13 developing immature adult neuron clusters. Some clusters are present across all stages of larval development, while others are stage specific (such as developing adult neurons). We identify genes that are differentially expressed in each cluster, as well as genes that are differentially expressed at distinct stages of larval life. These differentially expressed genes provide promising candidates for regulating the function of specific neuronal and glial types in the larval nervous system, or the specification and differentiation of adult neurons. The cell transcriptome Atlas of the Drosophila larval nervous system is a valuable resource for developmental biology and systems neuroscience and provides a basis for elucidating how genes regulate neural development and function.

Single cell RNA-seq analysis reveals temporally-regulated and quiescence-regulated gene expression in Drosophila larval neuroblasts

The mechanisms that generate neural diversity during development remains largely unknown. Here, we use scRNA-seq methodology to discover new features of the Drosophila larval CNS across several key developmental timepoints. We identify multiple progenitor subtypes - both stem cell-like neuroblasts and intermediate progenitors - that change gene expression across larval development, and report on new candidate markers for each class of progenitors. We identify a pool of quiescent neuroblasts in newly hatched larvae and show that they are transcriptionally primed to respond to the insulin signaling pathway to exit from quiescence, including relevant pathway components in the adjacent glial signaling cell type. We identify candidate "temporal transcription factors" (TTFs) that are expressed at different times in progenitor lineages. Our work identifies many cell type specific genes that are candidates for functional roles, and generates new insight into the differentiation trajectory of larval neurons.

Search performance and octopamine neuronal signaling mediate parasitoid induced changes in Drosophila oviposition behavior

Making the appropriate responses to predation risk is essential for the survival of an organism; however, the underlying mechanisms are still largely unknown. Here, we find that Drosophila has evolved an adaptive strategy to manage the threat from its parasitoid wasp by manipulating the oviposition behavior. Through perception of the differences in host search performance of wasps, Drosophila is able to recognize younger wasps as a higher level of threat and consequently depress the oviposition. We further show that this antiparasitoid behavior is mediated by the regulation of the expression of Tdc2 and Tβh in the ventral nerve cord via LC4 visual projection neurons, which in turn leads to the dramatic reduction in octopamine and the resulting dysfunction of mature follicle trimming and rupture. Our study uncovers a detailed mechanism underlying the defensive behavior in insects that may advance our understanding of predator avoidance in animals.

Octopaminergic/tyraminergic Tdc2 neurons regulate biased sperm usage in female Drosophila melanogaster

In polyandrous internally fertilizing species, a multiply-mated female can use stored sperm from different males in a biased manner to fertilize her eggs. The female's ability to assess sperm quality and compatibility is essential for her reproductive success, and represents an important aspect of postcopulatory sexual selection. In Drosophila melanogaster, previous studies demonstrated that the female nervous system plays an active role in influencing progeny paternity proportion, and suggested a role for octopaminergic/tyraminergic Tdc2 neurons in this process. Here, we report that inhibiting Tdc2 neuronal activity causes females to produce a higher-than-normal proportion of first-male progeny. This difference is not due to differences in sperm storage or release, but instead is attributable to the suppression of second-male sperm usage bias that normally occurs in control females. We further show that a subset of Tdc2 neurons innervating the female reproductive tract is largely responsible for the progeny proportion phenotype that is observed when Tdc2 neurons are inhibited globally. On the contrary, overactivation of Tdc2 neurons does not further affect sperm storage, release or progeny proportion. These results suggest that octopaminergic/tyraminergic signaling allows a multiply-mated female to bias sperm usage, and identify a new role for the female nervous system in postcopulatory sexual selection.

Regulation of Drosophila oviduct muscle contractility by octopamine

Octopamine is essential for egg-laying in Drosophila melanogaster, but the neuronal pathways and receptors by which it regulates visceral muscles in the reproductive tract are not known. We find that the two octopamine receptors that have been previously implicated in egg-laying–OAMB and Octβ2R-are expressed in octopaminergic and glutamatergic neurons that project to the reproductive tract, peripheral ppk(+) neurons within the reproductive tract and epithelial cells that line the lumen of the oviducts. Further optogenetic and mutational analyses indicate that octopamine regulates both oviduct contraction and relaxation via Octβ2 and OAMB respectively. Interactions with glutamatergic pathways modify the effects of octopamine. Octopaminergic activation of Octβ2R on glutamatergic processes provides a possible mechanism by which octopamine initiates lateral oviduct contractions. We speculate that aminergic pathways in the oviposition circuit may be comparable to some of the mechanisms that regulate visceral muscle contractility in mammals.

