The octopamine receptor Octβ2R regulates ovulation in Drosophila melanogaster

In vitro evaluation of acaricidal activity of eugenol and benzaldehyde against Rhipicephalus annulatus

Economic importance of ticks for both humans and animals is significant primarily because of their involvement in disease transmission. The continuous use of synthetic chemical acaricides on animals and/or in the environment has resulted in the emergence of resistant tick populations. Consequently, there is a compelling need to explore newer natural alternatives that can address their adverse effects effectively. Since, there are no earlier reported studies on the acaricidal activity of eugenol and benzaldehyde against Rhipicephalus annulatus, the present study compared the in vitro adulticidal and larvicidal activities of these phytochemicals against R. annulatus. Concentration-dependent mortality and inhibition of fecundity were observed in the adult female ticks treated with both eugenol and benzaldehyde. The LC50 and LC90 values of eugenol against R. annulatus were 162.33 and 467.74 mg/mL for adult female, while it was 1.26 and 1.73 mg/mL for larvae respectively. The LC50 and LC90 values of benzaldehyde against R. annulatus were 178 and 395 mg/mL for adult female and 0.69 and 4.32 mg/mL for larvae respectively.

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.

An octopamine-specific GRAB sensor reveals a monoamine relay circuitry that boosts aversive learning

Octopamine (OA), analogous to norepinephrine in vertebrates, is an essential monoamine neurotransmitter in invertebrates that plays a significant role in various biological functions, including olfactory associative learning. However, the spatial and temporal dynamics of OA in vivo remain poorly understood due to limitations associated with the currently available methods used to detect it. To overcome these limitations, we developed a genetically encoded GPCR  activation-based (GRAB) OA sensor called GRABOA1.0. This sensor is highly selective for OA and exhibits a robust and rapid increase in fluorescence in response to extracellular OA. Using GRABOA1.0, we monitored OA release in the Drosophila mushroom body (MB), the fly's learning center, and found that OA is released in response to both odor and shock stimuli in an aversive learning model. This OA release requires acetylcholine (ACh) released from Kenyon cells, signaling via nicotinic ACh receptors. Finally, we discovered that OA amplifies aversive learning behavior by augmenting dopamine-mediated punishment signals via Octβ1R in dopaminergic neurons, leading to alterations in synaptic plasticity within the MB. Thus, our new GRABOA1.0 sensor can be used to monitor OA release in real time under physiological conditions, providing valuable insights into the cellular and circuit mechanisms that underlie OA signaling.

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.

Comparative transcriptomic characterization of the ovary in the spawning process of the mud crab Scylla paramamosain

Oviposition is induced upon mating in most insects. Spawning is a physiological process that is fundamental for the reproduction of Scylla paramamosain. However, the molecular mechanisms underlying the spawning process in this species are poorly understood. Herein, comprehensive ovary transcriptomic analysis was conducted at the germinal vesicle breakdown stage (GVBD), spawning stage, 0.5 h post-spawning stage, and 24 h post-spawning stage of S. paramamosain for gene discovery. A total of 67,230 unigenes were generated, and 27,975 (41.61%) unigenes were annotated. Meanwhile, the differentially expressed genes (DEGs) between the different groups were identified, and Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis was subsequently conducted. These results suggested that octopamine (OA) and tyramine (TA) could induce oviposition, while dopamine (DA) and serotonin (5-hydroxytryptamine [5-HT]) inhibit oviposition. The 20-hydroxyecdysone (20E) and methyl farnesoate (MF) signal pathways might be positively associated with oviposition. Furthermore, numerous transcripts that encode neuropeptides and their G-protein-coupled receptors (GPCRs), such as CNMamide, RYamide, ecdysis-triggering hormone (ETH), GPA2/GPB5 receptor, and Moody receptor, appear to be differentially expressed during the spawning process. Eleven unigenes were selected for qRT-PCR and the pattern was found to be consistent with the transcriptome expression pattern. Our work is the first spawning-related investigation of S. paramamosain focusing on the ovary at the whole transcriptome level. These findings assist in improving our understanding of spawning regulation in S. paramamosain and provide information for oviposition studies in other crustaceans.

An octopamine-specific GRAB sensor reveals a monoamine relay circuitry that boosts aversive learning

Octopamine (OA), analogous to norepinephrine in vertebrates, is an essential monoamine neurotransmitter in invertebrates that plays a significant role in various biological functions, including olfactory associative learning. However, the spatial and temporal dynamics of OA in vivo remain poorly understood due to limitations associated with the currently available methods used to detect it. To overcome these limitations, we developed a genetically encoded GPCR activation-based (GRAB) OA sensor called GRABOA1.0. This sensor is highly selective for OA and exhibits a robust and rapid increase in fluorescence in response to extracellular OA. Using GRABOA1.0, we monitored OA release in the Drosophila mushroom body (MB), the fly's learning center, and found that OA is released in response to both odor and shock stimuli in an aversive learning model. This OA release requires acetylcholine (ACh) released from Kenyon cells, signaling via nicotinic ACh receptors. Finally, we discovered that OA amplifies aversive learning behavior by augmenting dopamine-mediated punishment signals via Octβ1R in dopaminergic neurons, leading to alterations in synaptic plasticity within the MB. Thus, our new GRABOA1.0 sensor can be used to monitor OA release in real-time under physiological conditions, providing valuable insights into the cellular and circuit mechanisms that underlie OA signaling.

