Vitellogenin induction by estradiol in channel catfish, Ictalurus punctatus

Endocrine patterns associated with ovarian development in female Pacific halibut (Hippoglossus stenolepis)

The Pacific halibut (Hippoglossus stenolepis) is a large migratory demersal flatfish species that occupies a top trophic role in the North Pacific Ocean and Bering Sea ecosystems, where it also supports various fisheries. As a first attempt to characterize the endocrine mechanisms driving sexual maturation in this important species, we collected pituitary, ovarian and blood samples from Pacific halibut females captured in the wild that were classified histologically into various female developmental stages. We conducted gene expression analyses of gonadotropin beta subunits in the pituitary and observed that mRNA expression levels of fshb gradually increased throughout vitellogenesis, remained elevated until before ovulation and declined after spawning. In contrast, the mRNA expression levels of lhb markedly increased during oocyte maturation and remained elevated until after spawning. Ovarian mRNA expression levels of the gonadotropin receptor genes fshr and lhr peaked during oocyte maturation and before spawning, respectively, immediately following the developmental stage at which pituitary fshb and lhb mRNA expression first reached maximum levels. The ovarian gene expression patterns of steroidogenic enzyme genes cyp19a1 and hsd20b2 paralleled those of fshr and lhr, respectively. Testosterone and 17β-estradiol (E2) plasma levels increased concomitantly with fshr and cyp19a1 mRNA expression levels, and vitellogenin plasma levels increased throughout vitellogenesis and reached maximum levels prior to spawning. These results are consistent with the notion that in female Pacific halibut, as in other teleosts, vitellogenesis and oocyte maturation and ovulation are likely under the control of pituitary gonadotropic hormones Fsh and Lh, respectively.

Characterization, specificity and sensibility of produced anti-Rhamdia quelen vitellogenin in Brazilian fish species

Endocrine-disrupting chemicals (EDCs) are widespread used and can interfere on hormone regulation with adverse consequences for both biota and human. Vitellogenin (vtg) is a yolk precursor protein synthesized by the liver in response to estrogen. In order to characterize the vtg of tropical fish Rhamdia quelen and establish a molecular biomarker, adult male individuals were exposed to 17-β-estradiol (E₂) for vtg induction and anti-R. quelen vtg polyclonal antibodies production. Vitellogenic female fish were used as positive control group. E₂-induced vtg was characterized as a glycolipophosphoprotein of high molecular mass with peptide mass fingerprint very similar in E₂-exposed male and vitellogenic female fish. A polyclonal serum containing anti-R. quelen vtg antibodies was produced and showed high specificity and sensibility to detect the vtg of three fish species: R. quelen, Piaractus mesopotamicus and Prochilodus lineatus. Wildlife and laboratory studies reported that EDCs released into the environment may alter the levels of plasma vtg in male fish, making this protein a valuable biomarker of xenoestrogens exposure. Then, we propose the use of anti-R. quelen vtg as a tool for biomonitoring studies and water quality assessment in Brazil and South American countries where the three fish species occur.

Profiling neuroendocrine gene expression changes following fadrozole-induced estrogen decline in the female goldfish

Teleost fish represent unique models to study the role of neuroestrogens because of the extremely high activity of brain aromatase (AroB; the product of cyp19a1b). Aromatase respectively converts androstenedione and testosterone to estrone and 17β-estradiol (E2). Specific inhibition of aromatase activity by fadrozole has been shown to impair estrogen production and influence neuroendocrine and reproductive functions in fish, amphibians, and rodents. However, very few studies have identified the global transcriptomic response to fadrozole-induced decline of estrogens in a physiological context. In our study, sexually mature prespawning female goldfish were exposed to fadrozole (50 μg/l) in March and April when goldfish have the highest AroB activity and maximal gonadal size. Fadrozole treatment significantly decreased serum E2 levels (4.7 times lower; P = 0.027) and depressed AroB mRNA expression threefold in both the telencephalon ( P = 0.021) and the hypothalamus ( P = 0.006). Microarray expression profiling of the telencephalon identified 98 differentially expressed genes after fadrozole treatment ( q value <0.05). Some of these genes have shown previously to be estrogen responsive in either fish or other species, including rat, mouse, and human. Gene ontology analysis together with functional annotations revealed several regulatory themes for physiological estrogen action in fish brain that include the regulation of calcium signaling pathway and autoregulation of estrogen receptor action. Real-time PCR verified microarray data for decreased (activin-βA) or increased (calmodulin, ornithine decarboxylase 1) mRNA expression. These data have implications for our understanding of estrogen actions in the adult vertebrate brain.

