Machine learning reveals sex-specific 17β-estradiol-responsive expression patterns in white perch (Morone americana) plasma proteins

With growing abundance and awareness of endocrine disrupting compounds (EDCs) in the environment, there is a need for accurate and reliable detection of EDC exposure. Our objective in the present study was to observe differences within and between the global plasma proteomes of sexually mature male and female white perch (Morone americana) before (Initial Control, IC) and after 17β-estradiol (E2 ) induction. Semiquantitative nanoLC-MS/MS data were analyzed by machine learning support vector machines (SVMs) and by two-way ANOVA. By ANOVA, the expression levels of 44, 77, and 57 proteins varied significantly by gender, treatment, and the interaction of gender and treatment, respectively. SVMs perfectly classified male and female perch IC and E2 -induced plasma samples using the protein expression data. E2 -induced male and female perch plasma proteomes contained significantly higher levels of the yolk precursors vitellogenin Aa and Ab (VtgAa, VtgAb), as well as latrophilin and seven transmembrane domain-containing protein 1 (Eltd1) and kininogen 1 (Kng1). This is the first report that Eltd1 and Kng1 may be E2 -responsive proteins in fishes and therefore may be useful indicators of estrogen induction.

Effects of nonylphenol and ethinylestradiol on copper redhorse (Moxostoma hubbsi), an endangered species

The copper redhorse, Moxostoma hubbsi, is an endangered species endemic to Quebec. The presence of contaminants, in particular endocrine disrupting chemicals (EDCs), in its habitat has been advanced as partly responsible for the reproductive difficulties encountered by the species. In the present study, immature copper redhorse were exposed to the estrogenic surfactant nonylphenol (NP; 1, 10 and 50µg/l) and the synthetic estrogen 17α-ethinylestradiol (EE2; 10ng/l) for 21 days in a flow-through system. The endpoints investigated included general health indicators (hepatosomatic index and hematocrit), thyroid hormones, sex steroids, brain aromatase activity, plasma and mucus vitellogenin (VTG), cytochrome P4501A protein expression and ethoxyresorufin-O-deethylase activity, heat shock protein 70 (HSP70) and muscle acetylcholinesterase. Exposure to 10ng EE2/l significantly increased brain aromatase activity. Exposure to 50µg NP/l resulted in a significant reduction of plasma testosterone concentrations and a significant induction of hepatic HSP70 protein expression. NP at 50µg/l also induced plasma and mucus VTG. The presence of elevated VTG levels in the surface mucus of immature copper redhorse exposed to NP, and its correlation to plasma VTG, supports the use of mucus VTG as a non-invasive biomarker to evaluate copper redhorse exposure to EDCs in the environment and contribute to restoration efforts of the species. The results of the present study indicate that exposure to high environmentally relevant concentrations of NP and EE2 can affect molecular endpoints related to reproduction in the copper redhorse.

Current and future assisted reproductive technologies for fish species

The Food and Agriculture Organization of the United Nations (FAO) estimates that in 2012 aquaculture production of fish will meet or exceed that of the capture fisheries for the first time. Thus, we have just turned the corner from a predominantly hunting gathering approach to meeting our nutritional needs from fish, to a farming approach. In 2012, 327 finfish species and five hybrids were covered by FAO aquaculture statistics, although farming of carps, tilapias, salmonids, and catfishes account for most of food-fish production from aquaculture. Although for most major species at least part of production is based on what might be considered domesticated animals, only limited production in most species is based on farming of improved lines of fish or is fully independent of wild seedstock. Consistent with the infancy of most aquaculture industries, much of the development and implementation of reproductive technologies over the past 100 years has been directed at completion of the life cycle in captivity in order to increase seed production and begin the process of domestication. The selection of species to farm and the emphasis of selective breeding must also take into account other ways to modify performance of an animal. Reproductive technologies have also been developed and implemented to affect many performance traits among fishes. Examples include technologies to control gender, alter time of sexual maturation, and induce sterilization. These technologies help take advantage of sexually dimorphic growth, overcome problems with growth performance and flesh quality associated with sexual maturation, and genetic containment. Reproductive technologies developed to advance aquaculture and how these technologies have been implemented to advance various sectors of the aquaculture industry are discussed. Finally, we will present some thoughts regarding future directions for reproductive technologies and their applications in finfish aquaculture.

