Distinct octopamine cell population residing in the CNS abdominal ganglion controls ovulation in Drosophila melanogaster

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.

Neurobiology of egg-laying behavior in Drosophila: neural control of the female reproductive system

Egg-laying is one of the key aspects of female reproductive behavior in insects. Egg-laying has been studied since the dawn of Drosophila melanogaster as a model organism. The female's internal state, hormones, and external factors, such as nutrition, light, and social environment, affect egg-laying output. However, only recently, neurobiological features of egg-laying behavior have been studied in detail. fruitless and doublesex, two key players in the sex determination pathway, have become focal points in identifying neurons of reproductive significance in both central and peripheral nervous systems. The reproductive tract and external terminalia house sensory neurons that carry the sensory information of egg maturation, mating and egg-laying. These sensory signals include the presence of male accessory gland products and mechanical stimuli. The abdominal neuromere houses neurons that receive information from the reproductive tract, including sex peptide abdominal ganglion neurons (SAGs), and send their information to the brain. In the brain, neuronal groups like aDNs and pC1 clusters modulate egg-laying decision-making, and other neurons like oviINs and oviDNs are necessary for egg-laying itself. Lastly, motor neurons involved in egg-laying, which are mostly octopaminergic, reside in the abdominal neuromere and orchestrate the muscle movements required for laying the egg. Egg-laying neuronal control is important in various evolutionary processes like cryptic female choice, and using different Drosophila species can provide intriguing avenues for the future of the field.

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.

Octopamine is required for successful reproduction in the classical insect model, Rhodnius prolixus

In insects, biogenic amines function as neurotransmitters, neuromodulators, and neurohormones, influencing various behaviors, including those related to reproduction such as response to sex pheromones, oogenesis, oviposition, courtship, and mating. Octopamine (OA), an analog of the vertebrate norepinephrine, is synthesized from the biogenic amine tyramine by the enzyme tyramine β-hydroxylase (TβH). Here, we investigate the mechanisms and target genes underlying the role of OA in successful reproduction in females of Rhodnius prolixus, a vector of Chagas disease, by downregulating TβH mRNA expression (thereby reducing OA content) using RNA interference (RNAi), and in vivo and ex vivo application of OA. Injection of females with dsTβH impairs successful reproduction at least in part, by decreasing the transcript expression of enzymes involved in juvenile hormone biosynthesis, the primary hormone for oogenesis in R. prolixus, thereby interfering with oogenesis, ovulation and oviposition. This study offers valuable insights into the involvement of OA for successful reproduction in R. prolixus females. Understanding the reproductive biology of R. prolixus is crucial in a medical context for controlling the spread of the disease.

Role of nuclear protein Akirin in the modulation of female reproduction in Nilaparvata lugens (Hemiptera: Delphacidae)

Introduction: Akirin as a highly conserved transcription factor, exerts a profound influence on the growth, development, immune response, and reproductive processes in animals. The brown planthopper (BPH), Nilaparvata lugens, a major pest in rice production in Asia, possesses high reproductive capacity, a critical factor contributing to reduced rice yields. The aims of this study were to demonstrate the regulatory role of Akirin in the reproduction of BPH. Methods: In this study, quantitative PCR (qPCR) was used to detect the mRNA expression of genes. RNA interference (RNAi) was used to downregulate the expression of Akirin gene, and RNA sequencing (RNA-seq) was used to screen for differentially expressed genes caused by Akirin downregulation. Hormone contents were measured with the enzyme linked immunosorbent assay (ELISA), and protein content was evaluated with the bicinchoninic acid (BCA) method. Results: Using BPH genome data, we screened for an Akirin gene (NlAkirin). An analysis of tissue-specific expressions showed that NlAkirin was expressed in all tissues tested in female BPH, but its expression level was highest in the ovary. After inhibiting the mRNA expression of NlAkirin in BPH females, the number of eggs laid, hatching rate, and number of ovarioles decreased. Transcriptome sequencing was performed, following a NlAkirin double-stranded RNA treatment. Compared with the genes of the control, which was injected with GFP double-stranded RNA, there were 438 upregulated genes and 1012 downregulated genes; the expression of vitellogenin (Vg) and vitellogenin receptor (VgR) genes as well as the mRNA expression of genes related to the target of rapamycin (TOR), juvenile hormone (JH), and insulin pathways involved in Vg synthesis was significantly downregulated. As a result of NlAkirin knockdown, the titers of JH III and Ecdysone (Ecd) were downregulated in unmated females but returned to normal levels in mated females. The ovarian protein contents in both unmated and mated females were downregulated. Discussion and conclusion: Our results suggest that NlAkirin affects female BPH reproduction by regulating the mRNA expression of genes related to the Vg, VgR, TOR, JH, and insulin signaling pathways, in addition to the titers of JH III and Ecd. The findings of this research provide novel insights into the regulatory role of Akirin in insect reproductive capacity.