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The receptors Octβ2 and OAMB mediate oviduct muscle contraction and relaxation

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The receptors are detectably expressed in neurons and epithelia but not muscle cells

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The control of visceral muscles in flies and mammals may share common features

Octopamine modulates insect mating and Oviposition

The neuro-mechanisms that regulate insect reproduction are not fully understood. Biogenic amines, including octopamine, are neuromodulators that have been shown to modulate insect reproduction in various ways, e.g., promote or inhibit insect mating or oviposition. In this study, we examined the role of octopamine in regulating the reproduction behaviors of a devastating underground insect pest, the dark black chafer (Holotrichia parallela). We first measured the abundance of octopamine in different neural tissues of the adult chafer pre- and post-mating, demonstrating that octopamine decreased in the abdominal ganglia of females but increased in males post-mating. We then fed the adult H. parallela with a concentration gradient of octopamine to test the effects on insect reproductive behaviors. Compared with its antagonist mianserin, octopamine at the concentration of 2 µg/mL resulted in the highest increase in males' preference for sex pheromone and females' oviposition, whereas the mianserin-treatment increased the survival rate and prolonged the lifespan of H. parallela. In addition, we did not observe significant differences in egg hatchability between octopamine and mianserin-treated H. parallela. Our results demonstrated that octopamine promotes H. parallela mating and oviposition with a clear low dosage effect, illustrated how neural substrates modulate insect behaviors, and provided insights for applying octopamine in pest management.

Alterations in biogenic amines levels associated with age-related muscular tissue impairment in Drosophila melanogaster

While holding on youth may be a universal wish, aging is a natural process associated with physical and physiological impairment in living organisms. Drosophila provides useful insights into aging-related events. Hence, this study was conducted to investigate the age-related changes in muscle function and architecture in relation to the biogenic amine titers. To achieve this aim, visceral and skeletal muscles performance was tested in newly-eclosed, sexually mature and old adult flies using climbing and gut motility assays. In addition, age-related ultrastructural alterations of muscular tissue were observed using transmission electron microscopy (TEM). The titer of selected biogenic amines was measured using high-performance liquid chromatography (HPLC). The results demonstrated that old flies were dramatically slower in upward movement than either newly-eclosed or sexually mature flies. Similarly, gut contraction rate was significantly lower in old flies than the sexually mature, although it was markedly higher than that in the newly-eclosed flies. In TEM examination, there were several ultrastructural changes in the midgut epithelium, legs and thorax muscles of old flies. Regarding biogenic amine titers, the old flies had significantly lower concentrations of octopamine, dopamine and serotonin than the sexually mature. We concluded that aging has adverse effects on muscular system function and ultrastructure, synchronized with biogenic amine titers changes. Our results highlighted the need for more researches on therapeutics that may balance the levels of age-related alterations in biogenic amines.

Arylalkalamine N-acetyltransferase-1 acts on a secondary amine in the yellow fever mosquito, Aedes aegypti

Arylalkylamine N-acetyltransferase (aaNAT) in Aedes aegypti is primarily involved in cuticle pigmentation and formation. The reported arylalkylamine substrates are all primary amines. In this study, we report a novel substrate, a secondary amine, of Ae. aegypti aaNAT1. The recombinant aaNAT1 protein exhibited high activity to a secondary amine, epinephrine, which has not been reported for any aaNATs previously. Structure-activity relationship study demonstrated that aaNAT1 has an epinephrine binding site, and molecular docking and dynamic simulation showed that epinephrine is quite stable in the active cavity. Further functional studies demonstrated that epinephrine affected mosquito fecundity, egg hatching and development. The new biochemical function of aaNAT1 in metabolizing epinephrine could reduce some negative effects of the compound in the mosquito.