Vitellogenin exists as charge isomers in the Indian freshwater murrel, Channa punctatus (Bloch)

Three charge isomeric forms of vitellogenin are reported in the blood of estrogen-treated murrel, Channa punctatus on the basis of the results of native and SDS-PAGE, isoelectric focusing, and Ferguson plot analysis. Vitellogenin was induced in adult murrels by exogenous administration of estradiol-17beta and labelled with 32P in vivo. Labelled vitellogenin isolated from other plasma proteins on Ultrogel AcA 34 columns resolve into three bands on native-PAGE. Ferguson plot analysis reveals free electrophoretic mobilities of the three bands as 6.0, 4.5, and 3.7, which are very similar to the isoelectric point values of 5.9, 4.6, and 3.8, respectively. The apparent molecular weight of native murrel vitellogenin is 530 kDa. It consists of a single peptide with a molecular weight of 175 kDa. All the three bands on native PAGE resolves into a single peptide on SDS-PAGE. N-terminal amino acid sequence for murrel vitellogenin peptide is MKAVVLALLL. The protein phosphorus:lipid phosphorus ratio for murrel vitellogenin is 0.9. The total lipid content is 32.8%, consisting of 45% neutral lipids and 30% phospholipids. Phosphatidyl choline is the major phospholipid whereas triglycerides are the major neutral lipids. Results of these analytical analyses indicate that murrel native vitellogenin circulates as three charge isomers; poor in phosphorus but rich in lipids content.

Multiple vitellogenins (Vgs) in mosquitofish (Gambusia affinis): identification and characterization of three functional Vg genes and their circulating and yolk protein products

The objectives of this study were to characterize multiple forms of vitellogenin (Vg) in mosquitofish (Gambusia affinis) and to discover the fate of each Vg during its processing into product yolk proteins. Two Vg preparations, with apparent masses of 600 kDa (600 Vg) and 400 kDa (400 Vg), were isolated from the plasma of fish treated with estradiol-17beta (E(2)) by various chromatographic procedures. Immunological analyses verified the presence of two different Vg proteins (600 VgA and 600 VgB) in the 600 Vg preparation and of a single protein in the 400 Vg preparation. Three major yolk proteins (Yps) with apparent masses of 560, 400, and 28 kDa were observed in extracts of ovarian follicles from vitellogenic females. Immunological analyses demonstrated that the 400 Vg underwent no change in native mass after being incorporated into oocytes. The 600 Vgs gave rise to a 28 kDa beta'-component and a native 560 kDa Yp, which was heterodimeric in structure, consisting of two types of complexes between phosvitin (Pv) and lipovitellin (Lv) heavy- and light-chains. Full-length cDNAs encoding the 600 VgA, 600 VgB, and 400 Vg were isolated from a liver cDNA library of E(2) treated fish. Similar to the zebrafish vg3 gene, the 400 Vg cDNA lacked a Pv domain and was classified as an incomplete or phosvitinless (C-type) Vg. The deduced primary structures of 600 VgA and 600 VgB were complete, and these were categorized as type A and type B Vgs, respectively, according to our recent classification scheme. This is the first report on the characterization of three functional Vg genes and their circulating and yolk protein products in any vertebrate species.

Vitellin processing and protein synthesis during cricket embryogenesis

At the start of insect embryogenesis most of the protein mass of the egg cytoplasm exists as vitellin (Vt) obtained endocytically during vitellogenesis. Of the new embryo polypeptides (EP) appearing in the egg during embryogenesis, many are synthesized de novo, while, in some species, others derive from developmentally programmed partial proteolysis of Vt. Earlier we showed that by the end of vitellogenesis the two native Vts in Acheta domesticus exist in opposing gradients along the longitudinal axis of the egg. Here we hypothesize that this ooplasmic Vt distribution presents a milieu for Vt processing out of which region-specific regulatory molecules could arise. The metabolic origin and stage-specific patterns of seven predominant EPs (EP 1-7) identified by SDS-PAGE were examined and the results correlated with developmental morphology during the 14 days of embryogenesis. Based on antibody reactivity, peptide mapping and in vitro radiolabeling, we determined that EPs 1-3, 6 and 7 are Vt-derived, while EPs 4 and 5 are produced de novo by the embryo. The five Vt-derived EPs appear during the first 24 h of embryogenesis when migrating cleavage nuclei and associated cytoplasm form the cellular blastoderm, and levels of EPs 4 and 5 increase during days 4-6 of embryogenesis when katatrepsis and yolk mass contraction occur. Positive periodic acid-Schiff staining indicated that EPs 1-3 and their Vt-precursor polypeptides are glycoproteins. This work shows that developmental stage-specific Vt processing occurs during A. domesticus embryogenesis and points next to investigation of the functional significance of Vt cleavage products during development.