Expression and potential regulatory functions of Drosophila octopamine receptors in the female reproductive tract

Aminergic 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, is required for ovulation as well as several other female reproductive processes. Two octopamine receptors have already been shown to be expressed in the Drosophila reproductive tract and to be required for egg-laying: OAMB and Octβ2R. The Drosophila genome contains 4 additional octopamine receptors-Octα2R, Octβ1R, Octβ3R, and Oct-TyrR-but their cellular patterns of expression in the reproductive tract and potential contribution(s) to egg-laying are not known. In addition, the mechanisms by which OAMB and Octβ2R regulate reproduction are incompletely understood. Using a panel of MiMIC Gal4 lines, we show that Octα2R, Octβ1R, Octβ3R, and Oct-TyrR receptors are not detectable in either epithelium or muscle but are clearly expressed in neurons within the female fly reproductive tract. Optogenetic activation of neurons that express at least 3 types of octopamine receptors stimulates contractions in the lateral oviduct. We also find that octopamine stimulates calcium transients in the sperm storage organs and that its effects in spermathecal, secretory cells, can be blocked by knock-down of OAMB. These data extend our understanding of the pathways by which octopamine regulates egg-laying in Drosophila and raise the possibility that multiple octopamine receptor subtypes could play a role in this process.

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.

Neuronal substrates of egg-laying behaviour at the abdominal ganglion of Drosophila melanogaster

Egg-laying in Drosophila is the product of post-mating physiological and behavioural changes that culminate in a stereotyped sequence of actions. Egg-laying harbours a great potential as a paradigm to uncover how the appropriate motor circuits are organized and activated to generate behaviour. To study this programme, we first describe the different phases of the egg-laying programme and the specific actions associated with each phase. Using a combination of neuronal activation and silencing experiments, we identify neurons (OvAbg) in the abdominal ganglion as key players in egg-laying. To generate and functionally characterise subsets of OvAbg, we used an intersectional approach with neurotransmitter specific lines-VGlut, Cha and Gad1. We show that OvAbg/VGlut neurons promote initiation of egg deposition in a mating status dependent way. OvAbg/Cha neurons are required in exploration and egg deposition phases, though activation leads specifically to egg expulsion. Experiments with the OvAbg/Gad1 neurons show they participate in egg deposition. We further show a functional connection of OvAbg neurons with brain neurons. This study provides insight into the organization of neuronal circuits underlying complex motor behaviour.

Identification of CYCLE targets that contribute diverse features of circadian rhythms in the mosquito Culex pipiens

Culex pipiens demonstrates robust circadian rhythms in adult eclosion, flight activity, mating, and development. These rhythmic patterns are believed to be controlled by the endogenous light-entrainable circadian clock that consists of positive and negative regulators working in a transcription-translation feedback loop. Moreover, these mosquitoes undergo seasonal diapause in exposure to the short photoperiod of late summer or early fall. However, the exact genetic and cellular mechanism behind the clock gene-mediated activity pattern, seasonal time measurement, and subsequent diapause initiation still need to be unraveled. To determine the possible linkage between clock genes and downstream processes, here we employed ChIP-sequencing to identify the direct targets of one of the core clock proteins, Cycle (CYC). The nearest genes with peaks mapping to their 1Kb upstream region of the transcription start site were extracted and scanned for consensus E box sequences, resulting in a dataset comprising the target genes possibly regulated by CYC. Based on the highest fold enrichment and functional relevance, we identified genes relating to five gene categories of potential interest, including peptide/receptors, neurotransmission, olfaction, immunity, and reproductive growth. Of these, we validated fourteen genes with ChIP-qPCR and qRT-PCR. These genes showed a significantly high expression in dusk compared to dawn in concert with the activity level of the CYC transcription factor and are thus strong candidates for mediating circadian rhythmicity and possibly regulating seasonal shifts in mosquito reproductive activity.

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.

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.

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.

Regulation of morphogen pathways by a Drosophila chondroitin sulfate proteoglycan Windpipe

Morphogens provide quantitative and robust signaling systems to achieve stereotypic patterning and morphogenesis. Heparan sulfate (HS) proteoglycans (HSPGs) are key components of such regulatory feedback networks. In Drosophila, HSPGs serve as co-receptors for a number of morphogens, including Hedgehog (Hh), Wingless (Wg), Decapentaplegic (Dpp) and Unpaired (Upd, or Upd1). Recently, Windpipe (Wdp), a chondroitin sulfate (CS) proteoglycan (CSPG), was found to negatively regulate Upd and Hh signaling. However, the roles of Wdp, and CSPGs in general, in morphogen signaling networks are poorly understood. We found that Wdp is a major CSPG with 4-O-sulfated CS in Drosophila. Overexpression of wdp modulates Dpp and Wg signaling, showing that it is a general regulator of HS-dependent pathways. Although wdp mutant phenotypes are mild in the presence of morphogen signaling buffering systems, this mutant in the absence of Sulf1 or Dally, molecular hubs of the feedback networks, produces high levels of synthetic lethality and various severe morphological phenotypes. Our study indicates a close functional relationship between HS and CS, and identifies the CSPG Wdp as a novel component in morphogen feedback pathways.

The auditory efferent system in mosquitoes

Whilst acoustic communication forms an integral component of the mating behavior of many insect species, it is particularly crucial for disease-transmitting mosquitoes; swarming males rely on hearing the faint sounds of flying females for courtship initiation. That males can hear females within the din of a swarm is testament to their fabulous auditory systems. Mosquito hearing is highly frequency-selective, remarkably sensitive and, most strikingly, supported by an elaborate system of auditory efferent neurons that modulate the auditory function - the only documented example amongst insects. Peripheral release of octopamine, serotonin and GABA appears to differentially modulate hearing across major disease-carrying mosquito species, with receptors from other neurotransmitter families also identified in their ears. Because mosquito mating relies on hearing the flight tones of mating partners, the auditory efferent system offers new potential targets for mosquito control. It also represents a unique insect model for studying auditory efferent networks. Here we review current knowledge of the mosquito auditory efferent system, briefly compare it with its counterparts in other species and highlight future research directions to unravel its contribution to mosquito auditory perception.

