A new ELISA for the three-spined stickleback (Gasterosteus aculeatus L.) spiggin, using antibodies against synthetic peptide

The aim of this study was to develop an enzyme-linked immunosorbent (ELISA) assay to quantify spiggin in the three-spined stickleback. Spiggin is a glue protein produced in the kidney of male three-spined stickleback under the control of androgens during the breeding period. Disturbances of spiggin production in male fish and abnormal induction of spiggin in female fish are considered as valuable biomarkers of exposure to (anti-)androgenic chemicals. Polyclonal antibodies against a peptide sequence of spiggin (HRD-16) were used and the specificity of the antibodies was verified by Western blotting and direct ELISA experiments. By using HRD-16 antibodies and spiggin standard preparation, a competitive ELISA was set-up and validated. This assay appears sensitive, with a detection limit of 0.5 U/mL, and specific, as shown by the competition curves, obtained by serial dilution of male and female kidney homogenates, that were parallel to the spiggin standard curves. The ability of the spiggin ELISA to quantify spiggin induction was achieved by exposing male and female three-spined sticklebacks to 0.1 and 1 microg/L of methyltestosterone. The results show a significant dose-dependent induction of spiggin in methyltestosterone-exposed female fish compared to controls.

Novel steroidogenic factor-1 homolog (ff1d) is coexpressed with anti-Mullerian hormone (AMH) in zebrafish

ff1d is a novel zebrafish FTZ-F1 gene with sequence characteristics indicating similar basic regulatory mechanisms as the previously characterized ff1 based on the presence of an FTZ-F1 box in the DNA binding domain and an interactive domain (I-Box) and an AF-2 in the ligand binding domain. The highest sequence similarity was found between ff1d and ff1b (NR5A4), a gene previously shown to be a functional homolog to the steroidogenic factor 1 (SF-1). The expression pattern of ff1d was comparable to ff1b both in brain and gonads in adults and in the pituitary and interrenal cells in embryos. SF-1 is crucial in mammalian steroidogenesis and in sex determination by regulating the anti-Mullerian hormone (AMH). In fish, AMH has not been described previously. In this study, we cloned a partial zebrafish AMH. AMH was detected in growing oocytes, the ovarian follicular layer and testicular Sertoli cells, similar to the mammalian pattern, suggesting a conserved role between zebrafish and mammalian AMH. Teleosts lack a gene homolog to SRY, which constitute the universal testis-determining factor in mammalian sex determination. Comparison of sequences and expression patterns indicate that ff1d is a new candidate for sex determination and differentiation in a way similar to SF-1, possibly involving AMH.

Regulation of Arctic char (Salvelinus alpinus) egg shell proteins and vitellogenin during reproduction and in response to 17beta-estradiol and cortisol

Estrogens induce both vitellogenin (Vtg) and egg shell (zona pellucida; ZP) protein synthesis in salmonids. However, while Vtg is strictly under estrogenic control, recent reports suggest that additional mechanisms are involved in ZP protein synthesis. During sexual maturation both estrogen and glucocorticoid levels increase in the circulation of female fish. As glucocorticoids have been shown to interfere with Vtg induction in fish we investigated whether cortisol (F) had similar effects on ZP regulation. In the present study we determined both the natural variation in Vtg and ZP during an annual reproductive cycle in female Arctic char (Salvelinus alpinus), and the effect of co-treatment of juvenile Arctic char with 17beta-estradiol (E2) and F. During sexual maturation the expression of Vtg and ZP correlated to plasma levels of E2 and F. Determination of Vtg and ZP protein levels following co-treatment with E2 and F showed that F antagonized E2 induction of Vtg. However, F was observed to potentiate the expression of ZP protein in the same fish. These results indicate that in Arctic char Vtg and ZP proteins are not regulated by the same mechanisms and suggest that ZP protein expression does not necessarily imply exposure to estrogenic compounds alone, and may thus not be ideally suited as a biomarker of exposure to estrogenic compounds.

Generating transparent zebrafish: a refined method to improve detection of gene expression during embryonic development

In zebrafish (Danio rerio) pigmentation is initiated during embryogenesis and begins in the retinal epithelium and in the melanophores. The pigment cells develop rapidly, and within hours they constitute a prominent feature of the embryo. In order to improve signal detection by whole mount in situ hybridization, confocal microscopy, or expression of GFP, embryos may be treated with 1-phenyl 2-thiourea (PTU) during embryogenesis. PTU inhibits melanogenesis by blocking all tyrosinase-dependent steps in the melanin pathway but can be toxic at high concentrations. The embryos remain transparent as long as the PTU treatment is continued. However, PTU treatment must be initiated before the initial pigmentation because it does not remove already formed pigment. Here we provide a protocol for generating transparent zebrafish while avoiding the toxic and teratogenic effects of PTU treatment.

