"Insects do not have sex hormones": a myth?

Evolutionary history of sexual differentiation mechanism in insects

Alternative splicing underpins functional diversity in proteins and the complexity and diversity of eukaryotes. An example is the doublesex gene, the key transcriptional factor in arthropod sexual differentiation. doublesex is controlled by sex-specific splicing and promotes both male and female differentiation in holometabolan insects, whereas in hemimetabolan species, doublesex has sex-specific isoforms but is not required for female differentiation. How doublesex evolved to be essential for female development remains largely unknown. Here, we investigate ancestral states of doublesex using Thermobia domestica belonging to Zygentoma, the sister group of Pterygota, that is, winged insects. We find that, in T. domestica, doublesex expresses sex-specific isoforms but is only necessary for male differentiation of sexual morphology. This result supports the hypothesis that doublesex initially promoted male differentiation during insect evolution. However, T. domestica doublesex has a short female-specific region and upregulates the expression of vitellogenin homologs in females, suggesting that doublesex may already play some role in female morphogenesis of the common ancestor of Pterygota. Reconstruction of the ancestral sequence and prediction of protein structures show that the female-specific isoform of doublesex has an extended C-terminal disordered region in holometabolan insects but not in nonholometabolan species. We propose that doublesex acquired its function in female morphogenesis through a change in the protein motif structure rather than the emergence of the female-specific exon.

Sexual Dimorphism in Immune Responses and Infection Resistance in Aedes aegypti and Other Hematophagous Insect Vectors

Sexual dimorphism in immune function is prevalent across different species, where males trade their ability to fight pathogens for a practical reproductive function while females favor an extended lifespan. In insects, these differences in immune function reflect an evolutionary life strategy, where females have a presumably more robust immune system than insect males. Here, we evaluate immune functioning in four male and female insect vectors, Aedes aegypti (Diptera, Culicidae), Anopheles aquasalis (Diptera, Culicidae), Lutzomyia longipalpis (Diptera, Psychodidae) and Rhodnius prolixus (Hemiptera, Reduviidae). We show evidence that challenges the concept of immune sexual dimorphism in three of these insect vectors. In the three Diptera species, A. aegypti, A. aquasalis and L. longipalpis that transmit arboviruses, Plasmodium spp. (Haemospororida, Plasmodiidae) and Leishmania spp. (Trypanosomatida, Trypanosomatidae), respectively, unchallenged adult males express higher levels of immune-related genes than adult females and immature developmental stages. The main components of the Toll, IMD, and Jak/STAT pathways and antimicrobial effectors are highly expressed in whole-body males. Additionally, males present lower midgut basal microbiota levels than females. In A. aegypti mosquitoes, the differences in immune gene expression and microbiota levels are established in adult mosquitoes but are not present at the recently emerged adults and pupal stage. Antibiotic treatment does not affect the consistently higher expression of immune genes in males, except defensin, which is reduced significantly after microbiota depletion and restored after re-introduction. Our data suggest that Diptera males have a basal state of activation of the immune system and that activation of a more robust response through systemic immune challenge acutely compromises their survival. The ones who survive clear the infection entirely. Females follow a different strategy where a moderate immune reaction render higher tolerance to infection and survival. In contrast, hematophagous adult males of the Hemiptera vector R. prolixus, which transmits Trypanosoma cruzi, present no differences in immune activation compared to females, suggesting that diet differences between males and females may influence immune sexual dimorphism. These findings expand our understanding of the biology of insect vectors of human pathogens, which can help to direct the development of new strategies to limit vector populations.

Potential risk of organophosphate exposure in male reproductive system of a non-target insect model Drosophila melanogaster

Based on several adverse reports of pesticides on reproductive efficiency of various organisms, studies on "reproductive toxicity" have gained importance. Fecundity, reflecting reproductive success of any organism, is governed by several factors from female and male reproductive systems. This present study explored morphological and biochemical alterations in the male reproductive system of a non-target model organism, Drosophila melanogaster following chronic sub-lethal exposure (1^st instar larvae differentially exposed to 1-6 μg/mL until adulthood) to the organophosphate (OP) pesticide, acephate (chronic LC₅₀ 8.71 μg/mL). This study demonstrates altered testis structure, decreased germ cell viability and gross body weight, increased activities of oxidative stress marker lipid peroxidase (LPO), and the endogenous antioxidant enzyme catalase (CAT)in addition with altered expression of reproductive marker proteins like vitellogenin and mitoferrin in acephate-exposed flies when compared to control counterparts. Altered reproductive behavior, indicated by a significant decline in the number of mating pairs, validates the adverse effect of chronic acephate exposure on male reproduction in the non-target insect model D. melanogaster.

Nature, Calcigender, Nurture: Sex-dependent differential Ca2+ homeostasis as the undervalued third pillar

After many years of sometimes heated discussions, the problem regarding the relative importance of two classical dogmas of the Nature (genes and sex-steroid hormones) versus Nurture (education, teaching-learning etc.) debate, is still awaiting a conclusive solution. Males and females differ in only a few (primordial) genes as is well documented by genomic analyses. However, their sex- and gender-specific behavior and physiology is nevertheless profoundly different, even if they grew up in a similar (educational) environment. By extending the “Calcigender-concept”, originally formulated in 2015, to the simplistic binary Nature versus Nurture concept, a novel framework showing that the sex-steroid hormone-dependent intracellular Calcium concentration is an important third factor may emerge. Although the principles of animal physiology and evolution strongly stress the fact that Nature is always dominant, Nurture can, to a limited extent, play a mitigating role.

Mode of Action of Farnesol, the "Noble Unknown" in Particular in Ca2+ Homeostasis, and Its Juvenile Hormone-Esters in Evolutionary Retrospect

Farnesol, the sesquiterpenoid precursor of insect juvenile hormones (JH) that itself has JH activity, existed already long before animals and their hormones came into being. Although it is omnipresent in all eukaryotes, this molecule remains a "noble unknown" in cell physiology. It is neither documented as a hormone nor as another type of signaling molecule. To date, its function as an intermediate in the synthesis of squalene-cholesterol-steroids in chordates/vertebrates, and of the insect/arthropod JHs, esters of farnesol, in the mevalonate biosynthetic pathway is assumed to be the only one. This assumption neglects that already two decades ago, farnesol has been shown to be a potent endogenous inhibitor of N-type voltage-gated Ca²⁺ channels in some mammalian cell types. The tandem mevalonate pathway and Ca²⁺ channels originated early in eukaryotic evolution, and has since been well conserved, "promoting" it as a ubiquitous player in Ca²⁺ homeostasis in all eukaryotes. This paper accentuates how this drastic change in thinking gained momentum after the discovery by Paroulek and Sláma that the huge amounts of JH I in male accessory glands of the Cecropia moth, are actually synthesized in these glands themselves and not in the corpora allata, the hitherto assumed unique synthesis site of such compounds. In addition, MAG-JHs have no hormonal- but an exocrine function. Here we hypothesize that MAG-JHs may function in protecting the spermatozoa against toxic Ca²⁺ concentrations, and in enabling their flagellum to undulate. They may do so by acting through membrane receptors. Our novel paradigm assigns to farnesol/JHs a function of flexible hydrophobic molecular valves for restricting untimely Ca²⁺-passage through some types of canonical Ca²⁺channels, using covalently bound farnesyl- or geranyl-geranyl group attachment as well as GPCRs-G proteins all containing a prenyl group. The high rotatable bond count, and their horseshoe-shape are instrumental to their valve function. In our paradigm, Met/Tai and Gce, to date generally thought to be the (only) functional (nuclear) receptors for JHs, are classified as probable Ca²⁺-sensitive transcription factors. Some theoretical and practical considerations for possible applications in a medical context will be discussed.