Octopamine and tyramine signalling in Aedes aegypti: Molecular characterization and insight into potential physiological roles

In insects, the biogenic amines octopamine (OA) and tyramine (TA) are involved in controlling several physiological and behavioural processes. OA and TA act as neurotransmitters, neuromodulators or neurohormones, performing their functions by binding to specific receptors belonging to the G protein-coupled receptor (GPCR) superfamily. OA and TA along with their receptors are involved in reproduction, smell perception, metabolism, and homeostasis. Moreover, OA and TA receptors are targets for insecticides and antiparasitic agents, such as the formamidine Amitraz. In the dengue and yellow fever vector, Aedes aegypti, limited research has been reported on their OA or TA receptors. Here, we identify and molecularly characterize the OA and TA receptors in A. aegypti. Bioinformatic tools were used to identify four OA and three TA receptors in the genome of A. aegypti. The seven receptors are expressed in all developmental stages of A. aegypti; however, their highest transcript abundance is observed in the adult. Among several adult A. aegypti tissues examined, including the central nervous system, antennae and rostrum, midgut, Malpighian tubules, ovaries, and testes, the type 2 TA receptor (TAR2) transcript is most abundant in the ovaries and the type 3 TA receptor (TAR3) is enriched in the Malpighian tubules, leading us to propose putative roles for these receptors in reproduction and diuresis, respectively. Furthermore, a blood meal influenced OA and TA receptor transcript expression patterns in adult female tissues at several time points post blood meal, suggesting these receptors may play key physiological roles associated with feeding. To better understand OA and TA signalling in A. aegypti, the transcript expression profiles of key enzymes in their biosynthetic pathway, namely tyrosine decarboxylase (Tdc) and tyramine β-hydroxylase (Tβh), were examined in developmental stages, adult tissues, and brains from blood-fed females. These findings provide information for better understanding the physiological roles of OA, TA, and their receptors in A. aegypti, and additionally, may help in the development of novel strategies for the control of these human disease vectors.

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.

Intermediate conductance Ca2+-activated potassium channels are activated by functional coupling with stretch-activated nonselective cation channels in cricket myocytes

Cooperative gating of localized ion channels ranges from fine-tuning excitation-contraction coupling in muscle cells to controlling pace-making activity in the heart. Membrane deformation resulting from muscle contraction activates stretch-activated (SA) cation channels. The subsequent Ca2+ influx activates spatially localized Ca2+-sensitive K+ channels to fine-tune spontaneous muscle contraction. To characterize endogenously expressed intermediate conductance Ca2+-activated potassium (IK) channels and assess the functional relevance of the extracellular Ca2+ source leading to IK channel activity, we performed patch-clamp techniques on cricket oviduct myocytes and recorded single-channel data. In this study, we first investigated the identification of IK channels that could be distinguished from endogenously expressed large-conductance Ca2+-activated potassium (BK) channels by adding extracellular Ba2+. The single-channel conductance of the IK channel was 62 pS, and its activity increased with increasing intracellular Ca2+ concentration but was not voltage-dependent. These results indicated that IK channels are endogenously expressed in cricket oviduct myocytes. Second, the Ca2+ influx pathway that activates the IK channel was investigated. The absence of extracellular Ca2+ or the presence of Gd3+ abolished the activity of IK channels. Finally, we investigated the proximity between SA and IK channels. The removal of extracellular Ca2+, administration of Ca2+ to the microscopic region in a pipette, and application of membrane stretching stimulation increased SA channel activity, followed by IK channel activity. Membrane stretch-induced SA and IK channel activity were positively correlated. However, the emergence of IK channel activity and its increase in response to membrane mechanical stretch was not observed without Ca2+ in the pipette. These results strongly suggest that IK channels are endogenously expressed in cricket oviduct myocytes and that IK channel activity is regulated by neighboring SA channel activity. In conclusion, functional coupling between SA and IK channels may underlie the molecular basis of spontaneous rhythmic contractions.

Molecular and Pharmacological Characterization of β-Adrenergic-like Octopamine Receptors in the Endoparasitoid Cotesia chilonis (Hymenoptera: Braconidae)

Octopamine (OA) is structurally and functionally similar to adrenaline/noradrenaline in vertebrates, and OA modulates diverse physiological and behavioral processes in invertebrates. OA exerts its actions by binding to specific octopamine receptors (OARs). Functional and pharmacological characterization of OARs have been investigated in several insects. However, the literature on OARs is scarce for parasitoids. Here we cloned three β-adrenergic-like OARs (CcOctβRs) from Cotesia chilonis. CcOctβRs share high similarity with their own orthologous receptors. The transcript levels of CcOctβRs were varied in different tissues. When heterologously expressed in CHO-K1 cells, CcOctβRs induced cAMP production, and were dose-dependently activated by OA, TA and putative octopaminergic agonists. Their activities were inhibited by potential antagonists and were most efficiently blocked by epinastine. Our study offers important information about the molecular and pharmacological properties of β-adrenergic-like OARs from C. chilonis that will provide the basis to reveal the contribution of individual receptors to the physiological processes and behaviors in parasitoids.

De novo transcriptome assembly and identification of G-Protein-Coupled-Receptors (GPCRs) in two species of monogenean parasites of fish

Genomic resources for Platyhelminthes of the class Monogenea are scarce, despite the diversity of these parasites, some species of which are highly pathogenic to their fish hosts. This work aimed to generate de novo-assembled transcriptomes of two monogenean species, Scutogyrus longicornis (Dactylogyridae) and Rhabdosynochus viridisi (Diplectanidae), providing a protocol for cDNA library preparation with low input samples used in single cell transcriptomics. This allowed us to work with sub-microgram amounts of total RNA with success. These transcriptomes consist of 25,696 and 47,187 putative proteins, respectively, which were further annotated according to the Swiss-Prot, Pfam, GO, KEGG, and COG databases. The completeness values of these transcriptomes evaluated with BUSCO against Metazoa databases were 54.1% and 73%, respectively, which is in the range of other monogenean species. Among the annotations, a large number of terms related to G-protein-coupled receptors (GPCRs) were found. We identified 109 GPCR-like sequences in R. viridisi, and 102 in S. longicornis, including family members specific for Platyhelminthes. Rhodopsin was the largest family according to GRAFS classification. Two putative melatonin receptors found in S. longicornis represent the first record of this group of proteins in parasitic Platyhelminthes. Forty GPCRs of R. viridisi and 32 of S. longicornis that were absent in Vertebrata might be potential drug targets. The present study provides the first publicly available transcriptomes for monogeneans of the subclass Monopisthocotylea, which can serve as useful genomic datasets for functional genomic research of this important group of parasites.

