Synthesis and metabolism of vertebrate-type steroids by tissues of insects: a critical evaluation

Testosterone maintains male longevity and female reproduction in Chrysopa pallens

Vertebrate testosterone, an androgen present in the testes, is essential for male fertility. Vertebrate-type steroid hormones have been identified in insects, but their function remains unknown. Insect vitellogenin (Vg) is usually a female-specific protein involved in reproductive processes. However, males of some species, such as the green lacewing Chrysopa pallens, have Vg. Here, we demonstrated that the knockdown of C. pallens male Vg by RNAi significantly shortened the lifespan of males, suppressed the reproduction of post-mating females, and strikingly reduced the abundance of several immune-related compounds, including testosterone. LC-MS/MS revealed that C. pallens male testosterone had the same structure and molecular mass as vertebrate testosterone. Topical testosterone application partially restored the lifespan of Vg-deficient males and the reproduction of post-mating females. These results suggest that vertebrate-type testosterone maintains male longevity and female reproduction under the control of the male Vg in C. pallens.

GC-MS-based Metabolomics Unravels Metabolites across Larval Development and Diapause of a Specialist Insect

Plant-insect interactions are a driving force into ecosystem evolution and community dynamics. Many insect herbivores enter diapause, a developmental arrest stage in anticipation of adverse conditions, to survive and thrive through seasonal changes. Herein, we investigated the roles of medium- to non-polar metabolites during larval development and diapause in a specialist insect herbivore, Chlosyne lacinia, reared on Aldama robusta leaves. Varying metabolites were determined using gas chromatography-mass spectrometry (GC-MS)-based metabolomics. Sesquiterpenes and steroids were the main metabolites putatively identified in A. robusta leaves, whereas C. lacinia caterpillars were characterized by triterpenes, steroids, fatty acids, and long-chain alkanes. We found out that C. lacinia caterpillars biosynthesized most of the identified steroids and fatty acids from plant-derived ingested metabolites, as well as all triterpenes and long-chain alkanes. Steroids, fatty acids, and long-chain alkanes were detected across all C. lacinia instars and in diapausing caterpillars. Sesquiterpenes and triterpenes were also detected across larval development, yet they were not detected in diapausing caterpillars, which suggested that these metabolites were converted to other molecules prior to the diapause stage. Our findings shed light on the chemical content variation across C. lacinia development and diapause, providing insights into the roles of metabolites in plant-insect interactions.

Sex steroid profile during oocyte development and maturation in the intertidal worm Marphysa madrasi (Polychaeta: Eunicidae) from the east coast of India

Marphysa madrasi is a commercially valuable maturation diet in crustacean aquaculture. This study presents the first detailed investigation of oogenesis in the intertidal polychaete worm M. madrasi and reports the steroid profile during oocyte growth and development. Oogenesis is extraovarian type I, originating from coelomic epithelial cells, with four stages of development - primary growth, early vitellogenic, late vitellogenic, and maturation. The primary growth phase contains oogonial cells and previtellogenic oocyte clusters in the early, mid, and late stages of development form a dispersed ovary attached to blood vessels. The late previtellogenic oocytes detach from the ovary at the onset of vitellogenesis. The detached oocytes complete vitellogenesis and final maturation in the coelomic fluid as solitary free-floating cells without any connection with follicle cells. The worms display asynchronous reproduction with a heterogeneous population of developing oocytes. Steroid extracts from the polychaete homogenates in different stages of oogenesis were identified by HPLC and confirmed by LC-MS/MS. In M. madrasi, two vertebrate-type steroids, pregnenolone (P5) and 17α-hydroxyprogesterone (17-OHP) were detected and quantified. The P5 levels were low in immature worms but increased significantly by ∼ 8.3-fold in the previtellogenic stage and peaked during oocyte maturation. 17-OHP levels were low in immature worms but gradually increase as the oogenesis progress to the primary growth and early vitellogenic phase, with a significant increase (p < 0.001) during the late vitellogenic phase. Although an increase in the concentration of P5 and 17-OHP during vitellogenesis and maturation of oocytes points to a possible role in reproduction, the absence of other vertebrate-type steroids in the investigated polychaete signifies a plausible uptake of P5 and 17-OHP from the environment.

Specialization directs habitat selection responses to a top predator in semiaquatic but not aquatic taxa

Habitat selectivity has become an increasingly acknowledged mechanism shaping the structure of freshwater communities; however, most studies have focused on the effect of predators and competitors, neglecting habitat complexity and specialization. In this study, we examined the habitat selection of semiaquatic (amphibians: Bufonidae; odonates: Libellulidae) and aquatic organisms (true bugs: Notonectidae; diving beetles: Dytiscidae). From each family, we selected one habitat generalist species able to coexist with fish (Bufo bufo, Sympetrum sanguineum, Notonecta glauca, Dytiscus marginalis) and one species specialized in fishless habitats (Bufotes viridis, Sympetrum danae, Notonecta obliqua, Acilius sulcatus). In a mesocosm experiment, we quantified habitat selection decisions in response to the non-consumptive presence of fish (Carassius auratus) and vegetation structure mimicking different successional stages of aquatic habitats (no macrophytes; submerged and floating macrophytes; submerged, floating, and littoral-emergent macrophytes). No congruence between habitat specialists and generalists was observed, but a similar response to fish and vegetation structure defined both semiaquatic and aquatic organisms. While semiaquatic generalists did not distinguish between fish and fishless pools, specialists avoided fish-occupied pools and had a preferred vegetation structure. In aquatic taxa, predator presence affected habitat selection only in combination with vegetation structure, and all species preferred fishless pools with floating and submerged macrophytes. Fish presence triggered avoidance only in the generalist bug N. glauca. Our results highlight the significance of habitat selectivity for structuring freshwater ecosystems and illustrate how habitat selection responses to a top predator are dictated by specialization and life history.