Sexual dimorphism in immunity across animals: a meta-analysis

In animals, sex differences in immunity are proposed to shape variation in infection prevalence and intensity among individuals in a population, with females typically expected to exhibit superior immunity due to life-history trade-offs. We performed a systematic meta-analysis to investigate the magnitude and direction of sex differences in immunity and to identify factors that shape sex-biased immunocompetence. In addition to considering taxonomic and methodological effects as moderators, we assessed age-related effects, which are predicted to occur if sex differences in immunity are due to sex-specific resource allocation trade-offs with reproduction. In a meta-analysis of 584 effects from 124 studies, we found that females exhibit a significantly stronger immune response than do males, but the effect size is relatively small, and became non-significant after controlling for phylogeny. Female-biased immunity was more pronounced in adult than immature animals. More recently published studies did not report significantly smaller effect sizes. Among taxonomic and methodological subsets of the data, some of the largest effect sizes were in insects, further supporting previous suggestions that testosterone is not the only potential driver of sex differences in immunity. Our findings challenge the notion of pervasive biases towards female-biased immunity and the role of testosterone in driving these differences.

Nitrate: An Environmental Endocrine Disruptor? A Review of Evidence and Research Needs

Nitrate is heavily used as an agricultural fertilizer and is today a ubiquitous environmental pollutant. Environmental endocrine effects caused by nitrate have received increasing attention over the last 15 years. Nitrate is hypothesized to interfere with thyroid and steroid hormone homeostasis and developmental and reproductive end points. The current review focuses on aquatic ecotoxicology with emphasis on field and laboratory controlled in vitro and in vivo studies. Furthermore, nitrate is just one of several forms of nitrogen that is present in the environment and many of these are quickly interconvertible. Therefore, the focus is additionally confined to the oxidized nitrogen species (nitrate, nitrite and nitric oxide). We reviewed 26 environmental toxicology studies and our main findings are (1) nitrate has endocrine disrupting properties and hypotheses for mechanisms exist, which warrants for further investigations; (2) there are issues determining actual nitrate-speciation and abundance is not quantified in a number of studies, making links to speciation-specific effects difficult; and (3) more advanced analytical chemistry methodologies are needed both for exposure assessment and in the determination of endocrine biomarkers.

Only two sex forms but multiple gender variants: How to explain?

Are sex and gender interchangeable terms? In classical biology, both are sometimes but not always used on an equal basis for some groups of animals. However, for our own species the Homo sapiens, they are not. A major question is why are there only two types of gametes (sperm- and egg cells), two types of sex steroids, (androgens and estrogens in vertebrates, and two types of ecdysteroids in insects), while the reproduction-related behaviour of the gamete producers displays a much greater variability than just two prominent forms, namely heterosexual males and heterosexual females? It indicates that in addition to a few sex-determining genes ( = the first pillar), other factors play a role. A second possible pillar is the still poorly understood cognitive memory system in which electrical phenomena and its association with the plasma membrane membrane-cytoskeletal complex of cells play a major role (learning, imitation and imprinting). This paper advances a third pillar, that hitherto has been almost completely ignored, namely the cellular Ca²⁺-homeostasis system, more specifically its sex-specific differences. Differential male-female genetics- and hormone-based Ca²⁺-homeostasis with effects on gender-related processes has been named Calcigender before. It will be argued that it follows from the principles of Ca²⁺- physiology and homeostasis that all individuals of a sexually reproducing animal population have a personalized gender behaviour. Thus, subdividing gender-behaviours in hetero-, homo-, bi-, trans- etc. which all result from a differential use of the very same basic physiological principles, is too primitive a system that may yield false sociological interpretations.

Comparing the impacts of sediment-bound bifenthrin on aquatic macroinvertebrates in laboratory bioassays and field microcosms

We conducted two laboratory bioassays and two field microcosm exposures with bifenthrin (a synthetic pyrethroid) in order to evaluate the capacity of single-species laboratory bioassays to predict lethal and sublethal impacts on aquatic invertebrates in microcosms. For the laboratory species, Chironomus tepperi, larval survival was reduced by 24% at 53.66µg/g OC, while adult emergence was reduced at concentrations of 33.33µg/g OC and higher, with a 61% decrease at 77.78µg/g OC and no emergence at 126.67µg/g OC. The abundance of several other microcosm taxa was reduced in the microcosms at a similar concentration range (33.33µg/g OC and above), however there was no impact on the abundance of the congeneric species, Chironomus oppositus. The differences in impacts between test systems were potentially due to both differing species sensitivity and the interaction of ambient temperature with bifenthrin toxicity. Bifenthrin also was associated with early emergence of Chironomus sp. in both test systems, at concentrations of 10µg/g OC and higher (laboratory) and 43.90µg/g OC (microcosm), and with a significant decrease in the proportion of C. oppositus males in a microcosm. These findings indicate that while laboratory bioassays accurately predict many impacts in the field, there are some limitations to the predictive capacity of these tests.

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.

Parasites and steroid hormones: corticosteroid and sex steroid synthesis, their role in the parasite physiology and development

In many cases parasites display highly complex life cycles that include the penetration and permanence of the larva or adults within host organs, but even in those that only have one host, reciprocal, intricate interactions occur. Evidence indicates that steroid hormones have an influence on the development and course of parasitic infections. The host gender's susceptibility to infection, and the related differences in the immune response are good examples of the host-parasite interplay. However, the capacity of these organisms to synthesize their own steroidogenic hormones still has more questions than answers. It is now well-known that many parasites synthesize ecdysteroids, but limited information is available on sex steroid and corticosteroid synthesis. This review intends to summarize some of the existing information in the field. In most, but not all parasitosis the host's hormonal environment determines the susceptibility, the course, and severity of parasite infections. In most cases the infection disturbs the host environment, and activates immune responses that end up affecting the endocrine system. Furthermore, sex steroids and corticosteroids may also directly modify the parasite reproduction and molting. Available information indicates that parasites synthesize some steroid hormones, such as ecdysteroids and sex steroids, and the presence and activity of related enzymes have been demonstrated. More recently, the synthesis of corticosteroid-like compounds has been shown in Taenia solium cysticerci and tapeworms, and in Taenia crassiceps WFU cysticerci. In-depth knowledge of the parasite's endocrine properties will contribute to understand their reproduction and reciprocal interactions with the host, and may also help designing tools to combat the infection in some clinical situations.