Early expression of zona pellucida proteins under octylphenol exposure in Cichlasoma dimerus (Perciformes, Cichlidae)

An increasing number of widely used industrial and agricultural chemicals are being found to cause endocrine disruption. In fishes, xenoestrogens can induce female proteins, and in some cases, the development of testis-ova, demonstrating feminization of males. In this study we analyzed the effect of an acute exposure of adult male Cichlasoma dimerus fish to estradiol (E(2)) and octylphenol (OP). E(2) and OP were injected at 10 and 50 μg/g body weight doses, respectively. After a single OP dose, liver was processed for RNA extraction at 1, 3, 12, 24, and 72 h. PCR was performed using cDNA and primers for egg coat or zona pellucida proteins (ZP). Genes encoding ZPB and ZPC isoforms were sequenced. E(2)-induced fish were sacrificed at 72 h. Using multiple OP or E(2) injections, blood and surface mucus were sampled on days 0, 3, 6, 9, and 13. On day 13 fish were sacrificed for liver and testis dissection. Histological examination of E(2) and OP-treated fish livers showed cellular disarray and intense cytoplasmatic basophilia within hepatocytes, probably due to increased mRNA synthesis, as well as hypertrophied euchromatic nuclei, and conspicuous nucleoli, indicative of augmented cell activity. An abnormal amount of sperm and immature germ cells within the testis lumen were seen in treated fish, suggesting reproductive impairment. Both plasma and mucus revealed the presence of ZP (and vitellogenin) at day 3 and thereafter with E(2) treatment, using Western and Dot blot techniques; OP effects were delayed in time. These results validate the analysis of mucus by Dot blot as an easy and rapid technique to address endocrine disruption caused by OP. Quantitative gene expression showed induction of liver ZPB and ZPC upon OP injection; muscle, brain, and intestine did not express any ZP. Both ZPs were induced at 1h post injection, but only ZPB expression was statistically significant. At 12h, both ZPs increased significantly, reaching the same levels of E(2)-challenged males after 72 h. Therefore, OP mimicked the action of E(2) with a prompt and strong xenoestrogenic effect, evidenced by the early response through mRNA and protein expression of ZP and the concomitant histological liver and testis alterations.

Hybrid ELISAs for vitellogenins of the endangered copper redhorse Moxostoma hubbsi and the shorthead redhorse Moxostoma macrolepidotum (Cypriniformes, catostomidae)

The shorthead redhorse (sr) Moxostoma macrolepidotum is endemic in North America, while in Canada the copper redhorse (cr) Moxostoma hubbsi is classified as endangered. A commercial heterologous carp vitellogenin (VTG) sandwich ELISA underestimates VTGs in these species. Hybrid ELISAs, using anti-carp VTG antibodies and purified sr- and cr-VTGs as standards, were validated to measure VTGs in plasma and surface mucus of redhorse species. The hybrid ELISAs showed good precision, sensitivity and accuracy. Following induction with beta-estradiol 3-benzoate (E2B), levels of plasma VTG (mean+/-SEM) in male sr increased from 2.7+/-1.5 microg/ml to 16.5+/-2.2mg/ml. In immature cr, plasma VTG increased to 70.1+/-13.8 mg/ml after induction, from an initial value of 37.7+/-51.0 microg/ml. Levels of VTG in mucus from E2B-injected fish were highly correlated (p<0.0001) with levels in plasma, but not in a non-induced mature female. Hybrid assays are a good compromise between homologous and heterologous assays, especially for small-bodied or endangered fish species. The performance of the hybrid assays strongly suggests they could be used to determine exposure of these species to estrogenic contaminants and contribute to restoration efforts of the copper redhorse.