The Effects of Male Seminal Fluid Proteins on Gut/Gonad Interactions in Drosophila

Mating initiates broad physiological changes encompassing multiple organ systems in females. Elucidating the complex inter- and intra-organ signaling events that coordinate these physiological changes is an important goal in the field of reproductive biology. Further characterization of these complex molecular and physiological interactions is key to understanding how females meet the energetic demands of offspring production. Many recent studies of the fruit fly, Drosophila melanogaster, have described the mechanisms of post-mating changes within the female reproductive tract and digestive system. Additionally, other studies have described post-mating signaling crosstalk between these systems. Interestingly, male seminal fluid proteins have been linked to post-mating responses within the female reproductive tract and gut, and to signaling events between the two organ systems. However, information about the hormonal and neuronal signaling pathways underlying the post-mating signaling events within and between the reproductive tract and digestive systems that are triggered by seminal fluid proteins has yet to be combined into a single view. In this article, we summarize and integrate these studies into a single "network schematic" of the known signaling events within and between the reproductive and digestive systems downstream of male seminal fluid proteins. This synthesis also draws attention to the incomplete parts of these pathways, so that outstanding questions may be addressed in future studies.

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.

Oocyte Quiescence: From Formation to Awakening

Decades of work using various model organisms have resulted in an exciting and emerging field of oocyte maturation. High levels of insulin and active mammalian target of rapamycin signals, indicative of a good nutritional environment, and hormones such as gonadotrophin, indicative of the growth of the organism, work together to control oocyte maturation to ensure that reproduction happens at the right timing under the right conditions. In the wild, animals often face serious challenges to maintain oocyte quiescence under long-term unfavorable conditions in the absence of mates or food. Failure to maintain oocyte quiescence will result in activation of oocytes at the wrong time and thus lead to exhaustion of the oocyte pool and sterility of the organism. In this review, we discuss the shared mechanisms in oocyte quiescence and awakening and a conserved role of noradrenergic signals in maintenance of the quiescent oocyte pool under unfavorable conditions in simple model organisms.

Is the Natural Instinct to Oviposit in Mated Female Oriental Fruit Fly, Bactrocera dorsalis More of a Brain-Independent Act?

What physiological and neuro-molecular changes control the female oviposition behavior post-mating in insects? The molecular changes that occur in a gravid female insect are difficult to dissect out considering the distinct behavioral patterns displayed by different insect groups. To understand the role of the brain center in Oriental fruit fly, Bactrocera dorsalis oviposition, egg-laying behavior was analyzed in γ-octalactone exposed, decapitated mated B. dorsalis females. Interestingly, the females displayed a possible urge to oviposit, which suggests a natural instinct to pass on the gene pool. Expression analysis of certain genes involved in oviposition behavior was also carried out in these insects to explore the molecular aspects of such behavior. This study tries to assess the involvement of brain center in egg-laying and also explore the role of certain neurotransmitter-related receptors in decapitated B. dorsalis oviposition behavior. Our results indicate that B. dorsalis oviposition behavior could potentially have a bypass route of neuronal control devoid of the brain. The study reported here establishes that decapitation in gravid females fails to abolish their ability to sense ovipositional cues and also to oviposit.

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.

Octopamine signaling is involved in the female postmating state in Nilaparvata lugens Stål (Hemiptera: Delphacidae)

Mating triggers physiological and behavioral changes in female insects. In many species, females experience postmating behavioral and physiological changes that define a post-mated state. These changes are comprised of several conditions, including long-term refractoriness to re-mating and increased production and laying of eggs. Here, we report that mating led to several changes in brown planthopper (BPH) females, including increased octopamine (OA), cAMP concentrations, and activities of several enzymes. Mating also led to changes in the expression of several genes acting in female physiology, including those in the cAMP/PKA signal transduction pathway. OA injections into virgin females led to similar changes. RNAi silencing of the gene encoding tyramine β-hydroxylase, involved in the final step in OA synthesis, led to decreased expression of these genes, and reduced the cAMP/PKA signaling. At the whole-organism level, the RNAi treatments led to reduced fecundity, body weights, and longevity. RNAi silencing of genes acting in OA signaling led to truncated ovarian development, egg maturation, and ovarian vitellogenin (Vg) uptake. The impact of these decreases is also registered at the population level, seen as decreased population growth. We infer that OA signaling modulates the postmating state in female BPH and possibly other hemipterans.

An octopamine receptor confers selective toxicity of amitraz on honeybees and Varroa mites

The Varroa destructor mite is a devastating parasite of Apis mellifera honeybees. They can cause colonies to collapse by spreading viruses and feeding on the fat reserves of adults and larvae. Amitraz is used to control mites due to its low toxicity to bees; however, the mechanism of bee resistance to amitraz remains unknown. In this study, we found that amitraz and its major metabolite potently activated all four mite octopamine receptors. Behavioral assays using Drosophila null mutants of octopamine receptors identified one receptor subtype Octβ2R as the sole target of amitraz in vivo. We found that thermogenetic activation of octβ2R-expressing neurons mimics amitraz poisoning symptoms in target pests. We next confirmed that the mite Octβ2R was more sensitive to amitraz and its metabolite than the bee Octβ2R in pharmacological assays and transgenic flies. Furthermore, replacement of three bee-specific residues with the counterparts in the mite receptor increased amitraz sensitivity of the bee Octβ2R, indicating that the relative insensitivity of their receptor is the major mechanism for honeybees to resist amitraz. The present findings have important implications for resistance management and the design of safer insecticides that selectively target pests while maintaining low toxicity to non-target pollinators.

