Estradiol-17β: Tracing its metabolic significance in female fatbody of fifth instar larvae of silkworm, Bombyx mori L (race: Nistari)

Insect Sterols and Steroids

Insects are incapable of biosynthesising sterols de novo so they need to obtain them from their diets or, in certain cases, from symbiotic microorganisms. Sterols serve a structural role in cellular membranes and act as precursors for signalling molecules and defence compounds. Many phytophagous insects dealkylate phytosterols to yield primarily cholesterol, which is also the main sterol that carnivorous and omnivorous insects obtain in their diets. Some phytophagous species have secondarily lost the capacity to dealkylate and consequently use phytosterols for structural and functional roles. The polyhydroxylated steroid hormones of insects, the ecdysteroids, are derived from cholesterol (or phytosterols in non-dealkylating phytophagous species) and regulate many crucial aspects of insect development and reproduction by means of precisely regulated titres resulting from controlled synthesis, storage and further metabolism/excretion. Ecdysteroids differ significantly from vertebrate steroid hormones in their chemical, biochemical and biological properties. Defensive steroids (cardenolides, bufadienolides, cucurbitacins and ecdysteroids) can be accumulated from host plants or biosynthesised within the insect, depending on species, stored in significant amounts in the insect and released when it is attacked. Other allelochemical steroids serve as pheromones. Vertebrate-type steroids have also been conclusively identified from insect sources, but debate continues about their significance. Side chain dealkylation of phytosterols, ecdysteroid metabolism and ecdysteroid mode of action are targets of potential insect control strategies.

Feeding study for the mycotoxin zearalenone in yellow mealworm (Tenebrio molitor) larvae-investigation of biological impact and metabolic conversion

Edible insects as additional food and/or feed source may represent one important component to solve the problem of food security for a growing human population. Especially for covering the rising demand for protein of animal origin, seven insect species currently allowed as feed constituents in the European Union are gaining more interest. However, before considering insects such as yellow mealworm larvae (Tenebrio molitor) as suitable for, e.g. human consumption, the possible presence and accumulation of contaminants must be elucidated. The present work investigates the effects of the mycotoxin zearalenone (ZEN) and its metabolites on insect larvae. Seven different diets were prepared: toxin-free control, spiked and artificially contaminated (both containing approx.500 μg/kg and approx. 2000 μg/kg of ZEN) as well as two naturally contaminated diets (600 μg/kg and 900 μg/kg ZEN). The diets were used in a multiple-week feeding trial using T. molitor larvae as model insects. The amount of ZEN and its metabolites in the feed, larvae and the residue were measured by HPLC-MS/MS. A significantly enhanced individual larval weight was found for the insects fed on the naturally contaminated diets compared to the other feeding groups after 8 weeks of exposure. No ZEN or ZEN metabolites were detected in the T. molitor larvae after harvest. However, ZEN, α- and β-stereoisomers of zearalenol were found in the residue samples indicating an intense metabolism of ZEN in the larvae. No further ZEN metabolites could be detected in any sample. Thus, ZEN is not retained to any significant amount in T. molitor larvae.

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.

Effects of human contraceptive on reproduction and offspring in Chrysomya megacephala

OBJECTIVE

To investigate the effect of human contraceptive (HC) as ability to suppress the reproductive success of blow fly, Chrysomya megacephala (Fabricius) (C. megacephala) and offspring under controlled laboratory conditions.

METHODS

Adult C. megacephala were fed with low (0.036 mg/mL) and high dose (0.072 mg/mL) HC (Microgest®, Thailand), containing levonorgestrel and ethinyl estradiol, in their drinking water for 7 days. Three experiments were set; experiment I with fed only in parental males, experiment II with fed only in parental females and experiment III with fed in both males and females. All experiments were then maintained for 3 generations after crossing and inbreeding.

RESULTS

A lower ovariole production and less fully mature ovarioles were evident in F1, F2 and F3 than control when parent males, females and both had been fed with high dose HC. Cellular changes during spermatogenesis in F1, F2 and F3 testes was confirmed using transmission electron microscopy (TEM), showing the low level of condensed chromatin, necrotic chromatin, irregularities and degenerated nuclear envelope in the nucleus. In the cytoplasm, mitochondrial swelling, rough endoplasmic reticulum swelling as well as vacuolated cytoplasm were noticed. As for the sperm per se, we found the degenerated nuclei and/or incomplete mitochondrial derivative, axoneme and vacuolated flagella. Regarding deformity in F1, F2 and F3 ovariole, ultrastructural alteration observed by scanning electron microscopy (SEM) included malformations involving fragile enveloping peritoneal sheath, cracked ovarioles, peel away chorion, crumbled eggshell and incomplete development; whereas TEM presented malformed and disorganized mass of cells, proteic yolk granules and vacuolated vesicles.