Morphological allometry and intersexuality in horsehair-worm-infected mantids, Hierodula formosana (Mantodea: Mantidae)

Parasitic castration is a strategy used by parasites to minimize damage to the host by consuming its reproductive system, which results in the morphological alteration of the host. We determined that the forewing shape and density of the antennal sensilla of field-collected adult male mantids (Hierodula formosana), infected by horsehair worms (Chordodes formosanus) was partially feminized (intersexuality), and both male and female mantids infected by horsehair worms exhibited allometric changes in their wings and walking legs. In addition, the testes of most infected male adults disappeared or reduced in size, whereas the number of ovarioles in infected female adults was unaffected. The infection mainly influenced the structures related to host reproduction and locomotion, suggesting unbalanced energy exploitation and the reduction of parasitic virulence. In addition, the intersexuality of infected male adults indicated that sexual differentiation in insects, which researchers have considered to be an autonomous process, was influenced by the infection. The similarity of the antennae of infected male adults with those of last-instar female nymphs suggested that parasitic juvenilization may cause such feminization, but the mechanism of parasitic influence on insect sex characteristics should be studied further.

Expression of an Androgenic Gland-Specific Insulin-Like Peptide during the Course of Prawn Sexual and Morphotypic Differentiation

The crustacean male-specific androgenic gland (AG) regulates sexual differentiation. In the prawn Macrobrachium rosenbergii, silencing an AG-specific insulin-like encoding transcript (Mr-IAG) inhibited the development of male sexual characters, suggesting that Mr-IAG is a key androgenic hormone. We used recombinant pro-Mr-IAG peptide to generate antibodies that recognized the peptide in AG cells and extracts, as verified by mass spectrometry. We revealed the temporal expression pattern of Mr-IAG and studied its relevance to the timetable of sex differentiation processes in juveniles and after puberty. Mr-IAG was expressed from as early as 20 days after metamorphosis, prior to the appearance of external male sexual characters. Mr-IAG expression was lower in the less reproductively active orange-clawed males than in both the dominant blue-clawed males and the actively sneak mating small males. These results suggest a role for Mr-IAG both in the timing of male sexual differentiation and in regulating reproductive strategies.

Environmental chemical mediated male reproductive toxicity: Drosophila melanogaster as an alternate animal model

Industrialization and indiscriminate use of agrochemicals have increased the human health risk. Recent epidemiological studies raised a concern for male reproduction given their observations of reduced sperm counts and altered semen quality. Interestingly, environmental factors that include various metals, pesticides and their metabolites have been causally linked to such adversities by their presence in the semen at levels that correlate to infertility. The epidemiological observations were further supported by studies in animal models involving various chemicals. Therefore, in this review, we focused on male reproductive toxicity and the adverse effects of different environmental chemicals on male reproduction. However, it is beyond the scope of this review to provide a detailed appraisal of all of the environmental chemicals that have been associated with reproductive toxicity in animals. Here, we provided the evidence for reproductive adversities of some commonly encountered chemicals (pesticides/metals) in the environment. In view of the recent thrust for an alternate to animal models in research, we subsequently discussed the contributions of Drosophila melanogaster as an alternate animal model for quick screening of toxicants for their reproductive toxicity potential. Finally, we emphasized the genetic and molecular tools offered by Drosophila for understanding the mechanisms underlying the male reproductive toxicity.

Regulation and dysregulation of vitellogenin mRNA accumulation in daphnids (Daphnia magna)

The induction of vitellogenin in oviparous vertebrates has become the gold standard biomarker of exposure to estrogenic chemicals in the environment. This biomarker of estrogen exposure also has been used in arthropods, however, little is known of the factors that regulate the expression of vitellogenin in these organisms. We investigated changes in accumulation of mRNA products of the vitellogenin gene Vtg2 in daphnids (Daphnia magna) exposed to a diverse array of chemicals. We further evaluated the involvement of hormonal factors in the regulation of vitellogenin expression that may be targets of xenobiotic chemicals. Expression of the Vtg2 gene was highly responsive to exposure to various chemicals with an expression range spanning approximately four orders of magnitude. Chemicals causing the greatest induction were piperonyl butoxide, chlordane, 4-nonylphenol, cadmium, and chloroform. Among these, only 4-nonylphenol is recognized to be estrogenic. Exposure to several chemicals also suppressed Vtg2 mRNA levels, as much as 100-fold. Suppressive chemicals included cyproterone acetate, acetone, triclosan, and atrazine. Exposure to the estrogens diethylstilbestrol and bisphenol A had little effect on vitellogenin mRNA levels further substantiating that these genes are not induced by estrogen exposure. Exposure to the potent ecdysteroids 20-hydroxyecdysone and ponasterone A revealed that Vtg2 was subject to strong suppressive control by these hormones. Vtg2 mRNA levels were not significantly affected from exposure to several juvenoid hormones. Results indicate that ecdysteroids are suppressors of vitellogenin gene expression and that vitellogenin mRNA levels can be elevated or suppressed in daphnids by xenobiotics that elicit antiecdysteroidal or ecdysteroidal activity, respectively. Importantly, daphnid Vtg2 is not elevated in response to estrogenic activity.

Differential expression of ribosomal protein gene, gonadotrophin releasing hormone gene and Balbiani ring protein gene in silver nanoparticles exposed Chironomus riparius

The eco- and genotoxicity of silver nanoparticles (AgNPs) was investigated in the fourth instar larvae of the aquatic midge, Chironomus riparius. AgNPs did not have acute toxicity in C. riparius, but did exhibited chronic toxicity on development (pupation and emergence failure) and reproduction. Genotoxicity also occurred in AgNPs exposed C. riparius. Differential Display PCR (DD-PCR), based on the Annealing Control Primer (ACP) technique, was conducted to investigate the underlying toxic mechanism, which identified altered gene expression in C. riparius after treatment with AgNPs. The possible toxicity mechanism of AgNPs in C. riparius involves the down regulation of the ribosomal protein gene (CrL15) affecting the ribosomal assembly and consequently, protein synthesis. Up regulation of the gonadotrophin releasing hormone gene (CrGnRH1) might lead to the activation of gonadotrophin releasing hormone mediated signal transduction pathways and reproductive failure. Up regulation of the Balbiani ring protein gene (CrBR2.2) may be an indication of the organism's protection mechanism against the AgNPs. The overall results suggest that the toxicity of AgNPs towards aquatic organisms should be thoroughly investigated to allow for their safe use, as they seem to exhibit important toxicity towards C. riparius.

Wolbachia as an "infectious" extrinsic factor manipulating host signaling pathways

Wolbachia pipientis is a widespread endosymbiont of filarial nematodes and arthropods. While in worms the symbiosis is obligate, in arthropods Wolbachia induces several reproductive manipulations (i.e., cytoplasmic incompatibility, parthenogenesis, feminization of genetic males, and male-killing) in order to increase the number of infected females. These various phenotypic effects may be linked to differences in host physiology, and in particular to endocrine-related processes governing growth, development, and reproduction. Indeed, a number of evidences links Wolbachia symbiosis to insulin and ecdysteroid signaling, two multilayered pathways known to work antagonistically, jointly or even independently for the regulation of different molecular networks. At present it is not clear whether Wolbachia manipulates one pathway, thus affecting other related metabolic networks, or if it targets both pathways, even interacting at several points in each of them. Interestingly, in view of the interplay between hormone signaling and epigenetic machinery, a direct influence of the "infection" on hormonal signaling involving ecdysteroids might be achievable through the manipulation of the host's epigenetic pathways.