Knockdown of a β-Adrenergic-Like Octopamine Receptor Affects Locomotion and Reproduction of Tribolium castaneum

The neurohormone octopamine regulates many crucial physiological processes in insects and exerts its activity via typical G-protein coupled receptors. The roles of octopamine receptors in regulating behavior and physiology in Coleoptera (beetles) need better understanding. We used the red flour beetle, Tribolium castaneum, as a model species to study the contribution of the octopamine receptor to behavior and physiology. We cloned the cDNA of a β-adrenergic-like octopamine receptor (TcOctβ2R). This was heterologously expressed in human embryonic kidney (HEK) 293 cells and was demonstrated to be functional using an in vitro cyclic AMP assay. In an RNAi assay, injection of dsRNA demonstrated that TcOctβ2R modulates beetle locomotion, mating duration, and fertility. These data present some roles of the octopaminergic signaling system in T. castaneum. Our findings will also help to elucidate the potential functions of individual octopamine receptors in other insects.

Phenyl imidazolidin-2-ones antagonize a β-adrenergic-like octopamine receptor in diamondback moth (Plutella xylostella)

BACKGROUND

The diamondback moth (Plutella xylostella) is one of the most destructive lepidopteran pests on cruciferous vegetables. However, resistance has emerged to current chemical and biological insecticides used for P. xylostella control, indicating the necessity of screening new targets on P. xylostella, and finding new insecticides against P. xylostella. In particular, octopamine receptors are representative G protein-coupled receptors found only in invertebrates and are potential targets for identifying novel insecticides.

RESULTS

A β-adrenergic-like octopamine receptor gene (PxOA2B1) was cloned, and its pharmacological characteristics in P. xylostella were studied. The results demonstrated that octopamine could activate the PxOA2B1 receptor, with a half-maximal effective concentration (EC₅₀ ) of 49.5 nm. Amitraz, an insecticide and acaricide, and its metabolite (N-2,4-dimethylphenyl-N'-methylformamidine; DPMF) were also found to act as PxOAB1R agonists. We synthesized phenyl imidazolidin-2-one derivatives 3a-h using DPMF as the lead compound, and compounds 3a-h showed similar antagonist activities as phentolamine, mianserin and chlorpromazine. In particular, 3d, with an EC₅₀ of 25.2 nm, showed very similar antagonist activity to mianserin.

CONCLUSION

This research found that PxOAB1R might be a potential target for P. xylostella control. Phenyl imidazolidin-2-ones could be novel potential antagonists targeted at octopamine receptors and would be useful tools for the design and development of novel insecticides. © 2021 Society of Chemical Industry.

Sensitivity to expression levels underlies differential dominance of a putative null allele of the Drosophila tβh gene in behavioral phenotypes

The biogenic amine octopamine (OA) and its precursor tyramine (TA) are involved in controlling a plethora of different physiological and behavioral processes. The tyramine-β-hydroxylase (tβh) gene encodes the enzyme catalyzing the last synthesis step from TA to OA. Here, we report differential dominance (from recessive to overdominant) of the putative null tβh^nM18 allele in 2 behavioral measures in Buridan’s paradigm (walking speed and stripe deviation) and in proboscis extension (sugar sensitivity) in the fruit fly Drosophila melanogaster. The behavioral analysis of transgenic tβh expression experiments in mutant and wild-type flies as well as of OA and TA receptor mutants revealed a complex interaction of both aminergic systems. Our analysis suggests that the different neuronal networks responsible for the 3 phenotypes show differential sensitivity to tβh gene expression levels. The evidence suggests that this sensitivity is brought about by a TA/OA opponent system modulating the involved neuronal circuits. This conclusion has important implications for standard transgenic techniques commonly used in functional genetics.

Differential dominance occurs when genes associated with several phenotypes (pleiotropic genes) show different modes of inheritance (e.g., recessive, dominant or overdominant) depending on the phenotype. This study reveals that differential sensitivity to gene expression levels can mediate differential dominance, which can be a significant challenge for standard transgenic techniques commonly used to elucidate gene function.

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.

Characterization and functional analysis of a β-adrenergic-like octopamine receptor from the oriental armyworm (Mythimna separata Walker)

The β-adrenergic-like octopamine receptor (OA2B2), which binds the biogenic amine octopamine, belongs to the class of G-protein coupled receptors and significantly regulates many physiological and behavioral processes in insects. In this study, the putative open reading frame sequence of the MsOA2B2 gene in Mythimna separata was cloned, the full-length complementary DNA was 1191 bp and it encoded a 396-amino acid protein (GenBank accession number MN822800). Orthologous sequence alignment, phylogenetic tree analysis, and protein sequence analysis all showed that the cloned receptor belongs to the OA2B2 protein family. Real-time quantitative polymerase chain reaction of spatial and temporal expression analysis revealed that the MsOAB2 gene was expressed in all developmental stages of M. separata and was most abundant in egg stages and second and fourth instars compared with other developmental stages, while the expression level during the pupal stage was much lower than that at the other stages. Further analysis with sixth instar M. separata larvae showed that the MsOA2B2 gene was expressed 1.81 times higher in the head than in integument and gut tissues. Dietary ingestion of dsMsOA2B2 significantly reduced the messenger RNA level of MsOA2B2 and decreased mortality following amitraz treatment. This study provides both a pharmacological characterization and the gene expression patterns of OA2B2 in M. separata, facilitating further research for insecticides using MsOA2B2 as a target.

