Accessory gland as a site for prothoracicotropic hormone controlled ecdysone synthesis in adult male insects

Male-derived phospholipase A2 enhances WD46 expression and increases fertility in Ophraella communa

Successful bisexual reproduction requires interactions between males and females. Male-derived seminal fluid proteins (SFPs) transferred to females during mating profoundly affect females from pre- to post-mating, and the subsequent shift in female physiology enhances their fertility. SFPs have important evolutionary implications for the fitness of many insects. However, little is known about how females respond to male SFPs. In this study, we identified a male-derived SFP-phospholipase A2 (PLA2) in Ophraella communa. PLA2 is a vital enzyme in eicosanoid biosynthesis; however, it has not been identified as an insect SFP. We found that OcPLA2 is specifically expressed in males, especially in the male accessory glands (MAGs); it is transferred to the female during mating and functions as an SFP to enhance fertility. The expression of a female-derived gene encoding the WD repeat-containing protein 46 (WD46) was upregulated when OcPLA2 entered the female reproductive tract, and this contributed to female egg production by increasing triacylglycerol lipase (TGL) gene expression and the triglyceride (TG) content. This is the first study to identify PLA2 as an SFP in insects. Our findings also shed light on the regulatory role of OcPLA2 in beetle reproduction; the expression of OcPLA2 is initially correlated with female WD46 expression and later with the decline in TGL gene expression and the TG content. This represents a unique mechanism of reproductive regulation by an SFP.

Fecundity is optimized by levels of nutrient signal-dependent expression of Dve and EcR in Drosophila male accessory gland

Steroid hormones play various physiological roles including metabolism and reproduction. Steroid hormones in insects are ecdysteroids, and the major form in Drosophila melanogaster is ecdysone. In Drosophila males, the accessory gland is responsive to nutrient-dependent regulation of fertility/fecundity. The accessory gland is composed of two types of binucleated epithelial cells: a main cell and a secondary cell (SC). The transcription factors Defective proventriculus (Dve), Abdominal-B, and Ecdysone receptors (EcRs) are strongly expressed in adult SCs. We show that this EcR expression is regulated by parallel pathways of nutrient signaling and the Dve activity. Induction of Dve expression is also dependent on nutrient signaling, and it becomes nutrient signal-independent during a restricted period of development. Forced dve expression during the restricted period significantly increased the number of SCs. Here, we provide evidence that the level of nutrient signal-dependent Dve expression during the restricted period determines the number of SCs, and that ecdysone signaling is also crucial to optimize male fecundity through nutrient signal-dependent survival and maturation of SCs.

Transcriptome analysis and identification of genes related to environmental adaptation of Grylloprimevala jilina Zhou & Ren 2023

Grylloprimevala jilina is a true cave insect living in the dark areas of caves. It has the characteristics of sparse skin pigmentation, degeneration of the compound eyes and monocular eyes, and obvious preference for high-humidity and low-temperature environments. Given the highly specialized, rare, and limited distribution, G. jilina is considered an endangered species and also a first-level national protected insect in China. Cave creatures often undergo dramatic morphological changes in their sensory systems to adapt to the cave environment. Most previous studies mainly focused on morphological adaptive changes in cave insects, and only a few studied the changes at the gene level. In this study, we performed transcriptome analysis of G. jilina and constructed phylogenetic trees of genes that are related to environmental adaptation, including chemosensory, visual-related, reproduction-related, temperature adaptation-related, and winged morph differentiation-related genes. Besides, the expression levels of environmental adaption-related genes in different tissues, including antennae, heads, thoraxes, abdomens, legs, and tails, were analyzed. The results showed the loss of chemosensory genes and vision-related genes, the conservation of reproduction-related genes and temperature adaptation-related genes, and the conservation of wing-related genes despite the loss of wings, and the results were consistent with other cave insects. The identification and expression study of genes possibly related to the environmental adaptability in G. jilina provided basic data for the protection of this endangered species and increased knowledge about insect evolution in general.

The loss of Halloween gene function seriously affects the development and reproduction of Diaphorina citri (Hemiptera: Liviidae) and increases its susceptibility to pesticides

The citrus industry has suffered severe losses as a result of Huanglongbing spread by Diaphorina citri. Controlling the population of D. citri is the key to preventing and controlling the spread of Huanglongbing. Ecdysteroids are key hormones that regulate insect development and reproduction. Therefore, the Halloween gene family involved in the ecdysone synthesis of D. citri is an ideal target for controlling the population growth of this insect. In this study, we successfully cloned four Halloween genes expressed during D. citri development. Silencing of one of the four genes resulted in a significant decrease in 20E titers in nymphs and significant decreases in the developmental, survival and emergence rates. Inhibiting Halloween gene expression in adults impeded the growth of the female ovary, diminished yolk formation, lowered vitellogenin transcription levels, and hence impaired female fecundity. This showed that Halloween genes were required for D. citri development and reproduction. DcCYP315A1 and DcCYP314A1 were highly expressed when D. citri was exposed to thiamethoxam and cypermethrin, and silencing these two genes made D. citri more sensitive to these two pesticides. Inhibition of DcCYP315A1 and DcCYP314A1 expression not only significantly delayed the development and reproduction of D. citri but also increased its susceptibility to pesticides. Therefore, these two genes are more suitable as potential target genes for controlling D. citri.

Rethinking the ecdysteroid source during Drosophila pupal-adult development

Ecdysteroids, typified by 20-hydroxyecdysone (20E), are essential hormones for the development, reproduction and physiology of insects and other arthropods. For over half a century, the vinegar fly Drosophila melanogaster (Ephydroidea: Diptera) has been used as a model of ecdysteroid biology. Many aspects of the biosynthesis and regulation of ecdysteroids in this species are understood at the molecular level, particularly with respect to their secretion from the prothoracic gland (PG) cells of the ring gland, widely considered the dominant biosynthetic tissue during development. Discrete pulses of 20E orchestrate transitions during the D. melanogaster life cycle, the sources of which are generally well understood, apart from the large 20E pulse at the onset of pharate adult development, which has received little recent attention. As the source of this pharate adult pulse (PAP) is a curious blind spot in Drosophila endocrinology, we evaluate published biochemical and genetic data as they pertain to three hypotheses for the source of PAP 20E: the PG; an alternative biosynthetic tissue; or the recycling of stored 20E. Based on multiple lines of evidence, we contend the PAP cannot be derived from biosynthesis, with other data consistent with D. melanogaster able to recycle ecdysteroids before and during metamorphosis. Published data also suggest the PAP is conserved across Diptera, with evidence for pupal-adult ecdysteroid recycling occurring in other cyclorrhaphan flies. Further experimental work is required to test the ecdysteroid recycling hypothesis, which would establish fundamental knowledge of the function, regulation, and evolution of metamorphic hormones in dipterans and other insects.

Identification and characterization of CYP307A1 as a molecular target for controlling the small hive beetle, Aethina tumida

BACKGROUND

The molting hormone 20-hydroxyecdysone (20E) plays a key role in insect development, metamorphosis, and reproduction. Previous studies have shown that ecdysteroid metabolism is regulated by a series of CYP genes in most of the insect species. However, the roles of these CYP genes in a Coleopteran beetle, Aethina tumida (small hive beetle, SHB) have not yet been explored.

RESULTS

In the current study, we identified seven CYP genes (six Halloween genes and one AtCYP18A1 gene) related to 20E metabolism. Reverse transcription quantitative polymerase chain reaction (RT-qPCR) showed that AtCYP307A1 and AtCYP307B1 were primarily expressed in the embryonic stage and in the cephalothorax of larvae. RNA interference (RNAi) screening revealed that suppression of AtCYP307A1 expression caused a lethal phenotype during the larval-pupal metamorphosis. Furthermore, Hematoxylin and Eosin staining of the integument showed that the RNAi of AtCYP307A1 inhibited the apolysis and degradation of the old cuticle. In addition, silencing of AtCYP307A1 resulted in significant down-regulation of 20E titers and the expression levels of 20E signaling pathway genes. Finally, the AtCYP307A1 RNAi phenotype was rescued by topical application of 20E.

