Ecdysteroid titers in mated and unmated Drosophila melanogaster females

Mild traumatic brain injury in Drosophila melanogaster alters reactive oxygen and nitrogen species in a sex-dependent manner

Traumatic brain injury (TBI) is an outside force causing a modification in brain function and/or structural brain pathology that upregulates brain inducible nitric oxide synthase (iNOS), instigating increased levels of nitric oxide activity which is implicated in secondary pathology leading to behavioral deficits (Hall et al., 2012; Garry et al., 2015; Kozlov et al., 2017). In mammals, TBI-induced NO production activates an immune response and potentiates metabolic crisis through mitochondrial dysfunction coupled with vascular dysregulation; however, the direct influence on pathology is complicated by the activation of numerous secondary cascades and activation of other reactive oxygen species. Drosophila TBI models have demonstrated key features of mammalian TBI, including temporary incapacitation, disorientation, motor deficits, activation of innate immunity (inflammation), and autophagy responses observed immediately after injury (Katzenberger et al., 2013; Barekat et al., 2016; Simon et al., 2017; Anderson et al., 2018; Buhlman et al., 2021b). We hypothesized that acute behavioral phenotypes would be associated with deficits in climbing behavior and increased oxidative stress. Because flies lack mammalian-like cardiovascular and adaptive immune systems, we were able to make our observations in the absence of vascular disruption and adaptive immune system interference in a system where highly targeted interventions can be rapidly evaluated. To demonstrate the induction of injury, ten-day-old transgenic flies received an injury of increasing angles from a modified high impact trauma (HIT) device where angle-dependent increases occurred for acute neurological behavior assessments and twenty-four-hour mortality, and survival was significantly decreased. Injury caused sex-dependent effects on climbing activity and measures of oxidative stress. Specifically, after a single 60-degree HIT, female flies exhibited significant impairments in climbing activity beyond that observed in male flies. We also found that several measures of oxidative stress, including Drosophila NOS (dNOS) expression, protein nitration, and hydrogen peroxide production were significantly decreased in female flies. Interestingly, protein nitration was also decreased in males, but surpassed sham levels with a more severe injury. We also observed decreased autophagy demand in vulnerable dopaminergic neurons in female, but not male flies. In addition, mitophagy initiation was decreased in females. Collectively, our data suggest that TBI in flies induces acute behavioral phenotypes and climbing deficits that are analogous to mammalian TBI. We also observed that various indices of oxidative stress, including dNOS expression, protein tyrosine nitration, and hydrogen peroxide levels, as well as basal levels of autophagy, are altered in response to injury, an effect that is more pronounced in female flies.

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.

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.

Developmental mechanisms of sex differences: from cells to organisms

Male-female differences in many developmental mechanisms lead to the formation of two morphologically and physiologically distinct sexes. Although this is expected for traits with prominent differences between the sexes, such as the gonads, sex-specific processes also contribute to traits without obvious male-female differences, such as the intestine. Here, we review sex differences in developmental mechanisms that operate at several levels of biological complexity - molecular, cellular, organ and organismal - and discuss how these differences influence organ formation, function and whole-body physiology. Together, the examples we highlight show that one simple way to gain a more accurate and comprehensive understanding of animal development is to include both sexes.

Sexual Dimorphism: Ecdysone Modulates Sex Differences in the Gut

Sex differences in the Drosophila gut were discovered only recently. Recent work significantly extends our understanding of how steroid hormones specify these male-female differences by revealing a key role for ecdysone in regulating intestinal stem cell proliferation.

Nuclear receptors linking physiology and germline stem cells in Drosophila

Maternal nutrition and physiology are intimately associated with reproductive success in diverse organisms. Despite decades of study, the molecular mechanisms linking maternal diet to the production and quality of oocytes remain poorly defined. Nuclear receptors (NRs) link nutritional signals to cellular responses and are essential for oocyte development. The fruit fly, Drosophila melanogaster, is an excellent genetically tractable model to study the relationship between NR signaling and oocyte production. In this review, we explore how NRs in Drosophila regulate the earliest stages of oocyte development. Long-recognized as an essential mediator of developmental transitions, we focus on the intrinsic roles of the Ecdysone Receptor and its ligand, ecdysone, in oogenesis. We also review recent studies suggesting broader roles for NRs as regulators of maternal physiology and their impact specifically on oocyte production. We propose that NRs form the molecular basis of a broad physiological surveillance network linking maternal diet with oocyte production. Given the functional conservation between Drosophila and humans, continued experimental investigation into the molecular mechanisms by which NRs promote oogenesis will likely aid our understanding of human fertility.

Enteric neurons increase maternal food intake during reproduction

Reproduction induces increased food intake across females of many animal species1-4, providing a physiologically relevant paradigm for the exploration of appetite regulation. Here, by examining the diversity of enteric neurons in Drosophila melanogaster, we identify a key role for gut-innervating neurons with sex- and reproductive state-specific activity in sustaining the increased food intake of mothers during reproduction. Steroid and enteroendocrine hormones functionally remodel these neurons, which leads to the release of their neuropeptide onto the muscles of the crop-a stomach-like organ-after mating. Neuropeptide release changes the dynamics of crop enlargement, resulting in increased food intake, and preventing the post-mating remodelling of enteric neurons reduces both reproductive hyperphagia and reproductive fitness. The plasticity of enteric neurons is therefore key to reproductive success. Our findings provide a mechanism to attain the positive energy balance that sustains gestation, dysregulation of which could contribute to infertility or weight gain.