The octopamine receptor, OA2B2, modulates stress resistance and reproduction in Nilaparvata lugens Stål (Hemiptera: Delphacidae)

The brown planthopper (BPH), Nilaparvata lugens (Stål) is a resurgent pest of rice crops throughout Asia. We recently discovered that octopamine (OA) and OA2B2 operate in the BPH mating system, where it mediates a wide range of molecular, physiological and behavioural changes. Here, we report on outcomes of experiments designed to test the hypothesis that OA/OA2B2 signalling mediates responses to three abiotic stressors, starvation, high temperature (37 °C), and induced oxidative stress. We found per os RNAi-mediated OA2B2 silencing led to significantly decreased survival, measured in days, following exposure to each of these stressors. We selected a biologically costly process, reproductive biology, as a biotic stressor. Silencing of OA2B2 led to decreased total protein content in ovaries and fat bodies, downregulated expression of vitellogenin (Vg) and Vg receptor (VgR), inhibited fat body Vg protein synthesis, shortened the oviposition period, prolonged the preoviposition period, reduced the number of laid eggs, body weight and female longevity. In addition, the silencing treatments also led to inhibited ovarian development, and ovarian Vg uptake, reduced numbers of egg masses and offspring and lower hatching rates and population growth index. These data support our hypothesis that OA2B2 acts in mediating BPH resistance to biotic and abiotic stressors.

Cloning and characterization of tyrosine decarboxylase (TDC) from Litopenaeus vannamei, and its roles in biogenic amines synthesis, immune regulation, and resistance to Vibrio alginolyticus by RNA interference

The biogenic amines, tyramine and octopamine, in the octopaminergic synthesis pathway play critical roles in regulating physiological and immunological homeostasis in Litopenaeus vannamei. Tyrosine decarboxylase (TDC) is an enzyme catalyzing the first decarboxylation step in the biosynthesis of tyramine and octopamine. The full-length gene sequence of TDC cloned from the brain of L. vannamei (LvTDC) was predicted to encode a 779-amino acid protein with a pyridoxal-dependent decarboxylase-conserved domain in close phylogenetic relationship with arthropod TDCs. LvTDC gene expression was found to be abundant in nervous thoracic ganglia. RNA interference was used to assess the immune and physiological function of LvTDC. The LvTDC knockdown shrimp revealed significant decreases in the total haemocyte count, hyaline cells, antimicrobial peptides, respiratory bursts, gene expression, respiratory bursts of haemocytes per unit of haemolymph, and phagocytic activity and clearance efficiency toward Vibrio alginolyticus. Furthermore, LvTDC knockdown was accompanied by decreases in octopamine deficiency. In the V. alginolyticus challenge test, the survival rate of LvTDC knockdown shrimp was lower than the shrimp injected with DEPC-water or GAPDH-dsRNA. In conclusion, the cloned LvTDC was responsible for octopaminergic synthesis, which then regulated physiological and immune responses in L. vannamei.

Fatty ethanolamide of Bertholletia excelsa triglycerides (Brazil nuts): anti-inflammatory action and acute toxicity evaluation in Zebrafish (Danio rerio)

Fatty amides (N-alkylamides) are bioactive lipids that are widely distributed in microorganisms, animals, and plants. The low yield in the extraction process of spilantol, a fatty amide, which is mainly related to its diverse biological effects, compromises its application on a large scale. Thus, this study proposes an alternative method to synthesise fatty amides from Bertholletia excelsa (AGBe) oil, with a chemical structure similar to that of spilantol. Carrageenan-induced abdominal oedema in vivo models were used in zebrafish (Danio rerio). In in vivo studies, oral AGBe produced no signs of toxicity. In the histopathological study, AGBe did not cause significant changes in the main metabolising organs (liver, kidneys, and intestines). All doses of AGBe (100 mg/kg, 500 mg/kg, and 750 mg/kg) were effective in reducing oedema by 65%, 69%, and 95%, respectively, producing a dose-response effect compared to the control group, and spilantol-inhibited oedema by 48%. In the in silico study, with the use of molecular docking, it was observed that among the AGBe, the molecules 18:1, ω-7-ethanolamine, and 18:1, ω-9-ethanolamine stood out, with 21 interactions for COX-2 and 20 interactions for PLA₂, respectively, surpassing the spilantol standard with 15 interactions for COX-2 and PLA₂. The anti-inflammatory action hypothesis was confirmed in the in silico study, demonstrating the involvement of AGBe in the process of inhibiting the enzymes COX-2 and PLA₂. Therefore, based on all the results obtained and the fact that until the dose of 1000 mg/kg was administered orally in zebrafish, it was not possible to determine the LD₅₀; it can be said that AGBe is effective and safe for anti-inflammatory activity.