Role of Oxytocin/Vasopressin-Like Peptide and Its Receptor in Vitellogenesis of Mud Crab

Oxytocin (OT)/vasopressin (VP) signaling system is important to the regulation of metabolism, osmoregulation, social behaviours, learning, and memory, while the regulatory mechanism on ovarian development is still unclear in invertebrates. In this study, Spot/vp-like and its receptor (Spot/vpr-like) were identified in the mud crab Scylla paramamosain. Spot/vp-like transcripts were mainly expressed in the nervous tissues, midgut, gill, hepatopancreas, and ovary, while Spot/vpr-like were widespread in various tissues including the hepatopancreas, ovary, and hemocytes. In situ hybridisation revealed that Spot/vp-like mRNA was mainly detected in 6–9th clusters in the cerebral ganglion, and oocytes and follicular cells in the ovary, while Spot/vpr-like was found to localise in F-cells in the hepatopancreas and oocytes in the ovary. In vitro experiment showed that the mRNA expression level of Spvg in the hepatopancreas, Spvgr in the ovary, and 17β-estradiol (E₂) content in culture medium were significantly declined with the administration of synthetic SpOT/VP-like peptide. Besides, after the injection of SpOT/VP-like peptide, it led to the significantly reduced expression of Spvg in the hepatopancreas and subduced E₂ content in the haemolymph in the crabs. In brief, SpOT/VP signaling system might inhibit vitellogenesis through neuroendocrine and autocrine/paracrine modes, which may be realised by inhibiting the release of E₂.

Involvement of Ecdysone Signaling in the Expression of the doublesex Gene during Embryonic Development in the Silkworm, Bombyx mori

Steroid hormones, represented by estrogen and testosterone, act as sex hormones that play an essential role in the sexual differentiation of vertebrates. However, it remains unclear whether ecdysteroids, typical steroid hormones in insects, function as sex hormones. In this study, we investigated whether ecdysteroids or ecdysone signals are involved in the sexual differentiation of the silkworm (Bombyx mori) embryo. Quantitative analysis using LC-MS/MS demonstrated that there was no significant difference in the 20-hydroxyecdysone (20E) titer between sexes during embryonic development. Consistent with this result, expression levels of 2 genes encoding ecdysteroid-phosphate phosphatase (EPPase) and ecdysone 20-hydroxylase (E20OHase), which are essential for the biosynthesis of ecdysone and 20E in eggs, did not show a significant difference between male and female embryos. Expression levels of ecdysone receptor (EcR) and E75, which is one of a small set of genes induced directly by 20E, were also similar between the 2 sexes. However, knockdown of EPPase and one isoform of EcR (EcR-A) resulted in decreased expression of Bombyx doublesex (Bmdsx), a master regulatory gene for sexual differentiation of the silkworm in both male and female embryos. In vitro analysis with cultured testes revealed that expression levels of Bmdsx were increased in a dose-dependent manner of the ecdysone analog, ponasterone A. These results suggest that ecdysone signaling may play a role in indirectly regulating the expression of some genes involved in sexual differentiation through inducing expression of Bmdsx in the silkworm.

The synthesis of steroids by Taenia crassiceps WFU cysticerci and tapeworms is related to the developmental stages of the parasites

Taeniids tapeworms are hermaphroditic helminths that gradually develop testis and ovaries in their reproductive units. The larval stage of the tapeworms named cysticercus is a vesicle that contains the scolex and proliferates asexually in the abdominal cavity of mice. Once in the host, they evaginate, attach to the gut and develop into an adult organism, the tapeworm. We have previously reported reported that T. crassiceps ORF and solium cysticerci transform steroid precursors to androgens and estrogens. Taenia crassiceps WFU cysticerci can also synthesize corticosteroids. The aim of the present work is to investigate the relationship between steroid synthesis ability and the developmental stage of the parasite T. crassiceps WFU. To this purpose, cysticerci were obtained from the abdominal cavity of female mice, manually separated in invaginated (IC) and evaginated parasites (EC) and preincubated for 24 h in DMEM plus antibiotics/antimycotics. Next step consisted in incubation for different periods in the fresh media added with tritiated androstenedione (³H-A₄) or progesterone (³H-P₄) and incubated for different periods. Taenia crassiceps WFU tapeworms were recovered from the intestine of golden hamsters that had been orally infected with cysticerci. The worms were pre-cultured in DMEM plus FBS and antibiotics, and then incubated without FBS for different time periods, in the presence of ³H-A₄ or ³H-P₄. At the end of the experiments the media from cysticerci and tapeworms were analyzed by thin layer chromatography. Results showed that testosterone synthesis was significantly higher in the evaginated cysticerci and increased with time in culture. The invaginated and evaginated cysticerci also synthesized small quantities of 17ß-estradiol (E₂) and estrone. The evaginated cysticerci synthesized twice more ³H-deoxycorticosterone (³H-DOC) than the invaginated parasites, the production increased significantly with time in culture. Taenia crassiceps WFU tapeworms synthesized significant quantities of ³H-testosterone and small amounts of estrone after only 3 h of culture in the presence of ³H-A₄. The tapeworms also transformed ³H-P₄ to ³H-DOC and increased its synthesis after 24 h in culture. In summary, our data show the pathways that T. crassiceps WFU cysticerci use to synthesize sexual steroids in both larval developmental stages and reveals the steroidogenic capacity of the tapeworms.