A Mechanosensory Receptor TMC Regulates Ovary Development in the Brown Planthopper Nilaparvata lugens

Transmembrane channel-like (TMC) genes encode a family of evolutionarily conserved membrane proteins. Mutations in the TMC1 and TMC2 cause deafness in humans and mice. However, their functions in insects are is still not well known. Here we cloned three tmc genes, Nltmc3, Nltmc5, and Nltmc7 from brown planthoppers. The predicted amino acid sequences showed high identity with other species homologs and have the characteristic eight or nine transmembrane domains and TMC domain architecture. We detected these three genes in all developmental stages and examined tissues. Interestingly, we found Nltmc3 was highly expressed in the female reproductive organ especially in the oviduct. RNAi-mediated silencing of Nltmc3 substantially decreased the egg-laying number and impaired ovary development. Our results indicate that Nltmc3 has an essential role in the ovary development of brown planthoppers.

De novo transcriptome assembly from the gonads of a scleractinian coral, Euphyllia ancora: molecular mechanisms underlying scleractinian gametogenesis

BACKGROUND

Sexual reproduction of scleractinians has captured the attention of researchers and the general public for decades. Although extensive ecological data has been acquired, underlying molecular and cellular mechanisms remain largely unknown. In this study, to better understand mechanisms underlying gametogenesis, we isolated ovaries and testes at different developmental phases from a gonochoric coral, Euphyllia ancora, and adopted a transcriptomic approach to reveal sex- and phase-specific gene expression profiles. In particular, we explored genes associated with oocyte development and maturation, spermiogenesis, sperm motility / capacitation, and fertilization.

RESULTS

1.6 billion raw reads were obtained from 24 gonadal samples. De novo assembly of trimmed reads, and elimination of contigs derived from symbiotic dinoflagellates (Symbiodiniaceae) and other organisms yielded a reference E. ancora gonadal transcriptome of 35,802 contigs. Analysis of 4 developmental phases identified 2023 genes that were differentially expressed during oogenesis and 678 during spermatogenesis. In premature/mature ovaries, 631 genes were specifically upregulated, with 538 in mature testes. Upregulated genes included those involved in gametogenesis, gamete maturation, sperm motility / capacitation, and fertilization in other metazoans, including humans. Meanwhile, a large number of genes without homology to sequences in the SWISS-PROT database were also observed among upregulated genes in premature / mature ovaries and mature testes.

CONCLUSIONS

Our findings show that scleractinian gametogenesis shares many molecular characteristics with that of other metazoans, but it also possesses unique characteristics developed during cnidarian and/or scleractinian evolution. To the best of our knowledge, this study is the first to create a gonadal transcriptome assembly from any scleractinian. This study and associated datasets provide a foundation for future studies regarding gametogenesis and differences between male and female colonies from molecular and cellular perspectives. Furthermore, our transcriptome assembly will be a useful reference for future development of sex-specific and/or stage-specific germ cell markers that can be used in coral aquaculture and ecological studies.

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.].

Alpha- and beta-adrenergic octopamine receptors in muscle and heart are required for Drosophila exercise adaptations

Endurance exercise has broadly protective effects across organisms, increasing metabolic fitness and reducing incidence of several age-related diseases. Drosophila has emerged as a useful model for studying changes induced by chronic endurance exercise, as exercising flies experience improvements to various aspects of fitness at the cellular, organ and organismal level. The activity of octopaminergic neurons is sufficient to induce the conserved cellular and physiological changes seen following endurance training. All 4 octopamine receptors are required in at least one target tissue, but only one, Octβ1R, is required for all of them. Here, we perform tissue- and adult-specific knockdown of alpha- and beta-adrenergic octopamine receptors in several target tissues. We find that reduced expression of Octβ1R in adult muscles abolishes exercise-induced improvements in endurance, climbing speed, flight, cardiac performance and fat-body catabolism in male Drosophila. Importantly, Octβ1R and OAMB expression in the heart is also required cell-nonautonomously for adaptations in other tissues, such as skeletal muscles in legs and adult fat body. These findings indicate that activation of distinct octopamine receptors in skeletal and cardiac muscle are required for Drosophila exercise adaptations, and suggest that cell non-autonomous factors downstream of octopaminergic activation play a key role.

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.

Molecular and pharmacological characterization of a β-adrenergic-like octopamine receptor from the green rice leafhopper Nephotettix cincticeps

As the counterparts of noradrenaline and adrenaline in vertebrates, octopamine (OA) regulates multiple physiological and behavioral processes in invertebrate. OA mediates its effects via binding to specific octopamine receptors (OARs). Functional and pharmacological characterization of OARs have been reported in several insects. However, little work was documented in hemipteran insects. We cloned a β-adrenergic-like OAR (NcOA2B2) from Nephotettix cincticeps. NcOA2B2 shares high similarity with members of the OA2B2 receptor class. Transcript level of NcOA2B2 varied in various tissues and was highly expressed in the leg. After heterologous expression in CHO-K1 cells, NcOA2B2 was dose-dependently activated by OA (EC₅₀ = 2.56 nM) and tyramine (TA) (EC₅₀ = 149 nM). Besides putative octopaminergic agonists, dopaminergic agonists and amitraz and DPMF potently activated NcOA2B2 in a dose-dependent manner. Receptor activity was blocked by potential antagonists and was most efficiently antagonized by asenapine. Phentolamine showed both antagonist and agonist effects on NcOA2B2. Our results offer the important information about molecular and pharmacological characterization of an OAR from N. cincticeps that will provide the basis for forthcoming studies on its roles in physiological processes and behaviors, and facilitate the design of novel insecticides for pest control.