Endocrine signals fine-tune daily activity patterns in Drosophila

Animals need to balance competitive behaviors to maintain internal homeostasis. The underlying mechanisms are complex but typically involve neuroendocrine signaling. Using Drosophila, we systematically manipulated signaling between energy-mobilizing endocrine cells producing adipokinetic hormone (AKH), octopaminergic neurons, and the energy-storing fat body to assess whether this neuroendocrine axis involved in starvation-induced hyperactivity also balances activity levels under ad libitum access to food. Our results suggest that AKH signals via two divergent pathways that are mutually competitive in terms of activity and rest. AKH increases activity via the octopaminergic system during the day, while it prevents high activity levels during the night by signaling to the fat body. This regulation involves feedback signaling from octopaminergic neurons to AKH-producing cells (APCs). APCs are known to integrate a multitude of metabolic and endocrine signals. Our results add a new facet to the versatile regulatory functions of APCs by showing that their output contributes to shape the daily activity pattern under ad libitum access to food.

Tyramine synthesis, vesicular packaging, and the SNARE complex function coordinately in astrocytes to regulate Drosophila alcohol sedation

Identifying mechanisms underlying alcohol-related behaviors could provide important insights regarding the etiology of alcohol use disorder. To date, most genetic studies on alcohol-related behavior in model organisms have focused on neurons, leaving the causal roles of glial mechanisms less comprehensively investigated. Here, we report our studies on the role of Tyrosine decarboxylase 2 (Tdc2), which converts tyrosine to the catecholamine tyramine, in glial cells in Drosophila alcohol sedation. Using genetic approaches that drove transgene expression constitutively in all glia, constitutively in astrocytes and conditionally in glia during adulthood, we found that knockdown and overexpression of Tdc2, respectively, increased and decreased the sensitivity to alcohol sedation in flies. Manipulation of the genes tyramine β-hydroxylase and tyrosine hydroxylase, which respectively synthesize octopamine and dopamine from tyramine and tyrosine, had no discernable effect on alcohol sedation, suggesting that Tdc2 affects alcohol sedation by regulating tyramine production. We also found that knockdown of the vesicular monoamine transporter (VMAT) and disruption of the SNARE complex in all glia or selectively in astrocytes increased sensitivity to alcohol sedation and that both VMAT and the SNARE complex functioned downstream of Tdc2. Our studies support a model in which the synthesis of tyramine and vesicle-mediated release of tyramine from adult astrocytes regulates alcohol sedation in Drosophila. Considering that tyramine is functionally orthologous to norepinephrine in mammals, our results raise the possibility that gliotransmitter synthesis release could be a conserved mechanism influencing behavioral responses to alcohol as well as alcohol use disorder.

She's got nerve: roles of octopamine in insect female reproduction

The biogenic monoamine octopamine (OA) is a crucial regulator of invertebrate physiology and behavior. Since its discovery in the 1950s in octopus salivary glands, OA has been implicated in many biological processes among diverse invertebrate lineages. It can act as a neurotransmitter, neuromodulator and neurohormone in a variety of biological contexts, and can mediate processes including feeding, sleep, locomotion, flight, learning, memory, and aggression. Here, we focus on the roles of OA in female reproduction in insects. OA is produced in the octopaminergic neurons that innervate the female reproductive tract (RT). It exerts its effects by binding to receptors throughout the RT to generate tissue- and region-specific outcomes. OA signaling regulates oogenesis, ovulation, sperm storage, and reproductive behaviors in response to the female's internal state and external conditions. Mating profoundly changes a female's physiology and behavior. The female's OA signaling system interacts with, and is modified by, male molecules transferred during mating to elicit a subset of the post-mating changes. Since the role of OA in female reproduction is best characterized in the fruit fly Drosophila melanogaster, we focus our discussion on this species but include discussion of OA in other insect species whenever relevant. We conclude by proposing areas for future research to further the understanding of OA's involvement in female reproduction in insects.

