Metabolism of vertebrate-type steroids by tissues of three crustacean species

Identification and function analysis of steroid hormone synthesis pathway-related gene-Hsd3b in Scylla paramamosain

Mud crab (Scylla paramamosain) has become an important mariculture crab along the southeast coast of China due to its strong adaptability, delicious taste, and rich nutrition. Several vertebrate steroid hormones and their synthesis-related genes and receptors have been found in crustaceans, but there are few reports on their synthesis process and mechanism. 3-beta-hydroxysteroid dehydrogenase (HSD3B) is a member of the Short-chain Dehydrogenase/Reductase (SDR) family, and an indispensable protein in vertebrates' steroid hormone synthesis pathway. In this study, the SpHsd3b gene sequence was obtained from the transcriptome data of S. paramamosain, and its full-length open reading frame (ORF) was cloned. The spatial and temporal expression pattern of SpHsd3b was performed by quantitative real-time PCR (qRT-PCR). SpHsd3b dsRNA interference (RNAi) and HSD3B inhibitor (trilostane) were used to analyze the function of SpHSD3B. The results showed that the SpHsd3b gene has an 1113 bp ORF encoding 370 amino acids with a 3β-HSD domain. SpHSD3B has lower homology with HSD3B of vertebrates and higher homology with HSD3B of crustaceans. SpHsd3b was expressed in all examined tissues in mature crabs, and its expression was significantly higher in the testes than in the ovaries. SpHsd3b expression level was highest in the middle stage of testicular development, while its expression was higher in the early and middle stages of ovarian development. RNAi experiment and trilostane injection results showed that SpHSD3B had regulatory effects on several genes related to gonadal development and steroid hormone synthesis. 15-day trilostane suppression could also inhibit ovarian development and progesterone level of hemolymph. According to the above results, crustaceans may have steroid hormone synthesis pathways like vertebrates, and the Hsd3b gene may be involved in the gonadal development of crabs. This study provides further insight into the function of genes involved in steroid hormone synthesis in crustaceans.

Sex Hormones in Hemolymph of Red King Crabs from the Barents Sea

Simple Summary

Well-known sex hormones, testosterone and 17β-estradiol, play a crucial role in the reproduction of vertebrates. Biochemical assays have detected these substances in a few crustaceans, and it has been hypothesized that these hormones are involved in the regulation of crustacean reproduction. Red king crab is a large commercially important species harvested both in their native areas (North Pacific) and in the area of its introduction (Barents Sea). The presence of 17β-estradiol and testosterone and fluctuations of their concentrations in relation to different factors have not yet been investigated. For this reason, we provided a pilot study to reveal the levels of sex hormones in hemolymph of red king crabs captured in the coastal Barents Sea. These hormones were detected in the crabs and we compared our data with previously published data involving a wide range of crustaceans. We found seasonal variations in the level of testosterone with the maximum in the spawning period. Our data expand the current knowledge about the red king crab physiology and may be used for the development of its aquaculture.

Abstract

The presence of vertebrate-related steroid sex hormones has been reported in both freshwater and marine crustaceans. However, despite the commercial importance of king crabs, many aspects of their endocrinology are still unknown. For this reason, we examined hemolymph samples of the red king crab Paralithodes camtschaticus from the Barents Sea population for the presence of testosterone and 17β-estradiol using radioimmunoassay. The mean testosterone concentration was 0.46 ± 0.04 (range 0.08–1.39) ng mL^–1, whereas the mean 17β-estradiol concentration was 1248.9 ± 91.4 (range 217.7–4100.1) pg mL^–1. In general, the levels of 17β-estradiol and testosterone in red king crabs were higher than reported for the hemolymph of amphipods, crabs, and shrimps from warm and temperate waters, probably because the king crabs analyzed were larger and heavier than the other crustaceans. The concentrations of sex steroids did not differ significantly between males and females and between immature and mature red king crabs. Seasonal variations in the level of testosterone with the maximum value in the spawning period (May) indicate a potential role of the sex hormones in the maturation and reproduction processes of red king crab. Taking into account the slow growth rate in P. camtschaticus, our data could be useful not only for further physiological studies but also for the development of reliable techniques for red king crab aquaculture.