Concerted Actions of Octopamine and Dopamine Receptors Drive Olfactory Learning

Aminergic signaling modulates associative learning and memory. Substantial advance has been made in Drosophila on the dopamine receptors and circuits mediating olfactory learning; however, our knowledge of other aminergic modulation lags behind. To address this knowledge gap, we investigated the role of octopamine in olfactory conditioning. Here, we report that octopamine activity through the β-adrenergic-like receptor Octβ1R drives aversive and appetitive learning: Octβ1R in the mushroom body αβ neurons processes aversive learning, whereas Octβ1R in the projection neurons mediates appetitive learning. Our genetic interaction and imaging studies pinpoint cAMP signaling as a key downstream effector for Octβ1R function. The rutabaga-adenylyl cyclase synthesizes cAMP in a Ca²⁺/calmodulin-dependent manner, serving as a coincidence detector for associative learning and likely representing a downstream target for Octβ1R. Supporting this notion, the double heterozygous rutabaga/+;octβ1r/+ flies perform poorly in both aversive and appetitive conditioning, while individual heterozygous rutabaga/+ and octβ1r/+ flies behave like the wild-type control. Consistently, the mushroom body and projection neurons in the octβ1r brain exhibit blunted responses to octopamine when cAMP levels are monitored through the cAMP sensor. We previously demonstrated the pivotal functions of the D₁ receptor dDA1 in aversive and appetitive learning, and the α1 adrenergic-like receptor OAMB in appetitive learning. As expected, octβ1r genetically interacts with dumb (dDA1 mutant) in aversive and appetitive learning, but it interacts with oamb only in appetitive learning. This study uncovers the indispensable contributions of dopamine and octopamine signaling to aversive and appetitive learning. All experiments were performed on mixed sex unless otherwise noted.SIGNIFICANCE STATEMENT Animals make flexible behavioral choices that are constantly shaped by experience. This plasticity is vital for animals to appropriately respond to the cues predicting benefit or harm. In Drosophila, dopamine is known to mediate both reward-based and punishment-based learning while octopamine function is important only for reward. Here, we demonstrate that the octopamine-Octβ1R-cAMP pathway processes both aversive and appetitive learning in distinct neural sites of the olfactory circuit. Furthermore, we show that the octopamine-Octβ1R and dopamine-dDA1 signals together drive both aversive and appetitive learning, whereas the octopamine-Octβ1R and octopamine-OAMB pathways jointly facilitate appetitive, but not aversive, learning. This study identifies the cognate actions of octopamine and dopamine signaling as a key neural mechanism for associative learning.

A single-cell atlas of adult Drosophila ovary identifies transcriptional programs and somatic cell lineage regulating oogenesis

Oogenesis is a complex developmental process that involves spatiotemporally regulated coordination between the germline and supporting, somatic cell populations. This process has been modeled extensively using the Drosophila ovary. Although different ovarian cell types have been identified through traditional means, the large-scale expression profiles underlying each cell type remain unknown. Using single-cell RNA sequencing technology, we have built a transcriptomic data set for the adult Drosophila ovary and connected tissues. Using this data set, we identified the transcriptional trajectory of the entire follicle-cell population over the course of their development from stem cells to the oogenesis-to-ovulation transition. We further identify expression patterns during essential developmental events that take place in somatic and germline cell types such as differentiation, cell-cycle switching, migration, symmetry breaking, nurse-cell engulfment, egg-shell formation, and corpus luteum signaling. Extensive experimental validation of unique expression patterns in both ovarian and nearby, nonovarian cells also led to the identification of many new cell type-and stage-specific markers. The inclusion of several nearby tissue types in this data set also led to our identification of functional convergence in expression between distantly related cell types such as the immune-related genes that were similarly expressed in immune cells (hemocytes) and ovarian somatic cells (stretched cells) during their brief phagocytic role in nurse-cell engulfment. Taken together, these findings provide new insight into the temporal regulation of genes in a cell-type specific manner during oogenesis and begin to reveal the relatedness in expression between cell and tissues types.

Biogenic amine biosynthetic and transduction genes in the endoparasitoid wasp Pteromalus puparum (Hymenoptera: Pteromalidae)

Biogenic amines (BAs), such as octopamine, tyramine, dopamine, serotonin, and acetylcholine regulate various behaviors and physiological functions in insects. Here, we identified seven genes encoding BA biosynthetic enzymes and 16 genes encoding BA G protein-coupled receptors in the genome of the endoparasitoid wasp, Pteromalus puparum. We compared the genes with their orthologs in its host Pieris rapae and the related ectoparasitic wasp Nasonia vitripennis. All the genes show high (>90%) identity to orthologs in N. vitripennis. P. puparum and N. vitripennis have the smallest number of BA receptor genes among the insect species we investigated. We then analyzed the expression profiles of the genes, finding those acting in BA biosynthesis were highly expressed in adults and larvae and those encoding BA receptors are highly expressed in adults than immatures. Octα1R and 5-HT₇ genes were highly expressed in salivary glands, and a high messenger RNA level of 5-HT_1A was found in venom apparatuses. We infer that BA signaling is a fundamental component of the organismal organization, homeostasis and operation in parasitoids, some of the smallest insects.

Genomic insights into mite phylogeny, fitness, development, and reproduction

BACKGROUND

Predatory mites (Acari: Phytoseiidae) are the most important beneficial arthropods used in augmentative biological pest control of protected crops around the world. However, the genomes of mites are far less well understood than those of insects and the evolutionary relationships among mite and other chelicerate orders are contested, with the enigmatic origin of mites at one of the centres in discussion of the evolution of Arachnida.

RESULTS

We here report the 173 Mb nuclear genome (from 51.75 Gb pairs of Illumina reads) of the predatory mite, Neoseiulus cucumeris, a biocontrol agent against pests such as mites and thrips worldwide. We identified nearly 20.6 Mb (~ 11.93% of this genome) of repetitive sequences and annotated 18,735 protein-coding genes (a typical gene 2888 bp in size); the total length of protein-coding genes was about 50.55 Mb (29.2% of this assembly). About 37% (6981) of the genes are unique to N. cucumeris based on comparison with other arachnid genomes. Our phylogenomic analysis supported the monophyly of Acari, therefore rejecting the biphyletic origin of mites advocated by other studies based on limited gene fragments or few taxa in recent years. Our transcriptomic analyses of different life stages of N. cucumeris provide new insights into genes involved in its development. Putative genes involved in vitellogenesis, regulation of oviposition, sex determination, development of legs, signal perception, detoxification and stress-resistance, and innate immune systems are identified.