CONCLUSION

Our studies suggest that AtCYP307A1 involved in 20E synthesis is indispensable during the larval-pupal metamorphosis of beetles, which could serve as a putative insecticide target for pest control. © 2022 Society of Chemical Industry.

RNAi-Mediated Silencing of Putative Halloween Gene Phantom Affects the Performance of Rice Striped Stem Borer, Chilo suppressalis

The physiological and biochemical characterization of the "Halloween" genes has fundamental importance in the biosynthesis pathway of ecdysteroids. These genes were found to catalyze the final phases of ecdysteroid biosynthesis from dietary cholesterol to the molting hormone 20-hydroxyecdysone. We report the characterization of the Cs-Phm in a major insect pest in agriculture, the rice striped stem borer, Chilo suppressalis (C. suppressalis). A full-length transcript of Cs-Phm was amplified with an open reading frame (ORF) of 478 amino acids through 5' and 3' RACE. Cs-Phm shows five insect-conserved P450 motifs: Helix-C, Helix-I, Helix-K, PERF, and heme-binding motifs. Phylogenetic analysis clearly shows high similarity to Lepidoptera and evolutionary conservation in insects. The relative spatial and temporal transcript profile shows that Cs-Phm is highly expressed in the prothoracic glands and appears throughout the larval development, but with low expression at the start of the larval instar. It seems to peak in 3-4 days and decreases again before the larvae molt. Double-stranded RNA (dsRNA) injection of Cs-Phm at the larval stage efficiently knocked down the target gene and decreased its expression level. The dsRNA-treated group showed significantly decreased ecdysteroid titers, which leads to delayed larval development and higher larval mortality. Negative effects of larval development were rescued by treating 20E in the dsRNA-treated group. Thus, in conclusion, our results suggest that Cs-Phm is functionally conserved in C. suppressalis and encodes functional CYP that contributes to the biogenesis of 20E.

Drosophila ecdysone receptor activity-based ex vivo assay to assess the endocrine disruption potential of environmental chemicals

Insect pollinators, critical for both agricultural output and the ecosystem, are declining at an alarming levels partly due to human-made chemicals. Majority of environmental chemicals hamper the endocrine function and studies on the same in insects remain neglected. Here, we report a Drosophila-based ex vivo assay system that employs a reproductive tissue from transgenic males carrying a reporter gene (lacZ) downstream of ecdysone receptor response element (EcRE) and permits the evaluation of chemical-mediated activity modulation of all three isoforms of ecdysone receptor, which are critical for male fertility. We show agonistic [plasticizers, cypermethrin, atrazine, methyl parathion, imidacloprid, cadmium chloride, mercuric chloride or 3-(4-methylbenzylidene) camphor] or antagonistic (apigenin, tributyltin chloride) effects or lack of effect thereof (rutin hydrate, dichlorvos, lead acetate, parabens) for seven different classes of environmental chemicals on ecdysone receptor activity reflecting the specificity and sensitivity of the developed ex vivo assay. Exposure to a few of these chemicals in vivo hampers the fertility of Drosophila males, thus linking the observed endocrine disruption to a quantifiable reproductive phenotype. The developed ex vivo assay offers a quick Drosophila-based screening tool for throughput monitoring of environmental chemicals for their ability to hamper the endocrine function of insect pollinators and other invertebrates.

CYP314A1-dependent 20-hydroxyecdysone biosynthesis is involved in regulating the development of pupal diapause and energy metabolism in the Chinese citrus fruit fly, Bactrocera minax

BACKGROUND

Diapause is an environmentally preprogrammed period of arrested development, and characterized by metabolic depression that can occur during any development stage of insect. The insect steroid hormone 20-hydroxyecdysone (20E), is converted from ecdysone by the cytochrome P450 enzyme shade (CYP314A1), and it exerts a potent effect on the induction and maintenance of diapause in obligatory diapause insects. However, the regulatory mechanism of 20E in obligatory diapause development remains unclear. In this study, the function of 20E in the pupal diapause of Bactrocera minax was investigated.

RESULTS

We determined the expression pattern of Halloween P450 genes from larval to adult B. minax, and found differential expression of CYP314A1 from other P450 genes, with a high level in larvae and a low level in pupae. Dysfunction of CYP314A1 by dsCYP314A1 microinjection in third-instar larvae caused significant larval mortality or abnormal pupae. Compared with dsGFP and DEPC-water, dsCYP314A1-injected larvae had significantly reduced 20E titer and altered energy metabolism, and many individuals failed to pupate. Exogenous 20E microinjected into late third-instar larvae or 20E fed to early third-instar larvae both caused similar energy metabolism changes. The 20E-treated larvae of B. minax had reduced total lipids and increased amounts of trehalose and glycogen. Furthermore, 20E-treated diapause individuals showed rapid pupal development.

CONCLUSION

The 20E biosynthesis was regulated by the expression of CYP314A1, and was involved in the induction and termination phase of obligate diapause by regulating energy metabolism in B. minax. © 2022 Society of Chemical Industry.

Endocrine control of glycogen and triacylglycerol breakdown in the fly model

Over the last decade, the combination of genetics, transcriptomic and proteomic approaches yielded substantial insights into the mechanisms behind the synthesis and breakdown of energy stores in the model organisms. The fruit fly Drosophila melanogaster has been particularly useful to unravel genetic regulations of energy metabolism. Despite the considerable evolutionary distance between humans and flies, the energy storage organs, main metabolic pathways, and even their genetic regulations remained relatively conserved. Glycogen and fat are universal energy reserves used in all animal phyla and several of their endocrine regulators, such as the insulin pathway, are highly evolutionarily conserved. Nevertheless, some of the factors inducing catabolism of energy stores have diverged significantly during evolution. Moreover, even within a single insect species, D. melanogaster, there are substantial developmental and context-dependent variances in the regulation of energy stores. These differences include, among others, the endocrine pathways that govern the catabolic events or the predominant fuel which is utilized for the given process. For example, many catabolic regulators that control energy reserves in adulthood seem to be largely dispensable for energy mobilization during development. In this review, we focus on a selection of the most important catabolic regulators from the group of peptide hormones (Adipokinetic hormone, Corazonin), catecholamines (octopamine), steroid hormones (20-hydroxyecdysone), and other factors (extracellular adenosine, regulators of lipase Brummer). We discuss their roles in the mobilization of energy reserves for processes such as development through non-feeding stages, flight or starvation survival. Finally, we conclude with future perspectives on the energy balance research in the fly model.

Endocrine Regulation of Lifespan in Insect Diapause

Diapause is a physiological adaptation to conditions that are unfavorable for growth or reproduction. During diapause, animals become long-lived, stress-resistant, developmentally static, and non-reproductive, in the case of diapausing adults. Diapause has been observed at all developmental stages in both vertebrates and invertebrates. In adults, diapause traits weaken into adaptations such as hibernation, estivation, dormancy, or torpor, which represent evolutionarily diverse versions of the traditional diapause traits. These traits are regulated through modifications of the endocrine program guiding development. In insects, this typically includes changes in molting hormones, as well as metabolic signals that limit growth while skewing the organism's energetic demands toward conservation. While much work has been done to characterize these modifications, the interactions between hormones and their downstream consequences are incompletely understood. The current state of diapause endocrinology is reviewed here to highlight the relevance of diapause beyond its use as a model to study seasonality and development. Specifically, insect diapause is an emerging model to study mechanisms that determine lifespan. The induction of diapause represents a dramatic change in the normal progression of age. Hormones such as juvenile hormone, 20-hydroxyecdysone, and prothoracicotropic hormone are well-known to modulate this plasticity. The induction of diapause-and by extension, the cessation of normal aging-is coordinated by interactions between these pathways. However, research directly connecting diapause endocrinology to the biology of aging is lacking. This review explores connections between diapause and aging through the perspective of endocrine signaling. The current state of research in both fields suggests appreciable overlap that will greatly contribute to our understanding of diapause and lifespan determination.

