Multihormonal control of vitellogenesis in lower vertebrates

Microscopic Analysis of Nuclear Speckles in a Viviparous Reptile

Nuclear speckles are compartments enriched in splicing factors present in the nucleoplasm of eucaryote cells. Speckles have been studied in mammalian culture and tissue cells, as well as in some non-mammalian vertebrate cells and invertebrate oocytes. In mammals, their morphology is linked to the transcriptional and splicing activities of the cell through a recruitment mechanism. In rats, speckle morphology depends on the hormonal cycle. In the present work, we explore whether a similar situation is also present in non-mammalian cells during the reproductive cycle. We studied the speckled pattern in several tissues of a viviparous reptile, the lizard Sceloporus torquatus, during two different stages of reproduction. We used immunofluorescence staining against splicing factors in hepatocytes and oviduct epithelium cells and fluorescence and confocal microscopy, as well as ultrastructural immunolocalization and EDTA contrast in Transmission Electron Microscopy. The distribution of splicing factors in the nucleoplasm of oviductal cells and hepatocytes coincides with the nuclear-speckled pattern described in mammals. Ultrastructurally, those cell types display Interchromatin Granule Clusters and Perichromatin Fibers. In addition, the morphology of speckles varies in oviduct cells at the two stages of the reproductive cycle analyzed, paralleling the phenomenon observed in the rat. The results show that the morphology of speckles in reptile cells depends upon the reproductive stage as it occurs in mammals.

Reproductive and Developmental Effects of Sex-Specific Chronic Exposure to Dietary Arsenic in Zebrafish (Danio rerio)

The present study investigated the reproductive and developmental effects of sex-specific chronic exposure to dietary arsenic in zebrafish. Adult zebrafish (Danio rerio) were exposed to environmentally realistic doses of arsenic via diet [0 (control; no added arsenic), 30 (low), 60 (medium), and 100 (high) μg/g dry weight, as arsenite] for 90 days. Following exposure, arsenic-exposed females from each dietary treatment were mated with control males, and similarly, arsenic-exposed males from each dietary treatment were mated with control females. In females, arsenic exposure resulted in a dose-dependent decrease in reproductive performance (fecundity, fertilization success, and hatching success). Moreover, a dose-dependent increase in developmental toxicity (larval deformities and larval mortality) was observed with maternal exposure to arsenic. In contrast, in males, arsenic exposure also induced similar reproductive and developmental toxicity; however, the adverse effects were mainly evident only in the medium and high dietary arsenic treatment groups. We also examined the sex-specific effects of dietary arsenic exposure on the expression of genes that regulate the hypothalamus-pituitary-gonadal-liver (HPG-L) axis in fish. The gene expression results indicated the downregulation of HPG-L axis genes in females irrespective of the arsenic treatment dose; however, the reduced expression of HPG-L axis genes in males was recorded only in the medium and high arsenic treatment groups. These observations suggest that chronic arsenic exposure in either females or males causes reproductive and developmental toxicity in zebrafish. However, these toxic effects are markedly higher in females than in males. Our results also suggest that arsenic can act as an endocrine disruptor and mediate reproductive and developmental toxicity by disrupting the HPG-L axis in zebrafish.

Molecular cloning of estrogen receptor and its function on vitellogenesis in pompano (Trachinotus ovatus)

Estrogen receptors (ERs) play a critical role in vitellogenesis (Vtgs). However, the contribution of each ER for the regulation of vtgs expression was not analyzed clearly in teleosts. In the present study, three ers isoforms (erα, erβ1, and erβ2) were cloned in pompano (Trachinotus ovatus). Real-time PCR and enzyme-linked immunosorbent assay (ELISA) was used to detect the effects of 17β-estradiol (E2) on ERs and Vtgs in the liver of pompano. In vivo injection experiments showed that E2 significantly increased the expressions of ers and vtgs. ER broad spectrum antagonist Fulvestrant significantly attenuated the E2- induced up-regulation of ers and vtgs in a dose-dependent manner. ERα antagonist Methyl-piperidino pyrazole (MPP) significantly attenuated the up-regulation of erα, erβ2, vtg-B and vtg-C, and promoted the expressions of erβ1 and vtg-A. ERβ antagonist Cyclofenil significantly inhibited the expressions of erβ1, erβ2, vtg-A and vtg-C, and promoted the expressions of erα and vtg-B. In addition, E2 significantly increased the protein level of Vtg, while Fulvestrant, MPP and Cyclofenil significantly inhibited the protein level of Vtg in a dose-dependent manner. Our results indicate that E2 may regulate the expression of each vtg with different subtypes of ERs, and shows a distinct compensatory expression effect on the regulation for ers and vtgs, which provides a theoretical basis for reproductive endocrinology study in pompano.

Endocrine disruptive toxicity of cypermethrin in Labeo catla: Involvement of genes and proteins related to the HPG axis

Cypermethrin (CYP) is a synthetic pyrethroid abundantly used in agriculture and aquaculture. It is an established potent endocrine disruptor to fish, yet the molecular mechanism behind its reproductive toxicity remains unclear. In this study, fish Labeo catla (Catla) was exposed to environmentally relevant concentration of CYP (0.7 μg/L) and 0.14 μg/L for 30 days. The changes in circulating sex steroids, genes, and hormones linked to the hypothalamic-pituitary-gonadal (HPG) axis, stress response and associated histological alterations were studied. Significant decline (P < 0.05) in serum 17 beta (β) estradiol (E2), 11 ketotestosterone (11-KT), and brain (FSH and GnRH) were observed in 0.7 μg/L dose of CYP. These effects may be due to the down-regulated expression of the upstream genes of the HPG axis i.e. Kiss 1 and Kiss 2, which further downregulates the expression of the GnRH gene. The decreased level of E2 and 11-KT also affects the vitellogenin (Vtg) gene expression, reducing the production of Vtg, a crucial protein for ovarian development. Principal component analysis (PCA) revealed the relationship between CYP and the biosynthesis of sex steroids. The toxic effect of CYP was also visible in antioxidant enzyme assay and related histological alterations. Overall, the study elucidated that long-term exposure to CYP, even at an environmentally relevant dose, may affect reproductive potential and fish recruitment. The study provides important insights into molecular mechanisms underlying CYP-induced endocrine disruption in fish, and it also raises questions about CYP's potential toxicity at environmentally relevant concentration in terms of understanding ecological risk.

Rescue of bmp15 deficiency in zebrafish by mutation of inha reveals mechanisms of BMP15 regulation of folliculogenesis

As an oocyte-specific growth factor, bone morphogenetic protein 15 (BMP15) plays a critical role in controlling folliculogenesis. However, the mechanism of BMP15 action remains elusive. Using zebrafish as the model, we created a bmp15 mutant using CRISPR/Cas9 and demonstrated that bmp15 deficiency caused a significant delay in follicle activation and puberty onset followed by a complete arrest of follicle development at previtellogenic (PV) stage without yolk accumulation. The mutant females eventually underwent female-to-male sex reversal to become functional males, which was accompanied by a series of changes in secondary sexual characteristics. Interestingly, the blockade of folliculogenesis and sex reversal in bmp15 mutant could be partially rescued by the loss of inhibin (inha-/-). The follicles of double mutant (bmp15-/-;inha-/-) could progress to mid-vitellogenic (MV) stage with yolk accumulation and the fish maintained their femaleness without sex reversal. Transcriptome analysis revealed up-regulation of pathways related to TGF-β signaling and endocytosis in the double mutant follicles. Interestingly, the expression of inhibin/activin βAa subunit (inhbaa) increased significantly in the double mutant ovary. Further knockout of inhbaa in the triple mutant (bmp15-/-;inha-/-;inhbaa-/-) resulted in the loss of yolk granules again. The serum levels of estradiol (E2) and vitellogenin (Vtg) both decreased significantly in bmp15 single mutant females (bmp15-/-), returned to normal in the double mutant (bmp15-/-;inha-/-), but reduced again significantly in the triple mutant (bmp15-/-;inha-/-;inhbaa-/-). E2 treatment could rescue the arrested follicles in bmp15-/-, and fadrozole (a nonsteroidal aromatase inhibitor) treatment blocked yolk accumulation in bmp15-/-;inha-/- fish. The loss of inhbaa also caused a reduction of Vtg receptor-like molecules (e.g., lrp1ab and lrp2a). In summary, the present study provided comprehensive genetic evidence that Bmp15 acts together with the activin-inhibin system in the follicle to control E2 production from the follicle, Vtg biosynthesis in the liver and its uptake by the developing oocytes.