CONCLUSIONS

Our genomics and developmental transcriptomics analyses of N. cucumeris provide invaluable resources for further research on the development, reproduction, and fitness of this economically important mite in particular and Arachnida in general.

Molecular features and expression profiles of octopamine receptors in the brown planthopper, Nilaparvata lugens

BACKGROUND

Octopamine, the invertebrate counterpart of adrenaline and noradrenaline, regulates and modulates many physiological and behavioral processes in insects. It mediates its effects by binding to specific octopamine receptors, which belong to the superfamily of G-protein coupled receptors (GPCRs). The expression profiles of octopamine receptor genes have been well documented in different developmental stages and multiple tissue types in several different insect orders. However, little work has addressed this issue in Hemiptera.

RESULTS

In this study, we cloned four octopamine receptor genes from brown planthopper. The deduced amino acid sequences share high identity with other insect homologues and have the characteristic GPCRs domain architecture: seven transmembrane domains. These genes were expressed in all developmental stages and examined tissues. The expression of NlOA2B3 and NlOA3 was relatively higher in egg and first instar nymph stage than in other stages and other receptor genes. All of these receptor genes were more highly expressed in brain than other tissues.

CONCLUSION

The identification of octopamine receptor genes in this study will provide a foundation for investigating the diverse roles played by NlOARs and for exploring specific target sites for chemicals that control agricultural pests. © 2019 Society of Chemical Industry.

Trace Amines and Their Receptors

Trace amines are endogenous compounds classically regarded as comprising β-phenylethyalmine, p-tyramine, tryptamine, p-octopamine, and some of their metabolites. They are also abundant in common foodstuffs and can be produced and degraded by the constitutive microbiota. The ability to use trace amines has arisen at least twice during evolution, with distinct receptor families present in invertebrates and vertebrates. The term "trace amine" was coined to reflect the low tissue levels in mammals; however, invertebrates have relatively high levels where they function like mammalian adrenergic systems, involved in "fight-or-flight" responses. Vertebrates express a family of receptors termed trace amine-associated receptors (TAARs). Humans possess six functional isoforms (TAAR1, TAAR2, TAAR5, TAAR6, TAAR8, and TAAR9), whereas some fish species express over 100. With the exception of TAAR1, TAARs are expressed in olfactory epithelium neurons, where they detect diverse ethological signals including predators, spoiled food, migratory cues, and pheromones. Outside the olfactory system, TAAR1 is the most thoroughly studied and has both central and peripheral roles. In the brain, TAAR1 acts as a rheostat of dopaminergic, glutamatergic, and serotonergic neurotransmission and has been identified as a novel therapeutic target for schizophrenia, depression, and addiction. In the periphery, TAAR1 regulates nutrient-induced hormone secretion, suggesting its potential as a novel therapeutic target for diabetes and obesity. TAAR1 may also regulate immune responses by regulating leukocyte differentiation and activation. This article provides a comprehensive review of the current state of knowledge of the evolution, physiologic functions, pharmacology, molecular mechanisms, and therapeutic potential of trace amines and their receptors in vertebrates and invertebrates.

A comprehensive anatomical map of the peripheral octopaminergic/tyraminergic system of Drosophila melanogaster

The modulation of an animal’s behavior through external sensory stimuli, previous experience and its internal state is crucial to survive in a constantly changing environment. In most insects, octopamine (OA) and its precursor tyramine (TA) modulate a variety of physiological processes and behaviors by shifting the organism from a relaxed or dormant condition to a responsive, excited and alerted state. Even though OA/TA neurons of the central brain are described on single cell level in Drosophila melanogaster, the periphery was largely omitted from anatomical studies. Given that OA/TA is involved in behaviors like feeding, flying and locomotion, which highly depend on a variety of peripheral organs, it is necessary to study the peripheral connections of these neurons to get a complete picture of the OA/TA circuitry. We here describe the anatomy of this aminergic system in relation to peripheral tissues of the entire fly. OA/TA neurons arborize onto skeletal muscles all over the body and innervate reproductive organs, the heart, the corpora allata, and sensory organs in the antennae, legs, wings and halteres underlining their relevance in modulating complex behaviors.

Pharmacological characterization of a β-adrenergic-like octopamine receptor in Plutella xylostella

The β-adrenergic-like octopamine receptor (OA2B2) belongs to the class of G-protein coupled receptors. It regulates important physiological functions in insects, thus is potentially a good target for insecticides. In this study, the putative open reading frame sequence of the Pxoa2b2 gene in Plutella xylostella was cloned. Orthologous sequence alignment, phylogenetic tree analysis, and protein sequence analysis all showed that the cloned receptor belongs to the OA2B2 protein family. PxOA2B2 was transiently expressed in HEK-293 cells. It was found that PxOA2B2 could be activated by both octopamine and tyramine, resulting in increased intracellular cyclic AMP (cAMP) levels, whereas dopamine and serotonin were not effective in eliciting cAMP production. Further studies with series of PxOA2B2 agonists and antagonists showed that all four tested agonists (e.g., naphazoline, clonidine, 2-phenylethylamine, and amitraz) could activate the PxOA2B2 receptor, and two of tested antagonists (e.g., phentolamine and mianserin) had significant antagonistic effects. However, antagonist of yohimbine had no effects. Quantitative real-time polymerase chain reaction analysis showed that Pxoa2b2 gene was expressed in all developmental stages of P. xylostella and that the highest expression occurred in male adults. Further analysis with fourth-instar P. xylostella larvae showed that the Pxoa2b2 gene was mainly expressed in Malpighian tubule, epidermal, and head tissues. This study provides both a pharmacological characterization and the gene expression patterns of the OA2B2 in P. xylostella, facilitating further research for insecticides using PxOA2B2 as a target.