Roles of peripheral clocks: lessons from the fly

To adapt to and anticipate rhythmic changes in the environment such as daily light-dark and temperature cycles, internal timekeeping mechanisms called biological clocks evolved in a diverse set of organisms, from unicellular bacteria to humans. These biological clocks play critical roles in organisms' fitness and survival by temporally aligning physiological and behavioral processes to the external cues. The central clock is located in a small subset of neurons in the brain and drives daily activity rhythms, whereas most peripheral tissues harbor their own clock systems, which generate metabolic and physiological rhythms. Since the discovery of Drosophila melanogaster clock mutants in the early 1970s, the fruit fly has become an extensively studied model organism to investigate the mechanism and functions of circadian clocks. In this review, we primarily focus on D. melanogaster to survey key discoveries and progresses made over the past two decades in our understanding of peripheral clocks. We discuss physiological roles and molecular mechanisms of peripheral clocks in several different peripheral tissues of the fly.

Knockdown of Uridine Diphosphate Glucosyltransferase 86Dg Enhances Susceptibility of Tribolium castaneum (Coleoptera: Tenebrionidae) to Artemisia vulgaris (Asterales: Asteraceae) Essential Oil

Uridine diphosphate glucosyltransferases (UGTs), which are phase II detoxification enzymes, are found in various organisms. These enzymes play an important role in the detoxification mechanisms of plant allelopathy and in insects. Artemisia vulgaris L. (Asterales: Asteraceae: Artemisia) essential oil has strong contact toxicity to Tribolium castaneum Herbst (Coleoptera: Tenebrionidae) larvae. However, the effect of A. vulgaris essential oil on UGTs is unclear. In this study, A. vulgaris essential oil was shown to significantly induce the expression of the TcUgt86Dg transcript. Furthermore, treatment of TcUgt86Dg-silenced individuals with A. vulgaris essential oil resulted in higher mortality than for the control individuals, indicating that TcUgt86Dg is involved in detoxification of A. vulgaris essential oil in T. castaneum. The developmental expression profile showed that the expression of TcUgt86Dg in late adults was higher than in other developmental stages. Furthermore, the expression profile in adult tissues revealed higher expression of TcUgt86Dg in the head, antenna, fat body, and accessory gland than in other tissues. These data show that TcUgt86Dg may be involved in the metabolism of exogenous toxins by T. castaneum; thus, our results have elucidated one possible mechanism of resistance to A. vulgaris essential oil and provide a theoretical basis for a control scheme for T. castaneum.

Topical Application of Synthetic Hormones Terminated Reproductive Diapause of a Univoltine Weed Biological Control Agent

Classical biological control is an important method for controlling invasive alien weeds. Univoltine insects can be highly effective biological control agents of annual weeds because they are well synchronized with their host plant. However, having only one generation per year makes it difficult and slow to multiply them in the laboratory for initial field releases. If it were possible to terminate reproductive diapause early, then we could rear multiple generations per year, which would greatly increase annual production. We used a recently approved biocontrol agent, Ceratapion basicorne (a univoltine weevil), for yellow starthistle (Centaurea solstitialis) as a model system to study the use of two insect hormones, 20-hydroxyecdysone (20E) and methoprene, to terminate reproductive diapause. Methoprene (1 μg applied topically) terminated reproductive diapause of female weevils, whereas doses of 0.0, 0.01 and 0.1 μg did not. The combination of methoprene and 20E had a stronger effect and induced an increase in eggs (1.51 ± 0.16 eggs/day, mean ± SE) compared with a methoprene only group (1.00 ± 0.13 eggs/day), and a control group (0.21 ± 0.04 eggs/day). Thus, topical application of these hormones should enable us to rear the weevil out of its normal season and produce more than one generation per year, which will increase productivity of mass-rearing it for field release. Once released in the field, the insect would continue as a univoltine agent that is well-synchronized with its host plant.

Role of Endocrine System in the Regulation of Female Insect Reproduction

The proper synthesis and functioning of ecdysteroids and juvenile hormones (JHs) are very important for the regulation of vitellogenesis and oogenesis. However, their role and function contrast among different orders, and even in the same insect order. For example, the JH is the main hormone that regulates vitellogenesis in hemimetabolous insect orders, which include Orthoptera, Blattodea, and Hemiptera, while ecdysteroids regulate the vitellogenesis among the insect orders of Diptera, some Hymenoptera and Lepidoptera. These endocrine hormones also regulate each other. Even at some specific stage of insect life, they positively regulate each other, while at other stages of insect life, they negatively control each other. Such positive and negative interaction of 20-hydroxyecdysone (20E) and JH is also discussed in this review article to better understand the role of these hormones in regulating the reproduction. Therefore, the purpose of the present review is to deeply understand the complex interaction of endocrine hormones with each other and with the insulin signaling pathway. The role of microbiomes in the regulation of the insect endocrine system is also reviewed, as the endocrine hormones are significantly affected by the compounds produced by the microbiota.

Do holometabolous insects molt spontaneously after adulthood? An exceptional case report in fireflies (Coleoptera: Lampyridae), with discussion of its inferred endocrine regulation especially in relation to neoteny

It has been a traditionally held view that winged insects stop molting after they reach adulthood. We observed a fascinating phenomenon of a post-imago molt occurring in the neotenic females of a firefly species in Taiwan over the last two years. By rearing Lamprigera minor larvae to adults, four out of the five unmated females studied were found undergoing an extra molt 8-18 days after adult eclosion. They were reproductively mature when the post-imago molt occurred, as evidenced by the eggs inside their bodies. The four females died without oviposition whereas the only normal female laid eggs. A comparison of exuviae of different stages confirmed the existence of post-imago ecdysis. The adult skin differed from the pupal one mainly in the mouthparts and leg structures. No mix of pupal and adult traits was seen in the adult skin. The females retained the same morphology after the extra molt. A close examination of the post-imago molting females revealed that their oviduct openings were all blocked by larval or pupal skin and thus unable to lay eggs. The reproductive stress may invoke an endocrine disorder and lead to an extra molt. We propose that L. minor females retain their prothoracic glands even as adults, allowing them to molt as adults under certain environmental or physiological conditions. Thus, neoteny of L. minor is reflected in both the external morphology as well as the internal physiology. The possible developmental changes associated with the evolution of neoteny are discussed.

Metabolism and growth adaptation to environmental conditions in Drosophila

Organisms adapt to changing environments by adjusting their development, metabolism, and behavior to improve their chances of survival and reproduction. To achieve such flexibility, organisms must be able to sense and respond to changes in external environmental conditions and their internal state. Metabolic adaptation in response to altered nutrient availability is key to maintaining energy homeostasis and sustaining developmental growth. Furthermore, environmental variables exert major influences on growth and final adult body size in animals. This developmental plasticity depends on adaptive responses to internal state and external cues that are essential for developmental processes. Genetic studies have shown that the fruit fly Drosophila, similarly to mammals, regulates its metabolism, growth, and behavior in response to the environment through several key hormones including insulin, peptides with glucagon-like function, and steroid hormones. Here we review emerging evidence showing that various environmental cues and internal conditions are sensed in different organs that, via inter-organ communication, relay information to neuroendocrine centers that control insulin and steroid signaling. This review focuses on endocrine regulation of development, metabolism, and behavior in Drosophila, highlighting recent advances in the role of the neuroendocrine system as a signaling hub that integrates environmental inputs and drives adaptive responses.