Ecotoxicological multilevel-evaluation of the effects of fenbendazole exposure to Chironomus riparius larvae

Veterinary antibiotics may find their way into the aquatic environment through direct or indirect pathways due to their widespread use. Fenbendazole is a benzimidazole anthelmintic that is widely used in veterinary medicine. To evaluate the potential ecological risk of fenbendazole, we examined the molecular and biochemical responses of biomarker genes such as heat shock proteins (HSPs), cytochrome P450 (CYP450), glutathione S-transferases (GSTs) and hemoglobins (Hbs) in Chironomus riparius for long periods. The expression of HSP70, HSP40, HSP90 and CYP450 in C. riparius increased significantly after exposure to all concentrations of fenbendazole evaluated, while the levels of GST and HbA only increased in C. riparius exposed to relatively high concentrations of fenbendazole (30 microg L(-1)). HbB expression did not differ significantly between the control and treatment groups. Exposure to 30 microg L(-1) fenbendazole had significant effects on the survival, growth, sex balance of emergent adults and development of mouthpart deformity in C. riparius. These results should constitute an important contribution to the understanding of the toxicology of fenbendazole in C. riparius. Moreover, the responses of the biomarker genes also provide valuable information that will aid in understanding the effects of fenbendazole in aquatic ecosystems.

Arthropod nuclear receptors and their role in molting

The molting process in arthropods is regulated by steroid hormones acting via nuclear receptor proteins. The most common molting hormone is the ecdysteroid, 20-hydroxyecdysone. The receptors of 20-hydroxyecdysone have also been identified in many arthropod species, and the amino acid sequences determined. The functional molting hormone receptors consist of two members of the nuclear receptor superfamily, namely the ecdysone receptor and the ultraspiracle, although the ecdysone receptor may be functional, in some instances, without the ultraspiracle. Generally, the ecdysone receptor/ultraspiracle heterodimer binds to a number of ecdysone response elements, sequence motifs that reside in the promoter of various ecdysteroid-responsive genes. In the ensuing transcriptional induction, the ecdysone receptor/ultraspiracle complex binds to 20-hydroxyecdysone or to a cognate ligand that, in turn, leads to the release of a corepressor and the recruitment of coactivators. 3D structures of the ligand-binding domains of the ecdysone receptor and the ultraspiracle have been solved for a few insect species. Ecdysone agonists bind to ecdysone receptors specifically, and ligand-ecdysone receptor binding is enhanced in the presence of the ultraspiracle in insects. The basic mode of ecdysteroid receptor action is highly conserved, but substantial functional differences exist among the receptors of individual species. Even though the transcriptional effects are apparently similar for ecdysteroids and nonsteroidal compounds such as diacylhydrazines, the binding shapes are different between them. The compounds having the strongest binding affinity to receptors ordinarily have strong molting hormone activity. The ability of the ecdysone receptor/ultraspiracle complex to manifest the effects of small lipophilic agonists has led to their use as gene switches for medical and agricultural applications.

Can Drosophila melanogaster represent a model system for the detection of reproductive adverse drug reactions?

Once a molecule is identified as a potential drug, the detection of adverse drug reactions is one of the key components of its development and the FDA approval process. We propose using Drosophila melanogaster to screen for reproductive adverse drug reactions in the early stages of drug development. Compared with other non-mammalian models, D. melanogaster has many similarities to the mammalian reproductive system, including putative sex hormones and conserved proteins involved in genitourinary development. Furthermore, the D. melanogaster model would present significant advantages in time efficiency and cost-effectiveness compared with mammalian models. We present data on methotrexate (MTX) reproductive adverse events in multiple animal models, including fruit flies, as proof-of-concept for the use of the D. melanogaster model.

Clock-controlled rhythm of ecdysteroid levels in the haemolymph and testes, and its relation to sperm release in the Egyptian cotton leafworm, Spodoptera littoralis

In Spodoptera littoralis, testicular sperm release occurs in a daily rhythm, which is controlled by endogenous circadian oscillator located in the male reproductive system. Although this rhythm is essential for male fertility, factors that initiate and maintain daily sperm release are not understood. In this study, we investigated a modulatory role for ecdysteroids in the sperm release rhythm and identified the source of ecdysteroids in adult males. We found that the onset of sperm release occurs two days pre-eclosion and coincides with a significant decrease in haemolymph ecdysteroids levels. 20-HE injection into the pupae prior to the first sperm release delayed its initiation and disrupted the developing rhythm in a dose dependent manner. 20-HE injection into adults depressed the number of sperm bundles leaving the testes. A day before the initial sperm release, ecdysteroid levels in the haemolymph and testes begin to oscillate in a circadian fashion. Ecdysteroid rhythms continue throughout imaginal life and correlate with the rhythm of sperm release. In each cycle, testicular sperm release coincides with a trough in testicular ecdysteroid concentration. Rhythmic changes in ecdysteroid levels are regulated by an endogenous circadian oscillator that continues to function in decapitated males. The generation of a complete cycle of ecdysteroid release by testes cultured in vitro indicates that this oscillator is located in the gonads. The haemolymph ecdysteroid levels are significantly lower and arrhythmic in males with removed testes, indicating that the testes are an important ecdysteroid source that may contribute to oscillations in haemolymph ecdysteroid levels.

Anopheles gambiae males produce and transfer the vitellogenic steroid hormone 20-hydroxyecdysone to females during mating

In female insects, the steroid hormone 20-hydroxyecdysone (20E) plays a major role in activating vitellogenesis, a process required for egg development. By contrast with vertebrates, production of large amounts of hormonal steroids has not been reported in adult male insects. In the present study, we analyzed steroidogenesis in both male and female adult of the malaria mosquito Anopheles gambiae and we found that A. gambiae male mosquitoes produce high amounts of the steroid hormone 20E. Importantly, we found that male accessory glands, but not testes, are the source of 20E. Moreover, this steroid hormone is stored in male accessory glands and delivered to females during mating. These findings suggest that male 20E may not act as a true male sex steroid, but more likely as an allohormone. Our results give new insights into species-specific physiological processes that govern the reproductive success of the malaria mosquito. This could thus lead to the identification of new target genes for manipulating male and/or female reproductive success, a promising way to reduce or eliminate mosquito population and therefore to control malaria transmission.