Hormonal and pheromonal studies on amphibians with special reference to metamorphosis and reproductive behavior

In this article, we review studies which have been conducted to investigate the hormonal influence on metamorphosis in bullfrog (Rana catesbeiana) and Japanese toad (Bufo japonicus) larvae, in addition to studies conducted on the hormonal and pheromonal control of reproductive behavior in red-bellied newts (Cynops pyrrhogaster). Metamorphosis was studied with an emphasis on the roles of prolactin (PRL) and thyrotropin (TSH). The release of PRL was shown to be regulated by thyrotropin-releasing hormone (TRH) and that of TSH was evidenced to be regulated by corticotropin-releasing factor. The significance of the fact that the neuropeptide that controls the secretion of TSH is different from those encountered in mammals is discussed in consideration of the observation that the release of TRH, which stimulates the release of PRL, is enhanced when the animals are subjected to a cold temperature. Findings that were made by using melanin-rich cells of Bufo embryos and larvae, such as the determination of the origin of the adenohypophyseal primordium, identification of the pancreatic chitinase, and involvement of the rostral preoptic recess organ as the hypothalamic inhibitory center of α-melanocyte-stimulating hormone (α-MSH) secretion, are mentioned in this article. In addition, the involvement of hormones in eliciting courtship behavior in male red-bellied newts and the discovery of the peptide sex pheromones and hormonal control of their secretion are also discussed in the present article.

Chronic effects of environmental concentrations of antifoulant diuron on two marine fish: Assessment of hormone levels, immunity, and antioxidant defense system

The presence and toxicity of waterborne diuron in aquatic environments pose a severe threat to non-target organisms. However, the chronic impact of diuron in marine fish has been poorly investigated. In this study, we report the chronic effects (30 and 60 days) of environmentally relevant concentrations of diuron (0.1, 1, and 10 μg L^-1) on economically important marine fish, red seabream (Pagrus major), and black rockfish (Sebastes schlegelii) by evaluating several parameters, including hormone levels, immunity, hepatic function, and antioxidant defense. Significant decreases in 17β-estradiol and 11-ketotestosterone levels and gonadosomatic index were observed on day 60 in fish exposed to 10 μg L^-1 diuron. Parameters of immunity, such as alternative complement activity, lysozyme activity, and total immunoglobulin levels, were significantly lowered by 60-day exposure to 10 μg L^-1 diuron in both fish. Significant decreases in the hepatic enzyme activities of alanine transaminase and aspartate transaminase were observed with an induction of cortisol on day 60 in fish exposed to 10 μg L-¹ diuron. Intracellular malondialdehyde and glutathione levels were significantly increased by 10 μg L-¹ diuron at day 60 with an increase in the enzymatic activities of catalase and superoxide dismutase. Overall, black rockfish were more sensitive to diuron than red seabream. These results suggest that consistent exposure to environmentally relevant concentrations of diuron is detrimental to the reproduction, immunity, and health of marine fish.

Evolutionarily conserved aspects of animal nutrient uptake and transport in sea anemone vitellogenesis

The emergence of systemic nutrient transport was a key challenge during animal evolution, yet it is poorly understood. Circulatory systems distribute nutrients in many bilaterians (e.g., vertebrates and arthropods) but are absent in non-bilaterians (e.g., cnidarians and sponges), where nutrient absorption and transport remain little explored at molecular and cellular levels. Vitellogenesis, the accumulation of egg yolk, necessitates high nutrient influx into oocytes and is present throughout animal phyla and therefore represents a well-suited paradigm to study nutrient transport evolution. With that aim, we investigated dietary nutrient transport to the oocytes in the cnidarian Nematostella vectensis (Anthozoa). Using a combination of fluorescent bead labeling and marker gene expression, we found that phagocytosis, micropinocytosis, and intracellular digestion of food components occur within the gonad epithelium. Pulse-chase experiments further show that labelled fatty acids rapidly translocate from the gonad epithelium through the extracellular matrix (ECM) into oocytes. Expression of conserved lipid transport proteins vitellogenin (vtg) and apolipoprotein-B (apoB) and colocalization of labeled fatty acids with a fluorescently tagged ApoB protein further support the lipid-shuttling role of the gonad epithelium. Complementary oocyte expression of very low-density lipoprotein receptor (vldlr) orthologs, which mediate endocytosis of bilaterian ApoB- and Vtg-lipoproteins, supports that this evolutionarily conserved ligand/receptor pair underlies lipid transport during sea anemone vitellogenesis. In addition, we identified lipid- and ApoB-rich cells with potential lipid transport roles in the ECM. Altogether, our work supports a long-standing hypothesis that an ECM-based lipid transport system predated the cnidarian-bilaterian split and provided a basis for the evolution of bilaterian circulatory systems.

Molecular Characterization of Embryos with Different Buoyancy Levels in the Yellowtail Kingfish (Seriola lalandi)

Simple Summary

Low survival of embryos in Seriola lalandi captivity farming has been attributed to low buoyancy. This process is the result of oocyte hydration, which depends on the osmotic force exerted by free amino acids (FAA) generate of cathepsin-mediated yolk proteins proteolysis. In order to understand the molecular bases of buoyancy acquisition process and its loosing throughout the development of S. lalandi, the aim of this study was to compare gene expression and activity of cathepsins, as well as the FAA content between floating and low-floating embryos. Eggs, morula, blastula, gastrula and 24 h embryos were the stages collected in this study. These assessments were supplemented with morphometric and functional characterization of the embryos, where no differences in embryo and oil drop diameter, and constitutive gene expression were detected between floating and low-floating embryos. Cathepsin B did not show differences in expression or activity related to buoyancy condition. Both expression and activity of cathepsin D were higher in some low-floating developmental stages. By contrast, cathepsin L showed higher expression and activity in some floating early embryos. Higher FAA content was observed in floating embryos at least until gastrula stage in comparison to low-floating ones. In summary, expression and activity of cathepsins and FAA content, revealed specific pattern throughout development or buoyancy conditions of the embryos. This study identifies molecular differences between floating and low floating embryos at specific developmental stages where cathepsins and FAA are promising markers to evaluate the embryo quality in the farming of this species.