Immunolocalization and changes of 17beta-estradiol during ovarian development of Chinese mitten crab Eriocheir sinensis' [corrected]

17beta-estradiol (E₂) is important for crustacean ovarian development. This study aims to investigate the distribution and change pattern of E₂ in the ovary, hepatopancreas, thoracic ganglion and brain ganglion as well as Vg-mRNA expression level during ovarian development of Chinese mitten crab Eriocheir sinensis. Results showed that strongly positive signals of E₂ were mainly distributed in follicle cells of ovaries for all developmental stages as well as oocyte cytoplasm of stages III to V ovaries. In hepatopancreas, the E₂-positive signal was mainly detected in the cytoplasm and nucleus of fibrillar cells and the nucleus of resorptive cells, while the maximum fluorescence intensity was observed in stage III hepatopancreas. On the contrary, the E₂ immunoreactivities in nervous tissues were relatively stable during ovarian development. Moreover, the changing pattern of E₂ concentration was similar within hemolymph, ovary and hepatopancreas during the ovarian development. From stages I to III, the E₂ content in three tissues increased significantly, then decreased gradually until stage V. As for the Vg-mRNA expression level in hepatopancreas and ovaries, an increasing trend was found in ovaries but no significant difference was detected during the period of ovarian stages III to V. Hepatopancreatic Vg-mRNA expression level increased significantly during stages I to IV and dramatically decreased at stage V. In conclusion, our study suggests that ovary, hepatopancreas, hemolymph and nervous tissues are the target organs of E₂ in E. sinensis and E₂ concentrations in different tissues are closely related to vitellogenesis in ovary and hepatopancreas during ovarian development.

Elucidation of the role of estradiol and progesterone in regulating reproduction in the edible crab, Oziothelphusa senex senex

Vertebrate sex steroids are ubiquitous and important bioactive mediators for many physiological functions.

Ovarian Transcriptome Analysis of Portunus trituberculatus Provides Insights into Genes Expressed during Phase III and IV Development

Enhancing the production of aquatic animals is crucial for fishery management and aquaculture applications. Ovaries are specialized tissues that play critical roles in producing oocytes and hormones. Significant biochemical changes take place during the sexual maturation of Portunus trituberculatus, but the genetics of this process has not been extensively studied. Transcriptome sequencing can be used to determine gene expression changes within specific periods. In the current study, we used transcriptome sequencing to produce a comprehensive transcript dataset for the ovarian development of P. trituberculatus. Approximately 100 million sequencing reads were generated, and 126,075 transcripts were assembled. Functional annotation of the obtained transcripts revealed important pathways in ovarian development, such as those involving the vitellogenin gene. Also, we performed deep sequencing of ovaries in phases III and IV of sexual maturation in P. trituberculatus. Differential analysis of gene expression identified 506 significantly differentially expressed genes, which belong to 20 pathway, transporters, development, transcription factors, metabolism of other amino acids, carbohydrate and lipid, solute carrier family members, and enzymes. Taken together, our study provides the first comprehensive transcriptomic resource for P. trituberculatus ovaries, which will strengthen understanding of the molecular mechanisms underlying the sexual maturation process and advance molecular nutritional studies of P. trituberculatus.

Insights into hepatopancreatic functions for nutrition metabolism and ovarian development in the crab Portunus trituberculatus: gene discovery in the comparative transcriptome of different hepatopancreas stages

The crustacean hepatopancreas has different functions including absorption, storage of nutrients and vitellogenesis during growth, and ovarian development. However, genetic information on the biological functions of the crustacean hepatopancreas during such processes is limited. The swimming crab, Portunus trituberculatus, is a commercially important species for both aquaculture and fisheries in the Asia-Pacific region. This study compared the transcriptome in the hepatopancreas of female P. trituberculatus during the growth and ovarian maturation stages by 454 high-throughput pyrosequencing and bioinformatics. The goal was to discover genes in the hepatopancreas involved in food digestion, nutrition metabolism and ovarian development, and to identify patterns of gene expression during growth and ovarian maturation. Our transcriptome produced 303,450 reads with an average length of 351 bp, and the high quality reads were assembled into 21,635 contigs and 31,844 singlets. Based on BLASTP searches of the deduced protein sequences, there were 7,762 contigs and 4,098 singlets with functional annotation. Further analysis revealed 33,427 unigenes with ORFs, including 17,388 contigs and 16,039 singlets in the hepatopancreas, while only 7,954 unigenes (5,691 contigs and 2,263 singlets) with the predicted protein sequences were annotated with biological functions. The deduced protein sequences were assigned to 3,734 GO terms, 25 COG categories and 294 specific pathways. Furthermore, there were 14, 534, and 22 identified unigenes involved in food digestion, nutrition metabolism and ovarian development, respectively. 212 differentially expressed genes (DEGs) were found between the growth and endogenous stage of the hepatopancreas, while there were 382 DEGs between the endogenous and exogenous stage hepatopancreas. Our results not only enhance the understanding of crustacean hepatopancreatic functions during growth and ovarian development, but also represent a basis for further research on new genes and functional genomics of P. trituberculatus or closely related species.