Isovitexin-2'-O-beta-[6-O-E-p-coumaroylglucopyranoside] from UV-B irradiated leaves of rice, Oryza sativa L. inhibits fertility of Helicoverpa armigera

UV-B irradiated rice leaves (Oryza sativa L.) contained four closely related flavonoids, with either an isoorientin or isovitexin aglycone. These flavonoids have previously been purified and characterized, and were added to artificial diets of the African bollworm (Helicoverpa armigera Hübner) at 0.1x concentration found in irradiated rice leaves. Consumption of different diets had relatively small effects on laval, pupal and adult duration, weight and survival, indicating the insects lived near normal life cycles on all diets. However, one of the compounds, flavonoid IIa, isovitexin-2''-O-beta-[6-O-E-p-coumaroylglucopyranoside], dramatically reduced the number of fertile eggs laid to 7% of control insects (P<0.001) when added to insect diets at 18 nmol gFW(-1) (14 ppm). A similar antifertility effect was observed when only the male partner consumed diet containing flavonoid IIa, indicating that the reduced fertility may be male specific. In contrast, the fecundity and fertility of insects eating diets containing the closely related flavonoids, isoorientin-2''-O-beta-[6-O-E-p-coumaroylglucopyranoside] or isoorientin-2''-O-beta-[6-O-E-p-feruloylglucopyranoside], were not significantly different to control diets.

Effects of bisphenol A and ethynyl estradiol exposure on enzyme activities, growth and development in the fourth instar larvae of Chironomus riparius (Diptera, Chironomidae)

This study was conducted to determine the toxic effects of bisphenol A (BPA) and ethynyl estradiol (EE), well-known endocrine disruptors, on Chironomus riparius under controlled laboratory conditions. Mortality, enzyme activities, and growth/development parameters were studied as acute, biochemical, and physiological toxicities, respectively. The results of the present study showed activation of catalase and glutathione-S-transferase after BPA and EE exposure, as well as increased emergence failure after EE exposure. This study on the effects of BPA and EE on C. riparius can be an important addition to the knowledge that has been obtained regarding the toxicology of BPA and EE in aquatic organism, on which limited data are available. The data obtained from this study, however, are not sufficient to establish any correlation or casual relationship between these two compounds and the response of C. riparius. Thus, further research is required to come up with direct experimental demonstrations of the wider relationship between the biochemical effects of BPA and EE on C. riparius and their consequences at higher levels of biological organization.

The neural and genetic substrates of sexual behavior in Drosophila

fruitless (fru), originally identified with its mutant conferring male homosexuality, is a neural sex determination gene in Drosophila that produces sexually dimorphic sets of transcripts. In the nervous system, Fru is translated only in males. Fru proteins likely regulate the transcription of a set of downstream genes. The expression of Fru proteins is sufficient to induce male sexual behavior in females. A group of fru-expressing neurons called "mAL" neurons in the brain shows conspicuous sexual dimorphism. mAL is composed of 5 neurons in females and 30 neurons in males. It includes neurons with bilateral projections in males and contralateral projections in females. Terminal arborization patterns are also sexually dimorphic. These three characteristics are feminized in fru mutant males. The inactivation of cell death genes results in the production of additional mAL neurons that are of the male type in the female brain. This suggests that male-specific Fru inhibits mAL neuron death, leading to the formation of a male-specific neural circuit that underlies male sexual behavior. Fru orchestrates a spectrum of downstream genes as a master control gene to establish the maleness of the brain.

Development of a real-time PCR assay for measurement of yellow protein mRNA transcription in the desert locust Schistocerca gregaria: a basis for isolation of a peptidergic regulatory factor

A major unresolved issue in insect endocrinology concerns the question of whether or not insects have sex hormones. Conclusive evidence in favor of the presence of such hormones awaits the establishment of appropriate bioassays in males. The cuticle of sexually mature males of the desert locust Schistocerca gregaria turns yellow in gregarious conditions only. Neither females nor isolated males ever turn yellow. The yellowing is due to the deposition in the cuticle of a male-specific Yellow Protein (YP), of which the amino acid sequence is known. In this paper, we describe the partial cloning of the cDNA encoding this Yellow Protein. The tissue distribution and temporal expression of the YP-mRNA is studied in detail using RT-PCR. Furthermore, an RT-PCR based bioassay was developed, which may serve as a reliable tool to help identify the hormones controlling the yellowing process. In addition to juvenile hormone, we have shown that a factor present in the brain-corpora cardiaca is involved in the yellow coloration, as injection of an extract induces the expression of YP-mRNA in isolated gregarious males.

Molecular patterns of sex determination in the animal kingdom: a comparative study of the biology of reproduction

Determining sexual fate is an integral part of reproduction, used as a means to enrich the genome. A variety of such regulatory mechanisms have been described so far and some of the more extensively studied ones are being discussed. For the insect order of Hymenoptera, the choice lies between uniparental haploid males and biparental diploid females, originating from unfertilized and fertilized eggs accordingly. This mechanism is also known as single-locus complementary sex determination (slCSD). On the other hand, for Dipterans and Drosophila melanogaster, sex is determined by the ratio of X chromosomes to autosomes and the sex switching gene, sxl. Another model organism whose sex depends on the X:A ratio, Caenorhabditis elegans, has furthermore to provide for the brief period of spermatogenesis in hermaphrodites (XX) without the benefit of the "male" genes of the sex determination pathway. Many reptiles have no discernible sex determining genes. Their sexual fate is determined by the temperature of the environment during the thermosensitive period (TSP) of incubation, which regulates aromatase activity. Variable patterns of sex determination apply in fish and amphibians. In birds, while sex chromosomes do exist, females are the heterogametic (ZW) and males the homogametic sex (ZZ). However, we have yet to decipher which of the two (Z or W) is responsible for the choice between males and females. In mammals, sex determination is based on the presence of two identical (XX) or distinct (XY) gonosomes. This is believed to be the result of a lengthy evolutionary process, emerging from a common ancestral autosomal pair. Indeed, X and Y present different levels of homology in various mammals, supporting the argument of a gradual structural differentiation starting around the SRY region. The latter initiates a gene cascade that results in the formation of a male. Regulation of sex steroid production is also a major result of these genetic interactions. Similar observations have been described not only in mammals, but also in other vertebrates, emphasizing the need for further study of both normal hormonal regulators of sexual phenotype and patterns of epigenetic/environmental disruption.

Synthetic pyrethroid cypermethrin induced cellular damage in reproductive tissues of Drosophila melanogaster: Hsp70 as a marker of cellular damage

We tested a working hypothesis of whether the synthetic pyrethroid cypermethrin, used worldwide for insecticidal purpose, causes adverse effects on reproduction in Drosophila melanogaster. Freshly eclosed first instar larvae of a transgenic strain of Drosophila melanogaster, Bg9, transgenic for hsp70 (hsp70-lacZ), were transferred to different dietary concentrations of the test chemical (0.002, 0.02, 0.2, 0.5, and 50.0 ppm). Larval mortality was observed at the higher dosed groups (0.2, 0.5, and 50.0 ppm). Following pair mating of virgin flies emerging from the treatment groups, a significant (p<0.05) effect on reproduction was observed in the lowest two dietary concentrations of the test chemical as compared to control. The test chemical exhibited a hazardous effect on the reproductive organs of the exposed organism as evident by Hsp70 expression and tissue damage. The impact of damage was comparatively more prominent in male flies than in females. Hsp70 expression was restricted only within the testis lobes of male, while ovary in the female fly did not exhibit any Hsp70 expression. Interestingly, the accessory glands of male flies in these treatment groups reflected intense tissue damage as evident by Trypan Blue staining. This was further corroborated by ultrastructural changes like higher vacuolization and disorganized filamentous bodies in the accessory glands of these groups. The present study indicates a profound effect on reproduction by cypermethrin and suggests the protective role of hsp70.