Molecular cloning and distribution of oxytocin/vasopressin-like mRNA in the blue swimming crab, Portunus pelagicus, and its inhibitory effect on ovarian steroid release

This study was aimed to characterize the full length of mRNA of oxytocin/vasopressin (OT/VP)-like mRNA in female Portunus pelagicus (PpelOT/VP-like mRNA) using a partial PpelOT/VP-like sequence obtained previously in our transcriptome analysis (Saetan, 2014) to construct the primers. The PpelOT/VP-like mRNA was 626 bp long and it encoded the preprohormones containing 158 amino acids. This preprohormone consisted of a signal peptide, an active nonapeptide (CFITNCPPG) followed by the dibasic cleavage site (GKR), and the neurophysin domain. Sequence alignment of the PpelOT/VP-like peptide with those of other animals revealed strong molecular conservation. Phylogenetic analysis of encoded proteins revealed that the PpelOT/VP-like peptide was clustered within the group of crustacean OT/VP-like peptide. Analysis by RT-PCR revealed the expression of mRNA transcripts in the eyestalk, brain, ventral nerve cord (VNC), ovary, intestine and gill. The in situ hybridization demonstrated the cellular localizations of the transcripts in the central nervous system (CNS) and ovary tissues. In the eyestalk, the mRNA expression was observed in the neuronal clusters 1-5 but not in the sinus gland complex. In the brain and the VNC, the transcripts were detected in all neuronal clusters but not in the glial cell. In the ovary, the transcripts were found in all stages of oocytes (Oc1, Oc2, Oc3, and Oc4). In addition, synthetic PpelOT/VP-like peptide could inhibit steroid release from the ovary. The knowledge gained from this study will provide more understanding on neuro-endocrinological controls in this crab species.

On gonads and gadflies: the estrus angle

The first sex steroid to be crystallized was the vertebrate ovarian hormone, estrone - a less potent metabolite of 17β-estradiol, which in mammals stimulates the female urge to mate (estrus). The gadfly (Greek oistros) lent its name to the process of estrus, as an insect that bites and torments in classical Greek mythology. With the purification and crystallization of a moult-inducing steroid (ecdysone) from insects, an interesting parallel emerged between mating and moulting in lower mammals and arthropods. Ecdysterone (potent ecdysone metabolite) has anabolic effects in mammalian muscle cells that can be blocked by selective estrogen receptor antagonists. Insects utilize ecdysteroids in similar ways that vertebrates use estrogens, including stimulation of oocyte growth and maturation. Ecdysteroids also modify precopulatory insect mating behaviour, further reinforcing the gonad-gadfly/mate-moult analogy.

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.

Vertebrate estrogen regulates the development of female characteristics in silkworm, Bombyx mori

The vertebrate estrogens include 17-β-estradiol (E2), which has an analog in silkworm ovaries. In this study, the Bombyx mori vitellogenin gene (BmVg) was used as a biomarker to analyze the function of the E2 in silkworm. In most oviparous animals, Vg has female-specific expression. However, BmVg expression was also detected in B. mori males. Stage specific fluctuation of BmVg expression was similar in males and females, but expression levels in males were lower than in females. E2 treatment by injection or feeding of male larvae in the final instar stage induced and stimulated male BmVg transcription and protein synthesis. When silkworm ovary primordia were transplanted into males, BmVg was induced in male fat bodies. Transplanted ovaries primordia were also able to develop into ovaries and produce mature eggs. When females were treated with E2 promoted BmVg/BmVn protein accumulation in hemolymph, ovaries and eggs. However, BmVg transcription was decreased in female fat bodies. An E2 analog was identified in the hemolymph of day 3 wandering silkworms using high-performance liquid chromatography. Estradiol titers from fifth late-instar larvae to pupal stage were determined by enzyme-linked immunosorbent assay. The results suggested that silkworms synthesized a vertebrate E2 analog. This study found that E2 promoted the synthesis of BmVg, a female typical protein in silkworms.

Farnesol-like endogenous sesquiterpenoids in vertebrates: the probable but overlooked functional "inbrome" anti-aging counterpart of juvenile hormone of insects?

Literature on the question whether the juvenile stage of vertebrates is hormonally regulated is scarce. It seems to be intuitively assumed that this stage of development is automated, and does not require any specific hormone(s). Such reasoning mimics the state of affairs in insects until it was shown that surgical removal of a tiny pair of glands in the head, the corpora allata, ended larval life and initiated metamorphosis. Decades later, the responsible hormone was found and named "juvenile hormone" (JH) because when present, it makes a larva molt into another larval stage. JH is a simple ester of farnesol, a sesquiterpenoid present in all eukaryotes. Whereas vertebrates do not have an anatomical counterpart of the corpora allata, their tissues do contain farnesol-like sesquiterpenoids (FLS). Some display typical JH activity when tested in appropriate insect bioassays. Some FLS are intermediates in the biosynthetic pathway of cholesterol, a compound that insects and nematodes (=Ecdysozoa) cannot synthesize by themselves. They ingest it as a vitamin. Until a recent (2014) reexamination of the basic principle underlying insect metamorphosis, it had been completely overlooked that the Ca(2+)-pump (SERCA) blocker thapsigargin is a sesquiterpenoid that mimics the absence of JH in inducing apoptosis. In our opinion, being in the juvenile state is primarily controlled by endogenous FLS that participate in controlling the activity of Ca(2+)-ATPases in the sarco(endo)plasmic reticulum (SERCAs), not only in insects but in all eukaryotes. Understanding the control mechanisms of being in the juvenile state may boost research not only in developmental biology in general, but also in diseases that develop after the juvenile stage, e.g., Alzheimer's disease. It may also help to better understand some of the causes of obesity, a syndrome that holometabolous last larval insects severely suffer from, and for which they found a very drastic but efficient solution, namely metamorphosis.