Ecdysone steroid hormone remote controls intestinal stem cell fate decisions via the PPARγ-homolog Eip75B in Drosophila

Developmental studies revealed fundamental principles on how organ size and function is achieved, but less is known about organ adaptation to new physiological demands. In fruit flies, juvenile hormone (JH) induces intestinal stem cell (ISC) driven absorptive epithelial expansion balancing energy uptake with increased energy demands of pregnancy. Here, we show 20-Hydroxy-Ecdysone (20HE)-signaling controlling organ homeostasis with physiological and pathological implications. Upon mating, 20HE titer in ovaries and hemolymph are increased and act on nearby midgut progenitors inducing Ecdysone-induced-protein-75B (Eip75B). Strikingly, the PPARγ-homologue Eip75B drives ISC daughter cells towards absorptive enterocyte lineage ensuring epithelial growth. To our knowledge, this is the first time a systemic hormone is shown to direct local stem cell fate decisions. Given the protective, but mechanistically unclear role of steroid hormones in female colorectal cancer patients, our findings suggest a tumor-suppressive role for steroidal signaling by promoting postmitotic fate when local signaling is deteriorated.

Stress-induced reproductive arrest in Drosophila occurs through ETH deficiency-mediated suppression of oogenesis and ovulation

BACKGROUND

Environmental stressors induce changes in endocrine state, leading to energy re-allocation from reproduction to survival. Female Drosophila melanogaster respond to thermal and nutrient stressors by arresting egg production through elevation of the steroid hormone ecdysone. However, the mechanisms through which this reproductive arrest occurs are not well understood.

RESULTS

Here we report that stress-induced elevation of ecdysone is accompanied by decreased levels of ecdysis triggering hormone (ETH). Depressed levels of circulating ETH lead to attenuated activity of its targets, including juvenile hormone-producing corpus allatum and, as we describe here for the first time, octopaminergic neurons of the oviduct. Elevation of steroid thereby results in arrested oogenesis, reduced octopaminergic input to the reproductive tract, and consequent suppression of ovulation. ETH mitigates heat or nutritional stress-induced attenuation of fecundity, which suggests that its deficiency is critical to reproductive adaptability.

CONCLUSIONS

Our findings indicate that, as a dual regulator of octopamine and juvenile hormone release, ETH provides a link between stress-induced elevation of ecdysone levels and consequent reduction in fecundity.

Identification and expression analyses of vitellogenin in Bactericera cockerelli (Šulc)

The potato psyllid, Bactericera cockerelli (Šulc) (Hemiptera: Triozidae), is a phloem-feeding insect with preference for Solanaceae. This insect species is vector of the pathogenic bacteria 'Candidatus Liberibacter solanacearum' the causative agent of zebra chip, an important disease of commercial potatoes in several countries worldwide. The recent classification of psyllids among the most dangerous vectors has promoted their study, but still many biological processes such as reproduction and vitellogenesis need to be investigated. As a first step towards the elucidation of vitellogenesis in B. cockerelli, one candidate vitellogenin transcript (6622 bases long) was identified and the expression of the transcript and the protein were analyzed in virgin and mated females between 1 and 7days old. In virgin females, Vg expression increased up to 5days old; while mating significantly up-regulated Vg expression in 5- and 7-day-old females. To determine the role of juvenile hormone in B. cockerelli Vg expression, topical applications of juvenile hormone III were performed on virgin females, resulting in an up-regulation of Vg expression and an increase in the number of mature oocytes present in female reproductive organs. Overall, this study represents the first step to understand vitellogenesis of B. cockerelli and it highlights the role of JH III in the hormonal regulation of Vg expression and oocyte development.

Ovarian ecdysteroid biosynthesis and female germline stem cells

The germline stem cells (GSCs) are critical for gametogenesis throughout the adult life. Stem cell identity is maintained by local signals from a specialized microenvironment called the niche. However, it is unclear how systemic signals regulate stem cell activity in response to environmental cues. In our previous article, we reported that mating stimulates GSC proliferation in female Drosophila. The mating-induced GSC proliferation is mediated by ovarian ecdysteroids, whose biosynthesis is positively controlled by Sex peptide signaling. Here, we characterized the post-eclosion and post-mating expression pattern of the genes encoding the ecdysteroidogenic enzymes in the ovary. We further investigated the biosynthetic functions of the ovarian ecdysteroid in GSC maintenance in the mated females. We also briefly discuss the regulation of the ecdysteroidogenic enzyme-encoding genes and the subsequent ecdysteroid biosynthesis in the ovary of the adult Drosophila.

Sperm-less males modulate female behaviour in Ceratitis capitata (Diptera: Tephritidae)

In the Mediterranean fruit fly, Ceratitis capitata (Wiedemann)(Diptera: Tephritidae), mating has a strong impact on female biology, leading to a decrease in sexual receptivity and increased oviposition and fecundity. Previous studies suggest that sperm transfer may play a role in inducing these behavioural changes. Here we report the identification of a medfly innexin gene, Cc-inx5, whose expression is limited to the germ-line of both sexes. Through RNA interference of this gene, we generated males without testes and, consequently, sperm, but apparently retaining all the other reproductive organs intact. These sperm-less males were able to mate and, like their wild-type counterparts, to induce in their partners increased oviposition rates and refractoriness to remating. Interestingly, matings to sperm-less males results in oviposition rates higher than those induced by copulation with control males. In addition, the observed female post-mating behavioural changes were congruent with changes in transcript abundance of genes known to be regulated by mating in this species. Our results suggest that sperm transfer is not necessary to reduce female sexual receptivity and to increase oviposition and fecundity. These data pave the way to a better understanding of the role/s of seminal components in modulating female post-mating responses. In the long term, this knowledge will be the basis for the development of novel approaches for the manipulation of female fertility, and, consequently, innovative tools to be applied to medfly control strategies in the field.