In Silico Identification of New Secretory Peptide Genes in Drosophila melanogaster

Bioactive peptides play critical roles in regulating most biological processes in animals. The elucidation of the amino acid sequence of these regulatory peptides is crucial for our understanding of animal physiology. Most of the (neuro)peptides currently known were identified by purification and subsequent amino acid sequencing. With the entire genome sequence of some animals now available, it has become possible to predict novel putative peptides. In this way, BLAST (Basic Local Alignment Searching Tool) analysis of the Drosophila melanogaster genome has allowed annotation of 36 secretory peptide genes so far. Peptide precursor genes are, however, poorly predicted by this algorithm, thus prompting an alternative approach described here. With the described searching program we scanned the Drosophila genome for predicted proteins with the structural hallmarks of neuropeptide precursors. As a result, 76 additional putative secretory peptide genes were predicted in addition to the 43 annotated ones. These putative (neuro)peptide genes contain conserved motifs reminiscent of known neuropeptides from other animal species. Peptides that display sequence similarities to the mammalian vasopressin, atrial natriuretic peptide, and prolactin precursors and the invertebrate peptides orcokinin, prothoracicotropic hormones, trypsin modulating oostatic factor, and Drosophila immune induced peptides (DIMs) among others were discovered. Our data hence provide further evidence that many neuropeptide genes were already present in the ancestor of Protostomia and Deuterostomia prior to their divergence. This bioinformatic study opens perspectives for the genome-wide analysis of peptide genes in other eukaryotic model organisms.

Sexual differentiation of identified motor terminals inDrosophila larvae

In Drosophila, we have found that some of the motor terminals in wandering third-instar larvae are sexually differentiated. In three out of the four body-wall muscle fibers that we examined, we found female terminals that produced a larger synaptic response than their male counterparts. The single motor terminal that innervates muscle fiber 5 produces an EPSP that is 69% larger in females than in males. This is due to greater release of transmitter from female than male synaptic terminals because the amplitude of spontaneous miniature EPSPs was similar in male and female muscle fibers. This sexual difference exists throughout the third-instar: it is seen in both early (foraging) and late (wandering) third-instar larvae. The sexual differentiation appears to be neuron specific and not muscle specific because the same axon produces Is terminals on muscle fibers 2 and 4, and both terminals produce larger EPSCs in females than males. Whereas, the Ib terminals innervating muscle fibers 2 and 4 are not sexually differentiated. The differences in transmitter release are not due to differences in the size of the motor terminals. For the terminal on muscle fiber 5 and the Is terminal on muscle fiber 4, there were no differences in terminal length, the number of branches, or the number of synaptic boutons in males compared to females. These sexual differences in neuromuscular synaptic physiology may be related to male-female differences in locomotion.

The screening of chemicals for juvenoid-related endocrine activity using the water flea Daphnia magna

U.S. Environmental Protection Agency is charged with developing a screening and testing paradigm for detecting endocrine toxicity of chemicals that are subject to regulation under the Food Quality Protection and the Safe Drinking Water Acts. In this study, we developed and evaluated a screening assay that could be employed to detect juvenoid-related endocrine-modulating activity in an invertebrate species. Juvenoid activity, anti-juvenoid activity, and juvenoid potentiator activity of chemicals was assessed using the water flea Daphnia magna. Male sex determination is under the regulatory control of juvenoid hormone, presumably methyl farnesoate, and this endpoint was used to detect juvenoid modulating activity of chemicals. Eighteen chemicals were evaluated for juvenoid agonist activity. Positive responses were detected with the juvenoid hormones methyl farnesoate and juvenile hormone III along with the insect growth regulating insecticides pyriproxyfen, fenoxycarb, and methoprene. Weak juvenoid activity also was detected with the cyclodiene insecticide dieldrin. Assays performed repetitively with compounds that gave either strong positive, weak positive, or negative response were 100% consistent indicating that the assay is not prone to false positive or negative responses. Five candidate chemicals were evaluated for anti-juvenoid activity and none registered positive. Four chemicals (all trans-retinoic acid, methoprene, kinoprene, bisphenol A) also were evaluated for their ability to potentiate the activity of methyl farnesoate. All registered positive. Results demonstrate that an in vivo assay with a crustacean species customarily employed in toxicity testing can be used to effectively screen chemicals for juvenoid-modulating activity.

No evidence of androgenic hormone from the testes of the glowworm, Lampyris noctiluca

The widely accepted concept, stating that insects have no true sex hormones, and that primary as well as secondary sex characteristics are controlled by the genetic inventory of each single cell, is challenged by the report of Naisse, J. [1966a. Contrôle endocrinien de la différenciation sexuelle chez l'Insecte Lampyris noctiluca (Coléoptère Malacoderme Lampyride). I. Rôle androgène des testicules, Arch. Biol. Liège, 77, 139-201] on the discovery of an androgenic hormone in the glowworm, Lampyris noctiluca. This case is of special interest, since it may point to an ancestral mode of sex differentiation in arthropods, considering that androgenic hormones have been discovered and characterized in crustaceans. With the intention to further characterize the androgenic hormone in the glowworm, and to establish a bioassay, we tried to repeat Naisses's transplantation experiments, according to which, androgen producing testes implanted into female larvae should masculinize the female's gonads and all other female features of the sexually strongly dimorphic pupae and beetles. We found, however, that larval development of the glowworm proceeded differently than reported by Naisse, and that sexing of larvae was not possible. Therefore, "blind" transplantations had to be performed. The results of our experiments showed, however, unequivocally, that an androgenic hormone, allegedly synthesized by the apical tissue of larval testes, was not involved in sex differentiation. We found, that in transplants, where testes and ovaries were even located closely to each other, both matured and formed spermatozoa in the testes and vitellogenic oocytes in the ovaries. Masculinization of ovaries was never observed, and the sex of the recipient was always in accordance with the sex of its own gonads. We therefore conclude that Lampyris noctiluca does not synthesize an androgenic hormone in the larval testes, and that sex differentiation is probably regulated as in other insect species. (The apical testis tissue of the glowworm was previously shown to represent progenitors of spermatogonial cyst cells [Balles, S., Maas, U., Sehn, E., Dorn, A., 2002. Testis differentiation in the glowworm, Lampyris noctiluca, with special reference to the apical tissue. J. Morphol. 251, 22-37].).

The NMDA receptor antagonist MK-801 inhibits vitellogenesis in the flesh fly Neobellieria bullata and in the desert locust Schistocerca gregaria

We found that in the flesh fly Neobellieria bullata, vitellogenesis can be inhibited in a dose-dependent way by two injections of 60 microg MK-801/g body mass. In the desert locust Schistocerca gregaria, vitellogenesis can also be fully inhibited but only by repeated injections of 200-400 microg/g body mass. In this species, the inhibition can be overruled by coapplication of juvenile hormone. Vitellogenin bands remained visible in electropherograms of hemolymph of MK-801-treated female locusts, but vitellogenin did not accumulate as might be expected when only its uptake by the oocytes, and not its synthesis by the fat body, would be affected. Whether MK-801 acts by inhibiting juvenile hormone synthesis by the corpora allata remains to be investigated.