Abstract

The buoyancy of eggs and embryos is associated with successful development in pelagic fish. Buoyancy is the result of oocyte hydration, which depends on the osmotic force exerted by free amino acids (FAA) generated by yolk proteolysis, and cathepsins are the main enzymes involved in this process. Seriola lalandi is a pelagic fish whose farming has been hampered by development failure that have been partially attributed to decreased buoyancy of embryos. Therefore, the aim of this study was to compare the mRNA expression and activity of cathepsins B, D, and L, as well as the FAA content in floating and low-floating embryos at different developmental stages. The chosen stages were eggs, morula, blastula, gastrula and 24 h embryos. Complementary assessments showed that there were no differences attributed to buoyancy status in embryo and oil droplet diameters, as well as the transcriptional status at any developmental stage. Cathepsin B did not show differences in mRNA expression or activity related to buoyancy at any stage. Cathepsin D displayed higher transcript and activity levels only in low-floating eggs compared with those floating. Cathepsin L showed higher expression in floating eggs and 24 h embryos compared with that of low-floating, but the activity of this enzyme was higher in floating eggs and morula. Total FAA content constantly decreased throughout development in floating embryos, but it was always higher than low-floating embryos until gastrula stage. In 24 h embryos floating and low-floating embryos share similar quantities of FAA. In summary, differences in the expression and activity of cathepsins between floating and low-floating embryos could be revealed at specific embryonic stages, suggesting different functions of these enzymes throughout development. Besides 24 h embryos, FAA content seems to be a decisive factor for buoyancy of embryos during early development of S. lalandi. Overall, considering the main role of cathepsins and FAA in buoyancy acquisition process and therefore in both embryo quality and viability, our study identifies good marker candidates to evaluate embryo quality in the farming of this species.

Open questions on the functional biology of the yolk granules during embryo development

Biogenesis and consumption of the yolk are well-conserved aspects of the reproductive biology in oviparous species. Most egg-laying animals accumulate yolk proteins within the oocytes thus creating the source of nutrients and energy that will feed embryo development. Yolk accumulation drives the generation of a highly specialized oocyte cytoplasm with maternal mRNAs, ribosomes, mitochondria, and, mainly, a set of organelles collectively referred to as yolk granules (Ygs). Following fertilization, the Ygs are involved in regulated mechanisms of yolk degradation to fuel the anabolic metabolism of the growing embryo. Thus, yolk accumulation and degradation are essential processes that allow successful development in many species. Nevertheless, the molecular machinery and mechanisms dedicated to the programmed yolk mobilization throughout development are still enigmatic and remain mostly unexplored. Moreover, while the Ygs functional biology as a nutritional source for the embryo has been acknowledged, several reports have suggested that Ygs cargoes and functions go far beyond yolk storage. Evidence of the role of Ygs in gene expression, microbiota harboring, and paracrine signaling has been proposed. In this study, we summarize the current knowledge of the Ygs functional biology pointing to open questions and where further investigation is needed.

Sex steroids are correlated with environmental factors and body condition during the reproductive cycle in females of the lizard Sceloporus torquatus

Reproduction is regulated by multiple factors that influence physiology and behavior to ensure the continuity of species. However, more work is needed to examine the complex relationships between environmental factors and endocrine transducers that modulate reproductive cycles, particularly in lizards. Here, we aimed to characterize the variation in plasma sex steroid levels in different stages of the reproductive cycle in the lizard Sceloporus torquatus and assess whether sex steroid levels were related to environmental factors (temperature, photoperiod, precipitation, and relative humidity) and body condition. Plasma concentrations of estradiol (E₂) and progesterone (P₄) from blood samples were quantified by enzyme-linked immunosorbent assay (ELISA) and radioimmunoanalysis (RIA), respectively. Our results indicate that sex steroid concentrations were positively related to follicular development but negatively related to temperature and precipitation. E₂ increased as the follicles grew, and its concentrations were highest in the preovulatory phase. P₄ showed a similar pattern and persisted during pregnancy. Changes in body condition were non-significant and mainly unrelated to the reproductive stage and plasma sex steroids. Our findings indicate that sex steroids change depending on the season and reproductive stage. We observed high concentrations of E₂ and P₄ in the late vitellogenic and preovulatory stages, probably because of their role in promoting vitellogenesis and ovulation. Additionally, we observed that follicular development is correlated with temperature and photoperiod. To better understand the mechanisms underlying reproduction, future studies of captive populations where environmental factors can be manipulated are needed.

Profile of gene expression changes during estrodiol-17β-induced feminization in the Takifugu rubripes brain

Background

As the critical tissue of the central nervous system, the brain has been found to be involved in gonad development. Previous studies have suggested that gonadal fate may be affected by the brain. Identifying brain-specific molecular changes that occur during estrodiol-17β (E₂) -induced feminization is crucial to our understanding of the molecular control of sex differentiation by the brains of fish.

Results

In this study, the differential transcriptomic responses of the Takifugu rubripes larvae brain were compared after E₂ treatment for 55 days. Our results showed that 514 genes were differentially expressed between E₂-treated-XX (E-XX) and Control-XX (C-XX) T. rubripes, while 362 genes were differentially expressed between E₂-treated-XY (E-XY) and Control-XY (C-XY). For example, the expression of cyp19a1b, gnrh1 and pgr was significantly up-regulated, while st, sl, tshβ, prl and pit-1, which belong to the growth hormone/prolactin family, were significantly down-regulated after E₂ treatment, in both sexes. The arntl1, bhlbe, nr1d2, per1b, per3, cry1, cipc and ciart genes, which are involved in the circadian rhythm, were also found to be altered. Differentially expressed genes (DEGs), which were identified between E-XX and C-XX, were significantly enriched in neuroactive ligand-receptor interaction, arachidonic acid metabolism, cytokine-cytokine receptor interaction and the calcium signaling pathway. The DEGs that were identified between E-XY and C-XY were significantly enriched in tyrosine metabolism, phenylalanine metabolism, arachidonic acid metabolism and linoleic acid metabolism.

Conclusion

A number of genes and pathways were identified in the brain of E₂-treated T. rubripes larvae by RNA-seq. It provided the opportunity for further study on the possible involvement of networks in the brain-pituitary-gonadal axis in sex differentiation in T. rubripes.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12864-021-08158-0.

Biomarkers of reproduction in endangered green sea turtles (Chelonia mydas) nesting at Tortuguero, Costa Rica

Understanding the timing of vitellogenesis is essential for identifying threats to the reproductive success of endangered oviparous vertebrate species, such as sea turtles. We measured concentrations of testosterone (T) and vitellogenin (VTG) in green sea turtles (Chelonia mydas) nesting at Tortuguero, Costa Rica, as biomarkers of ovarian development. Testosterone concentration increased from the first to second month and VTG concentration increased at the third week of sampling. These results show that Tortuguero green sea turtles were still producing both biomarkers early into the nesting season. VTG concentration was negatively correlated with female weight, suggesting that larger females start nesting earlier at Tortuguero and that we may have sampled larger females further into their reproductive cycle.

The RNA helicase DDX3 is required for ovarian development and oocyte maturation in Locusta migratoria

DDX3 represents a well-defined subfamily of DEAD-box RNA helicase and exerts multiple functions in RNA metabolism, cell cycle, tumorigenesis, signal pathway, and fertility. Our previous study has shown that LmDDX3, the ortholog of DDX3 in Locusta migratoria, is ubiquitously expressed, and with a high abundance in testis and ovary. Knockdown of LmDDX3 results in a lethal phenotype in nymph, but it still remains unclear for its role in reproductive process. In this study, we therefore characterized LmDDX3 expression in female adult locust and analyzed its function in oocyte development. LmDDX3 was expressed in all tissues examined with significant more transcripts in ovary and hindgut. In ovary, a strong expression level was detected at the day just after adult eclosion, and a dramatic reduction then occurred during the oocyte development. LmDDX3 RNAi led to a reduced vitellogenin (Vg) expression in fat body via partially at least, the JH signaling pathway, and caused an upregulation of vitellogenin receptor (VgR) in ovary, and thus blocked the ovarian development and oocyte maturation. Sequence and phylogenetic analysis indicated that LmDDX3 was closely related to termite DDX3. Taken together, these data reveal a critical role for LmDDX3 in regulating the transcription of Vg and VgR, two major factors in vitellogenesis that is a key process required for ovary development and oocyte maturation in locust, and contribute thereof a new putative target for locust biological control.