Endocrine archeology: do insects retain ancestrally inherited counterparts of the vertebrate releasing hormones GnRH, GHRH, TRH, and CRF?

Vertebrate releasing hormones include gonadotropin releasing hormone (GnRH), growth hormone releasing hormone (GHRH), corticotropin releasing hormone (CRF), and thyrotropin-releasing hormone (TRH). They are synthesized in the hypothalamus and stimulate the release of pituitary hormones. Here we review the knowledge on hormone releasing systems in the protostomian lineage. We address the question: do insects have peptides that may be phylogenetically related to an ancestral GnRH, GHRH, TRH, and CRF? Such endocrine archeology has become possible thanks to the growing list of fully sequenced genomes as well as to the continuously improving bioinformatic tool set. It has recently been shown that the ecdysozoan (nematodes and arthropods) adipokinetic hormones (AKHs), the lophotrochozoan (annelids and mollusks) GnRHs as well as the protochordate GnRHs are structurally related. The adipokinetic hormone precursor-related peptides (APRPs), in locusts encoded by the same gene that contains the AKH-coding region, have been forwarded as the structural counterpart of GHRH of vertebrates. CRF is relatively well conserved in insects, in which it functions as a diuretic hormone. Members of TRH-receptor family seem to have been conserved in some arthropods, but other elements of the thyroid hormone signaling system are not. A challenging idea is that in insects the functions of the thyroid hormones were taken over by juvenile hormone (JH). Our reconstruction suggests that, perhaps, the ancestral releasing hormone precursors played a role in controlling energy metabolism and water balance, and that releasing hormone functions as present in extant vertebrates were probably secondarily acquired.

Fecal hormones measured within giant Pacific octopuses Enteroctopus dofleini

The captive husbandry of giant Pacific octopuses Enteroctopus dofleini is well understood, but their endocrine signatures are not well documented. The major vertebrate reproductive hormones--estrogen, progesterone, and testosterone--and the stress-related hormone corticosterone are relatively well known for many vertebrate species. However, few studies on these hormones within invertebrates have been conducted. Our hypothesis was that endocrine signatures within octopuses are similar to those found within vertebrates in response to reproductive activity and stress. Using standard immunoassay techniques, we measured fecal steroids within fecal samples collected from five female and three male giant Pacific octopuses housed at the Seattle Aquarium. The mean estrogen level ranged from 3.67 to 99.39 ng/g of feces, progesterone ranged from 44.35 to 231.71 ng/g feces, testosterone ranged from 9.30 to 18.18 ng/g feces, and corticosterone ranged from 10.91 to 22.14 ng/g feces. The results suggest that octopus fecal hormones are similar to those in vertebrates and may be useful in measuring ovarian activity and stress within captive female giant Pacific octopuses.

The endocrine control of reproduction in Nereidae: a new multi-hormonal model with implications for their functional role in a changing environment

Nereidae are vital to the functioning of estuarine ecosystems and are major components in the diets of over-wintering birds and commercial fish. They use environmental cues to synchronize reproduction. Photoperiod is the proximate cue, initiating vitellogenesis in a temperature-compensated process. The prevailing paradigm in Nereidae is of a single 'juvenile' hormone controlling growth and reproduction. However, a new multi-hormone model is presented here that integrates the environmental and endocrine control of reproduction. This is supported by evidence from in vitro bioassays. The juvenile hormone is shown to be heat stable and cross reactive between species. In addition, a second neuro-hormone, identified here as a gonadotrophic hormone, is shown to be present in mature females and is found to promote oocyte growth. Furthermore, dopamine and melatonin appear to switch off the juvenile hormone while serotonin and oxytocin promote oocyte growth. Global warming is likely to uncouple the phase relationship between temperature and photoperiod, with significant consequences for Nereidae that use photoperiod to cue reproduction during the winter in northern latitudes. Genotypic adaptation of the photoperiodic response may be possible, but significant impacts on fecundity, spawning success and recruitment are likely in response to short-term extreme events. Endocrine-disrupting chemicals may also impact on putative steroid hormone pathways in Nereidae with similar consequences. These impacts may have significant implications for the functional role of Nereidae and highlight the importance of comparative endocrinology studies in these and other invertebrates.

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.

Gonadal ecdysteroidogenesis in arthropoda: occurrence and regulation

Ecdysteroids are multifunctional hormones in male and female arthropods and are stored in oocytes for use during embryogenesis. Ecdysteroid biosynthesis and its hormonal regulation are demonstrated for insect gonads, but not for the gonads of other arthropods. The Y-organ in the cephalothorax of crustaceans and the integument of ticks are sources of secreted ecdysteroids in adults, as in earlier stages, but the tissue source is not known for adults in many arthropod groups. Ecdysteroid metabolism occurs in several tissues of adult arthropods. This review summarizes the evidence for ecdysteroid biosynthesis by gonads and its metabolism in adult arthropods and considers the apparent uniqueness of ecdysteroid hormones in arthropods, given the predominance of vertebrate-type steroids in sister invertebrate groups and vertebrates.

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.