Steroid hormone production by parasites: the case of Taenia crassiceps and Taenia solium cysticerci

Many examples of reciprocal endocrine interactions between parasites and hosts have been found in insects, arthropods and mammals. Cysticercosis produced by Taenia solium metacestodes is a widely distributed parasite infection that affects the human and the pig. Taenia crassiceps experimental murine cysticercosis has been used to explore the role of biological factors involved in host-parasite interactions. We had shown that T. crassiceps cysticercosis affects the serum concentration of steroid hormones and the reproduction behavior of the male mice host. In an effort to understand the biology of the parasite, we had investigated the parasite capacity to produce sex steroids. For this purpose, T. crassiceps cysticerci were incubated in the presence of different steroid precursors. TLC and recrystallization procedures showed that testosterone is produced from 3H-androstenedione in cysticerci. The conversion of 3H-testosterone to androstenedione, although present is much less significant. In addition, we had studied the production of testosterone by T. solium cysticerci. For this purpose, cysticerci were dissected from pork meat and incubated as above described. The results showed that T. solium cysticerci also produce testosterone. We have speculated about the importance of androgens in the growth of T. crassiceps cysticerci and found that the addition of the antiandrogen flutamide to the culture media of the parasites significantly decreased 3H-thymidine incorporation. We therefore hypothesized, that the ability of cysticerci to produce testosterone from steroid precursors might be important for the parasite growth and development.

Developmental toxicity of testosterone in the crustacean Daphnia magna involves anti-ecdysteroidal activity

Testosterone has been shown to cause developmental arrest of embryonic daphnids (Daphnia magna). The present study was undertaken to determine whether this toxicity might be due to anti-ecdysteroidal activity associated with testosterone. The effect of testosterone on molt frequency of early instar daphnids was first evaluated to determine whether testosterone interfered with this ecdysteroid-regulated process. Molt frequency was delayed by exposure to testosterone and this effect was mitigated by co-exposure to the ecdysteroid 20-hydroxyecdysone. Testosterone exposure concentrations that interfered with molting also elicited developmental abnormalities among neonatal organisms produced by maternal organisms that were continuously exposed to testosterone or among embryos that were removed from unexposed mothers and exposed directly to the hormone. Embryos were significantly protected against the developmental toxicity of testosterone by co-exposure to 20-hydroxyecdysone. Taken together, these results demonstrated that the embryo toxicity of testosterone to daphnids is due largely to its ability to interfere with ecdysteroid control of development. Experiments next were conducted to determine whether testosterone interfered with ecdysteroidal activity by acting as an ecdysone receptor antagonist or by reducing endogenous ecdysone levels. Testosterone significantly antagonized the action of 20-hydroxyecdysone in an ecdysone-responsive cell line. Testosterone had no discernable effect on endogenous ecdysone levels in daphnids. These results demonstrated that (1). ecdysteroids regulate critical processes in daphnid embryo development, (2). testosterone elicits embryo toxicity to daphnids by interfering with ecdysteroid activity, and (3). ecdysteroid receptor antagonism could be one mechanism by which testosterone elicits these effects.

Feminizing Wolbachia in an insect, Ostrinia furnacalis (Lepidoptera: Crambidae)

Wolbachia, which forms a group of maternally inherited bacteria in arthropods, often cause reproduction alterations in their hosts, such as cytoplasmic incompatibility, parthenogenesis, male-killing, hybrid breakdown and feminization. To date, Wolbachia-induced feminization has been reported only in isopods. Here we report that a Wolbachia strain feminizes an insect host, Ostrinia furnacalis. Among 79 wild females of O. furnacalis examined, Wolbachia infection was detected in 13 females. Twelve of the 13 infected females produced all-female progenies, and this trait was maternally inherited. Tetracycline treatment of thelygenic matrilines resulted in the production of all-male progenies. The present findings indicate that the Wolbachia infection induces feminization of genetic males in O. furnacalis. Differences in the Wolbachia-induced feminization in O. furnacalis and that in isopods are discussed along with the differences in sex determination mechanisms between insects and isopods. Phylogenetic analysis of the wsp gene sequence of Wolbachia suggests independent evolutionary origins for the Wolbachia-induced feminizations in O. furnacalis and in isopods. Our findings over 5 years suggest that the infection has been maintained at a low prevalence in the O. furnacalis population.

Preparation of an active recombinant peptide of crustacean androgenic gland hormone

In crustaceans, male sexual characteristics are induced by a hormone referred to as androgenic gland hormone. We have recently cloned a candidate cDNA in the terrestrial isopod Armadillidium vulgare. In order to prove that this cDNA encodes the hormone, recombinant single-chain precursor molecules consisting of B chain, C peptide and A chain were produced using both baculovirus and bacterial expression systems. Neither recombinant precursors showed activity. Digestion of only the precursor carrying a glycan moiety with lysyl endopeptidase gave a heterodimeric peptide with hormonal activity by removing a part of C peptide. These results indicate that the cDNA encodes the hormone.

Testis differentiation in the glowworm, Lampyris noctiluca, with special reference to the apical tissue

The gonads of Lampyris noctiluca are sexually undifferentiated during the first larval instars. They consist of many gonadal follicles that include the germ stem cells enclosed by the somatic cells of the follicle wall. Follicle wall cells are more numerous at the follicle apices than at the distal parts, but different cell types cannot be distinguished. In male larvae, the appearance of apical follicle tissue, derived from follicle wall cells, marks the onset of testis differentiation. When maximally expressed, the apical tissue occupies about the upper half of the testis follicles and can be observed in larvae of the fifth and sixth instar. The apical tissue is characterized by its "light" appearance (due to poor stainability) caused by the small number cellular organelles, especially a paucity of free ribosomes. Maximal expression of the apical tissue must be very brief, since in most examined fifth and sixth instar larvae the apical tissue is partly or mostly translocated into the center of the upper half of the follicles and spermatogonia then occupy the apical follicle tips. During and after translocation apical cells form projections that grow around clusters of spermatogonia (spermatocysts). Thus, the apical cells transform into spermatocyst envelope cells. They retain their "light" appearance but undergo dramatic subcellular differentiation: smooth ER becomes extremely prominent, forming stacks and whorls of parallel cisternae. Golgi complexes are also conspicuous. The cellular organization suggests secretory activity. The possibility of ecdysteroid production and its function is discussed. The spermatocyst envelope cells persist into the pupal stage. When spermiohistogenesis takes place in cysts, cyst envelope cells show signs of regression. At all stages of testis development apical cells and their derivatives, the spermatocyst envelope cells, phagocytize degenerating spermatogonia. Although this is an important task of these cells, the impressive formation of sER in the cyst envelope cells is indicative of an additional, as yet unknown, function.