The Molecular Machinery of Gametogenesis in Geodia Demosponges (Porifera): Evolutionary Origins of a Conserved Toolkit across Animals

All animals are capable of undergoing gametogenesis. The ability of forming haploid cells from diploid cells through meiosis and recombination appeared early in eukaryotes, whereas further gamete differentiation is mostly a metazoan signature. Morphologically, the gametogenic process presents many similarities across animal taxa, but little is known about its conservation at the molecular level. Porifera are the earliest divergent animals and therefore are an ideal phylum to understand evolution of the gametogenic toolkits. Although sponge gametogenesis is well known at the histological level, the molecular toolkits for gamete production are largely unknown. Our goal was to identify the genes and their expression levels which regulate oogenesis and spermatogenesis in five gonochoristic and oviparous species of the genus Geodia, using both RNAseq and proteomic analyses. In the early stages of both female and male gametogenesis, genes involved in germ cell fate and cell-renewal were upregulated. Then, molecular signals involved in retinoic acid pathway could trigger the meiotic processes. During later stages of oogenesis, female sponges expressed genes involved in cell growth, vitellogenesis, and extracellular matrix reassembly, which are conserved elements of oocyte maturation in Metazoa. Likewise, in spermatogenesis, genes regulating the whole meiotic cycle, chromatin compaction, and flagellum axoneme formation, that are common across Metazoa were overexpressed in the sponges. Finally, molecular signals possibly related to sperm capacitation were identified during late stages of spermatogenesis for the first time in Porifera. In conclusion, the activated molecular toolkit during gametogenesis in sponges was remarkably similar to that deployed during gametogenesis in vertebrates.

Celebrating 50+ years of research on the reproductive biology and endocrinology of the green frog: An overview

This issue is dedicated to the late Professor Giovanni Chieffi, and this article is an overview of the research on Comparative Endocrinology of reproduction using Rana esculenta (alias Pelophylax esculentus) as a model system. Starting from the early 1970s till today, a large quantity of work have been conducted both in the fields of experimental endocrinology and in the definition of the diffuse neuroendocrine system, with a major focus on the increasing role of regulatory peptides. The various aspects investigated concerned the histological descriptions of principal endocrine glands of the hypothalamic-pituitary-gonadal (HPG) axis, the localization and distribution in the HPG of several different substances (i.e. neurosteroids, hypothalamic peptide hormones, pituitary gonadotropins, gonadal sex steroids, and other molecules), the determination of sex hormone concentrations in both serum and tissues, the hormone manipulations, as well as the gene and protein expression of steroidogenic enzymes and their respective receptors. All together these researches, often conducted considering different periods of the annual reproductive cycle of the green frog, allowed to understand the mechanism of cascade control/regulation of the HPG axis of R. esculenta, characterizing the role of different hormones in the two sexes, and testing the hypotheses about the function of single hormones in different target organs. It becomes evident from the review that, in their simplest form, several features of this species are specular as compared to those of other vertebrate species and that reproduction in this frog species is either under endogenous multi-hormonal control or by a wide array of different factors. Our excursus of this research, spanning almost five decades, shows that R. esculenta has been intensively and successfully used as an animal model in reproductive endocrinology as well as several field studies such as those involving environmental concerns that focus on the effects of endocrine disruptors and other environmental contaminants.

Mutations in cardinal are responsible for the red-1 and peach eye color mutants of the red flour beetle Tribolium castaneum

Ommochromes are the major pigments found in the eyes, eggs, wings and epidermis of insects. Here, we report the identification and characterization of the gene responsible for red-1 locus of Tribolium, whose mutants have white eyes due to lack of ommochrome pigments in the eyes. Using a candidate gene approach, we demonstrated that red-1 and peach mutants have molecular defects in the cardinal gene, which encodes a haem peroxidase that is considered to convert 3-hydroxykynurenine into ommochromes in pigment granules. Our experiments showed that the expression pattern of cardinal correlates well with the progression of eye pigmentation during pupal stages. We performed gene editing experiments using the Receptor-Mediated Ovary Transduction of Cargo (ReMOT) Control technique to disrupt the cardinal gene by adult injection, and were able to establish a novel cardinal mutant line. Our complementation test provided definitive genetic evidence that cardinal is located at the red-1 locus. The present study will lead to a greater understanding of the function and diversity of ommochrome pathway genes in insects. Our successful use of ReMOT Control in beetles will facilitate the development of more efficient and versatile systems for insect genome editing by simple adult injection.

Managing the Oocyte Meiotic Arrest-Lessons from Frogs and Jellyfish

During oocyte development, meiosis arrests in prophase of the first division for a remarkably prolonged period firstly during oocyte growth, and then when awaiting the appropriate hormonal signals for egg release. This prophase arrest is finally unlocked when locally produced maturation initiation hormones (MIHs) trigger entry into M-phase. Here, we assess the current knowledge of the successive cellular and molecular mechanisms responsible for keeping meiotic progression on hold. We focus on two model organisms, the amphibian Xenopus laevis, and the hydrozoan jellyfish Clytia hemisphaerica. Conserved mechanisms govern the initial meiotic programme of the oocyte prior to oocyte growth and also, much later, the onset of mitotic divisions, via activation of two key kinase systems: Cdk1-Cyclin B/Gwl (MPF) for M-phase activation and Mos-MAPkinase to orchestrate polar body formation and cytostatic (CSF) arrest. In contrast, maintenance of the prophase state of the fully-grown oocyte is assured by highly specific mechanisms, reflecting enormous variation between species in MIHs, MIH receptors and their immediate downstream signalling response. Convergence of multiple signalling pathway components to promote MPF activation in some oocytes, including Xenopus, is likely a heritage of the complex evolutionary history of spawning regulation, but also helps ensure a robust and reliable mechanism for gamete production.

Effects of 11-Ketotestosterone on Development of the Previtellogenic Ovary in the Sterlet, Acipenser ruthenus

11-ketotestosterone (11-KT) is a non-aromatizable and the most potent androgen in a few teleost. It has been reported that 11-KT in serum had a high concentration and increased sharply before the period of yolk deposition in females of few fishes. The aim of this study was to analyze the role of 11-KT both in vivo and in vitro on ovarian development, related gene expression levels, Vitellogenin (Vtg) synthesis, and serum sex steroid concentrations in previtellogenic cultured sterlet (Acipenser ruthenus). Silastic strips embedded with 11-KT (5 or 25 mg/kg) were implanted in vivo for 30 days. Ovarian masculinization or sex reversal was not observed. Histological analysis showed that 11-KT promoted sterlet ovarian development in a dose-dependent manner. Vtg and testosterone (T) increased significantly, while 17β-estradiol (E2) decreased with no significant difference among groups. The expression of genes androgen receptor (ar), vtg and lipoprotein lipase (lpl) were significantly increased in liver. However, 11-KT had no effect on the expression of foxl2 and cyp19a1 in ovary. In vitro, after incubation with 11-KT (10 and 100 μM) for 5 days, both T and E2 concentrations increased in both hepatic explants and ovarian explants culture medium; the concentration of Vtg also increased in hepatic explants culture medium. The expression of ar, era, vtg, and lpl increased significantly in hepatic explants. However, only the expression of era significantly increased in cultured ovarian explants. Altogether, these results suggest that 11-KT induced ovarian development, as well as Vtg and lipid synthesis, and could be an important factor facilitating the initiation of Vtg synthesis in the liver of the previtellogenic sterlet.