Does gender really matter in contaminant exposure? A case study using invertebrate models

Exposure to contaminants in the environment is indiscriminate and multiple species/populations of all sexes are potentially at risk. In this paper we examine the current information available on gender specific differences in invertebrates following exposure to environmental contaminants. Because of their close association with the environment and diversity of habitats, invertebrates are uniquely at risk for adverse responses to pollutants. Since 97% of all animal species are invertebrates, it would be impossible to cover each of the phyla in this review. Instead, this paper discusses major invertebrate species including insects (Periplaneta americana, Panorpa vulgaris, Lycosa hilaris, Haematobia irritans irritans (L.), and Drosophilia melanogaster), nematodes (Caenorhabditis elegans), crustaceans (Streptocephalus dichotomus, Amphiascus tenuiremis, Microarthridion littorale, Tisbe bulbisetosa, Acartia tonsa, and Palaemonetes pugio), mollusks (Pinctada fucata martensii, Ilyanassa obsoleta, Nucella lapillus, Hinia reticulata, Thais clavigera, and Mercenaria mercenaria), corals (Euphyllia ancora and Montipara capitata), and echinoderms (Asterias rubens) that have been used in studies examining the differences between males and females. Our discussion focuses on gender differences that occur in both toxicokinetic mechanisms (uptake and elimination, metabolism and physiology) and other toxicological endpoints (survival and behavior as well as morphology and development). It will become evident that the endocrine systems of invertebrates have many traits and/or pathways that are comparable to those observed in higher organisms. Yet the sensitivity of some elements of the invertebrate endocrine system, e.g., disruption of neuropeptide hormone signaling following TBT exposure, highlights the uniqueness of their systems and their potential for disruption.

Steroids in aquatic invertebrates

Steroid molecules are present in all invertebrates, and some of them have established hormonal roles: this is the case for ecdysteroids in arthropods and, to a lesser extent, for vertebrate-type steroids in molluscs. Steroids are not only hormones, they may also fulfill many other functions in chemical communication, chemical defense or even digestive physiology. The increasing occurrence of endocrine disruption problems caused by environmental pollutants, which interfere in particular with reproductive physiology of vertebrates but also of invertebrates has made necessary to better understand the endocrine physiology of the latter and the role of steroids in these processes. So many attempts are being made to better understand the endocrine roles of steroids in arthropods and molluscs, and to establish whether they also fulfill similar functions in other invertebrate phyla. At the moment, both the precise identification of these steroids, the determination of their origin (endogenous versus exogenous) and of their mechanism of action are under active investigation. This research takes profit of the development of genome sequencing programs on many invertebrate species, which allow the identification of receptors and/or biosynthetic enzymes, when related to their vertebrate counterparts, but the story is not so simple, as will be exemplified by estrogen receptors of molluscs.

Biochemical changes in dehydrogenase, hydroxylase and tyrosinase of a permethrin-resistant strain of housefly larvae, Musca domestica L

In the present study, a permethrin-resistant strain (ALHF) of housefly was used to understand some enzymic changes in normal biosynthetic pathways after insecticide selection. Aflatoxin B(1) (AFB(1)) as a natural substrate was used to verify the changes on the level of cytochrome P450-dependent monooxygenases and oxido-reductase activities in the ALHF strain compared to an insecticide-susceptible strain, aabys. ALHF yielded three major biotransformation products: aflatoxin B(2a) (AFB(2a)), aflatoxin M(1) (AFM(1)), and aflatoxicol (AFL) by larvae. These principal products were also found in aabys. AFL production rate of ALHF larvae was 5-fold lower than that of aabys. Differences between ALHF larvae and aabys in AFM(1) production were found. ALHF did not differ significantly from aabys in AFB(2a) production. The levels of 17α- and β-hydroxysteroid dehydrogenase (17α- and β-HSD) were also determined to elucidate which type of dehydrogenase activities could be changed. The cytosolic fraction of ALHF larvae yielded about 2-fold higher 17α-estradiol than that of aabys larvae. In contrast, the microsomal fraction of ALHF larvae produced about 2-fold lower amount of 17α-estradiol than that of aabys larvae. The production rate of microsomal fraction of 17β-estradiol ALHF larvae yielded 3-fold lower than that of aabys larvae. Inhibition studies on 17α-HSD and 17β-HSD activities by pyrethroid insecticides showed that there was no inhibition by pyrethroids on the enzyme activity. Therefore, there seems to be no changes on the enzyme structures. Changes on enzyme expression may occur in ALHF larvae in relation to 17α- or β-HSD. To assess biochemical changes of the cuticle formation phenylalanine 4-hydroxylase and tyrosinase activities were determined. The production rate of tyrosine from phenylalanine in ALHF was about 2-fold higher for larvae than that in aabys. l-(dihydroxylphenyl)alanine (DOPA) content was determined in larvae and ALHF possessed 1.6-fold larger amounts of DOPA than aabys. Tyrosinase activity of ALHF larval preparations showed 1.6-fold higher than aabys. In summary, many enzymic changes were found in ALHF strain compared to aabys strain and these changes may be resulted from the permethrin selection.