In-depth tanscriptomic analysis on giant freshwater prawns

Gene discovery in the Malaysian giant freshwater prawn (Macrobrachium rosenbergii) has been limited to small scale data collection, despite great interest in various research fields related to the commercial significance of this species. Next generation sequencing technologies that have been developed recently and enabled whole transcriptome sequencing (RNA-seq), have allowed generation of large scale functional genomics data sets in a shorter time than was previously possible. Using this technology, transcriptome sequencing of three tissue types: hepatopancreas, gill and muscle, has been undertaken to generate functional genomics data for M. rosenbergii at a massive scale. De novo assembly of 75-bp paired end Ilumina reads has generated 102,230 unigenes. Sequence homology search and in silico prediction have identified known and novel protein coding candidate genes (∼24%), non-coding RNA, and repetitive elements in the transcriptome. Potential markers consisting of simple sequence repeats associated with known protein coding genes have been successfully identified. Using KEGG pathway enrichment, differentially expressed genes in different tissues were systematically represented. The functions of gill and hepatopancreas in the context of neuroactive regulation, metabolism, reproduction, environmental stress and disease responses are described and support relevant experimental studies conducted previously in M. rosenbergii and other crustaceans. This large scale gene discovery represents the most extensive transcriptome data for freshwater prawn. Comparison with model organisms has paved the path to address the possible conserved biological entities shared between vertebrates and crustaceans. The functional genomics resources generated from this study provide the basis for constructing hypotheses for future molecular research in the freshwater shrimp.

Uptake and elimination, and effect of estrogen-like contaminants in estuarine copepods: an experimental study

BACKGROUND, AIM, AND SCOPE

In recent years, anthropogenic chemicals which can disrupt the hormonal systems of both humans and wildlife have been raised to a major cause of concern. The aim of the present work was to determine the bioconcentration factors of the two major alkylphenols (AP) of the Seine Estuary [4-nonylphenol (4 NP) and nonylphenol acetic acid (NP1EC)] and of the synthetic estrogen, estrogen ethinylestradiol (EE2), in Eurytemora affinis after exposure in a continuous flow-through system under environmental realistic conditions. Moreover, the elimination of these compounds in copepods from the Seine Estuary has been investigated by measuring concentrations after 1 week in clean water in comparison to background levels.

MATERIALS AND METHODS

In this study, the dominant copepod species of the Seine Estuary, E. affinis, was exposed at environmental relevant concentrations under laboratory-controlled conditions to selected waterborn contaminants, a mixture of 4 NP/NP1EC, and a synthetic EE2. The uptake and the elimination of these contaminants by E. affinis have been studied.

RESULTS

The results show that, at the end of the uptake period, both 4 NP and NP1EC, and also EE2 were accumulated in exposed copepods with respective concentration factors of 324, 3,020, and 5,383. A rapid elimination of these compounds was also observed in copepods placed in clean water since 54% of total NP1EC and 100% of EE2 amounts have been lost after 3 days. Pregnenolone was synthesized after exposure to EE2 and AP mixture.

DISCUSSION

These results demonstrate that E. affinis has the potency to accumulate but also to eliminate endocrine disrupters which suggests a non-negligible role of this copepod species in the biogeochemical cycles of these contaminants in estuarine ecosystems. Hence, these results also suggest that a transfer of 4 NP, NP1EC, and EE2 to copepod predators and subsequently that secondary poisoning of these organisms might be possible. Estrogen-like contaminants can induce pregnenolone synthesis and affect the reproduction of E. affinis.