Ultrasonographic and hormonal characterization of reproductive health and disease in wild, semiwild, and aquarium-housed southern stingrays (Hypanus americanus)

OBJECTIVE

To characterize physical examination, plasma biochemical, and ultrasonographic findings in aquarium-housed, managed semiwild, and wild southern stingrays (Hypanus americanus) with and without reproductive disease.

ANIMALS

Southern stingrays from aquarium (n = 48), lagoon (managed semiwild; 34), and wild (12) habitats.

PROCEDURES

Limited, opportunistic prosections were performed of presumed anatomically normal wild southern stingrays and compared with findings for aquarium-housed stingrays with reproductive disease. Ultrasonographic video data from both groups were used to assign a score (1 to 5) indicating increasing severity of ovarian and uterine reproductive disease. Plasma total 17β-estradiol, estrone, progesterone, and testosterone concentrations were measured with enzyme immunoassays validated for use in southern stingrays.

RESULTS

Ultrasonographic ovarian scores were significantly correlated with uterine scores. No reproductive disease was detected in semiwild or wild stingrays, but 65% (31/48) of aquarium-housed stingrays had developing or advanced reproductive disease (ie, ultrasonographic ovarian or uterine score of 4 or 5). Significant correlations were identified between ovarian and uterine disease status and plasma concentrations of all steroid hormones except testosterone.

CONCLUSIONS AND CLINICAL RELEVANCE

Findings suggested that ultrasonography and plasma hormone concentrations may be useful in the identification of reproductive disease and determination of disease severity in southern stingrays.

Some aspects of the hypothalamic and pituitary development, metamorphosis, and reproductive behavior as studied in amphibians

In this review article, information about the development of the hypothalamo-hypophyseal axis, endocrine control of metamorphosis, and hormonal and pheromonal involvements in reproductive behavior in some amphibian species is assembled from the works conducted mainly by our research group. The hypothalamic and pituitary development was studied using Bufo embryos and larvae. The primordium of the epithelial hypophysis originates at the anterior neural ridge and migrates underneath the brain to form a Rathke's pouch-like structure. The hypothalamo-hypophyseal axis develops under the influence of thyroid hormone (TH). For the morphological and functional development of the median eminence, which is a key structure in the transport of regulatory hormones to the pituitary, contact of the adenohypophysis with the undeveloped median eminence is necessary. For the development of proopiomelanocortin-producing cells, contact of the pituitary primordium with the infundibulum is required. The significance of avascularization in terms of the function of the intermediate lobe of the pituitary was evidenced with transgenic Xenopus frogs expressing a vascular endothelial growth factor in melanotropes. Metamorphosis progresses via the interaction of TH, adrenal corticosteroids, and prolactin (PRL). We emphasize that PRL has a dual role: modulation of the speed of metamorphic changes and functional development of organs for adult life. A brief description about a novel type of PRL (1B) that was detected was made. A possible reason why the main hypothalamic factor that stimulates the release of thyrotropin is not thyrotropin-releasing hormone, but corticotropin-releasing factor is considered in light of the fact that amphibians are poikilotherms. As regards the reproductive behavior in amphibians, studies were focused on the courtship behavior of the newt, Cynops pyrrhogaster. Male newts exhibit a unique courtship behavior toward sexually developed conspecific females. Hormonal interactions eliciting this behavior and hormonal control of the courtship pheromone secretion are discussed on the basis of our experimental results.

Mass spectrometry based detection of common vitellogenin peptides across fish species for assessing exposure to estrogenic compounds in aquatic environments

The identification of myriad of chemicals in the environment that mimic hormones and affect the endocrine functions of exposed organism is a daunting analytical challenge for environmental scientists and engineers. Many of these endocrine disrupting chemicals (EDCs) are present at very low concentrations in the aquatic systems, but yet affect the metabolic, developmental, and reproductive functions in exposed fish and wildlife. Vitellogenin (VTG) protein is a widely used biomarker in fish for assessing exposure to EDCs, and is commonly measured using species-specific immunochemical techniques. In this study, we developed a liquid chromatography tandem mass spectrometry (LC-MS/MS) method that can measure common peptides from digested VTG in multiple fish species. In the initial experiments using high resolution mass spectrometry, two peptides (ALHPELR and FIELIQLLR) were identified as common fragments in the digested VTG protein isolated from three different fish species (Pimephales promelas, Micropterus salmoides, and Fundulus heteroclitus). Then, a quantitative analysis using LC-MS/MS under selected reaction monitoring mode was developed for the detection of these two peptides in trypsin-digested plasma from female fish (positive control), estrogen-exposed male fish (test sample), and unexposed male fish (negative control) using two of the same species used for identifying the common peptides (P. promelas, and M. salmoides) and one new species (Ameiurus nebulosus) that was not included during the selection of peptides. Results from this study demonstrate the potential of LC-MS/MS as an effective cross-species method to detect VTG in fish, which can be an alternative analytical technique for assessing endocrine disruption in multiple fish species.

Egg Coat Proteins Across Metazoan Evolution

All animal oocytes are surrounded by a glycoproteinaceous egg coat, a specialized extracellular matrix that serves both structural and species-specific roles during fertilization. Egg coat glycoproteins polymerize into the extracellular matrix of the egg coat using a conserved protein-protein interaction module-the zona pellucida (ZP) domain-common to both vertebrates and invertebrates, suggesting that the basic structural features of egg coats have been conserved across hundreds of millions of years of evolution. Egg coat proteins, as with other proteins involved in reproduction, are frequently found to be rapidly evolving. Given that gamete compatibility must be maintained for the fitness of sexually reproducing organisms, this finding is somewhat paradoxical and suggests a role for adaptive diversification in reproductive protein evolution. Here we review the structure and function of metazoan egg coat proteins, with an emphasis on the potential role their evolution has played in the creation and maintenance of species boundaries.

Seasonal variation of pituitary gonadotropin subunit, brain-type aromatase and sex steroid receptor mRNAs, and plasma steroids during gametogenesis in wild sablefish

Pituitary-hormone signaling plays critical roles in the onset and progression of gametogenesis in vertebrates. This study characterized expression patterns of pituitary gonadotropin beta-subunits (fshb and lhb), brain-type aromatase (cyp19a1b), androgen (ar1, ar2) and estrogen receptors (esr1, esr2a, esr2b), and changes in plasma steroid levels by liquid chromatography/tandem mass spectrometry in wild sablefish (Anoplopoma fimbria, order Scorpaeniformes) during a complete reproductive cycle. Transcripts for fshb increased during early gametogenesis and peaked in late vitellogenic females and late recrudescent males, while expression of lhb reached maximum levels in periovulatory and spermiating fish. Pituitary levels of cyp19a1b and ar1 were strongly correlated with those of lhb in females and males, increasing during gametogenesis and reaching maximum levels prior to spawning. By contrast, expression of ar2, and the three estrogen receptors differed between female and male sablefish. 17β-estradiol (E2) was the dominant steroid in females during vitellogenesis, while a range of at least 6 steroids (11β-hydroxyandrostenedione, testosterone [T], E2, 11-ketotestosterone [11KT], 11-deoxycortisol, and 17α,20β,21-trihydroxyprogesterone) were detected at similar levels in males during testicular development. Prior to spawning, a marked increase in 4-androstenedione, T, 11KT and E2 was found in both periovulatory females and spermiating males. In conclusion, the concomitant changes in plasma androgen levels and pituitary ar1 expression during gametogenesis suggest a specific role for androgens in pituitary hormone regulation of reproduction in sablefish. Further, our data highlight the importance of E2 during final stages of maturation in this species, which may regulate the transcription of pituitary lhb in a paracrine fashion.