Seasonal changes in the production of two novel and abundant ovarian steroids in the channel catfish (Ictalurus punctatus)

Timely and appropriate changes in steroid plasma titers are necessary for successful reproduction in all vertebrates. Gonadal steroidogenesis of the most intensively cultured teleost species in North America, the channel catfish (Ictalurus punctatus), is poorly understood so a year-long study was conducted to investigate seasonal changes in ovarian steroidogenesis. Incubations of ovarian tissue were conducted monthly with [3H]pregnenolone and the medium was analyzed by high-performance liquid chromatography (HPLC) with radioactivity detection. The suite of steroids produced by the catfish ovary included the expected sex steroids (estradiol and testosterone) and 18 additional ovarian metabolites, including five steroids that have yet to be identified. Androstenedione, 20beta-dihydroprogesterone, 5|P-dihydrotestosterone, estriol, 11beta-hydroxyandrostenedione, 17-hydroxypregnenolone, 17-hydroxyprogesterone, 11beta-hydroxytestosterone, and progesterone were characterized by a combination of HPLC and thin-layer chromatography. Two of the most abundant steroids were isolated and analyzed by gas chromatography coupled with mass spectrometry (GC-MS). One of the steroids, 7alpha-hydroxypregnenolone (7P5), is a novel steroid in teleosts and was produced late in vitellogenic growth of the oocyte. Evidence suggests that the enzyme responsible for converting pregnenolone to 7P5, 7alpha-hydroxylase, is a cytochrome P450. The second abundant steroid metabolite was partially characterized by GC-MS as an hydroxylated form of 17-hydroxy-pregnenolone (chi,17P5). This steroid was most abundant when the ovary was regressed and during early vitellogenesis and rapidly decreased prior to spawning. In mammals, 7P5 has been identified as an important neurosteroid; however, the reproductive significance of 7P5 and chi,17P5 in catfish is unknown.

Gilthead seabream (Sparus aurata) vitellogenin: purification, partial characterization, and validation of an enzyme-linked immunosorbent assay (ELISA)

VTG was purified from seabream Sparus aurata plasma by ion exchange chromatography on a DEAE-Sepharose column. The vitellogenin was characterized and its properties were determined. The molecular mass of the native form, obtained by Sephadex G-200 column, was around 450 kDa, whereas an apparent molecular mass of 180 kDa was detected by electrophoresis under denaturing and reducing conditions, suggesting a dimeric form for the native protein. The presence of carbohydrates was determined using concanavalin A, while the presence of phosphate groups was detected by Stains-all, a cationic stain. These data together with the sex specificity, the estrogen inducibility, and the cross-reactivity of the abVTG against the major yolk proteins identifies this protein as vitellogenin. The validated ELISA was used for a rapid and reliable measurement of plasma VTG changes related with those of estradiol-17beta in female broodstock.

Annual changes in serum vitellogenin concentrations in viviparous eelpout, Zoarces elongatus

Vitellogenin of matrotrophic viviparous eelpout (Zoarces elongatus) was purified from estradiol-17 beta (E2) treated immature male sera by gel chromatography and anion exchange chromatography. Isolated vitellogenin has a molecular weight of 540 kDa estimated by gel chromatography. Serum levels of vitellogenin in females were measured during oocyte development and gestation by single radial immunodiffusion. Serum vitellogenin level was low (less than 0.2 mg/ml) during the early vitellogenic period, increased in the late vitellogenic period to a peak level (6.4 +/- 2.1 mg/ml) at the beginning of gestation. After that it rapidly decreased to a low level (0.1 +/- 0.1 mg/ml) during the early gestation period. Levels of vitellogenin remained low throughout the gestation period. Serum E2 levels in females showed increased from 1.3 to 3.0 ng/ml during the late vitellogenic period, and declined to 0.4 ng/ml during the early gestation period. Serum levels of E2 showed good correlation with serum vitellogenin levels, suggesting that the vitellogenin synthesis is controlled by E2 in this species. These results combined with the matrotrophic growth of embryo during gestation suggest that there is a shift in the synthesis of maternal nutritional products for embryos from the yolk to other nutrients.