The POU factor Ventral veins lacking regulates ecdysone and juvenile hormone biosynthesis during development and reproduction of the milkweed bug, Oncopeltus fasciatus

Recent studies have demonstrated endocrine roles for the POU domain transcription factor Ventral veins lacking (Vvl) during larval development of holometabolous insects - insects that undergo complete metamorphosis. In this study, the role of Vvl was examined in the milkweed bug, Oncopeltus fasciatus, a hemimetabolous insect. In the embryos, vvl was found to be expressed in the presumptive prothoracic glands. When vvl expression was knocked down using RNA interference (RNAi), embryos arrested their development after dorsal closure. Vvl double-stranded RNA (dsRNA)-injected nymphs failed to molt and had reduced expression of the ecdysone response gene, hormone receptor 3 (HR3), the ecdysone biosynthesis genes, disembodied and spook, and the juvenile hormone (JH) response gene, Krüppel homolog 1 (Kr-h1). Injection of 20-hydroxyecdysone rescued the molting phenotype and HR3 expression in vvl knockdown nymphs. In adults, vvl RNAi inhibited egg laying and suppressed the expression of Kr-h1 and vitellogenin in the fat body. Application of JH III or methoprene restored oviposition in vvl knockdown adults, indicating that Vvl regulates JH biosynthesis during reproduction. Thus, Vvl functions as a critical regulator of hormone biosynthesis throughout all developmental stages of O. fasciatus. Our study demonstrates that Vvl is a critical transcription factor involved in JH and ecdysteroid biosynthesis in both hemimetabolous and holometabolous insects.

Transcriptome of pleuropodia from locust embryos supports that these organs produce enzymes enabling the larva to hatch

Background

Pleuropodia are limb-derived glandular organs that transiently appear on the first abdominal segment in embryos of insects from majority of “orders”. They are missing in the genetic model Drosophila and little is known about them. Experiments carried out on orthopteran insects 80 years ago indicated that the pleuropodia secrete a “hatching enzyme” that digests the serosal cuticle to enable the larva to hatch, but evidence by state-of-the-art molecular methods is missing.

Results

We used high-throughput RNA-sequencing to identify the genes expressed in the pleuropodia of the locust Schistocerca gregaria (Orthoptera). First, using transmission electron microscopy we studied the development of the pleuropodia during 11 stages of the locust embryogenesis. We show that the glandular cells differentiate and start secreting just before the definitive dorsal closure of the embryo and the secretion granules outside the cells become more abundant prior to hatching. Next, we generated a comprehensive embryonic reference transcriptome for the locust and used it to study genome wide gene expression across ten morphologicaly defined stages of the pleuropodia. We show that when the pleuropodia have morphological markers of functional organs and produce secretion, they are primarily enriched in transcripts associated with transport functions. They express genes encoding enzymes capable of digesting cuticular protein and chitin. These include the potent cuticulo-lytic Chitinase 5, whose transcript rises just before hatching. Unexpected finding was the enrichment in transcripts for immunity-related enzymes. This indicates that the pleuropodia are equipped with epithelial immunity similarly as barrier epithelia in postembryonic stages.

Conclusions

These data provide transcriptomic support for the historic hypothesis that pleuropodia produce cuticle-degrading enzymes and function in hatching. They may also have other functions, such as facilitation of embryonic immune defense. By the genes that they express the pleuropodia are specialized embryonic organs and apparently an important though neglected part of insect physiology.

Mating induces switch from hormone-dependent to hormone-independent steroid receptor-mediated growth in Drosophila secondary cells

Male reproductive glands like the mammalian prostate and the paired Drosophila melanogaster accessory glands secrete seminal fluid components that enhance fecundity. In humans, the prostate, stimulated by environmentally regulated endocrine and local androgens, grows throughout adult life. We previously showed that in fly accessory glands, secondary cells (SCs) and their nuclei also grow in adults, a process enhanced by mating and controlled by bone morphogenetic protein (BMP) signalling. Here, we demonstrate that BMP-mediated SC growth is dependent on the receptor for the developmental steroid ecdysone, whose concentration is reported to reflect sociosexual experience in adults. BMP signalling appears to regulate ecdysone receptor (EcR) levels via one or more mechanisms involving the EcR's N terminus or the RNA sequence that encodes it. Nuclear growth in virgin males is dependent on ecdysone, some of which is synthesised in SCs. However, mating induces additional BMP-mediated nuclear growth via a cell type-specific form of hormone-independent EcR signalling, which drives genome endoreplication in a subset of adult SCs. Switching to hormone-independent endoreplication after mating allows growth and secretion to be hyperactivated independently of ecdysone levels in SCs, permitting more rapid replenishment of the accessory gland luminal contents. Our data suggest mechanistic parallels between this physiological, behaviour-induced signalling switch and altered pathological signalling associated with prostate cancer progression.

Ecdysteroidogenesis in Heliothis virescens (Lepidoptera: Noctuidae): Recombinant Prothoracicotropic Hormone and Brain Extract Show Comparable Effects

Prothoracicotropic hormone (PTTH) is a neuropeptide that triggers a cascade of events within the prothoracic gland (PG) cells, leading to the activation of all the crucial enzymes involved in ecdysone biosynthesis, the main insect steroid hormone. Studies concerning ecdysteroidogenesis predicted PTTH action using brain extract (BE), consisting in a complex mixture in which some components positively or negatively interfere with PTTH-stimulated ecdysteroidogenesis. Consequently, the integration of these opposing factors in steroidogenic tissues leads to a complex secretory pattern. A recombinant form of prothoracicotropic hormone (rPTTH) from the tobacco budworm Heliothis virescens (F.) (Lepidoptera: Noctuidae) was expressed and purified to perform in vitro tests in a standard and repeatable manner. A characterization of rPTTH primary and secondary structures was performed. The ability of rPTTH and H. virescens BE to stimulate ecdysteroidogenesis was investigated on the third day of fifth larval stage. rPTTH activity was compared with the BE mixture by enzyme immunoassay and western blot, revealing that they equally stimulate the production of significant amount of ecdysone, through a transduction cascade that includes the TOR pathway, by the phosphorylation of 4E binding protein (4E-BP) and S6 kinase (S6K), the main targets of TOR protein. The results of these experiments suggest the importance of obtaining a functional pure hormone to perform further studies, not depending on the crude brain extract, composed by different elements and susceptible to different uncontrollable variables.

Physiological and Environmental Factors Affecting the Composition of the Ejaculate in Mosquitoes and Other Insects

In addition to transferring sperm, male mosquitoes deliver several proteins, hormones and other factors to females in their seminal fluid that inhibit remating, alter host-seeking behaviors and stimulate oviposition. Recently, bioinformatics, transcriptomics and proteomics have been used to characterize the genes transcribed in male reproductive tissues and the individual proteins that are delivered to females. Thanks to these foundational studies, we now understand the complexity of the ejaculate in several mosquito species. Building on this work, researchers have begun to identify the functions of various proteins and hormones in the male ejaculate, and how they mediate their effects on female mosquitoes. Here, we present an overview of these studies, followed by a discussion of an under-studied aspect of male reproductive physiology: the effects of biotic and abiotic factors on the composition of the ejaculate. We argue that future research in this area would improve our understanding of male reproductive biology from a physiological and ecological perspective, and that researchers may be able to leverage this information to study key components of the ejaculate. Furthermore, this work has the potential to improve mosquito control by allowing us to account for relevant factors when implementing vector control strategies involving male reproductive biology.

Mining insect genomes for functionally affiliated genes

Several hundred insect genome assemblies are already publicly available, and this total grows on a weekly basis. A major challenge now confronting insect science is how best to use genomic data to improve our understanding of insect biology. We consider a framework for genome analysis based on functional affiliation, that is, groups of genes involved in the same biological process or pathway, and explore how such an approach furthers our understanding of several aspects of insect phenotype. We anticipate that this approach will prove useful for future research across the breadth of insect studies, whatever organism or trait it involves.