A histochemical study on the snout tentacles and snout skin of bristlenose catfish Ancistrus triradiatus

Histological sections of the tentacles of Ancistrus triradiatus revealed that they contain many goblet cells with granule-like sections distributed along the edge of the tentacles (mean 302 cells mm(-1)). Various histochemical methods were used to characterize the contents of the goblet cells. The results indicated that the contents were periodic acid-Schiff (PAS) positive, glycogen negative and no sulphated mucins could be found. The contents of the goblet cells were acid mucins and O-acetylated sialomucins which had high energy content. The snout skin of the male also contained goblet cells with higher density (mean 755 cells mm(-1)) than that of the tentacles. Snout skin of female A. triradiatus, on the contrary, did not contain any goblet cells. Instead, many minute spines could be found. Based on the acid mucins and O-acetylated sialomucins secretions of goblet cells which are of high nutritional values, it is hypothesized that snout tentacle secretions are used to provide nutrients to fish larvae when they are under paternal care.

Exposure to waterborne 4-tert-octylphenol induces vitellogenin synthesis and disrupts testis morphology in the South American freshwater fish Cichlasoma dimerus (Teleostei, Perciformes)

Exposure to environmental pollutants may disrupt endocrine functions and cause reproductive effects in human and wildlife populations. Various groups of chemicals have estrogen-like effects, including degradation products of alkylphenol polyethoxylates, such as 4-tert-octylphenol (OP). Laboratory studies have shown that exposure of male fish to xenoestrogens results in induction of circulating vitellogenin (Vtg), inhibition of testicular growth, testis abnormalities and formation of intersex gonads. In this study, the impact of the exposure to waterborne OP on reproductive aspects in the South American cichlid fish Cichlasoma dimerus was evaluated using qualitative changes in the levels of Vtg in plasma and surface mucus and histological alterations in the liver and gonads as endpoints. Adult males and females were exposed to OP via immersion during 60 days in aquaria under semi-static conditions, water changes being made every 84 h. Treatment groups were: control (ethanol 0.005%), OP 30, 150 and 300 microg/L. Using Western and Dot blot analysis, Vtg was detected in plasma and mucus of control and treated females and treated males, while no Vtg was observed in samples from control males. Morphological changes in the hepatocytes due to the accumulation of Vtg were observed in OP-exposed males. Impairment of testicular structure became apparent in males treated with the highest OP concentrations. The most salient pathological change was the alteration of lobular organization with increased testicular fibrosis and progressive disruption of spermatogenesis. No major changes were observed in ovarian architecture. Our results indicate that detection of Vtg in surface mucus may be a sensitive and non-invasive biomarker of the endocrine disrupting effects of environmental estrogens, resulting in a useful method for field monitoring.

Tributyltin-binding protein type 1 has a distinctive lipocalin-like structure and is involved in the excretion of tributyltin in Japanese flounder, Paralichthys olivaceus

Tributyltin-binding protein type 1 (TBT-bp1) is a newly discovered protein that binds with TBT in the blood of the Japanese flounder, Paralichthys olivaceus. We determined the genomic sequence of TBT-bp1 and found that this protein has a conserved exon-intron structure that is common to the lipocalin protein family. The secondary and tertiary structures of TBT-bp1, predicted from amino acid sequence, included at least two alpha-helices and eight beta-sheets that are conserved in all lipocalins and form a barrel structure that may bind with ligands. Analysis of the gene structure, secondary structure, and tertiary structure demonstrated that TBT-bp1 could be classified as a lipocalin. A homology search revealed the presence of TBT-bp1-like proteins in eight species of teleost. When flounder were injected intraperitoneally with TBT-d27 at 11.6mug/fish, TBT-d27 was detected in the blood and in the skin mucus. The concentration of TBT-d27 in mucus was approximately 1/100 of that in the serum. Western blotting analysis revealed that TBT-bp1 was present in the skin mucus. These results suggest that TBT-bp1 in Japanese flounder binds with TBT and is excreted from the body via the mucus.