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.

Integrated stress response signaling acts as a metabolic sensor in fat tissues to regulate oocyte maturation and ovulation

Reproduction is an energy-intensive process requiring systemic coordination. However, the inter-organ signaling mechanisms that relay nutrient status to modulate reproductive output are poorly understood. Here, we use Drosophila melanogaster as a model to establish the integrated stress response (ISR) transcription factor, Atf4, as a fat tissue metabolic sensor that instructs oogenesis. We demonstrate that Atf4 regulates lipase activity to mediate yolk lipoprotein synthesis in the fat body. Depletion of Atf4 in the fat body also blunts oogenesis recovery after amino acid deprivation and re-feeding, suggestive of a nutrient-sensing role for Atf4. We also discovered that Atf4 promotes secretion of a fat-body-derived neuropeptide, CNMamide, which modulates neural circuits that promote egg-laying behavior (ovulation). Thus, we posit that ISR signaling in fat tissue acts as a "metabolic sensor" that instructs female reproduction-directly by impacting yolk lipoprotein production and follicle maturation and systemically by regulating ovulation.

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.

olf413 an octopamine biogenesis pathway gene is required for axon growth and pathfinding during embryonic nervous system development in Drosophila melanogaster

OBJECTIVE

Neurotransmitters have been extensively studied as neural communication molecules. Genetic associations discovered, and indirect intervention studies in Humans and mammals have led to a general proposition that neurotransmitters have a role in structuring of neuronal network during development. olf413 is a Drosophila gene annotated as coding for dopamine beta-monooxygenase enzyme with a predicted function in octopaminergic pathway. The biological function of this gene is very little worked out. In this study we investigate the requirement of olf413 gene function for octopamine biogenesis and developmental patterning of embryonic nervous system.

RESULT

In our study we have used the newly characterized neuronal specific allele olf413SG1.1, and the gene disruption strain olf413MI02014 to dissect out the function of olf413. olf413 has an enhancer activity as depicted by reporter GFP expression, in the embryonic ventral nerve cord, peripheral nervous system and the somatic muscle bundles. Homozygous loss of function mutants show reduced levels of octopamine, and this finding supports the proposed function of the gene in octopamine biogenesis. Further, loss of function of olf413 causes embryonic lethality. FasII staining of these embryos reveal a range of phenotypes in the central and peripheral motor nerves, featuring axonal growth, pathfinding, branching and misrouting defects. Our findings are important as they implicate a key functional requirement of this gene in precise axonal patterning events, a novel developmental role imparted for an octopamine biosynthesis pathway gene in structuring of embryonic nervous system.

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.

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.

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.

Knockdown of the salivary protein gene NlG14 caused displacement of the lateral oviduct secreted components and inhibited ovulation in Nilaparvata lugens