Obesity and Aging in the Drosophila Model

Being overweight increases the risk of many metabolic disorders, but how it affects lifespan is not completely clear. Not all obese people become ill, and the exact mechanism that turns excessive fat storage into a health-threatening state remains unknown. Drosophila melanogaster has served as an excellent model for many diseases, including obesity, diabetes, and hyperglycemia-associated disorders, such as cardiomyopathy or nephropathy. Here, we review the connections between fat storage and aging in different types of fly obesity. Whereas obesity induced by high-fat or high-sugar diet is associated with hyperglycemia, cardiomyopathy, and in some cases, shortening of lifespan, there are also examples in which obesity correlates with longevity. Transgenic lines with downregulations of the insulin/insulin-like growth factor (IIS) and target of rapamycin (TOR) signaling pathways, flies reared under dietary restriction, and even certain longevity selection lines are obese, yet long-lived. The mechanisms that underlie the differential lifespans in distinct types of obesity remain to be elucidated, but fat turnover, inflammatory pathways, and dysregulations of glucose metabolism may play key roles. Altogether, Drosophila is an excellent model to study the physiology of adiposity in both health and disease.

Dehydration triggers ecdysone-mediated recognition-protein priming and elevated anti-bacterial immune responses in Drosophila Malpighian tubule renal cells

Background

Drosophila is a powerful model for the study of factors modulating innate immunity. This study examines the effect of water-loss dehydration on innate immune responsiveness in the Drosophila renal system (Malpighian tubules; MTs), and how this leads to elevated host defense and contributes to immunosenescence.

Results

A short period of desiccation-elevated peptidoglycan recognition protein-LC (PGRP-LC) expression in MTs, increased antimicrobial peptide (AMP) gene induction, and protected animals from bacterial infection. We show that desiccation increased ecdysone synthesis in MTs, while inhibition of ecdysone synthesis or ecdysone receptor expression, specifically within MTs, prevented induction of PGRP-LC and reduced protection from bacterial infection. Additionally, aged flies are constitutively water-stressed and have elevated levels of ecdysone and PGRP-LC. Conversely, adults aged at high relative humidity show less water loss and have reduced expression of PGRP-LC and AMPs.

Conclusions

The Drosophila renal system is an important contributor to host defense and can modulate immune responses in an organ autonomous manner, responding to environmental changes such as desiccation. Desiccation primes immune responsiveness by elevating PGRP-LC expression specifically in MTs. In response to desiccation, ecdysone is produced in MTs and acts in a paracrine fashion to increase PGRP-LC expression, immune responsiveness, and improve host defense. This activity of the renal system may contribute to the immunosenescence observed in Drosophila.

Electronic supplementary material

The online version of this article (10.1186/s12915-018-0532-5) contains supplementary material, which is available to authorized users.

Gonadal ecdysone titers are modulated by protein availability but do not impact protein appetite

How animals survey internal nutrient availability to modulate specific appetites is currently largely unknown. Dietary proteins have a profound impact on the reproductive capacity and the selection of food sources in insects. When deprived of dietary proteins, insects stop producing eggs and develop strong protein appetites. In many adult insects, the ovaries are the site of synthesis of the ecdysone hormone. Therefore, an attractive hypothesis is that protein availability changes the gonadal production of ecdysone, which instructs the brain to increase its preference for yeast. We combine quantitative feeding assays, dietary manipulations, hormonal measurements, and genetic germline manipulations to test this hypothesis in Drosophila melanogaster. Our results show that upon yeast deprivation mated adult female Drosophila develop a strong yeast appetite and strongly reduce their egg production. This dietary manipulation also leads to a drastic reduction in ecdysone titers. However, the drop in ecdysone is not linked to the increase in yeast appetite as mutants with impaired oogenesis are able to adapt yeast intake to their nutrient state while displaying a constitutive low ecdysone titer. Interestingly, a low ecdysone titer is correlated with a lower level of overall food intake. Our data therefore show that in mated females the level of ecdysone reflects the level of protein in the diet and the physiological state of the ovaries. While the ovaries and ecdysone are unlikely to instruct the brain to develop a yeast appetite upon protein deprivation, they seem to be able to control overall food intake.

FoxO mediates the timing of pupation through regulating ecdysteroid biosynthesis in the red flour beetle, Tribolium castaneum

The steroid hormone 20-hydroxyecdysone (20E), the major developmental hormone in insects, controls all the developmental transitions including ecdysis and metamorphosis. In our study with last larval stages of the red flour beetle, Tribolium castaneum, dsRNA-mediated gene silencing of Forkhead box protein O (FoxO) resulted in reduced food intake and larval mass and this agreed with a reduction in the expression of insulin signaling-related genes (insulin-like peptides 2, 3, 4, and chico). Interestingly, we also observed a significant delay in the moment of the pupation and these FoxO-silenced larvae then turned brown at the middle pupal stage followed by death. The observed delay of pupation concurred with a significant delay in 20E titer in dsFoxO-injected larvae and this in turn agreed with a significant delay in expression of prothoracicotropic hormone (ptth) that is a gene stimulating ecdysteroid biosynthesis, and of spook (spo) that is one of the early Halloween genes involved in ecdysteroid biosynthesis. In addition, there was also a delayed expression of the ecdysteroid response gene hormone receptor 3 (HR3). In an attempt to rescue the effects by dsFoxO, injection of 20E into T. castaneum larvae stimulated the expression of HR3 and induced one extra larval-larval molt, confirming the responsiveness for ecdysteroid signaling in dsFoxO-injected larvae. The observations of this project suggest that FoxO is a player in the timing of pupation via the regulating of ecdysteroid biosynthesis, together with the regulation of both insulin signaling and nutrition.

Ultrastructure of male accessory glands in the scorpionfly Sinopanorpa tincta (Navás, 1931) (Mecoptera: Panorpidae)

The ultrastructure of male reproductive accessory glands was investigated in the scorpionfly Sinopanorpa tincta (Navás, 1931) (Mecoptera: Panorpidae) using light and transmission electron microscopy. The male accessory glands comprise one pair of mesodermal glands (mesadenia) and six pairs of ectodermal glands (ectadenia). The former opens into the vasa deferentia and the latter into the ejaculatory sac. The mesadenia consist of a mono-layered elongated columnar epithelium, the cells of which are highly microvillated and extrude secretory granules by means of merocrine mechanisms. The epithelium of ectadenia consists of two types of cells: the large secretory cells and the thin duct-forming cells. These two types of cells that join with a cuticular duct constitute a functional glandular unit, corresponding to the class III glandular cell type of Noirot and Quennedey. The cuticular duct consists of a receiving canal and a conducting canal. The secretory granules were taken up by the receiving canal and then plunged into the lumen through the conducting canal.

RNA interference-mediated knockdown of the Halloween gene Spookiest (CYP307B1) impedes adult eclosion in the western tarnished plant bug, Lygus hesperus

Ecdysteroids play a critical role in coordinating insect growth, development and reproduction. A suite of cytochrome P450 monooxygenases coded by what are collectively termed Halloween genes mediate ecdysteroid biosynthesis. In this study, we describe cloning and RNA interference (RNAi)-mediated knockdown of the CYP307B1 Halloween gene (Spookiest) in the western tarnished plant bug, Lygus hesperus. Transcripts for Ly. hesperus Spookiest (LhSpot) were amplified from all life stages and correlated well with timing of the pre-moult ecdysteroid pulse. In adults, LhSpot was amplified from heads of both genders as well as female reproductive tissues. Heterologous expression of a LhSpot fluorescent chimera in cultured insect cells co-localized with a fluorescent marker of the endoplasmic reticulum/secretory pathway. RNAi-mediated knockdown of LhSpot in fifth instars reduced expression of ecdysone-responsive genes E74 and E75, and prevented adult development. This developmental defect was rescued following application of exogenous 20-hydroxyecdysone but not exogenous 7-dehydrocholesterol. The unequivocal RNAi effects on Ly. hesperus development and the phenotypic rescue by 20-hydroxyecdysone are causal proof of the involvement of LhSpot in ecdysteroid biosynthesis and related developmental processes, and may provide an avenue for development of new control measures against Ly. hesperus.