CONCLUSIONS

Administer of HC to adult C. megacephala caused ovariole reduction, less matured ovariole and affected cellular changes in testes and ovariole of offspring up to F3.

Effects of bisphenol A in the ring-legged earwig, Euborellia annulipes

Bisphenol A is a known endocrine disruptor in vertebrates that mimics the action of estrogens by interacting with hormone receptors. It also affects reproduction and development in many invertebrate animals, though mechanisms of action are unclear. Terrestrial insects, despite their abundance and profound ecological significance, have been largely overlooked as a group that might be affected by vertebrate endocrine disrupting chemicals. We evaluated potential effects of bisphenol A on the ring-legged earwig, Euborellia annulipes, as a model for terrestrial arthropods. Dosages of 0, 0.12, 1.2 and 12 microg bisphenol A were injected over a 6 day period into newly eclosed males and newly mated (7-day) females. The lowest dosage (0.12 microg) was most effective in eliciting significant effects including reducing weight gain while increasing testis size and seminal vesicle size; higher dosages were less effective or ineffective. In females, treatment with 0.12 microg bisphenol A enhanced clutch size but higher dosages were required to affect the duration of embryogenesis in offspring of treated mothers. Hatching success and the onset of the second reproductive cycle were not affected by treatments. No gross abnormalities were observed as a result of treatment in the reproductive structures of either males or females. Similarly, injection of varying concentrations of estradiol into males enhanced testis length, though it had no effect on seminal vesicle size. Lastly, we administered bisphenol A in drinking water for up to 2 weeks. Surprisingly, as little as 1 microg/L inhibited testis growth; 100 microg/L inhibited ovarian growth.

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.

Characterization of heat shock protein 90 in the shrimp Metapenaeus ensis: Evidence for its role in the regulation of vitellogenin synthesis

Estrogen hormones play a vital role in the regulation of female reproductive maturation. In oviparous vertebrates, the synthesis of vitellogenin (VTG) is tightly controlled by estrogen hormone signal transduction pathway, which is mediated by estrogen receptor and heat shock protein 90 (Hsp90). In order to investigate whether a similar mechanism exists in crustaceans, the Hsp90 gene was cloned and isolated from the shrimp Metapenaeus ensis by homology cloning strategy. The Hsp90 is 2,524 bp in length, containing an open reading frame of 2,163 bp that encodes a 720 amino acid polypeptide (83 kD). The Hsp90-coding region is interrupted by four introns. MeHsp90 is differentially expressed in eyestalk, ovary, and hepatopancreas at different ovarian maturation stages, and consistently expressed in other tissues including heart, gill, gut, muscle, and central nervous system. In vitro ovary explant assay reveals that MeHsp90 expression in immature ovary can be induced by the addition of exogenous estradiol-17beta, but expression in fully mature ovary exhibits no response to estradiol-17beta treatment. In situ hybridization shows that MeHsp90 is highly expressed in previtellogenic oocytes and its expression decreases with the progress of maturation, and finally stops in late-vitellogenic oocytes. Our results indicate a strong correlation between estrogen hormones and Hsp90 expression in shrimp, suggesting that the expression of VTG may be under the regulation of estrogen hormones through a mechanism similar to that in vertebrates. The result provides insights on the control of vitellogenesis in invertebrates.

Endocrine disrupting chemicals accumulate in earthworms exposed to sewage effluent

Endocrine disrupting chemicals (EDCs) can alter endocrine function in exposed animals. Such critical effects, combined with the ubiquity of EDCs in sewage effluent and potentially in tapwater, have led to concerns that they could be major physiological disruptors for wildlife and more controversially for humans. Although sewage effluent is known to be a rich source of EDCs, there is as yet no evidence for EDC uptake by invertebrates that live within the sewage treatment system. Here, we describe the use of an extraction method and GC-MS for the first time to determine levels of EDCs (e.g., dibutylphthalate, dioctylphthalate, bisphenol-A and 17beta-estradiol) in tissue samples from earthworms (Eisenia fetida) living in sewage percolating filter beds and garden soil. To the best of our knowledge, this is the first such use of these techniques to determine EDCs in tissue samples in any organism. We found significantly higher concentrations of these chemicals in the animals from sewage percolating filter beds. Our data suggest that earthworms can be used as bioindicators for EDCs in these substrates and that the animals accumulate these compounds to levels well above those reported for waste water. The potential transfer into the terrestrial food chain and effects on wildlife are discussed.