Reproductive life history of sablefish (Anoplopoma fimbria) from the U.S. Washington coast

Sablefish (Anoplopoma fimbria) is a marine groundfish that supports valuable fisheries in the North Pacific Ocean and holds promise for marine aquaculture. Limited information is available, however, about its reproductive biology. This study aimed to characterize the complete reproductive cycle, including seasonal changes in gonadal development (macroscopic and histological), plasma sex steroid levels (17β-estradiol -E2-, and 11-ketotestosterone -11KT-), gonadosomatic and hepatosomatic indices (GSI, and HSI), and condition factor (K) of female and male sablefish captured off the Washington coast. Adult fish (209 females, 159 males) were caught by longline monthly from August 2012 to August 2013. Early signs of recruitment of ovarian follicles into secondary growth, indicated by oocytes containing small yolk granules and cortical alveoli, were first observed in March. Oogenesis progressed during spring and summer, and fully vitellogenic follicles were first observed in July. Vitellogenic growth was correlated with increases in plasma E2, GSI, HSI and K. Periovulatory females, indicated by fully-grown oocytes with migrating germinal vesicles and hydrated oocytes, were found from November to February. At this stage, plasma E2 and GSI reached maximal levels. In males, proliferating cysts containing spermatocytes were first observed in April. Testicular development proceeded during spring and summer, a period during which all types of male germ cells were found. The first clusters of spermatozoa appeared in July, concomitant with a 5.2-fold increase in GSI. Spermiating males were observed from November to April; at this time, spermatids were absent or greatly reduced, and testis lobules were filled with spermatozoa. The highest levels of plasma 11KT were found in males at this stage. Postspawning ovaries and testes, and basal steroids levels were found in fish captured from February to April. These results suggest that sablefish in coastal Washington initiate their reproductive cycle in March/April and spawn primarily in January/February.

Dynamics of ovarian maturation throughout the reproductive cycle of the Neotropical cichlid fishCichlasomadimerus(Teleostei, Cichliformes)

In this study, we analyzed gene expression profiles, plasma steroids concentrations, and gonadal morphology throughout the reproductive cycle of female Cichlasoma dimerus (Heckel, 1840), a monogamous cichlid fish exhibiting social hierarchies. Fish were analyzed at six phases encompassing their annual cycle, namely resting (during the nonreproductive period), prespawning, 30 h post spawning, 4 days post spawning, 10 days post spawning, and subordinate (during the reproductive period). The histological and histomorphometric analysis showed that C. dimerus exhibits asynchronous ovarian development. Similar to resting females, subordinate females showed low gonadosomatic index, reduced expression levels of vitellogenin (vtgAb), zona pellucida (zpB), gonadal aromatase (cyp19a1A), and low concentrations of plasma sex steroids, thus indicating that social intimidation by dominant conspecifics elicited reproductive arrest. In reproductively active females, a direct positive correlation between plasma estradiol, vtgAb expression, percentage of late vitellogenic oocytes, and gonadosomatic index was observed. These parameters were maximal at the prespawning phase, decreased at 30 h post spawning and 4 days post spawning, and then reached a peak at 10 days post spawning. Our results indicate that female C. dimerus become spawning capable after 10 days post spawning, coincidently with the shortest time interval between successive spawns recorded in captivity.

Cloning, expression and functional characterization on vitellogenesis of estrogen receptors in Scatophagus argus

Estrogen receptors (Er) play a critical role in vitellogenesis. Three ers (erα, erβ1 and erβ2) and vitellogenins (vtg-A, vtg-B and vtg-C) subtypes were isolated in various fish species, while the contribution of each Er to the regulation of vtgs expression was not analyzed in detail. Here, erα, erβ1 and erβ2 were cloned and all were found to be expressed in female liver in Scatophagus argus. During proteic vitellogenesis stage, erα was simultaneously up-regulated, while erβ1 and erβ2 were not, with three vtgs in female liver. The effects of 17β-estradiol (E₂) alone or combined with Er antagonists on ers, vtgs mRNA expressions and Vtg protein content in incubated male liver were examined by real-time PCR and enzyme-linked immunosorbent assay (ELISA), respectively. The expressions of erα, erβ1, vtgs mRNA and Vtg protein increased significantly after 24h incubation with E₂ (0.1, 1 and 10μM), while Er nonselective antagonist ICI 182 780 (0.01, 0.1 and 1μM) significantly attenuated the up-regulation effects of E₂ on ers, vtgs mRNA and Vtg protein in a dose-dependent manner. Erα selective antagonist Methyl-piperidinopyrazole (MPP) (0.01, 0.1 and 1μM) significantly attenuated the up-regulation effects of E₂ on erα, vtg-B, vtg-C mRNA and Vtg protein, while promoted the expression of erβ1 and vtg-A. Erβ selective antagonist Cyclofenil (0.01, 0.1 and 1μM) attenuated the up-regulation effects of E₂ on erβ1, erβ2, vtg-A, vtg-C mRNA and Vtg protein while promoted the expression of erα and vtg-B. Our results suggest that the regulation of Ers on different vtgs was divergent in S. argus.

A comparison of techniques for studying oogenesis in the European eel Anguilla anguilla

A multi-technique approach was used to study the changes occurring in European eel Anguilla anguilla ovaries during hormonally-induced vitellogenesis. Aside from classic techniques used to monitor the vitellogenic process, such as ovary histology, fat content analysis, sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE) and vitellogenin enzyme linked immunosorbent assay (ELISA), a new technique, Fourier-transform infrared (FT-IR) microspectroscopy, was used to analyse A. anguilla ovaries. The results from the different techniques provided different ways of approaching the same process. Although it is considered a time consuming approach, of all the employed techniques, histology provided the most direct evidences about vitellogenesis. SDS-PAGE and ELISA were also useful for studying vitellogenesis, whereas fat analysis cannot be used for this purpose. The FT-IR analysis provided a representative IR spectrum for each ovarian stage (previtellogenic stage, early vitellogenic stage, mid-vitellogenic stage and late vitellogenic stage), demonstrating that it is a valid method able to illustrate the distribution of the oocytes within the ovary slices. The chemical maps obtained confirmed changes in lipid concentrations and revealed their distribution within the oocytes at different maturational stages. When the results and the accuracy of the FT-IR analysis were compared with those of the traditional techniques commonly used to establish the vitellogenic stage, it became evident that FT-IR is a useful and reliable tool, with many advantages, including the fact that it requires little biological material, the costs involved are low, analysis times are short and last but not least, the fact that it offers the possibility of simultaneously analysing various biocomponents of the same oocyte.

Ovarian yolk formation in fishes: Molecular mechanisms underlying formation of lipid droplets and vitellogenin-derived yolk proteins

Fish egg yolk is largely derived from vitellogenins, which are synthesized in the liver, taken up from the maternal circulation by growing oocytes via receptor-mediated endocytosis and enzymatically processed into yolk proteins that are stored in the ooplasm. Lipid droplets are another major component of fish egg yolk, and these are mainly composed of neutral lipids that may originate from maternal plasma lipoproteins. This review aims to briefly summarize our current understanding of the molecular mechanisms underlying yolk formation in fishes. A hypothetical model of oocyte growth is proposed based on recent advances in our knowledge of fish yolk formation.