Tilapia (Oreochromis niloticus) vitellogenins: development of homologous and heterologous ELISAs and analysis of vitellogenin pathway through the ovarian follicle

Vitellogenin (VTG) of Oreochromis niloticus was again purified, due to the conflicting results found in the literature. Three purification processes have been used: electrophoresis and electro-elution, double chromatography (gel filtration and ion-exchange chromatography) and single ion-exchange chromatography. Using SDS-PAGE we confirmed in all cases the presence of two polypeptidic forms of plasma VTG of 130 kDa (VTG1) and 170 kDa (VTG2). We raised polyclonal antibodies against each VTG form and we demonstrated the complete cross-reactivity of each antibody with both forms of VTG by Enzyme Immuno-Assay (EIA) and Western blots. The homologous ELISAs developed exhibited a detection limit of 6 ng x ml(-1), equivalent to 60 ng x ml(-1) of plasma VTG and allowed us to quantify the total plasma VTG of O. niloticus with high specificity and sensitivity. Using photonic and electron immunomicroscopy, we followed the pathway of VTG into the ovarian follicle (OF) demonstrating that VTG enters the oocyte at stage 3 of OF development, at the same time as cortical alveoli and lipid globules appear. Heterologous ELISAs performed on other cichlid species allowed us to quantify plasma VTG in Oreochromis aureus and Sarotherodon melanotheron and to detect it in Hemichromis fasciatus, Hemichromis bimaculatus and Tilapia zillii, constituting a reliable tool for monitoring the presence of xeno-estrogens in the environment of these fish species.

Proteomics profiling of epidermal mucus secretion of a cichlid (Symphysodon aequifasciata) demonstrating parental care behavior

The discus fish (Symphysodon aequifasciata) is a cichlid demonstrating advanced mode of parental care towards fry. Both male and female fish utilized epidermal mucus secreted from specialized epidermal cells to feed developing fry. We utilized proteomics to compare protein profile from parental and nonparental fish. Gel analysis revealed a total of 35 spots that were up-regulated in parental mucus. In tandem, another 18 spots were uniquely expressed in parental mucus. MS analysis of these spots identified proteins such as fructose biphosphate aldolase, nucleoside diphosphate kinase, and heat shock proteins, which are essential to support energy provision, cell repair and proliferation, stress mediation, and defense mechanism in parental fish during parental-care period. Concurrently, the detection of several antioxidant-related proteins such as thioredoxin peroxidase and hemopexin suggests a need to overcome oxidative stress during hypermucosal production in parental-care behavior. A C-type lectin was also found to be uniquely expressed in parental mucus and could have important role in providing antimicrobial defense to both parental fish and fry. In summary, our study shows that discus mucus proteome undergoes changes in protein expression during parental-care period.

Identification of estrogen-responsive genes in the testis of sea bream (Sparus auratus) using suppression subtractive hybridization

There is growing evidence that estrogens play important roles in both normal and xenoestrogen disrupted testis physiology. However, the mechanisms and signaling pathways involved, in particular in fish, are largely unknown. We have used suppression subtractive hybridization to isolate 152 candidate estrogen-responsive genes in the testis of male estradiol (E2)-treated sea bream (Sparus aurata). The E2 up-regulation of some of the genes (e.g., choriogenin L and H, vitellogenin I and II, apolipoprotein A-I, fibrinogen beta and gamma, and thyroid receptor interacting protein 4) was confirmed by reverse transcriptase polymerase chain reaction in fish treated with 0.1-10 mg/kg E2. Many of these genes are typical E2-induced genes in liver, and this is the first report of its up regulation with E2 in testis. Moreover, low levels of expression were also found for nontreated fish. Hepatic differential expression for these genes was also confirmed, although, contrary to testis, fibrinogen beta, and gamma were downregulated. The possible significance of these findings in normal testis physiology and in endocrine disruption is discussed.