Plasma vitellogenin of grouper (Epinephelus malabaricus): isolation and properties

Radiolabelled vitellogenin produced by juvenile grouper following injection of 3H-leucine, 32P-orthophosphate and estradiol-stimulation was purified by anion-exchange and gel filtration chromatography and characterized by electrophoresis and chemical analysis. The radiolabelled product was found to exist in two heterogeneous molecular weight forms by electrophoresis under nondenaturing conditions on polyacrylamide gel with M(r), of 260,000 and 525,000. It showed two protein monomers (M(r) 113,000 and 140,000) on electrophoresis under denaturing condition on a sodium dodecyl sulphate-polyacrylamide gel. The purified material contained 17.2% total lipid with 1.3% cholesterol and 2.1% triglycerides, 8-21 micrograms/mg protein total carbohydrate and 6.8 micrograms phosphate/mg protein; amino acid analysis showed a profile comparable to that found for vitellogenins isolated from the grouper, medaka, goldfish and rainbow trout. The study showed grouper vitellogenin to be a glycophospholipoprotein similar in composition to vitellogenins from other teleosts and demonstrated that vitellogenins can be induced in juveniles by injection with estradiol-17 beta.

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.

Vitellogenins of Oreochromis niloticus: identification, isolation, and biochemical and immunochemical characterization

Two native forms of vitellogenin (EIP1 and EIP2) were identified in the plasma of Oreochromis niloticus. They were present in females and were estrogen-inducible in males. Both were phosphoglycolipoproteins and both immunoreacted with the antiserum raised against egg proteins. Two prominent bands (EIpp1 and EIpp2; corresponding to 185 and 120 kDa, respectively), observed on sodium dodecyl sulfate-polyacrylamide gels, were induced by estradiol treatment of males and immunoreacted with the antiserum against egg proteins. EIP1 and EIP2 were isolated by precipitation with Mg2+ ions and ethylenediamine tetraacetic acid, preparative polyacrylamide gel electrophoresis, and electroelution. During purification the fractions containing EIP1 and EIP2 also retained EIpp2 and EIpp1, respectively. Immunoblot analyses using affinity-purified antibodies against EIP1, EIP2, EIpp1, and EIpp2 confirmed that EIP1 and EIP2 were at least composed of EIpp2 and EIpp1, respectively. These results suggest that at least two immunochemically different proteins are induced and are secreted into the blood to serve as vitellogenin and to provide a source of nutrient for the developing embryo of Oreochromis niloticus.

Purification, characterization and immunoassay of striped bass (Morone saxatilis) vitellogenin

The egg yolk precursor, vitellogenin (VTG), was purified from blood plasma of striped bass by chromatography on hydroxylapatite or DEAE-agarose. The fish were first implanted with estradiol-17β (E2), which induced vitellogenesis. A rabbit antiserum (a-FSPP) raised against plasma from mature female striped bass, and then adsorbed with mature male plasma, was used to detect female-specific plasma protein (FSPP) in the chromatography fractions. Striped bass VTG (s-VTG) was collected from the peak fraction that was induced by E2, reacted with a-FSPP, and contained all detectable phosphoprotein. It appeared as a single band (Mr ≂ 170,000) in SDS-PAGE or Western blots using a-FSPP, and as a pair of closely-spaced phospholipoprotein bands in native gradient-PAGE, suggesting that there is more than one circulating form of s-VTG. The relationship of s-VTG to the yolk proteins was verified using a-FSPP. The antiserum reacted with the main peak from gel filtration of saline ovary extracts, and it specifically immunostained the two main bands in Western blots of the extracts and the yolk granules of mature oocytes. The amino acid composition of s-VTG was similar to that of VTG from other fish and Xenopus. A radial immunodiffusion assay for s-VTG was developed using a-FSPP and purified s-VTG as standard. The s-VTG was not detected in blood plasma of males, immature females, or regressed adult females, but plasma s-VTG levels were highly correlated with plasma E2 and testosterone levels, and oocyte growth, in maturing females. The results indicate that the maturational status of female striped bass can be identified by s-VTG immunoassay.