Estrogen-induced yolk precursors in European sea bass, Dicentrarchus labrax: Status and perspectives on multiplicity and functioning of vitellogenins

The estrogen-inducible egg yolk precursor, vitellogenin, of the European sea bass (Dicentrarchus labrax) has received considerable scientific attention by virtue of its central importance in determination of oocyte growth and egg quality in this important aquaculture species. However, the multiplicity of vitellogenins in the sea bass has only recently been examined. Recent cloning and homology analyses have revealed that the sea bass possesses the three forms of vitellogenin, VtgAa, VtgAb and VtgC, reported to occur in some other highly evolved teleosts. Progress has been made in assessing the relative abundance and special structural features of the three Vtgs and their likely roles in oocyte maturation and embryonic nutrition. This report discusses these findings in the context of our prior knowledge of vitellogenesis in this species and of the latest advances in our understanding of the evolution and function of multiple Vtgs in acanthomorph fishes.

In silico and in vivo analysis of binding affinity of estrogens with estrogen receptor alpha in Channa punctatus (Bloch)

In the present study, potential interaction between natural estrogens i.e., estrone (E(1)), estradiol (E(2)) and estriol (E(3)) with human estrogen receptor (hER) was seen by in silico study. Molecular docking studies were carried out using Glide and ligand docking program. The binding affinity, assessed by Glide score, indicates stronger interaction of E(3) with hER followed by E(2) and E(1). Real-time PCR analysis of vga and vgb expressions, in the liver of different groups of Channa punctatus injected with the three natural estrogens, supported the docking analysis and indicated E(3) to be the most potent estrogen in inducing vga and vgb expressions followed by E(2) and E(1). This study lays the groundwork for studying interactions of various estrogenic substances with different estrogen receptors and to assess estrogenicity of various chemicals which are being released into the environment by employing molecular docking technique.

Expression profiles of Fsh-regulated ovarian genes during oogenesis in coho salmon

The function of follicle-stimulating hormone (Fsh) during oogenesis in fishes is poorly understood. Using coho salmon as a fish model, we recently identified a suite of genes regulated by Fsh in vitro and involved in ovarian processes mostly unexplored in fishes, like cell proliferation, differentiation, survival or extracellular matrix (ECM) remodeling. To better understand the role of these Fsh-regulated genes during oocyte growth in fishes, we characterized their mRNA levels at discrete stages of the ovarian development in coho salmon. While most of the transcripts were expressed at low levels during primary growth (perinucleolus stage), high expression of genes associated with cell proliferation (pim1, pcna, and mcm4) and survival (ddit4l) was found in follicles at this stage. The transition to secondary oocyte growth (cortical alveolus and lipid droplet stage ovarian follicles) was characterized by a marked increase in the expression of genes related to cell survival (clu1, clu2 and ivns1abpa). Expression of genes associated with cell differentiation and growth (wt2l and adh8l), growth factor signaling (inha), steroidogenesis (cyp19a1a) and the ECM (col1a1, col1a2 and dcn) peaked in vitellogenic follicles, showing a strong and positive correlation with transcripts for fshr. Other genes regulated by Fsh and associated with ECM function (ctgf, wapl and fn1) and growth factor signaling (bmp16 and smad5l) peaked in maturing follicles, along with increases in steroidogenesis-related gene transcripts. In conclusion, ovarian genes regulated by Fsh showed marked differences in their expression patterns during oogenesis in coho salmon. Our results suggest that Fsh regulates different ovarian processes at specific stages of development, likely through interaction with other intra- or extra-ovarian factors.

Immunolocalization of hepatic estrogen and progesterone receptors in the female lizard Uromastyx acanthinura

The hormonal regulation of hepatic synthesis of vitellogenin during the annual reproductive cycle was performed for the first time in the deserticole, oviparous, diurnal and herbivorous Uromastyx acanthinura, a lizard belonging to the Agamidae family. In order to elucidate what kind of estrogen receptor is involved in this process, an immunohistochemical study was performed. Changes were obtained in the labeling and cellular distribution of the estrogen and progesterone receptors according to the period of the reproductive cycle and the experimental administration of 17β-estradiol. Only the ERβ subtype was present; it was found in all phases of the cycle with a variable localization: nuclear and cytosolic during vitellogenesis, mainly cytosolic in the female with egg retention (luteal phase) and strictly cytosolic in females at sexual rest. The progesterone receptors were present only at the luteal phase and during sexual rest and disappeared completely from females after 17β-estradiol treatment in sexual rest. Our data suggested that mediation of action of the 17β-estradiol in the vitellogenin synthesis in the lizard U. acanthinura occured via ERβ. PRA and PRB could both be necessary for the negative effect of progesterone on the hepatic synthesis of vitellogenin.

Effects of nonylphenol on vitellogenin synthesis in adult males of the spotted ray Torpedo marmorata

The aim of this investigation was to assess the effects of nonylphenol (NP), an oestrogen-like environmental pollutant, on the vitellogenin (VTG) synthesis in adult males of the aplacental viviparous cartilaginous fish Torpedo marmorata. The VTG recovery in males is considered a biomarker of xeno-oestrogenic pollution as this lipophosphoglycoprotein is physiologically induced by oestrogens only in females of oviparous and ovoviparous vertebrates. Using in situ hybridization and immunohistochemistry, T. marmorata males injected with nonylphenol showed the presence of VTG in the liver and the kidney. In particular, vtg messenger (m)RNA and VTG protein were expressed in the liver, whereas in the kidney cells only the presence of VTG was recorded. By contrast, no expression for VTG was detected in the testis. These results demonstrate that in T. marmorata NP induces the expression of vtg only in the liver; the presence of VTG in the kidney and its absence in the testis are discussed.

Expression of vitellogenin in the testis and kidney of the spotted ray Torpedo marmorata exposed to 17β-estradiol

In vertebrates, the liver was long thought to be the only site of vitellogenin (Vtg) production, but recent studies demonstrated that Vtg is also expressed in extrahepatic districts. The aim of this paper is to assess, by in situ hybridization and immunohistochemistry, the expression of Vtg in the testis and kidney of Torpedo marmorata exposed to 17β-estradiol (E(2)). In treated samples vtg mRNA and Vtg were detected contemporaneously only in the testis; differently the kidney cells were positive to Vtg antibody, but negative to vtg mRNA. This is the first study to assess that male germ cells, after an exposure to E(2), synthesize Vtg in a stage-dependent manner. The presence of Vtg and the modifications observed in the kidney after E(2) treatment are discussed.

Influence of temperature regime on endocrine parameters and vitellogenesis during experimental maturation of European eel (Anguilla anguilla) females

We examined the effect of temperature in European silver eels during their maturation induced by injections of carp pituitary extract on endocrine parameters: pituitary fshβ and lhβ expression, plasma 17β-estradiol (E2) and vitellogenin, estrogen receptor 1 (esr1), and vitellogenin 2 (vtg2) expression in liver. A variable thermal regime (T10) that increased from 10° to 14° and 17°C was compared with a constant 20°C regime (T20) during 12 weeks. T10 caused a faster development until week 8, higher fshβ, lhβ, esr1 expression, and higher E2 levels. The results strongly suggest that T10 is inducing a higher endogenous FSH level which increases the E2 circulating level during vitellogenesis. A variable thermal regime induced an fshβ expression and E2 profile in vitellogenic hormonally matured eel females that were more similar to the profile observed in other naturally maturing fish.

Differential expression of PTHrP and its receptor in pituitary gland and gills in estradiol-treated gilthead sea bream (Sparus auratus, L.)