Esterification of vertebrate-type steroids in the Eastern oyster (Crassostrea virginica)

Characteristics of acyl-coenzyme A (acyl-CoA):steroid acyltransferase from the digestive gland of the oyster Crassostrea virginica were determined by using estradiol (E2) and dehydroepiandrosterone (DHEA) as substrates. The apparent Km and Vmax values for esterification of E2 with the six fatty acid acyl-CoAs tested (C20:4, C18:2, C18:1, C16:1, C18:0, and C16:0) were in the range of 9-17 microM E2 and 35-74 pmol/min/mg protein, respectively. Kinetic parameters for esterification of DHEA (Km: 45-120 microM; Vmax: 30-182 pmol/min/mg protein) showed a lower affinity of the enzyme for this steroid. Formation of endogenous fatty acid esters of steroids by microsomes of digestive gland and gonads incubated in the presence of ATP and CoA was assessed, and at least seven E2 fatty acid esters and five DHEA fatty acid esters were observed. Some peaks eluted at the same retention times as palmitoleoyl-, linoleoyl-, oleoyl/palmitoyl-, and stearoyl-E2; and palmitoleoyl-, oleoyl/palmitoyl-, and stearoyl-DHEA. The same endogenous esters, although in different proportions, were produced by gonadal microsomes. The kinetic parameters for both E2 (Km: 10 microM; Vmax: 38 pmol/min/mg protein) and DHEA (Km: 61 microM; Vmax: 60 pmol/min/mg protein) were similar to those obtained in the digestive gland. Kinetic parameters obtained are similar to those observed in mammals; thus, fatty acid esterification of sex steroids appears to be a well-conserved conjugation pathway during evolution.

Expanded substrate screenings of human and Drosophila type 10 17beta-hydroxysteroid dehydrogenases (HSDs) reveal multiple specificities in bile acid and steroid hormone metabolism: characterization of multifunctional 3alpha/7alpha/7beta/17beta/20beta/21-HSD

17beta-hydroxysteroid dehydrogenases (17beta-HSDs) catalyse the conversion of 17beta-OH (-hydroxy)/17-oxo groups of steroids, and are essential in mammalian hormone physiology. At present, eleven 17beta-HSD isoforms have been defined in mammals, with different tissue-expression and substrate-conversion patterns. We analysed 17beta-HSD type 10 (17beta-HSD10) from humans and Drosophila, the latter known to be essential in development. In addition to the known hydroxyacyl-CoA dehydrogenase, and 3alpha-OH and 17beta-OH activities with sex steroids, we here demonstrate novel activities of 17beta-HSD10. Both species variants oxidize the 20beta-OH and 21-OH groups in C21 steroids, and act as 7beta-OH dehydrogenases of ursodeoxycholic or isoursodeoxycholic acid (also known as 7beta-hydroxylithocholic acid or 7beta-hydroxyisolithocholic acid respectively). Additionally, the human orthologue oxidizes the 7alpha-OH of chenodeoxycholic acid (5beta-cholanic acid, 3alpha,7alpha-diol) and cholic acid (5beta-cholanic acid). These novel substrate specificities are explained by homology models based on the orthologous rat crystal structure, showing a wide hydrophobic cleft, capable of accommodating steroids in different orientations. These properties suggest that the human enzyme is involved in glucocorticoid and gestagen catabolism, and participates in bile acid isomerization. Confocal microscopy and electron microscopy studies reveal that the human form is localized to mitochondria, whereas Drosophila 17beta-HSD10 shows a cytosolic localization pattern, possibly due to an N-terminal sequence difference that in human 17beta-HSD10 constitutes a mitochondrial targeting signal, extending into the Rossmann-fold motif.

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.

Transformation of steroids by Bacillus strains isolated from the foregut of water beetles (Coleoptera: Dytiscidae): II. Metabolism of 3 beta-hydroxypregn-5-en-20-one (pregnenolone)

The in vitro metabolism of pregnenolone by two Bacillus strains (HA-V6-3 and HA-V6-11) isolated from the foregut of the water beetle Agabus affinis (Payk.) was examined in the course of our studies about a possible participation of gut micro-organisms in the biosynthesis of prothoracic defensive steroids of dytiscids. The transformation products were identified by EI GC--MS of culture extracts after derivatization. The dominating reactions were hydroxylations, with 7 alpha-hydroxypregnenolone as the major product. With considerably lower yields, 7 beta- and 15xi-hydroxypregenolone were formed by both strains, while 11, 17 and 16 alpha-hydroxypregnenolone were produced only by HA-V6-3. The occurrence of 7, 11 alpha- and 7 beta, 11 alpha-dihydroxypregnenolone as well as several minor products containing a 17 alpha-OH group proved the capability of HA-V6-11 to hydroxylate pregenenolone at C(11) and C(17) as well. The monohydroxylated 7-OH-pregnenolones were partly oxidized to 7-oxopregnenolone by both strains. In trace amounts, HA-V6-3 performed 3 beta-acetylation of pregnenolone.

Estradiol-17beta in Bombyx mori: possible significance and its effect on silk production

Although estrogen is well known as a vertebrate sex steroid, its presence in insects, including Bombyx mori, raises questions about its precise role in the physiology of insects. It was reported earlier that estradiol-17beta (E(2)) exerts a specific effect on silk-gland function in B. mori and that it may act in a nuclear-mediated way. To evaluate further the effect of E(2) on cocoon characters, larval growth and development, 1µg/g of E(2) was applied topically to the first and second day of fifth instar larvae. This resulted in a significant enhancement of cocoon characters, such as cocoon shell weight, silk filament length per cocoon, denier per filament and reelability of the cocoons, without any adverse effect on fecundity and hatchability. In the present study, E(2) levels in the haemolymph were quantified on different days of the fifth instar larvae and age-dependent changes in the endogenous E(2) titre have been demonstrated. These age-dependent variations in E(2) content coincide with physiological events occurring during the fifth instar. Such observations exclude the possibility of a dietary origin for E(2), as a sudden and sharp rise of the E(2) level in the haemolymph was observed on the 10th day of the fifth instar, preceded by a small increase on the ninth day after an eight-day feeding period. The increased level of estradiol in the haemolymph of larvae treated topically with E(2) indicates effective penetration of this hormone through the larval cuticle. Moreover, similar patterns of alteration of E(2) levels on different days of the fifth instar in both control and treated groups suggests the existence of some internal metabolic pathway in the silkworm body to regulate the hormone titre. Thus, the present investigation offers a system for investigating the unique function of E(2) in B. mori and offers potential for improvement of silk production.