Steroid Hormone Signaling Is Essential for Pheromone Production and Oenocyte Survival

Many of the lipids found on the cuticles of insects function as pheromones and communicate information about age, sex, and reproductive status. In Drosophila, the composition of the information-rich lipid profile is dynamic and changes over the lifetime of an individual. However, the molecular basis of this change is not well understood. To identify genes that control cuticular lipid production in Drosophila, we performed a RNA interference screen and used Direct Analysis in Real Time and gas chromatography mass spectrometry to quantify changes in the chemical profiles. Twelve putative genes were identified whereby transcriptional silencing led to significant differences in cuticular lipid production. Amongst them, we characterized a gene which we name spidey, and which encodes a putative steroid dehydrogenase that has sex- and age-dependent effects on viability, pheromone production, and oenocyte survival. Transcriptional silencing or overexpression of spidey during embryonic development results in pupal lethality and significant changes in levels of the ecdysone metabolite 20-hydroxyecdysonic acid and 20-hydroxyecdysone. In contrast, inhibiting gene expression only during adulthood resulted in a striking loss of oenocyte cells and a concomitant reduction of cuticular hydrocarbons, desiccation resistance, and lifespan. Oenocyte loss and cuticular lipid levels were partially rescued by 20-hydroxyecdysone supplementation. Taken together, these results identify a novel regulator of pheromone synthesis and reveal that ecdysteroid signaling is essential for the maintenance of cuticular lipids and oenocytes throughout adulthood.

Pheromones are used by many animals to control social behaviors such as mate choice and kin recognition. The pheromone profile of insects is dynamic and can change depending on environmental, physiological, and social conditions. While many genes responsible for the biosynthesis of insect pheromones have been identified, much less is known about how pheromone production is systemically regulated over the lifetime of an animal. In this work, we identify 12 genes in Drosophila melanogaster that play a role in pheromone production. We characterized the function of one gene, which we name spidey, and which encodes a steroid dehydrogenase. Silencing spidey expression during the larval stage results in the rapid inactivation of an essential insect steroid, 20-hydroxyecdysone, and developmental arrest. In adults, spidey is needed for maintaining the viability of oenocytes, specialized cells that produce pheromones and also regulate energy homeostasis. Our work reveals a novel role for ecdysteroids in the adult animal and uncovers a regulatory mechanism for oenocyte activity. Potentially, ecdysteroid signaling serves as a mechanism by which environmental or social conditions shape pheromone production. Exploitation of this conserved pathway could be useful for interfering with the mating behavior and lifespan of disease-bearing insects or agricultural pests.

Mating-Induced Increase in Germline Stem Cells via the Neuroendocrine System in Female Drosophila

Mating and gametogenesis are two essential components of animal reproduction. Gametogenesis must be modulated by the need for gametes, yet little is known of how mating, a process that utilizes gametes, may modulate the process of gametogenesis. Here, we report that mating stimulates female germline stem cell (GSC) proliferation in Drosophila melanogaster. Mating-induced increase in GSC number is not simply owing to the indirect effect of emission of stored eggs, but rather is stimulated by a male-derived Sex Peptide (SP) and its receptor SPR, the components of a canonical neuronal pathway that induces a post-mating behavioral switch in females. We show that ecdysteroid, the major insect steroid hormone, regulates mating-induced GSC proliferation independently of insulin signaling. Ovarian ecdysteroid level increases after mating and transmits its signal directly through the ecdysone receptor expressed in the ovarian niche to increase the number of GSCs. Impairment of ovarian ecdysteroid biosynthesis disrupts mating-induced increase in GSCs as well as egg production. Importantly, feeding of ecdysteroid rescues the decrease in GSC number caused by impairment of neuronal SP signaling. Our study illustrates how female GSC activity is coordinately regulated by the neuroendocrine system to sustain reproductive success in response to mating.

Ovarian Ecdysteroidogenesis in Both Immature and Mature Stages of an Acari, Ornithodoros moubata

Ecdysteroidogenesis is essential for arthropod development and reproduction. Although the importance of ecdysteroids has been demonstrated, there is little information on the sites and enzymes for synthesis of ecdysteroids from Chelicerates. Ecdysteroid functions have been well studied in the soft tick Ornithodoros moubata, making this species an excellent candidate for elucidating ecdysteroidogenesis in Chelicerates. Results showed that O. moubata has at least two ecdysteroidogenic enzymes, Spook (OmSpo) and Shade (OmShd). RNAi showed both enzymes were required for ecdysteroidogenesis. Enzymatic assays demonstrated OmShd has the conserved functions of ecdysone 20-hydroxylase. OmSpo showed specific expression in the ovaries of final nymphal and adult stages, indicating O. moubata utilizes the ovary as an ecdysteroidogenic tissue instead of specific tissues as seen in other arthropods. On the other hand, OmShd expression was observed in various tissues including the midgut, indicating functional ecdysteroids can be produced in these tissues. In nymphal stages, expression of both OmSpo and OmShd peaked before molting corresponding with high ecdysteroid titers in the hemolymph. In fed adult females, OmSpo expression peaked at 8–10 days after engorgement, while OmShd expression peaked immediately after engorgement. Mated females showed more frequent surges of OmShd than virgin females. These results indicate that the regulation of synthesis of ecdysteroids differs in nymphs and adult females, and mating modifies adult female ecdysteroidogenesis. This is the first report to focus on synthesis of ecdysteroids in ticks and provides essential knowledge for understanding the evolution of ecdysteroidogenesis in arthropods.