In the gilthead sea bream (Sparus auratus) 17β-estradiol (E₂) plays an important role in the synthesis of vitellogenin. During vitellogenesis, vitellogenin as a nutritional precursor protein is loaded with calcium, which requires elevated plasma calcium levels. This is accomplished via E₂-dependent processes. Reports have shown that hypercalcemic effects of E₂ are possibly mediated by another hypercalcemic factor, viz. parathyroid hormone related protein (PTHrP). To further investigate the possibility of PTHrP as a mediator of E₂-induced hypercalcemia, we investigated the local expression levels of the pthrp mRNA and of the gene coding for the PTHrP receptor, PTH1R (pth1r) in two tissues involved in the calcium regulation (gills, pituitary gland) of the sea bream treated with E₂. Compared to control, treatment with E₂ resulted in: significantly increased total calcium and plasma PTHrP levels (P<0.01), a down-regulation of pthrp mRNA in the pituitary gland (P<0.01), and up-regulation of expression levels for both pthrp and pth1r in the branchial system (P<0.05). These findings provide direct evidence for a mediating role of PTHrP in E₂ induced hypercalcemia, and in addition support the idea for the presence of two independent systems, an endocrine pituitary PTHrP system and a peripheral paracrine branchial PTHrP system.

Involvement of cAMP and calmodulin in endocytic yolk uptake during Xenopus laevis oogenesis

The aim of the present study was to show the participation and physiological role of calmodulin (CaM) and cAMP during vitellogenin endocytic uptake in the amphibian Xenopus laevis. The results showed a differential distribution of CaM in the ovary follicles during oogenesis. The CaM intracellular localization was not affected by gap junction's downregulation and CaM inhibition did not completely abolished the endocytic activity of oocytes. We showed that cAMP was able to completely rescue the endocytic competence in follicles in which gap junctional communication had been disrupted by octanol. Moreover cAMP was capable of restoring oocyte endocytic capability in the presence of octanol and stelazine, a CaM inhibitor. We propose that, in Vtg uptake regulation, cAMP is upstream of CaM during the endocytic signalling pathway.

Broodstock management and hormonal manipulations of fish reproduction

Control of reproductive function in captivity is essential for the sustainability of commercial aquaculture production, and in many fishes it can be achieved by manipulating photoperiod, water temperature or spawning substrate. The fish reproductive cycle is separated in the growth (gametogenesis) and maturation phase (oocyte maturation and spermiation), both controlled by the reproductive hormones of the brain, pituitary and gonad. Although the growth phase of reproductive development is concluded in captivity in most fishes-the major exemption being the freshwater eel (Anguilla spp.), oocyte maturation (OM) and ovulation in females, and spermiation in males may require exogenous hormonal therapies. In some fishes, these hormonal manipulations are used only as a management tool to enhance the efficiency of egg production and facilitate hatchery operations, but in others exogenous hormones are the only way to produce fertilized eggs reliably. Hormonal manipulations of reproductive function in cultured fishes have focused on the use of either exogenous luteinizing hormone (LH) preparations that act directly at the level of the gonad, or synthetic agonists of gonadotropin-releasing hormone (GnRHa) that act at the level of the pituitary to induce release of the endogenous LH stores, which, in turn act at the level of the gonad to induce steroidogenesis and the process of OM and spermiation. After hormonal induction of maturation, broodstock should spawn spontaneously in their rearing enclosures, however, the natural breeding behavior followed by spontaneous spawning may be lost in aquaculture conditions. Therefore, for many species it is also necessary to employ artificial gamete collection and fertilization. Finally, a common question in regards to hormonal therapies is their effect on gamete quality, compared to naturally maturing or spawning broodfish. The main factors that may have significant consequences on gamete quality-mainly on eggs-and should be considered when choosing a spawning induction procedure include (a) the developmental stage of the gonads at the time the hormonal therapy is applied, (b) the type of hormonal therapy, (c) the possible stress induced by the manipulation necessary for the hormone administration and (d) in the case of artificial insemination, the latency period between hormonal stimulation and stripping for in vitro fertilization.

Revealing genes associated with vitellogenesis in the liver of the zebrafish (Danio rerio) by transcriptome profiling

Background

In oviparous vertebrates, including fish, vitellogenesis consists of highly regulated pathways involving 17β-estradiol (E2). Previous studies focused on a relatively small number of hepatic expressed genes during vitellogenesis. This study aims to identify hepatic genes involved in vitellogenesis and regulated by E2, by using zebrafish microarray gene expression profiling, and to provide information on functional distinctive genes expressed in the liver of a vitellogenic female, using zebrafish as a model fish.

Results

Genes associated with vitellogenesis were revealed by the following paired t-tests (SAM) comparisons: a) two-month old vitellogenic (Vit2) females were compared with non-vitellogenic (NV) females, showing 825 differentially expressed transcripts during early stages of vitellogenesis, b) four-month old vitellogenic (Vit4) females were compared with NV females, showing 1,046 differentially expressed transcripts during vitellogenesis and c) E2-treated males were compared with control males, showing 1,828 differentially expressed transcripts regulated by E2. A Venn diagram revealed 822 common transcripts in the three groups, indicating that these transcripts were involved in vitellogenesis and putatively regulated by E2. In addition, 431 transcripts were differentially expressed in Vit2 and Vit4 females but not in E2-treated males, indicating that they were putatively not up-regulated by E2. Correspondence analysis showed high similarity in expression profiles of Vit2 with Vit4 and of NV females with control males. The E2-treated males differed from the other groups. The repertoire of genes putatively regulated by E2 in vitellogenic females included genes associated with protein synthesis and reproduction. Genes associated with the immune system processes and biological adhesion, were among the genes that were putatively not regulated by E2. E2-treated males expressed a large array of transcripts that were not associated with vitellogenesis.

The study revealed several genes that were not reported before as being regulated by E2. Also, the hepatic expression of several genes was reported here for the first time.

Conclusion

Gene expression profiling of liver samples revealed 1,046 differentially expressed transcripts during vitellogenesis of which at least ~64% were regulated by E2. The results raise the question on the regulation pattern and temporal pleiotropic expression of hepatic genes in vitellogenic females.

Seasonal regulation of vitellogenin by growth hormone in the goldfish liver

Goldfish, like many other fish species, undergo well-documented annual cycles, which include well-defined somatic and reproductive states. It is known that part of the year is spent in a somatotropic state (usually from late spring to late fall), followed by transition into the reproductive state (usually from late Fall to late Spring). The onset of reproductive cycle is characterized by synthesis of phosphoglycoprotein vitellogenin (Vg), a precursor to the egg yolk proteins in the liver and its uptake in the oocyte. Hormones regulate the process of vitellogenesis and circulating 17-beta-estradiol is known to be a key factor during the reproductive period. During vitellogenesis, pituitary produces growth hormone (GH), but the fish divert most of the energy towards reproduction rather than growth. In this study we investigated the role of GH in the regulation of Vg in goldfish. The goldfish Vg cDNA was partially cloned (1348 amino acids), which included a highly conserved lipoprotein N-terminal domain, and used as a probe for Northern blot analysis. Treatment of female liver in vitro with recombinant goldfish GH increased Vg mRNA in goldfish at early stages of recrudescence (September), but was without effect in mid-late stages of vitellogenesis and post-spawning period (February-June). There was a correlation between GH activity and basal expression levels of the growth hormone receptor (GHR). Like Vg, GHR transcript was increased by treatment with GH in September but not February or June. Overall, the present study provides novel information on the role of GH in the season-dependent regulation of Vg and GHR gene expression.