Saliva plays important roles in insect feeding, but its roles in insect reproduction were rarely reported. Here we reported that the knockdown of a salivary gland-specific gene NlG14 disrupted the reproduction through inhibiting the ovulation of the brown planthopper (BPH), Nilaparvata lugens (Stål), one of the most devastating rice pests in Asia. NlG14 knockdown caused the displacement of the lateral oviduct secreted components (LOSC), leading to the ovulation disorder and the accumulation of mature eggs in the ovary. The RNAi-treated females laid much less eggs than their control counterparts, though they had the similar oviposition behavior on rice stems as controls. NlG14 protein was not secreted into the hemolymph, indicating an indirect effect of NlG14 knockdown on BPH reproduction. NlG14 knockdown caused the malformation of A-follicle of the principal gland and affected the underlying endocrine mechanism of salivary glands. NlG14 reduction might promote the secretion of insulin-like peptides NlILP1 and NlILP3 from the brain, which up-regulated the expression of Nllaminin gene and then caused the abnormal contraction of lateral oviduct muscle. Another explanation was NlG14 reduction disrupted the ecdysone biosynthesis and action through the insulin-PI3K-Akt signaling in ovary. Altogether, this study indicated that the salivary gland specific protein NlG14 indirectly mediated BPH ovulation process, which established a connexon in function between insect salivary gland and ovary.

Octopamine-MAPK-SKN-1 signaling suppresses mating-induced oxidative stress in Caenorhabditis elegans gonads to protect fertility

Sexual conflict over mating is costly to female physiology. Caenorhabditis elegans hermaphrodites generally produce self-progeny, but they can produce cross-progeny upon successfully mating with a male. We have uncovered that C. elegans hermaphrodites experience sexual conflict over mating, resulting in severe costs in terms of their fertility and longevity. We show that reactive oxygen species (ROS) accumulate on the apical surfaces of spermathecal bag cells after successful mating and induce cell damage, leading to ovulation defects and fertility suppression. To counteract these negative impacts, C. elegans hermaphrodites deploy the octopamine (OA) regulatory pathway to enhance glutathione (GSH) biosynthesis and protect spermathecae from mating-induced ROS. We show that the SER-3 receptor and mitogen-activated protein kinase (MAPK) KGB-1 cascade transduce the OA signal to transcription factor SKN-1/Nrf2 in the spermatheca to upregulate GSH biosynthesis.

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.

Integrated Stress Response signaling acts as a metabolic sensor in fat tissues to regulate oocyte maturation and ovulation

Reproduction is an energy-intensive process requiring systemic coordination. However, the inter-organ signaling mechanisms that relay nutrient status to modulate reproductive output are poorly understood. Here, we use Drosophila melanogaster as a model to establish the Integrated Stress response (ISR) transcription factor, Atf4, as a fat tissue metabolic sensor which instructs oogenesis. We demonstrate that Atf4 regulates the lipase Brummer to mediate yolk lipoprotein synthesis in the fat body. Depletion of Atf4 in the fat body also blunts oogenesis recovery after amino acid deprivation and re-feeding, suggestive of a nutrient sensing role for Atf4. We also discovered that Atf4 promotes secretion of a fat body-derived neuropeptide, CNMamide, which modulates neural circuits that promote egg-laying behavior (ovulation). Thus, we posit that ISR signaling in fat tissue acts as a "metabolic sensor" that instructs female reproduction: directly, by impacting yolk lipoprotein production and follicle maturation, and systemically, by regulating ovulation.

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.

Environmentally responsive reproduction: neuroendocrine signalling and the evolution of eusociality

Eusociality is a rare but successful life-history strategy that is defined by the reproductive division of labour. In eusocial species, most females forgo their own reproduction to support that of a dominant female or queen. In many eusocial insects, worker reproduction is inhibited via dominance hierarchies or by pheromones produced by the queen and her brood. Here, we consider whether these cues may act as generic 'environmental signals', similar to temperature or nutrition stress, which induce a state of reproductive dormancy in some solitary insects. We review the recent findings regarding the mechanisms of reproductive dormancy in insects and highlight key gaps in our understanding of how environmental cues inhibit reproduction.

The modulatory effects of biogenic amines on male mating performance in Bactrocera dorsalis