Transformation of steroids by Bacillus strains isolated from the foregut of water beetles (Coleoptera:Dytiscidae): I. Metabolism of androst-4-en-3,17-dione (AD)

Two Bacillus strains were isolated from the foregut of the water beetle Agabus affinis (Payk.) and tested for their steroid transforming ability. After incubation with androst-4-en-3,17-dione (AD), 13 different transformation products were detected. AD was hydroxylated at C6, C7, C11 and C14, resulting in formation of 6beta-, 7alpha-, 11alpha- and 14alpha-hydroxy-AD. One strain also produced small amounts of 6beta,14alpha-dihydroxy-AD. Partly, the 6beta-hydroxy group was further oxidized to the corresponding 6-oxo steroids. In addition, a specific reduction of the delta4-double bond was observed, leading to the formation of 5alpha-androstane derivatives. In minor yields the carbonyl functions at C3 and C17 were reduced leading to the formation of 3zeta-OH or 17beta-OH steroids. EI mass spectra of the trimethylsilyl and O-methyloxime trimethylsilyl ether derivatives of some transformation products are presented for the first time.

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

Mammals have two genes (SRY and DMT1) for testis formation-androgenesis, an anti-testis gene, DAX1, an anti-Müllerian duct hormone, and steroid sex hormones. Drosophila uses the sex-lethal, transformer, and doublesex genes for sexual differentation and is supposed to lack sex hormones. However, the statement that insects do not have sex hormones loses much of its credibility if one considers (1) the classical endocrinological work on sexual differentiation in the firefly Lampyris and in the hevea tussock moth Orgyia; (2) the recent identification of an androgenic hormone and its role in sex determination in the isopod Armadillidium; (3) the similarity between steroidogenic factor 1 (SF-1) of mammals and fushi tarazu factor 1 (FTZ-F1) of Drosophila; and (4) the steroidogenic effect of gonadotropins secreted by the brain of female locusts and mosquitoes and of male gypsy moth. In our model, based on data from the literature, ecdysone, when present in high concentrations, might function as an androgenic sex steroid. It is also the precursor of 20-OH-ecdysone, which is the moulting hormone of insects, and in vitellogenic females of many species, the counterpart of estrogens as well. Other gender-specific hormones are likely to exist in the brain-gonad axis.

Action of estradiol-17beta on the synthetic activity of the silk gland in Bombyx mori L

The effects of estradiol-17beta (E(2)) were studied on several metabolic parameters in the silk gland of Bombyx mori L. race Nistari. Topical application of different doses (0.05-4.0&mgr;g/g body weight) of E(2) on the first and second day of the fifth instar larvae showed a dose dependent effect when studied on the fifth day. A significant increase in silk gland weight and fibroin content was observed between the doses 0.05 and 0.1, and 0.1 and 1.0&mgr;g/g of E(2). A similar pattern of dose-dependent rise in DNA and RNA content of posterior silk gland (PSG) was observed with the doses of E(2) when the contents were expressed per pair of PSG. Higher doses of E(2) (2.0 or 4.0&mgr;g/g) demonstrated relatively less increase, unchanged level or a decrease in the above parameters in comparison to the control values. The glutamate-pyruvate transaminase of PSG showed a significant increase from 0.1 to 2.0&mgr;g/g of E(2) doses in comparison to the control value. Simultaneous injection of ICI-182780 (1.0&mgr;g/g), a very pure and specific antiestrogenic compound, with E(2) (1.0&mgr;g/g) caused a significant counteraction of E(2)-induced increase in silk gland activity, which was reflected in DNA and RNA content of PSG, wet weight and fibroin content of silk gland, and on glutamate-pyruvate transaminase activity. Cycloheximide (0.5&mgr;g/g), a protein synthesis blocker, caused a significant inhibition of the E(2) (1.0&mgr;g/g)-induced silk gland activity when treated along with estradiol. From this study it appears that estradiol has a specific effect on silk gland function and that it may act in a nuclear mediated way.

Progesterone in Periplaneta americana and Neobellieria bullata adults from the procuticle phase until first progeny production

A significant amount of progesterone-like immunoreactive material (150 ng/g) was measured by EIA in the procuticle phase of adult of both sexes of Periplaneta americana. This peak markedly decreased to 1-10 ng/g during sclerotization and was unlikely to be of dietary origin. In the case of 0-hr-old P. americana adults 96-98% of progesterone-like material was localized in the digestive tract and Malpighian tubules. In contrast, a relatively low level of progesterone-like immunoreactive material was measured in 0-hr-old Neobellieria bullata adults. Activity of 3beta-HSD/isomerase converting pregnenolone to progesterone was high (22-43 fmol/mg protein/20 min) in 0-hr-old P. americana adults and significantly fell during sclerotization. High progesterone levels (13-16 ng/g), measured by HPLC-RIA, coexist with high levels of 3beta-HSD/isomerase activity. Orally active human contraceptives (ethisterone, ethynodiol, ethynodiol diacetate, lynestrenol, mestranol, norgestrel, norethynodrel, tamoxifen citrate, and mifepristone) which act on mammalian steroid receptors had no significant effects on progeny production in either polytrophic or meroistic insect ovaries even at concentration of 5000 mg/kg.