CONCLUSIONS

These results suggest the important role of this copepod species in biogeochemical cycles of non-ionic surfactants as well as synthetic steroids in estuarine ecosystems.

RECOMMENDATIONS AND PERSPECTIVES

E. affinis could be a non-negligible route of exposure for juvenile fish and underline the potential for deleterious effects on copepod predators.

Steroid metabolism in cnidarians: insights from Nematostella vectensis

Cnidarians occupy a key evolutionary position as a sister group to bilaterian animals. While cnidarians contain a diverse complement of steroids, sterols, and other lipid metabolites, relatively little is known of the endogenous steroid metabolism or function in cnidarian tissues. Incubations of cnidarian tissues with steroid substrates have indicated the presence of steroid metabolizing enzymes, particularly enzymes with 17beta-hydroxysteroid dehydrogenase (17beta-HSD) activity. Through analysis of the genome of the starlet sea anemone, Nematostella vectensis, we identified a suite of genes in the short chain dehydrogenase/reductase (SDR) superfamily including homologs of genes that metabolize steroids in other animals. A more detailed analysis of Hsd17b4 revealed complex evolutionary relationships, apparent intron loss in several taxa, and predominantly adult expression in N. vectensis. Due to its ease of culture and available molecular tools N. vectensis is an excellent model for investigation of cnidarian steroid metabolism and gene function.

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.

Endocrine disruptors in marine organisms: approaches and perspectives

Organic pollutants exhibiting endocrine disrupting activity (Endocrine Disruptors--EDs) are prevalent over a wide range in the aquatic ecosystems; most EDs are resistant to environmental degradation and are considered ubiquitous contaminants. The actual potency of EDs is low compared to that of natural hormones, but environmental concentrations may still be sufficiently high to produce detrimental biological effects. Most information on the biological effects and mechanisms of action of EDs has been focused on vertebrates. Here we summarize recent progress in studies on selected aspects of endocrine disruption in marine organisms that are still poorly understood and that certainly deserve further research in the near future. This review, divided in four sections, focuses mainly on invertebrates (effects of EDs and mechanisms of action) and presents data on top predators (large pelagic fish and cetaceans), a group of vertebrates that are particularly at risk due to their position in the food chain. The first section deals with basic pathways of steroid biosynthesis and metabolism as a target for endocrine disruption in invertebrates. In the second section, data on the effects and alternative mechanisms of action of estrogenic compounds in mussel immunocytes are presented, addressing to the importance of investigating full range responses to estrogenic chemicals in ecologically relevant invertebrate species. In the third section we review the potential use of vitellogenin (Vtg)-like proteins as a biomarker of endocrine disruption in marine bivalve molluscs, used worldwide as sentinels in marine biomonitoring programmes. Finally, we summarize the results of a recent survey on ED accumulation and effects on marine fish and mammals, utilizing both classical biomarkers of endocrine disruption in vertebrates and non-lethal techniques, such as non-destructive biomarkers, indicating the toxicological risk for top predator species in the Mediterranean. Overall, the reviewed data underline the potential to identify specific types of responses to specific groups of chemicals such as EDs in order to develop suitable biomarkers that could be useful as diagnostic tools for endocrine disruption in marine invertebrates and vertebrates.

17Beta-hydroxysteroid dehydrogenase (17beta-HSD) in scleractinian corals and zooxanthellae

Steroid metabolism studies have yielded evidence of 17beta-hydroxysteroid dehydrogenase (17beta-HSD) activity in corals. This project was undertaken to clarify whether there are multiple isoforms of 17beta-HSD, whether activity levels vary seasonally, and if zooxanthellae contribute to activity. 17Beta-HSD activity was characterized in zooxanthellate and azooxanthellate coral fragments collected in summer and winter and in zooxanthellae cultured from Montipora capitata. More specifically, 17beta-HSD activity was characterized with regard to steroid substrate and inhibitor specificity, coenzyme specificity, and Michaelis constants for estradiol (E2) and NADP+. Six samples each of M. capitata and Tubastrea coccinea (three summers, three winters) were assayed with E2 and NADP+. Specific activity levels (pmol/mg protein) varied 10-fold among M. capitata samples and 6-fold among T. coccinea samples. There was overlap of activity levels between summer and winter samples. NADP+/NAD+ activity ratios varied from 1.6 to 22.2 for M. capatita, 2.3 to 3.8 for T. coccinea and 0.7 to 1.1 for zooxanthellae. Coumestrol was the most inhibitory of the steroids and phytoestrogens tested. Our data confirm that corals and zooxanthellae contain 17beta-HSD and are consistent with the presence of more than one isoform of the enzyme.