In insects, the emergence of mating behavior requires the interplay among sex-determination hierarchy mechanisms that regulate sex-specific differentiation, perception and integration of different sensory cues, and precisely patterned behavioral outputs. Biogenic amines, including octopamine (OA), dopamine (DA), tyramine (TA), serotonin and histamine, have been identified and proposed as putative neurotransmitters, neurohormones and/or neuromodulators in the central nervous system of insects to influence multiple physiologies and behaviors. The current study provides the physiological roles and pharmacology of these biogenic amines in the mating performance of Bactrocera dorsalis. Silencing gene expressions coding for biosynthetic enzymes of DA and serotonin in male flies could decrease mating rates, while OA, TA and histamine had no such effects on mating. Furthermore, injection of DA or the DA receptor antagonist chlorpromazine could affect mating rate, as well as injection of serotonin. Pharmacological treatments with other biogenic amines or their receptor antagonists in male flies have no roles in regulating mating performance. We conclude that DA and its receptors are involved in regulating male mating behaviors in B. dorsalis, while changes in serotonin levels in male flies could also affect mating rates. In the current study, the modulatory effects of these biogenic amines on mating performance were investigated, and these results will be helpful in providing a new strategy for controlling B. dorsalis.

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.

Octopamine receptor genes are involved in the starvation response of Rhopalosiphum padi (Hemiptera: Aphididae)

Insect octopamine (OA) receptors are G-protein coupled receptors (GPCRs) that play essential roles in physiological and behavioural processes. However, there is little information about the function of OA receptors in the aphids' response to stress. From the genome sequence of Rhopalosiphum padi genome sequence, a cosmopolitan cereal pest, we identified six OA receptor genes RpOAMB, RpOctR, RpOctβ1R, RpOctβ2R, RpOctβ3R, RpOctR-like with two, one, one, four, four, seven exons, respectively. All the OA receptors contain seven transmembrane domains, which were the signature of GPCRs. Our results showed that (1) the contents of OA increased significantly after food starvation, (2) the transcription levels of RpOAMB, RpOctR, RpOctβ2R and RpOctβ3R increased after starvation and were restored after re-feeding, and (3) the expression levels of these four genes decreased significantly 48 h post-injection of dsRNA that targeted the respective genes. Knockdown of RpOctR, RpOctβ2R or RpOctβ3R genes significantly increased aphid mortality under 24 h starvation conditions. Mortality of R. padi injected with dsRpOctR or dsRpOctβ2R was significantly higher than control under 48 h starvation treatments. This is the first report on the role of OA receptors in the starvation response of aphids. The current study provides knowledge for a better understanding the physiological roles of insect OA receptors.

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.

Molecular characterization and functional analysis of Bxy-octr-1 in Bursaphelenchus xylophilus

Bursaphelenchus xylophilus is an invasive plant-parasitic nematode causing the notorious pine wilt disease (PWD) worldwide, which results in huge economic losses. G protein-coupled receptors (GPCRs) play an essential role in mating and reproduction behavior of animals. As a unique biogenic amine in invertebrates, octopamine (OA) can regulate a variety of physiological and behavioral responses by binding specific GPCRs. These specific GPCRs are also called octopamine receptors (OARs), and octr-1 is one of them. However, Bxy-octr-1 is unknown in B. xylophilus. Therefore, we investigated the expression pattern and biological function of Bxy-octr-1. Bioinformatics analysis indicated that Bxy-octr-1 was evolutionarily conserved. The real-time quantitative PCR data revealed that Bxy-octr-1 expression was required throughout the entire life of B. xylophilus. mRNA in situ hybridization showed that Bxy-octr-1 was mainly located in the cephalopharynx, body wall muscle, intestine, and gonadal organs of B. xylophilus. RNA interference (RNAi) showed that embryo hatching rates and locomotion speeds were both dramatically decreased. Obvious abnormal phenotypes were observed in the second-stage of juveniles after RNAi treated. Furthermore, its ontogenesis was stunting. Lack of Bxy-octr-1 reduced fecundity of females, of which 31.25% of them could not successfully ovulate. In addition, the error positioning ratio of the nematode was significantly increased. Our study suggests that Bxy-octr-1 is indispensable for locomotion, early ontogenesis and mating behavior in B. xylophilus.

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.