Steroid Signaling Establishes a Female Metabolic State and Regulates SREBP to Control Oocyte Lipid Accumulation

Disruptions in energy homeostasis severely affect reproduction in many organisms and are linked to several reproductive disorders in humans. As a result, understanding the mechanisms that control nutrient accumulation in the oocyte will provide valuable insights into the links between metabolic disease and reproductive dysfunction. We show that the steroid hormone ecdysone functions in Drosophila to control lipid metabolism and support oocyte production. First, local EcR-mediated signaling induces a stage-specific accumulation of lipids in stage-10 oocytes. EcR induces lipid accumulation by promoting the activation of the lipogenic transcription factor SREBP and by controlling the expression of the low-density lipoprotein (LDL) receptor homolog, LpR2. Second, global signaling via the ecdysone receptor, EcR, establishes a female metabolic state and promotes whole-body triglyceride and glycogen storage at high levels. EcR acts in the CNS to mediate these effects, in part by promoting higher levels of feeding in females. Thus, ecdysone functions at two levels to support reproduction: first by inducing lipid accumulation in the late stages of oocyte development and second by providing a signal that coordinates lipid metabolism in the germline with whole-animal lipid homeostasis. Ecdysone regulation allows females to assess the demands of oogenesis and alter their behavior and metabolic state to support the biosynthetic requirements of oocyte production.

Matrix metalloproteinase 2 is required for ovulation and corpus luteum formation in Drosophila

Ovulation is critical for successful reproduction and correlates with ovarian cancer risk, yet genetic studies of ovulation have been limited. It has long been thought that the mechanism controlling ovulation is highly divergent due to speciation and fast evolution. Using genetic tools available in Drosophila, we now report that ovulation in Drosophila strongly resembles mammalian ovulation at both the cellular and molecular levels. Just one of up to 32 mature follicles per ovary pair loses posterior follicle cells (“trimming”) and protrudes into the oviduct, showing that a selection process prefigures ovulation. Follicle cells that remain after egg release form a “corpus luteum (CL)” at the end of the ovariole, develop yellowish pigmentation, and express genes encoding steroid hormone biosynthetic enzymes that are required for full fertility. Finally, matrix metalloproteinase 2 (Mmp2), a type of protease thought to facilitate mammalian ovulation, is expressed in mature follicle and CL cells. Mmp2 activity is genetically required for trimming, ovulation and CL formation. Our studies provide new insights into the regulation of Drosophila ovulation and establish Drosophila as a model for genetically investigating ovulation in diverse organisms, including mammals.

Sexual reproduction is thought to be a highly divergent process due to fast evolution and speciation. For example, sperm from one species can seldom fertilize eggs from another species, indicating that different molecular machinery for fertilization is applied in different species. In contrast to this divergent view, ovulation, the process of liberating mature eggs from the ovary, is a general phenomenon throughout the Metazoa. We provide evidence that basic mechanisms of ovulation are conserved. Like mammalian follicles, Drosophila follicles consist of single oocytes surrounded by a layer of follicle cells. Drosophila follicles degrade their posterior follicle cells to allow the oocyte to rupture into the oviduct during ovulation. The residual postovulatory follicles reside in the ovary, accumulate yellowish pigmentation, and produce the steroid hormone ecdysone, features which resemble the mammalian corpus luteum. We also showed that matrix metalloproteinase, a type of proteinase proposed to degrade the mammalian follicle wall during ovulation, is required in Drosophila for posterior follicle cell degradation and ovulation. These findings are particularly important because this simple genetic model system will speed up the identification of many conserved regulators required for regulating matrix metalloproteinase activity and ovulation in human, processes that influence ovarian cancer formation and cancer metastasis.

Steroid signaling promotes stem cell maintenance in the Drosophila testis

Stem cell regulation by local signals is intensely studied, but less is known about the effects of hormonal signals on stem cells. In Drosophila, the primary steroid twenty-hydroxyecdysone (20E) regulates ovarian germline stem cells (GSCs) but was considered dispensable for testis GSC maintenance. Male GSCs reside in a microenvironment (niche) generated by somatic hub cells and adjacent cyst stem cells (CySCs). Here, we show that depletion of 20E from adult males by overexpressing a dominant negative form of the Ecdysone receptor (EcR) or its heterodimeric partner ultraspiracle (usp) causes GSC and CySC loss that is rescued by 20E feeding, uncovering a requirement for 20E in stem cell maintenance. EcR and USP are expressed, activated and autonomously required in the CySC lineage to promote CySC maintenance, as are downstream genes ftz-f1 and E75. In contrast, GSCs non-autonomously require ecdysone signaling. Global inactivation of EcR increases cell death in the testis that is rescued by expression of EcR-B2 in the CySC lineage, indicating that ecdysone signaling supports stem cell viability primarily through a specific receptor isoform. Finally, EcR genetically interacts with the NURF chromatin-remodeling complex, which we previously showed maintains CySCs. Thus, although 20E levels are lower in males than females, ecdysone signaling acts through distinct cell types and effectors to ensure both ovarian and testis stem cell maintenance.

Is the rapid post-mating inhibition of pheromone response triggered by ecdysteroids or other factors from the sex accessory glands in the male moth Agrotis ipsilon?

In many animals, male copulation is dependent on the detection and processing of female-produced sex pheromones, which is generally followed by a sexual refractory post-ejaculatory interval (PEI). In the male moth, Agrotis ipsilon, this PEI is characterized by a transient post-mating inhibition of behavioral and central nervous responses to sex pheromone, which prevents males from re-mating until they have refilled their reproductive tracts for a potential new ejaculate. However, the timing and possible factors inducing this rapid olfactory switch-off are still unknown. Here, we determined the initial time delay and duration of the PEI. Moreover, we tested the hypothesis that the brain, the testis and/or the sex accessory glands (SAGs) could produce a factor inducing the PEI. Lastly, we investigated the possible involvement of ecdysteroids, hormones essential for development and reproduction in insects, in this olfactory plasticity. Using brain and SAG cross-injections in virgin and newly-mated males, surgical treatments, wind tunnel behavioral experiments and EIA quantifications of ecdysteroids, we show that the PEI starts very shortly after the onset of copulation, and that SAGs contain a factor, which is produced/accumulated after copulation to induce the PEI. Moreover, SAGs were found to be the main source of ecdysteroids, whose concentration decreased after mating, whereas it increased in the haemolymph. 20-Hydroxyecdysone (20E) was identified as the major ecdysteroid in SAGs of A. ipsilon males. Finally, 20E injections did not reduce the behavioral pheromone response of virgin males. Altogether our data indicate that 20E is probably not involved in the PEI.