Molecular cloning and characterization of spiggin. An androgen-regulated extraorganismal adhesive with structural similarities to von Willebrand Factor-related proteins

One of the most definitive examples of a vertebrate extraorganismal structural protein can be found in three-spined sticklebacks (Gasterosteus aculeatus). In the breeding male the kidney hypertrophies and synthesizes an adhesive protein called "spiggin," which is secreted into the urinary bladder from where it is employed as a structural thread for nest building. This paper describes the first molecular characterization of spiggin and demonstrates that this adhesive is a protein complex assembled from a potential of three distinct subunits (alpha, beta, and gamma). These subunits arise by alternative splicing, and 11-ketoandrogens induce their expression in stickleback kidneys. Analysis of the predicted amino acid sequence of each subunit reveals a modular organization whose structural elements display a similarity to the multimerization domains found within von Willebrand Factor-related proteins. These results implicate that spiggin utilizes a conserved multimerization mechanism for the formation of a viscous agglutinate from its constituent subunits in the urinary bladders of male sticklebacks. This novel extraorganismal structural protein is therefore ideally suited to its function as an adhesive thread.

Bioaccumulation of selected PCBs in zebrafish, three-spined stickleback, and arctic char after three different routes of exposure

The uptake and elimination of 20 structurally diverse tetra- to heptachlorinated biphenyls were studied in zebrafish (Danio rerio), three-spined stickleback (Gasterosteus aculeatus), and Arctic char (Salvelinus alpinus). The polychlorinated biphenyls (PCBs) were administered to the fish through food, intraperitoneal injection of peanut oil, or intraperitoneal implantation of silicone capsules. The retention of the PCBs in fish exposed through their diet was related with the substitution patterns of the compounds. Ortho-substituted congeners with no unsubstituted meta-para positions had high biomagnification potential. PCBs with low biomagnification all had adjacent vicinal hydrogens, indicating that congeners with this feature may have been metabolically eliminated. The retention characteristics of the PCBs in the diet-exposed and the injected zebrafish were similar. The pattern of congeners in Arctic char indicates that they have a lower capacity to metabolize PCBs compared to three-spined sticklebacks and zebrafish. The levels in the fish exposed to the PCBs through a silastic implant were negatively correlated with the hydrophobicity of the congeners. Most probably congener-specific release rates of the PCBs from the implants mask their retention characteristics. It is suggested that food, mimicking the natural intake route, should be used in PCB exposure studies to validate extrapolations to natural situations.

Expression of three vitelline envelope protein genes in arctic char

Several studies have shown effects of estrogenic substances on endocrine and reproductive systems in wildlife. Measurement of plasma vitellogenin (VTG) is a commonly used method to determine exposure to estrogenic substances in fish. There is, however, a growing need for additional sensitive and accurate methods to detect estrogenic substances in vivo. The vitelline envelope proteins (VEPs) have been suggested, in other studies, as suitable biomarkers for estrogenic substances. The present study investigates the induction of VEPs in juvenile Arctic char (Salvelinus alpinus). The results demonstrate that VEP mRNA exhibits earlier induction than estrogen receptor mRNA or VTG mRNA following injection of juvenile Arctic char with a single dose of 17beta-estradiol (E2; 10 mg/kg bw). These results indicate that the VEPs have a higher sensitivity for E2 than VTG. However, an early and sex-independent expression of VEPbeta in estrogen-unchallenged juvenile Arctic char was observed. These findings suggests that the regulatory mechanisms of VEPs might be more complex than previously thought, which in turn may have implications for the usage of VEPs as biomarkers for xenoestrogen exposure.

Cloning of rainbow trout egg envelope proteins: members of a unique group of structural proteins

All vertebrate eggs are surrounded by an extracellular envelope that protects the egg and is vital for a successful fertilization. The terminology and functions of the egg envelope vary in different vertebrate groups, but the envelope itself is consistently composed of a few major proteins that are deposited around the oocyte during oocyte growth. Here, we describe the deduced amino acid sequences and tissue expression patterns of the three major egg envelope proteins for rainbow trout (Oncorhynchus mykiss). All three vitelline envelope proteins (VEPs) are expressed in the livers of both male and female fish, with higher expression in females. In addition, VEPgamma mRNA is also detected in the female gonads. To our knowledge, this is the first time that expression of a VEP protein gene has been demonstrated to occur in more than one organ. Sequence comparison reveals that all three VEP proteins share distinct homology with their amphibian, avian, and mammalian counterparts. Whereas mammalian zona pellucida protein 3 isoforms contain two conserved serines needed for sperm binding, these are not conserved in teleost species, in which sperm entry is restricted to the micropyle. Besides the difference in VEPgamma sperm-binding function, the high sequence homology suggests that the egg envelope proteins from these distinct vertebrate groups share a common ancestry and form a unique group of structural proteins.