Regulation of Mating-Induced Increase in Female Germline Stem Cells in the Fruit Fly Drosophila melanogaster

In many insect species, mating stimuli can lead to changes in various behavioral and physiological responses, including feeding, mating refusal, egg-laying behavior, energy demand, and organ remodeling, which are collectively known as the post-mating response. Recently, an increase in germline stem cells (GSCs) has been identified as a new post-mating response in both males and females of the fruit fly, Drosophila melanogaster. We have extensively studied mating-induced increase in female GSCs of D. melanogaster at the molecular, cellular, and systemic levels. After mating, the male seminal fluid peptide [e.g. sex peptide (SP)] is transferred to the female uterus. This is followed by binding to the sex peptide receptor (SPR), which evokes post-mating responses, including increase in number of female GSCs. Downstream of SP-SPR signaling, the following three hormones and neurotransmitters have been found to act on female GSC niche cells to regulate mating-induced increase in female GSCs: (1) neuropeptide F, a peptide hormone produced in enteroendocrine cells; (2) octopamine, a monoaminergic neurotransmitter synthesized in ovary-projecting neurons; and (3) ecdysone, a steroid hormone produced in ovarian follicular cells. These humoral factors are secreted from each organ and are received by ovarian somatic cells and regulate the strength of niche signaling in female GSCs. This review provides an overview of the latest findings on the inter-organ relationship to regulate mating-induced female GSC increase in D. melanogaster as a model. We also discuss the remaining issues that should be addressed in the future.

Maintenance of quiescent oocytes by noradrenergic signals

All females adopt an evolutionary conserved reproduction strategy; under unfavorable conditions such as scarcity of food or mates, oocytes remain quiescent. However, the signals to maintain oocyte quiescence are largely unknown. Here, we report that in four different species - Caenorhabditis elegans, Caenorhabditis remanei, Drosophila melanogaster, and Danio rerio - octopamine and norepinephrine play an essential role in maintaining oocyte quiescence. In the absence of mates, the oocytes of Caenorhabditis mutants lacking octopamine signaling fail to remain quiescent, but continue to divide and become polyploid. Upon starvation, the egg chambers of D. melanogaster mutants lacking octopamine signaling fail to remain at the previtellogenic stage, but grow to full-grown egg chambers. Upon starvation, D. rerio lacking norepinephrine fails to maintain a quiescent primordial follicle and activates an excessive number of primordial follicles. Our study reveals an evolutionarily conserved function of the noradrenergic signal in maintaining quiescent oocytes.

Juvenile hormone signaling promotes ovulation and maintains egg shape by inducing expression of extracellular matrix genes

It is well documented that the juvenile hormone (JH) can function as a gonadotropic hormone that stimulates vitellogenesis by activating the production and uptake of vitellogenin in insects. Here, we describe a phenotype associated with mutations in the Drosophila JH receptor genes, Met and Gce: the accumulation of mature eggs with reduced egg length in the ovary. JH signaling is mainly activated in ovarian muscle cells and induces laminin gene expression in these cells. Meanwhile, JH signaling induces collagen IV gene expression in the adult fat body, from which collagen IV is secreted and deposited onto the ovarian muscles. Laminin locally and collagen IV remotely contribute to the assembly of ovarian muscle extracellular matrix (ECM); moreover, the ECM components are indispensable for ovarian muscle contraction. Furthermore, ovarian muscle contraction externally generates a mechanical force to promote ovulation and maintain egg shape. This work reveals an important mechanism for JH-regulated insect reproduction.

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.

The neuropeptide allatostatin C from clock-associated DN1p neurons generates the circadian rhythm for oogenesis

Metazoan species optimize the timing of reproduction to maximize fitness. To understand how biological clocks direct reproduction, we investigated the neural substrates that produce oogenesis rhythms in the genetically amenable model organism Drosophila melanogaster. The neuropeptide allatostatin C (AstC) is an insect counterpart of the vertebrate neuropeptide somatostatin, which suppresses gonadotropin production. A subset of the brain circadian pacemaker neurons produces AstC. We have uncovered that these clock-associated AstC neurons generate the circadian oogenesis rhythm via brain insulin-producing cells and the insect gonadotropin juvenile hormone. Identification of a conserved neuropeptide pathway that links female reproduction and the biological clock offers insight into the molecular mechanisms that direct reproductive timing.