A comparative study on androgen metabolism in three invertebrate species

A comparative approach was taken in this study to evaluate androgen (androstenedione and testosterone) metabolism in three invertebrate species: the gastropod Marisa cornuarietis, the amphipod Hyalella azteca, and the echinoderm Paracentrotus lividus. The existence of 17beta/3beta-hydroxysteroid dehydrogenase (HSD) and 5alpha-reductase catalyzed reactions was demonstrated in all three species. Androstenedione was primarily converted to 5alpha-androstanedione in M. cornuarietis, while it was primarily metabolized to testosterone in P. lividus and H. azteca. In addition, and consistent with vertebrate findings, tissue specific pathways and sexual dimorphism in androgen metabolism were observed. Namely, testosterone was metabolized to dihydrotestosterone in P. lividus gonads (via 5alpha-reductase), and metabolized to 4-androstene-3beta,17beta-diol in the digestive tube (via 3beta-hydroxysteroid dehydrogenase). Furthermore, the synthesis of 17beta-reduced metabolites of androstenedione (testosterone and dihydrotestosterone) was 3- to 4-fold higher in males of M. cornuarietis than in females. Organotin compounds, which have been shown to interfere with some aspects of androgen metabolism, had no major effect on testosterone metabolism in any of the three species. Fenarimol enhanced 5alpha-reductase-mediated catalysis in gonads of P. lividus. Overall, results demonstrate the ubiquity of some androgen biotransformation processes in invertebrates and reveals interphyla differences in androgen metabolic pathways, and different sensitivity of these pathways to some xenobiotics.

Metabolism of estrogens and androgens by scleractinian corals

Estrogens and androgens are steroids that act as reproductive hormones in vertebrates. These compounds have also been detected in reef-building corals and other invertebrates, where they are hypothesized to act as bioregulatory molecules. Experiments were conducted using labeled steroid substrates to evaluate metabolism of estrogens and androgens by coral homogenates. GC-MS analysis of 13C-labeled steroids showed that Montipora capitata coral homogenates or fragments could convert estradiol to estrone and testosterone to androstenedione and androstanedione, evidence that M. capitata contains 17beta-hydroxysteroid dehydrogenase and 5alpha-reductase. When homogenates from three coral species and symbiotic dinoflagellates (zooxanthellae) were incubated with tritiated steroid substrates, metabolites separated by thin-layer chromatography confirmed that 17beta-hydroxysteroid dehydrogenase activity occurred in all species tested. NADP+ was the preferred cofactor in dehydrogenation reactions with coral homogenates. Reduction of estrone and androstenedione occurred at lower rates and aromatization of androgens was not observed. It is unclear whether estrogens detected previously in coral tissues are produced endogenously or sequestered in coral tissue from dietary or environmental sources. Previous studies have demonstrated that corals can take up estrogens from the water column overlying coral reefs. Considered in total, these observations suggest corals could alter the concentration or form of steroids available to reef organisms.

Oestrogens have no hormonal effect on the development and reproduction of the harpacticoid copepod Nitocra spinipes

In recent years, reports have described endocrine-disruptive effects of environmental oestrogens in fish, but little is known about similar effects in crustaceans. The objective of the present study was therefore to examine whether the oestrogens 17-beta-oestradiol, 17-alpha-ethynylestradiol and diethylstilbestrol (DES), could affect mortality, larval development rate, fecundity and sex ratio in the sexually reproducing harpacticoid copepod Nitocra spinipes. Newly released nauplii (<24-h old) were exposed to 1/1,000, 1/100 and 1/10 (nominal concentrations) of each oestrogen's 96 h-LC50 value for < or = 18 days at 22 +/- 1 degrees C. The percentage of gravid females and the number of developed copepodites were both reduced at 0.03 mg l(-1) DES, although the latter response was not significant. None of the other two oestrogens induced any measurable effects. Since the only observed significant response appeared at a DES concentration no more than 10 times below the 96 h-LC50 value, there is no evidence of endocrine-disruptive activity in N. spinipes exposed to oestrogens.

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.