Influence of oral administration of estradiol-17β and testosterone on growth, digestion, food conversion and metabolism in the underyearling red sea bream, Chrysophrys major

Estradiol-17β (E2) administered in the diet to the red sea bream Chrysophrys major did not affect appetite, food conversion efficiency, protein efficiency ratio and specific growth rate. Serum concentrations of total protein, albumin, globulin, vitellogenin, α-amino acids, total lipid, free fatty acids, cholesterol and calcium were elevated. The hepatosomatic index was also increased. Activities of hepatic enzymes including lactate dehydrogenase, isocitrate dehydrogenase and glutamate-pyruvate transaminase were higher than found in untreated control fish. Intestinal activity of leucine aminopeptidase was augmented. However, there were no changes in muscle water, protein, lipid and glycogen content. In contrast, testosterone (T) given by the same route increased appetite, food conversion efficiency, protein efficiency ratio and specific growth rate. There were no alterations in serum protein and calcium concentrations but serum glucose, ammonia and triglyceride levels were elevated. Hepatic glycogen content was increased. The activities of hepatic fructose- 1,6-diphosphatase, glucose-6-phosphatase and glycogen synthetase and intestinal activities of alkaline phosphatase and τ-glutamyltransferase were higher than noted on control fish. The results reveal that estradiol-17β and testosterone exerted different metabolic effects in the red sea bream and they suggest that testosterone exerts its anabolic actions by increasing appetite, food conversion efficiency and activities of digestive enzymes.

Induction by beta-estradiol of vitellogenin in striped bass (Morone saxatilis): characterization and quantification in plasma and mucus

Striped bass (Morone saxatilis) were implanted with beta-estradiol to induce the production of vitellogenin, the egg yolk precursor produced by the liver. Electrophoretic analysis revealed that beta-estradiol caused marked production of a plasma protein of apparent molecular mass 170 kDa. Size exclusion chromatography suggested that the estradiol-induced protein circulated as a dimer. This protein was purified from the plasma of estradiol-treated fish by DEAE-agarose column chromatography and used to induce antibodies in rabbits and goats. Western blots revealed that the antiserum bound to the putative vitellogenin in plasma from estradiol-treated fish and adult females, but not with any proteins in male plasma. Western blot of ovarian extract revealed several smaller immunoreactive protein bands and supported the identity of the purified protein as vitellogenin. A competitive ELISA was developed with sensitivity in a range from 8 to 1000 ng/ml. Plasma concentrations of adult females during their spawning migration ranged from 100 to 600 micrograms/ml. Western blot of mucus extract revealed the presence of a 170-kDa protein in vitellogenic female fish along with several minor bands ranging from 50 to 110 kDa. Positive immunoreactivity was present in the surface mucus of all females and in none of the males collected during a spawning migration in the Hudson River.

Monoclonal antibody-based immunoassay of vitellogenin in the blood of male channel catfish (Ictalurus punctatus)

1. A monoclonal antibody to vitellogenin of channel catfish (Ictalurus punctatus) was made, and its specificity was demonstrated using Western blots of serum from female fish, estradiol-treated male fish, untreated male fish, vitellogenin purified by three different methods and egg extracts. 2. An enzyme-linked immunosorbent assay (ELISA), using this monoclonal antibody, detected vitellogenin in the plasma of 59 out of 60 untreated 17-24-month-old male channel catfish with a mean concentration of 338 micrograms/ml and a maximum concentration of 4240 micrograms/ml. 3. Vitellogenin levels in male channel catfish were unrelated to testicular stage, gonadosomatic index and month.

Granulomatous inflammation and monstrous giant cells in response to intraperitoneal hormone implants in channel catfish (Ictalurus punctatus)

Plastic implants (2.7 mm maximum dimension) of an ethyl vinyl acetate copolymer (EVAc) matrix, containing inulin, bovine serum albumin (BSA) and luteinizing hormone releasing hormone (LHRH), were covered with impervious EVAc and then surgically placed into the peritoneal cavity of 1-year-old channel catfish, Ictalurus punctatus. In fish kept in cold water (13 degrees C), 10 per cent of the implants per month were encapsulated by granulation tissue. In fish kept in warm water (27 degrees C), 20 per cent of the implants per month were encapsulated, with a total of 86 per cent encapsulated at 5 months. In addition to fibroblasts and capillaries, the granulation tissue included macrophages, neutrophils, lymphocytes, plasma cells, multinucleated giant cells and a matrix of collagen fibres. The density of the fibrous capsule increased with time. In a separate investigation, it was found that the thickness of the capsule was directly proportional to the degree of exposure of the EVAc matrix to the fish (exposure influenced by the rate of dissolution of the capsule content). Monstrous giant cells with up to 600 nuclei per 5 microns thick section were seen in capsules around implants. On intraperitoneally implanted cover glasses, whole giant cells contained up to 6000 nuclei and were interconnected by cytoplasmic bridges. Signs of neoplasia, implant expulsion or massive adhesions were not seen.