The link between the biological clock and reproduction is evident in most metazoans. The fruit fly Drosophila melanogaster, a key model organism in the field of chronobiology because of its well-defined networks of molecular clock genes and pacemaker neurons in the brain, shows a pronounced diurnal rhythmicity in oogenesis. Still, it is unclear how the circadian clock generates this reproductive rhythm. A subset of the group of neurons designated “posterior dorsal neuron 1” (DN1p), which are among the ∼150 pacemaker neurons in the fly brain, produces the neuropeptide allatostatin C (AstC-DN1p). Here, we report that six pairs of AstC-DN1p send inhibitory inputs to the brain insulin-producing cells, which express two AstC receptors, star1 and AICR2. Consistent with the roles of insulin/insulin-like signaling in oogenesis, activation of AstC-DN1p suppresses oogenesis through the insulin-producing cells. We show evidence that AstC-DN1p activity plays a role in generating an oogenesis rhythm by regulating juvenile hormone and vitellogenesis indirectly via insulin/insulin-like signaling. AstC is orthologous to the vertebrate neuropeptide somatostatin (SST). Like AstC, SST inhibits gonadotrophin secretion indirectly through gonadotropin-releasing hormone neurons in the hypothalamus. The functional and structural conservation linking the AstC and SST systems suggest an ancient origin for the neural substrates that generate reproductive rhythms.

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.

Genetic reduction of tyramine β hydroxylase suppresses Tau toxicity in a Drosophila model of tauopathy

Tauopathies are a class of neurodegenerative diseases characterized by the abnormal phosphorylation and accumulation of the microtubule-associated protein, Tau. These diseases are associated with degeneration and dysfunction of the noradrenergic system, a critical regulator of memory, locomotion, and the fight or flight response. Though Tau pathology accumulates early in noradrenergic neurons, the relationship between noradrenaline signaling and tauopathy pathogenesis remains unclear. The fruit fly, Drosophila melanogaster, is a valuable model organism commonly used to investigate factors that promote Tau-mediated degeneration. Moreover, Drosophila contain the biogenic amine, octopamine, which is the functional homolog to noradrenaline. Using a Drosophila model of tauopathy, we conducted a candidate modifier screen targeting tyramine β hydroxylase (tβh), the enzyme that controls the production of octopamine in the fly, to determine if levels of this enzyme modulate Tau-induced degeneration in the fly eye. We found that genetic reduction of tβh suppresses Tau toxicity, independent of Tau phosphorylation. These findings show that reduction of tβh, a critical enzyme in the octopaminergic pathway, suppresses Tau pathogenicity and establishes an interaction that can be further utilized to determine the relationship between noradrenergic-like signaling and Tau toxicity in Drosophila.

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.

Circuit and Behavioral Mechanisms of Sexual Rejection by Drosophila Females

The mating decisions of Drosophila melanogaster females are primarily revealed through either of two discrete actions: opening of the vaginal plates to allow copulation, or extrusion of the ovipositor to reject the male. Both actions are triggered by the male courtship song, and both are dependent upon the female's mating status. Virgin females are more likely to open their vaginal plates in response to song; mated females are more likely to extrude their ovipositor. Here, we examine the neural cause and behavioral consequence of ovipositor extrusion. We show that the DNp13 descending neurons act as command-type neurons for ovipositor extrusion, and that ovipositor extrusion is an effective deterrent only when performed by females that have previously mated. The DNp13 neurons respond to male song via direct synaptic input from the pC2l auditory neurons. Mating status does not modulate the song responses of DNp13 neurons, but rather how effectively they can engage the motor circuits for ovipositor extrusion. We present evidence that mating status information is mediated by ppk⁺ sensory neurons in the uterus, which are activated upon ovulation. Vaginal plate opening and ovipositor extrusion are thus controlled by anatomically and functionally distinct circuits, highlighting the diversity of neural decision-making circuits even in the context of closely related behaviors with shared exteroceptive and interoceptive inputs.