Neuropeptide F signaling regulates parasitoid-specific germline development and egg-laying in Drosophila

Drosophila larvae and pupae are at high risk of parasitoid infection in nature. To circumvent parasitic stress, fruit flies have developed various survival strategies, including cellular and behavioral defenses. We show that adult Drosophila females exposed to the parasitic wasps, Leptopilina boulardi, decrease their total egg-lay by deploying at least two strategies: Retention of fully developed follicles reduces the number of eggs laid, while induction of caspase-mediated apoptosis eliminates the vitellogenic follicles. These reproductive defense strategies require both visual and olfactory cues, but not the MB247-positive mushroom body neuronal function, suggesting a novel mode of sensory integration mediates reduced egg-laying in the presence of a parasitoid. We further show that neuropeptide F (NPF) signaling is necessary for both retaining matured follicles and activating apoptosis in vitellogenic follicles. Whereas previous studies have found that gut-derived NPF controls germ stem cell proliferation, we show that sensory-induced changes in germ cell development specifically require brain-derived NPF signaling, which recruits a subset of NPFR-expressing cell-types that control follicle development and retention. Importantly, we found that reduced egg-lay behavior is specific to parasitic wasps that infect the developing Drosophila larvae, but not the pupae. Our findings demonstrate that female fruit flies use multimodal sensory integration and neuroendocrine signaling via NPF to engage in parasite-specific cellular and behavioral survival strategies.

Octopaminergic neurons have multiple targets in Drosophila larval mushroom body calyx and can modulate behavioral odor discrimination

Discrimination of sensory signals is essential for an organism to form and retrieve memories of relevance in a given behavioral context. Sensory representations are modified dynamically by changes in behavioral state, facilitating context-dependent selection of behavior, through signals carried by noradrenergic input in mammals, or octopamine (OA) in insects. To understand the circuit mechanisms of this signaling, we characterized the function of two OA neurons, sVUM1 neurons, that originate in the subesophageal zone (SEZ) and target the input region of the memory center, the mushroom body (MB) calyx, in larval Drosophila. We found that sVUM1 neurons target multiple neurons, including olfactory projection neurons (PNs), the inhibitory neuron APL, and a pair of extrinsic output neurons, but relatively few mushroom body intrinsic neurons, Kenyon cells. PN terminals carried the OA receptor Oamb, a Drosophila α1-adrenergic receptor ortholog. Using an odor discrimination learning paradigm, we showed that optogenetic activation of OA neurons compromised discrimination of similar odors but not learning ability. Our results suggest that sVUM1 neurons modify odor representations via multiple extrinsic inputs at the sensory input area to the MB olfactory learning circuit.

The Neurotransmitters Involved in Drosophila Alcohol-Induced Behaviors

Alcohol is a widely used and abused substance with numerous negative consequences for human health and safety. Historically, alcohol's widespread, non-specific neurobiological effects have made it a challenge to study in humans. Therefore, model organisms are a critical tool for unraveling the mechanisms of alcohol action and subsequent effects on behavior. Drosophila melanogaster is genetically tractable and displays a vast behavioral repertoire, making it a particularly good candidate for examining the neurobiology of alcohol responses. In addition to being experimentally amenable, Drosophila have high face and mechanistic validity: their alcohol-related behaviors are remarkably consistent with humans and other mammalian species, and they share numerous conserved neurotransmitters and signaling pathways. Flies have a long history in alcohol research, which has been enhanced in recent years by the development of tools that allow for manipulating individual Drosophila neurotransmitters. Through advancements such as the GAL4/UAS system and CRISPR/Cas9 mutagenesis, investigation of specific neurotransmitters in small subsets of neurons has become ever more achievable. In this review, we describe recent progress in understanding the contribution of seven neurotransmitters to fly behavior, focusing on their roles in alcohol response: dopamine, octopamine, tyramine, serotonin, glutamate, GABA, and acetylcholine. We chose these small-molecule neurotransmitters due to their conservation in mammals and their importance for behavior. While neurotransmitters like dopamine and octopamine have received significant research emphasis regarding their contributions to behavior, others, like glutamate, GABA, and acetylcholine, remain relatively unexplored. Here, we summarize recent genetic and behavioral findings concerning these seven neurotransmitters and their roles in the behavioral response to alcohol, highlighting the fitness of the fly as a model for human alcohol use.