The Drosophila Accessory Gland as a Model for Prostate Cancer and Other Pathologies

The human prostate is a gland of the male reproductive tract, which together with the seminal vesicles, is responsible for most seminal fluid production. It is a common site of cancer, and unlike other glands, it typically enlarges in aging men. In flies, the male accessory glands make many major seminal fluid components. Like their human equivalents, they secrete proteins from several conserved families, including proteases, lectins, and cysteine-rich secretory proteins, some of which interact with sperm and affect fertility. A key protein, sex peptide, is not conserved in vertebrates but plays a central role in mediating long-term effects on females after mating. Although postmitotic, one epithelial cell type in the accessory glands, the secondary cell, continues to grow in adults. It secretes microvesicles called exosomes from the endosomal multivesicular body, which, after mating, fuse with sperm. They also appear to affect female postmating behavior. Remarkably, the human prostate epithelium also secretes exosomes, which fuse to sperm in vitro to modulate their activity. Exosomes from prostate and other cancer cells are increasingly proposed to play fundamental roles in modulating the tumor microenvironment and in metastasis. Here we review a diverse accessory gland literature, which highlights functional analogies between the male reproductive glands of flies and humans, and a critical role for extracellular vesicles in allowing seminal fluid to promote male interests within the female. We postulate that secondary cells and prostate epithelial cells use common mechanisms to control growth, secretion, and signaling, which are relevant to prostate and other cancers, and can be genetically dissected in the uniquely tractable fly model.

Circadian control of prothoracicotropic hormone release in an adult insect and the induction of its rhythmicity by light cues

The insect neuropeptide prothoracicotropic hormone (PTTH) is a critical regulator of larval development. We recently demonstrated that PTTH is also present in adult Rhodnius prolixus and is released by adult brains in vitro with a clear daily rhythm during egg development. Here, we employ a well-established in vitro bioassay, to show that the daily rhythm of PTTH release by brains in vitro is under circadian control since it persists in aperiodic conditions with a free running period of around 24h that is temperature compensated. Prolonged exposure (3weeks) of insects to continuous constant light (LL) completely eliminated PTTH release. Subsequent transfer of such insects from LL to constant darkness (DD) rapidly induced rhythmic PTTH release, indicating that the circadian rhythm of PTTH release is induced by photic cues. Western analysis identified PTTH in the adult hemolymph, suggesting that PTTH acts as a functional neurohormone in the adult insect. Dot blot analysis revealed that PTTH levels in the hemolymph also cycled with a daily rhythm that persisted in DD and was synchronous with the rhythm of PTTH release by brains in vitro. We conclude that the previously documented photosensitive clock in the brain regulates rhythmic PTTH release and thus generates the rhythm seen in the hemolymph. These results emphasize the importance of rhythmic PTTH release in the adult insect and support a role for PTTH in adult physiology and possibly within the adult circadian system.

Hormonal Modulation of Pheromone Detection Enhances Male Courtship Success

During the lifespans of most animals, reproductive maturity and mating activity are highly coordinated. In Drosophila melanogaster, for instance, male fertility increases with age, and older males are known to have a copulation advantage over young ones. The molecular and neural basis of this age-related disparity in mating behavior is unknown. Here, we show that the Or47b odorant receptor is required for the copulation advantage of older males. Notably, the sensitivity of Or47b neurons to a stimulatory pheromone, palmitoleic acid, is low in young males but high in older ones, which accounts for older males' higher courtship intensity. Mechanistically, this age-related sensitization of Or47b neurons requires a reproductive hormone, juvenile hormone, as well as its binding protein Methoprene-tolerant in Or47b neurons. Together, our study identifies a direct neural substrate for juvenile hormone that permits coordination of courtship activity with reproductive maturity to maximize male reproductive fitness.

Transcriptome analysis to identify genes for peptides and proteins involved in immunity and reproduction from male accessory glands and ejaculatory duct of Bactrocera dorsalis

In the male reproductive system of insects, the male accessory glands and ejaculatory duct (MAG/ED) are important organs and their primary function is to enhance the fertility of spermatozoa. Proteins secreted by the MAG/ED are also known to induce post-mating changes and immunity responses in the female insect. To understand the gene expression profile in the MAG/ED of the oriental fruit fly Bactrocera dorsalis (Hendel), that is an important pest in fruits, we performed an Illumina-based deep sequencing of mRNA. This yielded 54,577,630 clean reads corresponding to 4.91Gb total nucleotides that were assembled and clustered to 30,669 unigenes (average 645bp). Among them, 20,419 unigenes were functionally annotated to known proteins/peptides in Gene Orthology, Clusters of Orthologous Groups, Kyoto Encyclopedia of Genes and Genomes pathway databases. Typically, many genes were involved in immunity and these included microbial recognition proteins and antimicrobial peptides. Subsequently, the inducible expression of these immunity-related genes was confirmed by qRT-PCR analysis when insects were challenged with immunity-inducible factors, suggesting their function in guaranteeing fertilization success. Besides, we identified some important reproductive genes such as juvenile hormone- and ecdysteroid-related genes in this de novo assembly. In conclusion, this transcriptomic sequencing of B. dorsalis MAG/ED provides insights to facilitate further functional research of reproduction, immunity and molecular evolution of reproductive proteins in this important agricultural pest.

The endocrine system controlling sexual reproduction in animals: Part of the evolutionary ancient but well conserved immune system?

Drastic changes in hormone titers, in particular of steroid hormones, are intuitively interpreted as necessary and beneficial for optimal functioning of animals. Peaks in progesterone- and estradiol titers that accompany the estrus cycle in female vertebrates as well as in ecdysteroids at each molt and during metamorphosis of holometabolous insects are prominent examples. A recent analysis of insect metamorphosis yielded the view that, in general, a sharp rise in sex steroid hormone titer signals that somewhere in the body some tissue(s) is undergoing programmed cell death/apoptosis. Increased steroid production is part of this process. Typical examples are ovarian follicle cells in female vertebrates and invertebrates and the prothoracic gland cells, the main production site of ecdysteroids in larval insects. A duality emerges: programmed cell death-apoptosis is deleterious at the cellular level, but it may yield beneficial effects at the organismal level. Reconciling both opposites requires reevaluating the probable evolutionary origin and role of peptidic brain hormones that direct steroid hormone synthesis. Do e.g. Luteinizing Hormone in vertebrates and Prothoracicotropic Hormone (PTTH: acting through the Torso receptor) in insects still retain an ancient role as toxins in the early immune system? Does the functional link of some neuropeptides with Ca(2+)-induced apoptosis make sense in endocrine archeology? The endocrine system as a remnant of the ancient immune system is undoubtedly counterintuitive. Yet, we will argue that such paradigm enables the logical framing of many aspects, the endocrine one inclusive of both male and female reproductive physiology.

RNA interference suppression of the receptor tyrosine kinase Torso gene impaired pupation and adult emergence in Leptinotarsa decemlineata

In Drosophila melanogaster prothoracic gland (PG) cells, Torso mediates prothoracicotropic hormone (PTTH)-triggered mitogen activated protein kinase (MAPK) pathway (consisting of four core components Ras, Raf, MEK and ERK) to stimulate ecdysteroidogenesis. In this study, LdTorso, LdRas, LdRaf and LdERK were cloned in Leptinotarsa decemlineata. The four genes were highly or moderately expressed in the larval prothoracic glands. At the first- to third-instar stages, their expression levels were higher just before and right after the molt, and were lower in the mid instars. At the fourth-instar stage, their transcript levels were higher before prepupal stage. RNA interference-mediated knockdown of LdTorso delayed larval development, increased pupal weight, and impaired pupation and adult emergence. Moreover, knockdown of LdTorso decreased the mRNA levels of LdRas, LdRaf and LdERK, repressed the transcription of two ecdysteroidogenesis genes (LdPHM and LdDIB), lowered 20E titer, and downregulated the expression of several 20E-response genes (LdEcR, LdUSP, LdHR3 and LdFTZ-F1). Furthermore, silencing of LdTorso induced the expression of a JH biosynthesis gene LdJHAMT, increased JH titer, and activated the transcription of a JH early-inducible gene LdKr-h1. Thus, our results suggest that Torso transduces PTTH-triggered MAPK signal to regulate ecdysteroidogenesis in the PGs in a non-drosophiline insect.