Drosophila Insulin-Like Peptide 8 (DILP8) in Ovarian Follicle Cells Regulates Ovulation and Metabolism

In Drosophila melanogaster eight insulin-like peptides (DILP1-8) are encoded on separate genes. These DILPs are characterized by unique spatial and temporal expression patterns during the lifecycle. Whereas, functions of several of the DILPs have been extensively investigated at different developmental stages, the role of DILP8 signaling is primarily known from larvae and pupae where it couples organ growth and developmental transitions. In adult female flies, a study showed that a specific set of neurons that express the DILP8 receptor, Lgr3, is involved in regulation of reproductive behavior. Here, we further investigated the expression of dilp8/DILP8 and Lgr3 in adult female flies and the functional role of DILP8 signaling. The only site where we found both dilp8 expression and DILP8 immunolabeling was in follicle cells around mature eggs. Lgr3 expression was detected in numerous neurons in the brain and ventral nerve cord, a small set of peripheral neurons innervating the abdominal heart, as well as in a set of follicle cells close to the oviduct. Ovulation was affected in dilp8 mutants as well as after dilp8-RNAi using dilp8 and follicle cell Gal4 drivers. More eggs were retained in the ovaries and fewer were laid, indicating that DILP8 is important for ovulation. Our data suggest that DILP8 signals locally to Lgr3 expressing follicle cells as well as systemically to Lgr3 expressing efferent neurons in abdominal ganglia that innervate oviduct muscle. Thus, DILP8 may act at two targets to regulate ovulation: follicle cell rupture and oviduct contractions. Furthermore, we could show that manipulations of dilp8 expression affect starvation resistance suggesting effects on metabolism. Possibly this reflects a feedback signaling between ovaries and the CNS that ensures nutrients for ovary development. In summary, it seems that DILP8 signaling in regulation of reproduction is an ancient function, conserved in relaxin signaling in mammals.

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.].

miRNAs and Neural Alternative Polyadenylation Specify the Virgin Behavioral State

How are diverse regulatory strategies integrated to impose appropriately patterned gene expression that underlie in vivo phenotypes? Here, we reveal how coordinated miRNA regulation and neural-specific alternative polyadenylation (APA) of a single locus controls complex behaviors. Our entry was the unexpected observation that deletion of Bithorax complex (BX-C) miRNAs converts virgin female flies into a subjective post-mated behavioral state, normally induced by seminal proteins following copulation. Strikingly, this behavioral switch is directly attributable to misregulation of homothorax (hth). We localize specific CNS abdominal neurons where de-repressed Hth compromises virgin behavior in BX-C miRNA mutants. Moreover, we use genome engineering to demonstrate that precise mutation of hth 3' UTR sites for BX-C miRNAs or deletion of its neural 3' UTR extension containing most of these sites both induce post-mated behaviors in virgins. Thus, facilitation of miRNA-mediated repression by neural APA is required for virgin females to execute behaviors appropriate to their internal state.

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 Drosophila Post-mating Response: Gene Expression and Behavioral Changes Reveal Perdurance and Variation in Cross-Tissue Interactions

Examining cross-tissue interactions is important for understanding physiology and homeostasis. In animals, the female gonad produces signaling molecules that act distally. We examine gene expression in Drosophila melanogaster female head tissues in 1) virgins without a germline compared to virgins with a germline, 2) post-mated females with and without a germline compared to virgins, and 3) post-mated females mated to males with and without a germline compared to virgins. In virgins, the absence of a female germline results in expression changes in genes with known roles in nutrient homeostasis. At one- and three-day(s) post-mating, genes that change expression are enriched with those that function in metabolic pathways, in all conditions. We systematically examine female post-mating impacts on sleep, food preference and re-mating, in the strains and time points used for gene expression analyses and compare to published studies. We show that post-mating, gene expression changes vary by strain, prompting us to examine variation in female re-mating. We perform a genome-wide association study that identifies several DNA polymorphisms, including four in/near Wnt signaling pathway genes. Together, these data reveal how gene expression and behavior in females are influenced by cross-tissue interactions, by examining the impact of mating, fertility, and genotype.

Characterization of Drosophila octopamine receptor neuronal expression using MiMIC-converted Gal4 lines

Octopamine, the invertebrate analog of norepinephrine, is known to modulate a large variety of behaviors in Drosophila including feeding initiation, locomotion, aggression, and courtship, among many others. Significantly less is known about the identity of the neurons that receive octopamine input and how they mediate octopamine-regulated behaviors. Here, we characterize adult neuronal expression of MiMIC-converted Trojan-Gal4 lines for each of the five Drosophila octopamine receptors. Broad neuronal expression was observed for all five octopamine receptors, yet distinct differences among them were also apparent. Use of immunostaining for the octopamine neurotransmitter synthesis enzyme Tdc2, along with a novel genome-edited conditional Tdc2-LexA driver, revealed all five octopamine receptors express in Tdc2/octopamine neurons to varying degrees. This suggests autoreception may be an important circuit mechanism by which octopamine modulates behavior.