Effect of bile on Vibrio parahaemolyticus

Many enteric pathogens are thought to enter a viable but nonculturable state when deprived of nutrients. Virulent strains of the enteric pathogen Vibrio parahaemolyticus are rarely isolated from their low-nutrient aquatic environments, possibly due to their nonculturability. Host factors such as bile may trigger release from dormancy and increase virulence in these strains. In this study, the addition of bile or the bile acid deoxycholic acid to estuarine water-cultured bacteria led to an increase in the direct viable count and colony counts among the virulent strains. This effect was not demonstrated in the nonvirulent strains, and it was reversed by extraction of bile acids with cholestyramine. Bile-treated V. parahaemolyticus had lower levels of intracellular calcium than untreated cells, and this effect coincided with an increase in the number of metabolically active cells. Chelation of intracellular calcium with BAPTA/AM (R. Y. Tsien, Biochemistry 19:2396-2402, 1980) produced similar results. Addition of bile to V. parahaemolyticus cultures in laboratory medium enhanced factors associated with virulence such as Congo red binding, bacterial capsule size, and adherence to epithelial cells. These results suggest that a bile acid-containing environment such as that found in the human host favors growth of virulent strains of V. parahaemolyticus and that bile acids enhance the expression of virulence factors. These effects seem to be mediated by a decrease in intracellular calcium.

Involvement of a 3beta-hydroxysteroid dehydrogenase activity in ecdysteroid biosynthesis

Ecdysteroid biosynthesis was analyzed in vitro using dissociated Y-organ cells from the shore crab Carcinus maenas. 3-Dehydroecdysone (3DE) was detected as a minor secretory product, in addition to the formerly identified end-products 25-deoxyecdysone and ecdysone (E). In conversion studies, 3DE was formed from tritiated 5beta-ketodiol (2,22,25-trideoxyecdysone), 2,22-deoxyecdysone and 2-deoxyecdysone but not from E. Further experiments were performed in order to understand the interconversions between 3-oxo and 3beta-OH compounds in the crab Y-organ. The enzyme involved in 3beta-dehydrogenation was not ecdysone oxidase, a soluble enzyme found in peripheral tissues of many arthropods but it presented strong similarities with 3beta-hydroxysteroid dehydrogenase enzymes from vertebrates: it was membrane-bound and NAD+-dependent. Moreover, a NADH-dependent 3beta-reduction of several 3-oxo-ecdysteroids was obtained using the same microsomal fraction (100,000 x g pellet) of Y-organs, indicating that the reaction might be reversible. As this activity was specific of molting glands, we hypothesize that there is at least one 3beta-hydroxysteroid dehydrogenase enzyme involved in the biosynthetic pathway of ecdysteroids.

Homologies between enzymes involved in steroid and xenobiotic carbonyl reduction in vertebrates, invertebrates and procaryonts

Evidence is reported for the existence of a structurally and functionally related and probably evolutionarily conserved class of membrane-bound liver carbonyl reductases/hydroxysteroid dehydrogenases involved in steroid and xenobiotic carbonyl metabolism. Carbonyl reduction was investigated in liver microsomes of 8 vertebrate species, as well as in insect larvae total homogenate and in purified 3 alpha-hydroxysteroid dehydrogenase preparations of the procaryont Pseudomonas testosteroni, using the ketone compound 2-methyl-1,2 di-(3-pyridyl)-1-propanone (metyrapone) as substrate. The enzyme activities involved in the metyrapone metabolism were screened for their sensitivity to several steroids as inhibitors. In all fractions tested, steroids of the adrostane or pregnane class strongly inhibited xenobiotic carbonyl reduction, whereas only in the insect and procaryotic species could ecdysteroids inhibit this reaction. Immunoblot analysis with antibodies against the respective microsomal mouse liver metyrapone reductase revealed strong crossrections in all fractions tested, even in those of the insect and the procaryont. A similar crossreaction pattern was achieved when the same fractions were incubated with antibodies against 3 alpha-hydroxysteroid dehydrogenase from Pseudomonas testosteroni. The mutual immunoreactivity of the antibody species against proteins from vertebrate liver microsomes, insects and procaryonts suggests the existence of structural homologies within these carbonyl reducing enzymes. This is further confirmed by limited proteolysis of purified microsomal mouse liver carbonyl reductase and subsequent analysis of the peptide fragments with antibodies specifically purified by immunoreactivity against this respective crossreactive antigen. These immunoblot experiments revealed a 22 kDa peptide fragment which was commonly recognized by all antibodies and which might represent a conserved domain of the enzyme.

On the origin of vertebrate-type steroids present in Locusta migratoria: do they originate from the food?

1. This study investigates the origin of vertebrate-type steroids which were reported to be present in Locusta migratoria: are the steroids synthesized by the locust or are they derived from the diet, i.e. grass and rolled oats? 2. It is unlikely that the steroids are synthesized by locust tissues. In vitro incubations of eleven different tissues with labeled pregnenolone or androstenedione did not result in androgen or estrogen synthesis respectively. 3. Steroid synthesis was also not detected when tissues were incubated in the presence of the early precursors cholesterol and isopentenyl pyrophosphate. 4. It is unlikely that the steroids are derived from the diet. Feeding experiments indicate that only low amounts of steroids are capable of crossing the gut-body barrier. 5. Injection of testosterone in the hemolymph also resulted in rapid excretion, instead of storage in tissues. 6. Moreover, radioimmunological measurements indicate that vertebrate-type steroids are absent in the food of locusts. 7. Specificity studies indicate that substances other than vertebrate-type steroids are detected by radioimmunoassay in locust tissue extracts. 8. Because vertebrate-type steroids are absent in locust tissues, it can be concluded that vertebrate-type steroids do not have a physiological function in Locusta.