Hepatic and extrahepatic expression of vitellogenin genes in the zebrafish, Danio rerio

Vitellogenins (Vtgs) are yolk precursor proteins in oviparous species and are cleaved into three portions-lipovitellin I (LVI), phosvitin (PV), and lipovitellin II (LVII)-in oocytes in vertebrates. In the present study, we found that the zebrafish genome contains at least seven vtg genes (vtg1-7) encoding heterogeneous vitellogenins with three distinct types of Vtgs: type I (Vtg1, 4-7) contains all the three major portions but lacks the C-terminal half of LVII; type II (Vtg2) is the only one including intact three portions; type III (Vtg3) lacks both PV and the LVII C-terminal half. The seven vtgs were located in two different chromosomes: one (vtg3) in LG11 and the rest closely linked in LG22, probably arisen from local gene duplication events. All of the seven vtgs are predominantly expressed in female liver and can be induced in male liver by 17beta-estradiol (E2). The level of vtg1 mRNA was about 100x and 1000x higher than those of vtg2 and vtg3 mRNAs. We also found vtg mRNAs in several non-liver tissues, but the expression level is generally <10% of that in the liver. In situ hybridization experiments confirmed that the extrahepatic expression was actually in adipocytes associated with several organs such as the intestine, ovary, and E2-induced testis.

Effects of estradiol-17beta treatment on in vitro and in vivo synthesis of two distinct vitellogenins in tilapia

Two distinct vitellogenins (VTG) were purified from the blood of estradiol-17beta (E(2))-injected tilapia, Oreochromis mossambicus. Enzyme-linked immunosorbent assays (ELISA) of each VTG were developed to examine effects of E(2) treatment on induction of VTG synthesis in the primarily cultured tilapia hepatocytes. Two VTG molecules (VTG210 and VTG140) had apparent molecular masses of 370 and 220 kDa by gel filtration and 210 and 140 kDa by SDS-PAGE, respectively. Western blot analyses showed that antibodies raised against the purified VTG210 and VTG140 reacted only with each protein band. Furthermore, ELISA for each VTG was specific for target VTG. When E(2) was added into the media of primarily cultured tilapia hepatocytes, VTG210 and VTG140 were both detected from E(2) concentrations of 1x10(-7) M and 5x10(-7) M, respectively. Time course experiments showed that there was a difference in the detection time of VTG210 and VTG140 after the hormone treatment. Although the injection of different E(2) doses induced both VTGs in the plasma of male tilapia, the concentration of VTG210 was nearly five to eight times higher than that of VTG140. These results suggest that E(2) is a direct inducer of both VTGs in the tilapia hepatocytes in vitro and in vivo, and that there is difference in the hormone response in inducing the VTGs in the tilapia hepatocytes.

Paternal mouthbrooding in the black-chinned tilapia, Sarotherodon melanotheron (Pisces: cichlidae): changes in gonadal steroids and potential for vitellogenin transfer to larvae

The black-chinned tilapia (Sarotherodon melanotheron) is a paternal mouthbrooder. Pairs of adult black-chinned tilapia were raised in freshwater and the males were sampled during the mouthbrooding cycle. Sampling also occurred 10 days after release of the free-swimming fry for comparison. During the first week of incubation of the eggs, total androgens and estradiol were low (<5 and <0.3 ng/ml, respectively). During the second week of brooding, when the eggs have hatched and they are called newly hatched embryos, plasma levels of gonadal steroids increased (13-38 ng androgen/ml and >0.6 ng estradiol/ml). The plasma concentrations of vitellogenin (VTG) in male parents changed during mouthbrooding, with decreases occurring between egg pickup and hatching of the embryo (Day 6 of mouthbrooding). The pattern of change in concentrations of VTG in surface mucus of male parents differed from the pattern in plasma, with peak concentrations occurring at the time of hatching. The amount of VTG in mucus was similar to that measured in the female Oreochromis mossambicus during mouthbrooding of embryos. The appearance of peak VTG levels in the mucus at the time of hatching when plasma levels have declined and the availability of comparable amounts of mucus VTG in both maternal and paternal mouthbrooding tilapia, despite unequivalent plasma levels, support the possibility that parental provisioning of the young occurs during mouthbrooding in tilapia.