Rapid sex-specific adaptation to high temperature in Drosophila

The pervasive occurrence of sexual dimorphism demonstrates different adaptive strategies of males and females. While different reproductive strategies of the two sexes are well-characterized, very little is known about differential functional requirements of males and females in their natural habitats. Here, we study the impact environmental change on the selection response in both sexes. Exposing replicated Drosophila populations to a novel temperature regime, we demonstrate sex-specific changes in gene expression, metabolic and behavioral phenotypes in less than 100 generations. This indicates not only different functional requirements of both sexes in the new environment but also rapid sex-specific adaptation. Supported by computer simulations we propose that altered sex-biased gene regulation from standing genetic variation, rather than new mutations, is the driver of rapid sex-specific adaptation. Our discovery of environmentally driven divergent functional requirements of males and females has important implications-possibly even for gender aware medical treatments.

Theory Demonstrated a "Coupled" Mechanism for O2 Activation and Substrate Hydroxylation by Binuclear Copper Monooxygenases

Multiscale simulations have been performed to address the longstanding issue of "dioxygen activation" by the binuclear copper monooxygenases (PHM and DβM), which have been traditionally classified as "noncoupled" binuclear copper enzymes. Our QM/MM calculations rule out that Cu_M(II)-O₂^• is an active species for H-abstraction from the substrate. In contrast, Cu_M(II)-O₂^• would abstract an H atom from the cosubstrate ascorbate to form a Cu_M(II)-OOH intermediate in PHM and DβM. Consistent with the recently reported structural features of DβM, the umbrella sampling shows that the "open" conformation of the Cu_M(II)-OOH intermediate could readily transform into the "closed" conformation in PHM, in which we located a mixed-valent μ-hydroperoxodicopper(I,II) intermediate, (μ-OOH)Cu(I)Cu(II). The subsequent O-O cleavage and OH moiety migration to Cu_H generate the unexpected species (μ-O^•)(μ-OH)Cu(II)Cu(II), which is revealed to be the reactive intermediate responsible for substrate hydroxylation. We also demonstrate that the flexible Met ligand is favorable for O-O cleavage reactions, while the replacement of Met with the strongly bound His ligand would inhibit the O-O cleavage reactivity. As such, the study not only demonstrates a "coupled" mechanism for O₂ activation by binuclear copper monooxygenases but also deciphers the full catalytic cycle of PHM and DβM in accord with the available experimental data. These findings of O₂ activation and substrate hydroxylation by binuclear copper monooxygenases could expand our understanding of the reactivities of the synthetic monocopper complexes.

Natural resistance to Fasciola hepatica (Trematoda) in Pseudosuccinea columella snails: A review from literature and insights from comparative "omic" analyses

The snail Pseudosuccinea columella is one of the main vectors of the medically-important trematode Fasciola hepatica. In Cuba, the existence of natural P. columella populations that are either susceptible or resistant to F. hepatica infection offers a unique snail-parasite for study of parasite-host compatibility and immune function in gastropods. Here, we review all previous literature on this system and present new "omic" data that provide a molecular baseline of both P. columella phenotypes from naïve snails. Comparison of whole snail transcriptomes (RNAseq) and the proteomes of the albumen gland (2D-electrophoresis, MS) revealed that resistant and susceptible strains differed mainly in an enrichment of particular biological processes/functions and a greater abundance of proteins/transcripts associated with immune defense/stress response in resistant snails. These results indicate a differential allocation of molecular resources to self-maintenance and survival in resistant P. columella that may cause enhanced responsiveness to stressors (i.e. F. hepatica infection or tolerance to variations in environmental pH/total water hardness), possibly as trade-off against reproduction and the ecological cost of resistance previously suggested in resistant populations of P. columella.