Role of D1- and D2-like receptors in age-specific regulation of juvenile hormone and 20-hydroxyecdysone levels by dopamine in Drosophila

In Drosophila females, the precursor of 20-hydroxyecdysone (20E), ecdysone, is synthesized in the ovary follicular cells. Juvenile hormone (JH) is synthesized de novo in the specialized endocrine gland, corpus allatum (CA); JH degradation is carried out by the enzymes synthesized in the fat body (FB). Earlier we have shown that in Drosophila females, dopamine up- or down-regulates 20E and JH levels depending on the developmental stage. The present study focuses on the role of D1- and D2-like receptors in the age-specific regulation of 20E and JH metabolism by dopamine. We show that in Drosophila melanogaster females D1- and D2-like receptor genes (DopR and DD2R accordingly) are expressed in CA and FB, but not in follicular cells. The level of DopR expression in CA is much higher in the young than in the mature females, whereas DD2R expression is much higher in the mature than in the young females. The DopR and DD2R expression patterns in FB are opposite to those observed in CA. In addition, we obtained data suggesting that the age-specific changes of DopR and DD2R expression in FB are under the control of 20E.

Ecdysone signaling in adult Drosophila melanogaster

The steroid hormone 20-hydroxyecdysone and its EcR/USP receptor are vital during arthropod development for coordinating molting and metamorphosis. Traditionally, little attention has been given to potential post-developmental functions for this hormone signaling system. However, recent studies in Drosophila melanogaster indicate that the hormone and receptor are present and active in adults and that mutations decreasing hormone or receptor levels affect diverse processes such as reproduction, behavior, stress resistance, and lifespan. We review the current state of knowledge regarding adult hormone production and titers and discuss receptor expression and activity in order to identify potential mechanisms which explain the observed mutant phenotypes. Finally, we describe future research directions focused on identifying isoform-specific functions of EcR, distinguishing effects from EcR/USP gene activation and repression, and determining how ecdysone signaling impacts different tissue types.

Ecdysone receptor expression and activity in adult Drosophila melanogaster

Disrupting components of the ecdysone/EcR/USP signaling pathway in insects leads to morphological defects and developmental arrest. In adult Drosophila melanogaster decreased EcR function affects fertility, lifespan, behavior, learning, and memory; however we lack a clear understanding of how EcR/USP expression and activity impacts these phenotypes. To shed light on this issue, we characterized the wild-type expression patterns and activity of EcR/USP in individual tissues during early adult life. EcR and usp were expressed in numerous adult tissues, but receptor activity varied depending on tissue type and adult age. Receptor activity did not detectably change in response to mating status, environmental stress, ecdysone treatment or gender but is reduced when a constitutively inactive ecdysone receptor is present. Since only a subset of adult tissues expressing EcR and usp contain active receptors, it appears that an important adult function of EcR/USP in some tissues may be repression of genes containing EcRE's.

Towards a semen proteome of the dengue vector mosquito: protein identification and potential functions

Background

No commercially licensed vaccine or treatment is available for dengue fever, a potentially lethal infection that impacts millions of lives annually. New tools that target mosquito control may reduce vector populations and break the cycle of dengue transmission. Male mosquito seminal fluid proteins (Sfps) are one such target since these proteins, in aggregate, modulate the reproduction and feeding patterns of the dengue vector, Aedes aegypti. As an initial step in identifying new targets for dengue vector control, we sought to identify the suite of proteins that comprise the Ae. aegypti ejaculate and determine which are transferred to females during mating.

Methodology and Principal Findings

Using a stable-isotope labeling method coupled with proteomics to distinguish male- and female-derived proteins, we identified Sfps and sperm proteins transferred from males to females. Sfps were distinguished from sperm proteins by comparing the transferred proteins to sperm-enriched samples derived from testes and seminal vesicles. We identified 93 male-derived Sfps and 52 predicted sperm proteins that are transferred to females during mating. The Sfp protein classes we detected suggest roles in protein activation/inactivation, sperm utilization, and ecdysteroidogenesis. We also discovered that several predicted membrane-bound and intracellular proteins are transferred to females in the seminal fluids, supporting the hypothesis that Ae. aegypti Sfps are released from the accessory gland cells through apocrine secretion, as occurs in mammals. Many of the Ae. aegypti predicted sperm proteins were homologous to Drosophila melanogaster sperm proteins, suggesting conservation of their sperm-related function across Diptera.

Conclusion and Significance

This is the first study to directly identify Sfps transferred from male Ae. aegypti to females. Our data lay the groundwork for future functional analyses to identify individual seminal proteins that may trigger female post-mating changes (e.g., in feeding patterns and egg production). Therefore, identification of these proteins may lead to new approaches for manipulating the reproductive output and vectorial capacity of Ae. aegypti.

Dengue is a potentially lethal infection that impacts millions of humans annually. This disease is caused by viruses transmitted by infected female Aedes aegypti mosquitoes during blood feeding. No commercial vaccine or treatment is available for dengue infection. One way to break the disease transmission cycle is to develop new tools to reduce dengue vector populations. Seminal fluid proteins (Sfps) produced in the reproductive glands of male mosquitoes and transferred to females in the ejaculate during mating could be the target of such a tool. In related insects, Sfps modulate female reproduction and feeding patterns. Here we report 145 proteins that are transferred to females in the Ae. aegypti ejaculate. The proteins, which include Sfps and sperm proteins, fall into biochemical classes that suggest important potential roles in mated females. Of particular interest are proteins that could play roles in fertility and hormonal activity (including pathways involved in egg development and utilization of the blood meal). Our results lay important groundwork for new control strategies by identifying candidate proteins that may alter the reproductive biology or blood-feeding patterns of female Ae. aegypti and ultimately reduce the global burden of dengue.