Recent progress in understanding the role of ecdysteroids in adult insects: Germline development and circadian clock in the fruit fly Drosophila melanogaster

Steroid hormones are one of the major bioactive molecules responsible for the coordinated regulation of biological processes in multicellular organisms. In insects, the principal steroid hormones are ecdysteroids, including 20-hydroxyecdysone. A great deal of research has investigated the roles played by ecdysteroids during insect development, especially the regulatory role in inducing molting and metamorphosis. However, little attention has been paid to the roles of these hormones in post-developmental processes, despite their undisputed presence in the adult insect body. Recently, molecular genetics of the fruit fly Drosophila melanogaster has revealed that ecdysteroid biosynthesis and signaling are indeed active in adult insects, and involved in diverse processes, including oogenesis, stress resistance, longevity, and neuronal activity. In this review, we focus on very recent progress in the understanding of two adult biological events that require ecdysteroid biosynthesis and/or signaling in Drosophila at the molecular level: germline development and the circadian clock.

The silkworm glutathione S-transferase gene noppera-bo is required for ecdysteroid biosynthesis and larval development

Insect molting and metamorphosis are tightly controlled by ecdysteroids, which are important steroid hormones that are synthesized from dietary sterols in the prothoracic gland. One of the ecdysteroidogenic genes in the fruit fly Drosophila melanogaster is noppera-bo (nobo), also known as GSTe14, which encodes a member of the epsilon class of glutathione S-transferases. In D. melanogaster, nobo plays a crucial role in utilizing cholesterol via regulating its transport and/or metabolism in the prothoracic gland. However, it is still not known whether the orthologs of nobo from other insects are also involved in ecdysteroid biosynthesis via cholesterol transport and/or metabolism in the prothoracic gland. Here we report genetic evidence showing that the silkworm Bombyx mori ortholog of nobo (nobo-Bm; GSTe7) is essential for silkworm development. nobo-Bm is predominantly expressed in the prothoracic gland. To assess the functional importance of nobo-Bm, we generated a B. mori genetic mutant of nobo-Bm using TALEN-mediated genome editing. We show that loss of nobo-Bm function causes larval arrest and a glossy cuticle phenotype, which are rescued by the application of 20-hydroxyecdysone. Moreover, the prothoracic gland cells isolated from the nobo-Bm mutant exhibit an abnormal accumulation of 7-dehydrocholesterol, a cholesterol metabolite. These results suggest that the nobo family of glutathione S-transferases is essential for development and for the regulation of sterol utilization in the prothoracic gland in not only the Diptera but also the Lepidoptera. On the other hand, loss of nobo function mutants of D. melanogaster and B. mori abnormally accumulates different sterols, implying that the sterol utilization in the PG is somewhat different between these two insect species.

Initiation of metamorphosis and control of ecdysteroid biosynthesis in insects: The interplay of absence of Juvenile hormone, PTTH, and Ca(2+)-homeostasis

The paradigm saying that release of the brain neuropeptide big prothoracicotropic hormone (PTTH) initiates metamorphosis by activating the Torso-receptor/ERK pathway in larval prothoracic glands (PGs) is widely accepted nowadays. Upon ligand-receptor interaction Ca(2+) enters the PG cells and acts as a secondary messenger. Ecdysteroidogenesis results, later followed by apoptosis. Yet, some data do not fit in this model. In some species decapitated animals can still molt, even repeatedly, and metamorphose. PTTH does not universally occur in all insect species. PGs may also have other functions; PGs as counterpart of the vertebrate thymus? There are also small PTTHs. Finally, PTTH remains abundantly present in adults and plays a role in control of ecdysteroidogenesis (=sex steroid production) in gonads. This is currently documented only in males. This urges a rethinking of the PTTH-PG paradigm. The key question is: Why does PTTH-induced Ca(2+) entry only result in ecdysteroidogenesis and apoptosis in specific cells/tissues, namely the PGs and gonads? Indeed, numerous other neuropeptides also use Ca(2+) as secondary messenger. The recent rediscovery that in both invertebrates and vertebrates at least some isoforms of Ca(2+)-ATPase need the presence of an endogenous farnesol/juvenile hormone(JH)-like sesquiterpenoid for keeping cytosolic [Ca(2+)]i below the limit of apoptosis-induction, triggered the idea that it is not primarily PTTH, but rather the drop to zero of the JH titer that acts as the primordial initiator of metamorphosis by increasing [Ca(2+)]i. PTTH likely potentiates this effect but only in cells expressing Torso. PTTH: an evolutionarily ancient gonadotropin?

RNA interference-mediated silencing of a Halloween gene spookier affects nymph performance in the small brown planthopper Laodelphax striatellus

Post-embryonic development of insects is highly dependent on ecdysteroid hormone 20-hydroxyecdysone. Halloween gene spookier (spok, cyp307a2) has been documented to be involved in ecdysteroidogenesis in Drosophila melanogaster and Bombyx mori. We describe here the cloning and characterization of Halloween gene spookier (Lsspok, Lscyp307a2) in the small brown planthopper Laodelphax striatellus, a hemipteran insect species. LsSPOK has three insect-conserved P450 motifs, that is, Helix-K, PERF motif and heme-binding domain. Temporal and spatial expression patterns of Lsspok were evaluated by quantitative polymerase chain reaction. Through the fouth-instar and the early fifth-instar stages, Lsspok showed two expression peaks in the second- and fifth-day fourth-instar nymphs, and two troughs in the first-day fourth and fifth instars. On day 5 of the fourth-instar nymphs, Lsspok clearly had a high transcript level in the thorax where prothoracic glands were located. Dietary introduction of double-stranded RNA of Lsspok in the nymph stage successfully knocked down the target gene, decreased expression level of ecdysone receptor (LsEcR) gene, caused nymphal lethality and delayed development. Ingestion of 20-hydroxyecdysone in Lsspok-dsRNA-exposed nymphs did not increase Lsspok expression level, but almost completely rescued the LsEcR mRNA level and relieved the negative effects on survival and development. Thus, our data suggest that the ecdysteroidogenic pathway is conserved in insects and LsSPOK is responsible for specific steps in ecdysteroidogenesis in L. striatellus.

Knockdown of Cs-Spook induces delayed larval molting in rice striped stem borer Chilo suppressalis

Spook has essential roles in the biogenesis of the molting hormone 20-hydroxyecdysone (20-E). The function of spook in the rice striped stem borer (SSB) Chilo suppressalis remains unclear, prompting our hypothesis that it exerts actions similar to those reported for other insect species. Here we amplified the full-length transcript of spook (Cs-Spook) in SSB by 5' and 3' rapid amplification of cDNA ends. Cs-Spook has conserved P450 motifs such as Helix-C, Helix-I, Helix-K, and PERF motif (PxxFxPxRF). It was highly expressed in late instar larvae but less so in newly molted larvae. Cs-Spook was highly expressed in prothoracic glands. Cs-Spook was knocked down by dsRNA treatments. Compared with controls, the gene expression level was reduced to 9% at 24 h post injection (PI), 33% at 48 h PI, and 24% at 72 h PI. The ecdysteroid titer decreased significantly in the dsRNA-treated group (P < 0.05), resulting in delayed larval development. The delayed development in dsRNA-treatment group was rescued by treating with 20-E. Our work demonstrates that Cs-Spook participates in the biogenesis of 20-E and regulates the molt of SSB, as seen in other species.