Intestinal uptake of lipovitellin from brine shrimp (Artemia franciscana) by larval inland silversides (Menidia beryllina) and striped bass (Morone saxatilis)

Intestinal uptake of lipovitellin (LV) from brine shrimp (Artemia franciscana) in larval inland silversides (Menidia beryllina) and striped bass (Morone saxatilis) was described using immunocytochemistry. Polyclonal antisera were raised against two subunits of LV (LV68 and LV190). When tested by immunocytochemistry, anti-LV68 showed cross-reactivity with some of the pancreatic cells especially in inland silversides. Therefore anti-LV190 was used to localize immunoreactive LV. Inland silversides at 14 days after hatching were fed Artemia nauplii and then sampled 4, 8, 12 hr after feeding. Similar experiments were carried out by using striped bass at 5 days and 15 days of age. They were sampled at 2, 4, 8, and 12 hr after feeding. Anterior enterocytes showed no evidence of uptake; however, the brush border of the cells of inland silversides reacted with the antiserum. Posterior enterocytes took up the LV and/or, possibly, their immunoreactive breakdown products. The pattern of uptake included accumulation in supranuclear vacuoles and digestion in supranuclear vacuoles, as suggested by the decay of the immunoreactivity over time. Thus, the posterior intestine of these larval fishes is the site of uptake and digestion of LV, an important nutritive component in the food of many larval fishes; this supports earlier findings using non-nutritive marker proteins.

Plasma vitellogenin levels during the annual reproductive cycle of the female rainbow trout (Oncorhynchus mykiss): establishment and validation of an ELISA

Rainbow trout, Oncorhynchus mykiss, vitellogenin (Vtg) was purified from plasma of E2-treated male by direct anion exchange chromatography and some of its biochemical characteristics were studied. Our results demonstrated that, under SDS-PAGE conditions, rainbow trout Vtg was composed of two molecular forms of 390 and 176 kDa representing, respectively, the dimeric form and the monomeric from of the molecule. The purified Vtg was used to raise a polyclonal antibody for Vtg (anti-Vtg). Using this anti-Vtg, a competitive enzyme-linked immunosorbent assay (ELISA) was developed for the quantification of rainbow trout Vtg. The practical sensitivity range of this ELISA was 20-320 ng/ml (80-20% of binding) and the detection limit was 9 ng/ml. The intra- and the inter-assay coefficients of variation (at 50% of binding) were estimated at 1.8% (n = 10) and 3.9% (n = 13), respectively. This ELISA was validated by detecting changes in Vtg levels in rainbow trout at different physiological stages, as well as in 2-year-old female rainbow trout throughout the reproductive cycle.

Characterization of vitellogenin induced by estradiol-17β in protandrous black porgy,Acanthopagrus schlegeli

The objectives of this study were to isolate and characterize vitellogenin from plasma of estradiol-treated protandrous black porgy,Acanthopagrus schlegeli. Vitellogenin concentrations in plasma measured by a validated enzyme-linked immunosorbent assay (ELISA) were also compared. Two-year-old black porgy (n=20) were fed with estradiol-17β (4 mg kg(-1) of feed). Plasma was collected for purification of vitellogenin. Two forms of vitellogenin were found in plasma after chromatography on Sepharose CL-2B column and hydroxylapatite, and polyacrylamide gel electrophoresis. Black porgy vitellogenins are phospho-lipo-glycoproteins based on their chemical staining properties. The apparent molecular weights of the two forms of vitellogenin were 636 kDa and 321 kDa, respectively. The amino acid composition of purified vitellogenin was also analyzed after acid hydrolysis. The presence of immunoreactive vitellogenin was identified in the plasma and mucus extract from control and estradiol-induced females on the basis of Western blotting. Serial dilution of the plasma and mucus extract taken from estradiol-induced black porgy showed reactivity to an antiserum against lipovitellin in the ELISA, whereas mucus extract and plasma from male fish did not. Significantly higher concentrations of plasma vitellogenin were detected in estradiol-stimulated black porgy than in the control males.