Myoinhibiting peptides are the ancestral ligands of the promiscuous Drosophila sex peptide receptor

Male insects change behaviors of female partners by co-transferring accessory gland proteins (Acps) like sex peptide (SP), with their sperm. The Drosophila sex peptide receptor (SPR) is a G protein-coupled receptor expressed in the female's nervous system and genital tract. While most Acps show a fast rate of evolution, SPRs are highly conserved in insects. We report activation of SPRs by evolutionary conserved myoinhibiting peptides (MIPs). Structural determinants in SP and MIPs responsible for this dual receptor activation are characterized. Drosophila SPR is also expressed in embryonic and larval stages and in the adult male nervous system, whereas SP expression is restricted to the male reproductive system. MIP transcripts occur in male and female central nervous system, possibly acting as endogenous SPR ligands. Evolutionary consequences of the promiscuous nature of SPRs are discussed. MIPs likely function as ancestral ligands of SPRs and could place evolutionary constraints on the MIP/SPR class.

Proteomic analysis of atrazine exposure in Drosophila melanogaster (Diptera: Drosophilidae)

Atrazine is a widely used herbicide that has been reported to induce the activity of certain detoxification enzymes and to affect insecticide toxicity in organisms experiencing simultaneous exposure to both atrazine and insecticides. In this study, the effects of atrazine (2-chloro-4-ethylamino-6-isopropylamino-1,3,5-triazine) exposure on protein expression in male and female Drosophila melanogaster adults in both microsomal and cytosolic cell fractions was investigated by 2-dimensional gel electrophoresis. Differentially expressed proteins (vs. controls) were identified using matrix assisted laser desorption-time (MALDI-TOF) of flight mass spectrometry (MS). We identified a total of 28 proteins associated with energy production including glycolysis and mitochondrial respiration as differentially expressed and nine proteins associated with detoxification and response to oxidative stress. Most of these proteins were expressed in one sex or the other but not in both. Surprisingly, the only proteins associated with detoxification were identified as glutathione transferases. No cytochrome P450s were identified which have previously been shown to be responsive to atrazine exposure in D. melanogaster and proposed to be associated with insecticide/atrazine interactions. Results of this investigation support the role of atrazine in affecting mitochondrial electron transport and oxidative stress. However, the role of atrazine in pesticide interactions remains uncertain.

Characterization of a vitellogenin gene reveals two phase regulation of vitellogenesis by engorgement and mating in the soft tick Ornithodoros moubata (Acari: Argasidae)

Synthesis of the precursor yolk protein vitellogenin (Vg) occurs after engorgement in haematophagous arthropods. We identified the Vg cDNA of the soft tick Ornithodoros moubata (OmVg) and compared its expression in mated and virgin females. Both mated and virgin females showed increases in OmVg expression after engorgement but expression was higher in mated females than virgin females particularly as time advanced. Delayed mating in virgin females induced an increase in OmVg expression. OmVg expression was observed in the midgut and fat body by whole mount in situ hybridization, but enlarged fat body with high expression occurred in only mated females during the late phase of vitellogenesis. Therefore, engorgement initially induces OmVg expression but mating is necessary for continued Vg expression to produce mature eggs.

Germline-dependent gene expression in distant non-gonadal somatic tissues of Drosophila

Background

Drosophila females commit tremendous resources to egg production and males produce some of the longest sperm in the animal kingdom. We know little about the coordinated regulation of gene expression patterns in distant somatic tissues that support the developmental cost of gamete production.

Results

We determined the non-gonadal gene expression patterns of Drosophila females and males with or without a germline. Our results show that germline-dependent expression in the non-gonadal soma is extensive. Interestingly, gene expression patterns and hormone titers are consistent with a hormone axis between the gonads and non-gonadal soma.

Conclusions

The germline has a long-range influence on gene expression in the Drosophila sexes. We suggest that this is the result of a germline/soma hormonal axis.

A receptor that mediates the post-mating switch in Drosophila reproductive behaviour

Mating in many species induces a dramatic switch in female reproductive behaviour. In most insects, this switch is triggered by factors present in the male's seminal fluid. How these factors exert such profound effects in females is unknown. Here we identify a receptor for the Drosophila melanogaster sex peptide (SP, also known as Acp70A), the primary trigger of post-mating responses in this species. Females that lack the sex peptide receptor (SPR, also known as CG16752), either entirely or only in the nervous system, fail to respond to SP and continue to show virgin behaviours even after mating. SPR is expressed in the female's reproductive tract and central nervous system. The behavioural functions of SPR map to the subset of neurons that also express the fruitless gene, a key determinant of sex-specific reproductive behaviour. SPR is highly conserved across insects, opening up the prospect of new strategies to control the reproductive and host-seeking behaviours of agricultural pests and human disease vectors.