The essence of female-male physiological dimorphism: differential Ca2+-homeostasis enabled by the interplay between farnesol-like endogenous sesquiterpenoids and sex-steroids? The Calcigender paradigm

Ca(2+) is the most omnipresent pollutant on earth, in higher concentrations a real threat to all living cells. When [Ca(2+)]i rises above 100 nM (=resting level), excess Ca(2+) needs to be confined in the SER and mitochondria, or extruded by the different Ca(2+)-ATPases. The evolutionary origin of eggs and sperm cells has a crucial, yet often overlooked link with Ca(2+)-homeostasis. Because there is no goal whatsoever in evolution, gametes did neither originate "with the purpose" of generating a progeny nor of increasing fitness by introducing meiosis. The explanation may simply be that females "invented the trick" to extrude eggs from their body as an escape strategy for getting rid of toxic excess Ca(2+) resulting from a sex-hormone driven increased influx into particular cells and tissues. The production of Ca(2+)-rich milk, seminal fluid in males and all secreted proteins by eukaryotic cells may be similarly explained. This view necessitates an upgrade of the role of the RER-Golgi system in extruding Ca(2+). In the context of insect metamorphosis, it has recently been (re)discovered that (some isoforms of) Ca(2+)-ATPases act as membrane receptors for some types of lipophilic ligands, in particular for endogenous farnesol-like sesquiterpenoids (FLS) and, perhaps, for some steroid hormones as well. A novel paradigm, tentatively named "Calcigender" emerges. Its essence is: gender-specific physiotypes ensue from differential Ca(2+)-homeostasis enabled by genetic differences, farnesol/FLS and sex hormones. Apparently the body of reproducing females gets temporarily more poisoned by Ca(2+) than the male one, a selective benefit rather than a disadvantage.

Development: a deep breath for endocrine organ evolution

Developmental biologists have made surprising discoveries on the evolutionary origins of cell types, organs and body plans. Now, an elegant study in Drosophila raises interesting questions about the origin of two major endocrine organs of insects.

Enzymes for ecdysteroid biosynthesis: their biological functions in insects and beyond

Steroid hormones are responsible for the coordinated regulation of many aspects of biological processes in multicellular organisms. Since the last century, many studies have identified and characterized steroidogenic enzymes in vertebrates, including mammals. However, much less is known about invertebrate steroidogenic enzymes. In the last 15 years, a number of steroidogenic enzymes and their functions have been characterized in ecdysozoan animals, especially in the fruit fly Drosophila melanogaster. In this review, we summarize the latest knowledge of enzymes crucial for synthesizing ecdysteroids, the principal insect steroid hormones. We also discuss the functional conservation and diversity of ecdysteroidogenic enzymes in other insects and even non-insect species, such as nematodes, vertebrates, and lower eukaryotes.

The POU factor ventral veins lacking/Drifter directs the timing of metamorphosis through ecdysteroid and juvenile hormone signaling

Although endocrine changes are known to modulate the timing of major developmental transitions, the genetic mechanisms underlying these changes remain poorly understood. In insects, two developmental hormones, juvenile hormone (JH) and ecdysteroids, are coordinated with each other to induce developmental changes associated with metamorphosis. However, the regulation underlying the coordination of JH and ecdysteroid synthesis remains elusive. Here, we examined the function of a homolog of the vertebrate POU domain protein, Ventral veins lacking (Vvl)/Drifter, in regulating both of these hormonal pathways in the red flour beetle, Tribolium castaneum (Tenebrionidae). RNA interference-mediated silencing of vvl expression led to both precocious metamorphosis and inhibition of molting in the larva. Ectopic application of a JH analog on vvl knockdown larvae delayed the onset of metamorphosis and led to a prolonged larval stage, indicating that Vvl acts upstream of JH signaling. Accordingly, vvl knockdown also reduced the expression of a JH biosynthesis gene, JH acid methyltransferase 3 (jhamt3). In addition, ecdysone titer and the expression of the ecdysone response gene, hormone receptor 3 (HR3), were reduced in vvl knockdown larvae. The expression of the ecdysone biosynthesis gene phantom (phm) and spook (spo) were reduced in vvl knockdown larvae in the anterior and posterior halves, respectively, indicating that Vvl might influence ecdysone biosynthesis in both the prothoracic gland and additional endocrine sources. Injection of 20-hydroxyecdysone (20E) into vvl knockdown larvae could restore the expression of HR3 although molting was never restored. These findings suggest that Vvl coordinates both JH and ecdysteroid biosynthesis as well as molting behavior to influence molting and the timing of metamorphosis. Thus, in both vertebrates and insects, POU factors modulate the production of major neuroendocrine regulators during sexual maturation.

Hormones play major roles in initiating major developmental transitions, such as puberty and metamorphosis. However, how organisms coordinate changes across multiple hormones remains unclear. In this study, we show that silencing the POU domain transcription factor Ventral veins lacking (Vvl)/Drifter in the red flour beetle Tribolium castaneum leads to precocious metamorphosis and an inability to molt. We show that Vvl regulates the biosynthesis and signaling of two key insect developmental hormones, juvenile hormone (JH) and ecdysteroids. Vvl therefore appears to act as a potential central regulator of developmental timing by influencing two major hormones. Because POU factors are known as a major regulator of the onset of puberty, POU factors play a major role during sexual maturation in both vertebrates and insects.

Microarray and RNAi analysis of P450s in Anopheles gambiae male and female steroidogenic tissues: CYP307A1 is required for ecdysteroid synthesis

In insects, the steroid hormone 20-hydroxyecdysone (20E) coordinates major developmental transitions. While the first and the final steps of 20E biosynthesis are characterized, the pathway from 7-dehydrocholesterol to 5β-ketodiol, commonly referred as the “black box”, remains hypothetical and whether there are still unidentified enzymes is unknown. The black box would include some oxidative steps, which are believed to be mediated by P450 enzymes. To identify new enzyme(s) involved in steroid synthesis, we analyzed by small-scale microarray the expression of all the genes encoding P450 enzymes of the malaria mosquito Anopheles gambiae in active steroidogenic organs of adults, ovaries from blood-fed females and male reproductive tracts, compared to inactive steroidogenic organs, ovaries from non-blood-fed females. Some genes encoding P450 enzymes were specifically overexpressed in female ovaries after a blood-meal or in male reproductive tracts but only three genes were found to be overexpressed in active steroidogenic organs of both females and males: cyp307a1, cyp4g16 and cyp6n1. Among these genes, only cyp307a1 has an expression pattern similar to other mosquito steroidogenic genes. Moreover, loss-of-function by transient RNAi targeting cyp307a1 disrupted ecdysteroid production demonstrating that this gene is required for ecdysteroid biosynthesis in Anopheles gambiae.

Molecular cloning and RNA interference-mediated functional characterization of a Halloween gene spook in the white-backed planthopper Sogatella furcifera

Background

Ecdysteroid hormones ecdysone and 20-hydroxyecdysone play fundamental roles in insect postembryonic development and reproduction. Five cytochrome P450 monooxygenases (CYPs), encoded by Halloween genes, have been documented to be involved in the ecdysteroidogenesis in insect species of diverse orders such as Diptera, Lepidoptera and Orthoptera. Up to now, however, the involvement of the Halloween genes in ecdysteroid synthesis has not been confirmed in hemipteran insect species.

Results

In the present paper, a Halloween gene spook (Sfspo, Sfcyp307a1) was cloned in the hemipteran Sogatella furcifera. SfSPO has three insect conserved P450 motifs, i.e., Helix-K, PERF and heme-binding motifs. Temporal and spatial expression patterns of Sfspo were evaluated by qPCR. Sfspo showed three expression peaks in late second-, third- and fourth-instar stages. In contrast, the expression levels were lower and formed three troughs in the newly-molted second-, third- and fourth-instar nymphs. On day 3 of the fourth-instar nymphs, Sfspo clearly had a high transcript level in the thorax where PGs were located. Dietary introduction of double-stranded RNA (dsRNA) of Sfspo into the second instars successfully knocked down the target gene, and greatly reduced expression level of ecdysone receptor (EcR) gene. Moreover, knockdown of Sfspo caused lethality and delayed development during nymphal stages. Furthermore, application of 20-hydroxyecdysone on Sfspo-dsRNA-exposed nymphs did not increase Sfspo expression, but could almost completely rescue SfEcR expression, and relieved the negative effects on nymphal survival and development.

Conclusion

In S. furcifera, Sfspo was cloned and the conservation of SfSPO is valid. Thus, SfSPO is probably also involved in ecdysteroidogenesis for hemiptera.