The regulation of human corticotrophin-releasing hormone gene expression in the placenta

Corticotrophin-releasing hormone (CRH) is a 41 amino acid neuropeptide that is expressed in the hypothalamus and the human placenta. Placental CRH production has been linked to the determination of gestational length in the human. Although encoded by a single copy gene, CRH expression in the placenta is regulated differently to the hypothalamus. Glucocorticoids stimulate CRH promoter activity in the placenta but inhibit it's activity in the hypothalamus, via mechanisms involving different regions of the CRH promoter. We discuss how various stimuli alter CRH promoter activity and why these responses are unique to the placenta.

Gonadotropins in insects: an overview

Control of gonad development in insects requires juvenile hormone, ecdysteroids, and a peptidic brain gonadotropin(s). Compared to vertebrates, the situation in insects with respect to the molecular structure of gonadotropins is far less uniform. Follicle Stimulating Hormone (FSH) and Luteinizing Hormone (LH) of vertebrates are glycoproteins that are synthezised in the hypothalamus and released from the anterior pituitary. They stimulate gonad development, the production of progesterone or of sex steroids (estrogens, androgens). None of the known insect gonadotropins is a glycoprotein, neither can they be grouped into a single peptide family. In Drosophila, two G-protein coupled receptors, structurally related to the mammalian glycoprotein hormone receptors, have been identified. Nothing is known about their natural ligands. The sex-steroids of insects are likely to be ecdysteroids (20E in females, E in males of some species). Some of the identified gonadotropins speed up vitellogenesis (locust OMP and some -PF/-RFamide peptides) or stimulate ecdysteroid production by the ovaries (locust-OMP and Aedes- OEH) or testis (testis ecdysiotropin of Lymantria). In flies, the only as yet identified gonadotropin is the cAMP-generating peptide of Neobellieria. The seeming absence of uniformity in gonadotropins in insects might be due to a multitude of factors that can stimulate ecdysteroid production and/or to the use of different bioassays. Arch.

Effects of the hormone mimetic insecticide tebufenozide on Chironomus riparius larvae in two different exposure setups

The effects of the molting-hormone agonistic insecticide tebufenozide on larvae of the midge Chironomus riparius Meigen were tested in two different exposure setups. After static contamination of first-instar larvae the NOEC, LOEC, and LC50 values were 13.2, 17.4, and 21.14 microg/L, respectively. Semistatic exposure of fourth-instar larvae revealed a lower susceptibility of elder larvae (NOEC 30 microg/L, LOEC 60 microg/L, and LC50 81.94 microg/L). In both cases mortality was not immediate; the effects were postponed and almost exclusively linked to the processes of pupation and emergence. Pupal mortality in the semistatic exposure scheme was twice as high in males as in females during a 100 microg/L treatment. This sex-specific effect probably resulted from the endocrine activity of tebufenozide. Its detection underlines the suitability of C. riparius as a model organism for investigating effects of endocrine-disrupting chemicals in aquatic insects.

Common phytochemicals are ecdysteroid agonists and antagonists: a possible evolutionary link between vertebrate and invertebrate steroid hormones

Many plant compounds are able to modulate growth and reproduction of herbivores by directly interacting with steroid hormone systems. In insects, several classes of phytochemicals, including the phytoestrogens, interfere with molting and reproduction. We investigated whether the anti-ecdysone activity may be due to interaction with the ecdysone receptor (EcR) using a reporter-gene assay and a cell differentiation assay of an ecdysone-responsive cell line, Cl.8+. We tested rutin (delays molt in insects); four flavones: luteolin and quercetin (metabolites of rutin), and apigenin and chrysin; and three non-flavones, coumestrol and genistein (both estrogenic) and tomatine (alters molt in insects). None of the phytochemicals tested were ecdysone agonists in the reporter-gene assay, but the flavones were able to significantly inhibit EcR-dependent gene transcription. In the Cl.8+ cells, quercetin and coumestrol were mixed agonists/antagonists, while genistein, tomatine and apigenin showed a synergistic effect with ecdysteroid in the reduction of cell growth. We suggest that the rutin effects on molting in insects are most likely due to the metabolites, luteolin or quercetin, while tomatine acts via a non-EcR pathway. Flavones not only interact with EcR and estrogen receptor (ER), but also signal nitrogen-fixing bacteria to form root nodules. The NodD protein which regulates this symbiosis has two ligand-binding domains similar to human ERalpha. The evolutionary significance of these findings are discussed.

The regulation of human corticotrophin-releasing hormone gene expression in the placenta

Corticotrophin-releasing hormone (CRH) is a 41 amino acid neuropeptide that is expressed in the hypothalamus and the human placenta. Placental CRH production has been linked to the determination of gestational length in the human. Although encoded by a single copy gene, CRH expression in the placenta is regulated differently to the hypothalamus. Glucocorticoids stimulate CRH promoter activity in the placenta but inhibit it's activity in the hypothalamus, via mechanisms involving different regions of the CRH promoter. We discuss how various stimuli alter CRH promoter activity and why these responses are unique to the placenta.

Immunological identification of crustacean androgenic gland hormone, a glycopeptide

Androgenic gland hormone (AGH) is known to be responsible for sex differentiation in crustaceans. The amino acid sequence of AGH-active fraction purified from androgenic glands of the terrestrial isopod Armadillidium vulgare was determined by immunoprecipitation employing three types of antibodies raised against differing parts of the amino acid sequence deduced from the putative AGH cDNA sequence. As all antibodies adsorbed AGH activity, it was confirmed that the sequence examined was that of AGH. The affinity of AGH to certain lectins indicated that AGH possesses a carbohydrate moiety, which is in agreement with the observation that AGH possesses an N-glycosylation consensus sequence.

Newly discovered functions for some myotropic neuropeptides in locusts

The field of neuropeptide research in insects during the past twenty years can be characterized by the enormous number of peptides that have been identified. In the locusts, Locusta migratoria and Schistocerca gregaria only, structural information is now available for more than 60 peptides. Quite a number of these peptides were isolated on the basis of their effect on visceral muscle contraction in vitro. A very limited number of reports describe the 'in vivo' function of a myotropic neuropeptide. Moreover, for most of the brain neuropeptides, we ignore whether they have a hormonal function. In this paper, we describe the recently discovered in vivo effects of some of the myotropic peptides, identified in locusts in the past decade. Schistocerca-neuropeptide F accelerates egg development; locustasulfakinin inhibits food intake and [His(7)]-corazonin induces body color pigmentation.

Characterization and cDNA cloning of androgenic gland hormone of the terrestrial isopod Armadillidium vulgare

The sex differentiation in crustaceans is known to be controlled by a peptide hormone called androgenic gland hormone (AGH). AGH was extracted and purified from the androgenic glands (AGs) of the male isopod Armadillidium vulgare by high-performance liquid chromatography. AGH consisted of two peptide chains and their N-terminal amino acid sequences were determined. A cDNA encoding AGH was cloned by PCR and sequenced. The cDNA had an open reading frame of 432 bp, which encoded a preproAGH consisting of a signal peptide (21 residues), B chain (44 residues), C peptide (46 residues), and A chain (29 residues). Through processing, the A and B chains might form a heterodimer interlinked by disulfide bonds. The A chain possessed a putative N-linked glycosylation site. A Northern blot analysis using the cDNA as a probe detected a hybridization signal with 0.8 kb in the RNA preparation only from the AGs.