Role of ecdysone 20-monooxygenase in regulation of 20-hydroxyecdysone levels by juvenile hormone and biogenic amines in Drosophila

The effects of increased levels of dopamine (feeding flies with dopamine precursor, L: -dihydroxyphenylalanine) and octopamine (feeding flies with octopamine) on ecdysone 20-monooxygenase activity in young (2 days old) wild type females (the strain wt) of Drosophila virilis have been studied. L: -dihydroxyphenylalanine and octopamine feeding increases ecdysone 20-monooxygenase activity by a factor of 1.6 and 1.7, respectively. Ecdysone 20-monooxygenase activity in the young (1 day old) octopamineless females of the strain Tbetah ( nM18 ), in females of the strain P845 (precursor of Tbetah ( nM18 ) strain) and in wild type females (Canton S) of Drosophila melanogaster have been measured. The absence of octopamine leads to a considerable decrease in the enzyme activity. We have also studied the effects of juvenile hormone application on ecdysone 20-monooxygenase activity in 2-day-old wt females of D. virilis and demonstrated that an increase in juvenile hormone titre leads to an increase in the enzyme activity. We discuss the supposition that ecdysone 20-monooxygenase occupies a key position in the regulation of 20-hydroxyecdysone titre under the conditions that lead to changes in juvenile hormone titre and biogenic amine levels.

Reproductive division of labor, dominance, and ecdysteroid levels in hemolymph and ovary of the bumble bee Bombus terrestris

To determine whether ecdysteroids are associated with reproductive division of labor in Bombus terrestris, we measured their levels in hemolymph and ovaries of queens and workers. Queens heading colonies had large active ovaries with high ecdysteroid content, whereas virgin gynes and mated queens before and after diapause had undeveloped ovaries with low ecdysteroid content. The hemolymph ecdysteroid titer was rather variable, but in a pooled analysis of mated queens before and after diapause versus colony-heading queens, ecdysteroid titers were higher in the latter group. In workers, agonistic behavior, ovarian activity, ovarian ecdysteroid content, and hemolymph ecdysteroid titers were positively correlated, and were lowest when a queen was present. In queenless workers, ecdysteroid levels were elevated in dominant workers, and were also influenced by the presence of brood and by group demography; hormone levels were higher in bees kept in larger groups. These findings are consistent with the premise that in B. terrestris the ovary is the primary site of ecdysteroid synthesis, and they show that ecdysteroids levels vary with the social environment.

Insulin signaling is necessary for vitellogenesis in Drosophila melanogaster independent of the roles of juvenile hormone and ecdysteroids: female sterility of the chico1 insulin signaling mutation is autonomous to the ovary

It has been suggested that insulin signaling mutations of Drosophila melanogaster are sterile and long-lived because of juvenile hormone (JH) and ecdysteroid deficiency. However, female sterility of an insulin/IGF-like signaling mutant (chico(1)) of D. melanogaster is not mediated by downstream systemic signaling in terms of major alterations in JH or ecdysteroid levels. chico(1) is a null mutation in the insulin substrate protein (CHICO) gene of D. melanogaster. Homozygous chico(1) females are sterile and their oocytes do not mature beyond the last previtellogenic stage. Homozygous chico(1) females exhibit approximately wild-type rates of JH biosynthesis, ovarian release of ecdysteroids and haemolymph ecdysteroid levels, suggesting that these two major hormone systems play no role in producing the sterility. Previtellogenic wild-type ovaries transplanted into homozygous chico(1) females underwent vitellogenesis, showing that systemic factors present in mutant females are sufficient to support normal vitellogenesis. chico(1) ovaries transplanted into wild-type females did not undergo vitellogenesis indicating that CHICO is necessary in the ovary for vitellogenic maturation. The ovary transplant experiments corroborate the endocrine results and demonstrate that insulin/insulin-like signaling (IIS) is necessary for vitellogenesis even when sufficient levels of JH, ecdysteroids or other factors are present.

Translating available food into the number of eggs laid by Drosophila melanogaster

In Drosophila and other insects egg production is related to the nutrients available. Somehow the nutritional status of the environment is translated into hormonal signs that can be "read" by each individual egg chamber, influencing the decision to either develop into an egg or die. We have shown that BR-C is a control gene during oogenesis and that the differential expression of BR-C isoforms plays a key role in controlling whether the fate of the egg chamber is to develop or undergo apoptosis.

Heat stress affects oogenesis differently in wild-type Drosophila virilis and a mutant with altered juvenile hormone and 20-hydroxyecdysone levels

The link between reproduction and environmental signals is poorly understood at the physiological, genetic and molecular levels. We describe a mutant strain of Drosophila virilis that has altered responses to heat stress. Heat stress in wild-type females results in oocyte maturation delays, degradation of early vitellogenic egg chambers, inhibition of yolk protein gene expression in follicle cells and accumulation of mature oocytes. The mutant females have increased levels of ecdysteroids and decreased juvenile hormone degradation, and show all of the heat-stress-induced reproductive effects observed in wild-type flies, without exposure to heat stress. During oogenesis in mutant females following heat stress there is an increase in early vitellogenic oocyte degradation and some degradation of late egg chambers. 20-Hydroxyecdysone levels, but not juvenile hormone degradation, change following heat stress in mutant females.

Slow aging during insect reproductive diapause: why butterflies, grasshoppers and flies are like worms

Diapause is a state of arrested development accompanied by physiology for somatic persistence. Diapause is common in many invertebrates and is familiar to biogerontology in the context of Caenorhabditis elegans dauer. Among insects, diapause may occur in embryos, larvae, pupae or adults. At the adult stage, reproductive diapause arrests development of oogenesis, vitellogenesis, accessory gland activity, and mating behavior. Reproductive diapause has been well studied in monarch butterflies, several grasshoppers, and several Diptera, including Drosophila and Phormia. In monarchs and in grasshoppers, reproductive diapause physiology has been experimentally induced by the surgical removal of the corpora allata, the source of adult juvenile hormone; allatectomy in each case was found to double adult longevity. Among Drosophila, the endemic D. triauraria of Japan, and D. littoralis of Finland over-winter as adults in reproductive diapause. How D. melanogaster winter is poorly understood, but reproductive diapause can be cued by cool temperature. In laboratory studies, the mortality rates of post-diapause D. melanogaster are similar to rates of newly enclosed, young flies. This implies that senescence during diapause is slow or negligible. Slow aging during the diapause period may involve elevated somatic stress resistance as well as reallocation of resources to somatic maintenance. Reproductive diapause in Drosophila is proximally controlled by down regulation of juvenile hormone, a phenotype that is also produced by mutants of the insulin-like receptor InR, homologue of C. elegans daf-2. We propose neuroendocrine control of reproductive diapause in D. melanogaster that includes phenotypic plasticity for rates of senescence.