TrpML-mediated astrocyte microdomain Ca2+ transients regulate astrocyte-tracheal interactions

Astrocytes exhibit spatially-restricted near-membrane microdomain Ca2+transients in their fine processes. How these transients are generated and regulate brain function in vivo remains unclear. Here we show that Drosophila astrocytes exhibit spontaneous, activity-independent microdomain Ca2+ transients in their fine processes. Astrocyte microdomain Ca2+ transients are mediated by the TRP channel TrpML, stimulated by reactive oxygen species (ROS), and can be enhanced in frequency by the neurotransmitter tyramine via the TyrRII receptor. Interestingly, many astrocyte microdomain Ca2+ transients are closely associated with tracheal elements, which dynamically extend filopodia throughout the central nervous system (CNS) to deliver O2 and regulate gas exchange. Many astrocyte microdomain Ca2+ transients are spatio-temporally correlated with the initiation of tracheal filopodial retraction. Loss of TrpML leads to increased tracheal filopodial numbers, growth, and increased CNS ROS. We propose that local ROS production can activate astrocyte microdomain Ca2+ transients through TrpML, and that a subset of these microdomain transients promotes tracheal filopodial retraction and in turn modulate CNS gas exchange.

Vesicular neurotransmitter transporters in Drosophila melanogaster

Drosophila melanogaster express vesicular transporters for the storage of neurotransmitters acetylcholine, biogenic amines, GABA, and glutamate. The large array of powerful molecular-genetic tools available in Drosophila enhances the use of this model organism for studying transporter function and regulation.

Cloning and characterisation of NMDA receptors in the Pacific oyster, Crassostrea gigas (Thunberg, 1793) in relation to metamorphosis and catecholamine synthesis

Bivalve metamorphosis is a developmental transition from a free-living larva to a benthic juvenile (spat), regulated by a complex interaction of neurotransmitters and neurohormones such as L-DOPA and epinephrine (catecholamine). We recently suggested an N-Methyl-D-aspartate (NMDA) receptor pathway as an additional and previously unknown regulator of bivalve metamorphosis. To explore this theory further, we successfully induced metamorphosis in the Pacific oyster, Crassostrea gigas, by exposing competent larvae to L-DOPA, epinephrine, MK-801 and ifenprodil. Subsequently, we cloned three NMDA receptor subunits CgNR1, CgNR2A and CgNR2B, with sequence analysis suggesting successful assembly of functional NMDA receptor complexes and binding to natural occurring agonists and the channel blocker MK-801. NMDA receptor subunits are expressed in competent larvae, during metamorphosis and in spat, but this expression is neither self-regulated nor regulated by catecholamines. In-situ hybridisation of CgNR1 in competent larvae identified NMDA receptor presence in the apical organ/cerebral ganglia area with a potential sensory function, and in the nervous network of the foot indicating an additional putative muscle regulatory function. Furthermore, phylogenetic analyses identified molluscan-specific gene expansions of key enzymes involved in catecholamine biosynthesis. However, exposure to MK-801 did not alter the expression of selected key enzymes, suggesting that NMDA receptors do not regulate the biosynthesis of catecholamines via gene expression.

Neuronal octopamine signaling regulates mating-induced germline stem cell increase in female Drosophila melanogaster

Stem cells fuel the development and maintenance of tissues. Many studies have addressed how local signals from neighboring niche cells regulate stem cell identity and their proliferative potential. However, the regulation of stem cells by tissue-extrinsic signals in response to environmental cues remains poorly understood. Here we report that efferent octopaminergic neurons projecting to the ovary are essential for germline stem cell (GSC) increase in response to mating in female Drosophila. The neuronal activity of the octopaminergic neurons is required for mating-induced GSC increase as they relay the mating signal from sex peptide receptor-positive cholinergic neurons. Octopamine and its receptor Oamb are also required for mating-induced GSC increase via intracellular Ca²⁺ signaling. Moreover, we identified Matrix metalloproteinase-2 as a downstream component of the octopamine-Ca²⁺ signaling to induce GSC increase. Our study provides a mechanism describing how neuronal system couples stem cell behavior to environmental cues through stem cell niche signaling.

Corrigendum: Cloning and Functional Characterization of Octβ2-Receptor and Tyr1-Receptor in the Chagas Disease Vector, Rhodnius prolixus

[This corrects the article DOI: 10.3389/fphys.2017.00744.].