Male contributions to egg production: the role of accessory gland products and sperm in Drosophila melanogaster

Drosophila melanogatser seminal fluid components, accessory gland proteins (Acps) and sperm, induce females to deposit high numbers of fertilized eggs for about 11 days. This high and sustained level of egg deposition requires that oogenesis be stimulated to provide the necessary mature oocytes. To investigate the relative timing and contributions of Acps and sperm in the egg-production process, we examined the rates of oogenic progression and egg deposition in females mated to genetically altered males that have seminal fluid deficient in Acps and/or sperm, and subjected these data to path analysis. We found that Acps and sperm are complementary stimuli necessary for inducing high rates of oogenic progression and rapid egg deposition. While egg deposition and oogenic progression can be induced by Acps alone, both Acps and sperm are required for maximum stimulation of oogenic progression and egg deposition immediately after mating.

Cyclic AMP-dependent and independent stimulations of ovarian steroidogenesis by brain factors in the blowfly, Phormia regina

The involvement of cyclic-AMP (cAMP) as a potential second messenger in the neurohormonal control of ovarian steroidogenesis was investigated in the adult female blowfly Phormia regina. Individual measurements of ovarian cAMP concentrations and of ovarian biosynthesis of ecdysteroids, stimulated after a protein meal, demonstrated that steroidogenesis is preceded by a peak of cAMP in the ovaries. In vitro, ovarian steroidogenesis was stimulated by cell-permeable analogues of cAMP and by forskolin. Crude brain extracts were also able to elicit a rise of cAMP in the ovaries in vitro and the secretion of ecdysteroids into the medium: such extracts were more active before than after the protein meal, suggesting a rapid release of neuroendocrine material after feeding. Extracts were then prepared from the dorso-medial part of the brain, containing the neurosecretory cells of the pars intercerebralis (PI): these extracts were again found to stimulate the ovarian ecdysteroid secretion, but surprisingly, they failed to trigger a rise of cAMP in the ovaries in vitro. However, extracts from the rest of the cephalic nervous mass, deprived of PI, were also steroidogenic and they increased ovarian cAMP. Experiments with Rp-cAMPS, a cAMP antagonist, were not able to prevent the ecdysteroid stimulation by PI extracts, but did so partly for the extracts deprived of PI. This study thus indicates that at least two different cephalic factors are able to stimulate ovarian steroidogenesis in the blowfly, one elaborated by PI and acting via a cAMP-independent mechanism, and the other elaborated outside PI and using cAMP as a second messenger.

Ecdysteroid titer, ovary status, and dominance in adult worker and queen bumble bees (Bombus terrestris)

The role of ecdysteroids in the regulation of dominance and reproduction in social Hymenoptera is little explored. In the current study we compared ecdysteroid titers in hemolymph of individual queen and worker bumble bees (Bombus terrestris) that differ in their behavior, reproductive status and social environment. Egg-laying queens that head colonies and have ovaries exhibiting all stages of follicle development, had a higher ecdysteroid titer than virgin queens whose ovaries contained only follicles at initial stages. In workers, the relationship between ecdysteroid titers and follicle development appears to be more complex and to be influenced by the bee's social status and social environment. Shortly after emergence, young workers had only follicles at the initial stages of oogenesis and they exhibited a low ecdysteroid titer. No significant correlation was detected between ovary status and ecdysteroid titer in workers, with some workers showing activated ovaries but low ecdysteroid titers. However, at six days of age, a trend towards higher ecdysteroid titer was observed for workers in queenless groups, a condition characterized by rapid follicle development relative to queenright conditions. In these queenless groups, high social status was associated with high ecdysteroid titers. By contrast, in queenright workers ecdysteroid titers were low, even for bees with presumably high social status that had activated ovaries and were observed performing oviposition behavior. This study suggests that ecdysteroids are involved in regulation of reproduction in B. terrestris.

Control of oocyte maturation in sexually mature Drosophila females

In many sexually mature insects egg production and oviposition are tightly coupled to copulation. Sex-Peptide is a 36-amino-acid peptide synthesized in the accessory glands of Drosophila melanogaster males and transferred to the female during copulation. Sex-Peptide stimulates vitellogenic oocyte progression through a putative control point at about stage 9 of oogenesis. Here we show that application of the juvenile hormone analogue methoprene mimics the Sex-Peptide-mediated stimulation of vitellogenic oocyte progression in sexually mature virgin females. Apoptosis is induced by 20-hydroxyecdysone in nurse cells of stage 9 egg chambers at physiological concentrations (10(-7) M). 20-Hydroxyecdysone thus acts as an antagonist of early vitellogenic oocyte development. Simultaneous application of juvenile hormone analogue, however, protects early vitellogenic oocytes from 20-hydroxyecdysone-induced resorption. These results suggest that the balance of these hormones in the hemolymph regulates whether oocytes will progress through the control point at stage 9 or undergo apoptosis. These data are further supported by a molecular analysis of the regulation of yolk protein synthesis and uptake into the ovary by the two hormones. We conclude that juvenile hormone is a downstream component in the Sex-Peptide response cascade and acts by stimulating vitellogenic oocyte progression and inhibiting apoptosis. Since juvenile hormone analogue does not elicit increased oviposition and reduced receptivity, Sex-Peptide must have an additional, separate effect on these two postmating responses.