The environmental toxicant ziram enhances neurotransmitter release and increases neuronal excitability via the EAG family of potassium channels

Environmental toxicants have the potential to contribute to the pathophysiology of multiple complex diseases, but the underlying mechanisms remain obscure. One such toxicant is the widely used fungicide ziram, a dithiocarbamate known to have neurotoxic effects and to increase the risk of Parkinson's disease. We have used Drosophila melanogaster as an unbiased discovery tool to identify novel molecular pathways by which ziram may disrupt neuronal function. Consistent with previous results in mammalian cells, we find that ziram increases the probability of synaptic vesicle release by dysregulation of the ubiquitin signaling system. In addition, we find that ziram increases neuronal excitability. Using a combination of live imaging and electrophysiology, we find that ziram increases excitability in both aminergic and glutamatergic neurons. This increased excitability is phenocopied and occluded by null mutant animals of the ether a-go-go (eag) potassium channel. A pharmacological inhibitor of the temperature sensitive hERG (human ether-a-go-go related gene) phenocopies the excitability effects of ziram but only at elevated temperatures. seizure (sei), a fly ortholog of hERG, is thus another candidate target of ziram. Taken together, the eag family of potassium channels emerges as a candidate for mediating some of the toxic effects of ziram. We propose that ziram may contribute to the risk of complex human diseases by blockade of human eag and sei orthologs, such as hERG.

Role of Biogenic Amines in Oviposition by the Diamondback Moth, Plutella xylostella L

Oviposition is an important reproductive behavior that is triggered by mating in insects, and biogenic amines might be involved in its regulation. The effects of biogenic amines on oviposition have only been studied in a few insect species, and the findings to date have not been conclusive. In addition, there are few studies on the effects of biogenic amines on oviposition of the diamondback moth, Plutella xylostella L. Here, we tested how mating and biogenic amines regulate oviposition of P. xylostella by injecting amines and amine receptor antagonists into virgin and mated females and counting the number of eggs laid afterward. Biogenic amines of octopamine and tyramine could induce virgin adults of P. xylostella to lay eggs, while dopamine and serotonin had no such effect on oviposition. Furthermore, the octopamine antagonists mianserin, epinastine, and phentolamine inhibited oviposition by mated females. The tyramine antagonist yohimbine, dopamine antagonist SCH23390, and serotonin antagonist ketanserin did not block oviposition by mated females, and octopamine and tyramine-inducing oviposition by virgin females could be inhibited by the octopamine antagonists mianserin and epinastine instead of the tyramine antagonist yohimbine. We conclude that octopamine and its receptors are involved in mating-triggered oviposition in P. xylostella, while tyramine acts as a subsidiary. Further, the inducing effect of tyramine on oviposition is achieved via octopamine receptors instead of tyramine receptors. This experiment is helpful to further understand the role of biogenic amines in mating regulation and to provide a new strategy for controlling P. xylostella.

The Corazonin-PTTH Neuronal Axis Controls Systemic Body Growth by Regulating Basal Ecdysteroid Biosynthesis in Drosophila melanogaster

Steroid hormones play key roles in development, growth, and reproduction in various animal phyla [1]. The insect steroid hormone, ecdysteroid, coordinates growth and maturation, represented by molting and metamorphosis [2]. In Drosophila melanogaster, the prothoracicotropic hormone (PTTH)-producing neurons stimulate peak levels of ecdysteroid biosynthesis for maturation [3]. Additionally, recent studies on PTTH signaling indicated that basal levels of ecdysteroid negatively affect systemic growth prior to maturation [4-8]. However, it remains unclear how PTTH signaling is regulated for basal ecdysteroid biosynthesis. Here, we report that Corazonin (Crz)-producing neurons regulate basal ecdysteroid biosynthesis by affecting PTTH neurons. Crz belongs to gonadotropin-releasing hormone (GnRH) superfamily, implying an analogous role in growth and maturation [9]. Inhibition of Crz neuronal activity increased pupal size, whereas it hardly affected pupariation timing. This phenotype resulted from enhanced growth rate and a delay in ecdysteroid elevation during the mid-third instar larval (L3) stage. Interestingly, Crz receptor (CrzR) expression in PTTH neurons was higher during the mid- than the late-L3 stage. Silencing of CrzR in PTTH neurons increased pupal size, phenocopying the inhibition of Crz neuronal activity. When Crz neurons were optogenetically activated, a strong calcium response was observed in PTTH neurons during the mid-L3, but not the late-L3, stage. Furthermore, we found that octopamine neurons contact Crz neurons in the subesophageal zone (SEZ), transmitting signals for systemic growth. Together, our results suggest that the Crz-PTTH neuronal axis modulates ecdysteroid biosynthesis in response to octopamine, uncovering a regulatory neuroendocrine system in the developmental transition from growth to maturation.