Analysis of the pmsCEAB gene cluster involved in biosynthesis of salicylic acid and the siderophore pseudomonine in the biocontrol strain Pseudomonas fluorescens WCS374

Mutants of Pseudomonas fluorescens WCS374 defective in biosynthesis of the fluorescent siderophore pseudobactin still display siderophore activity, indicating the production of a second siderophore. A recombinant cosmid clone (pMB374-07) of a WCS374 gene library harboring loci necessary for the biosynthesis of salicylic acid (SA) and this second siderophore pseudomonine was isolated. The salicylate biosynthesis region of WCS374 was localized in a 5-kb EcoRI fragment of pMB374-07. The SA and pseudomonine biosynthesis region was identified by transfer of cosmid pMB374-07 to a pseudobactin-deficient strain of P. putida. Sequence analysis of the 5-kb subclone revealed the presence of four open reading frames (ORFs). Products of two ORFs (pmsC and pmsB) showed homologies with chorismate-utilizing enzymes; a third ORF (pmsE) encoded a protein with strong similarity with enzymes involved in the biosynthesis of siderophores in other bacterial species. The region also contained a putative histidine decarboxylase gene (pmsA). A putative promoter region and two predicted iron boxes were localized upstream of pmsC. We determined by reverse transcriptase-mediated PCR that the pmsCEAB genes are cotranscribed and that expression is iron regulated. In vivo expression of SA genes was achieved in P. putida and Escherichia coli cells. In E. coli, deletions affecting the first ORF (pmsC) diminished SA production, whereas deletion of pmsB abolished it completely. The pmsB gene induced low levels of SA production in E. coli when expressed under control of the lacZ promoter. Several lines of evidence indicate that SA and pseudomonine biosynthesis are related. Moreover, we isolated a Tn5 mutant (374-05) that is simultaneously impaired in SA and pseudomonine production.

Effects of 17 beta-estradiol on levels and distribution of metallothionein and zinc in squirrelfish

Females of the squirrelfish family (Holocentridae) accumulate higher levels of zinc in the liver than any other known animal. This zinc accumulation is made possible by high expression of the zinc-binding protein, metallothionein (MT). In the present study, the squirrelfish (Holocentrus ascensionis) MT cDNA was cloned and sequenced. The deduced amino acid sequence was very similar to other teleost MT. The role of estrogens on zinc metabolism was investigated by injecting male and immature female squirrelfish with 17 beta-estradiol (E(2)). E(2) treatment triggered transient increases in plasma zinc and vitellogenin (VTG) levels, and both of these variables showed very similar time courses. These results suggest that E(2) is responsible for the large hepatoovarian translocation of zinc observed in female squirrelfish and that VTG might be a vehicle for zinc. E(2) did not directly alter the levels of zinc or MT mRNA in the liver. However, the hepatic MT protein concentration increased differentially in the nuclear fraction. Thus E(2) is probably responsible for the association of MT with the nuclear fraction previously observed in untreated mature female squirrelfish.

Developmental expression patterns of FTZ-F1 homologues in zebrafish (Danio rerio)

The fushi tarazu factor 1 (FTZ-F1) gene family constitutes a subgroup of orphan nuclear receptors which can be divided into two groups (LRH/FTF- and SF-1/Ad4BP-like) based on sequence homology, function, and tissue distribution. Analysis of zebrafish FTZ-F1 homologues (zFF1 and ff1b) during embryogenesis indicated distinct expression patterns for both genes. Besides the previously observed expression in pituitary/hypothalamus and mandibular arch, zFF1 transcripts were also detected in domains corresponding to the pronephric duct, somites, liver, and hindbrain. Additionally, ff1b transcripts were detected at other developmental stages than earlier documented. Comparative sequence analysis showed that zFF1 exhibited higher sequence similarity to the LRH/FTF group than the SF-1/Ad4BP group, whereas ff1b was indistinguishable between the groups. These observations, coupled with obtained expression patterns, indicate that zebrafish FTZ-F1 homologues exhibit characteristics that are indicative of both LRH/FTF- and SF-1/Ad4BP-like genes.

Two estrogen receptors expressed in the teleost fish, Sparus aurata: cDNA cloning, characterization and tissue distribution

Estrogen is an essential hormone for many reproductive and non-reproductive functions. The function of estrogen in the reproductive cycle of seabream (Sparus aurata), a protandrous hermaphrodite teleost fish, is complex but it is understood to be involved in sex inversion, a process that occurs in some individuals during the second reproductive season. Estrogen action is mediated by two estrogen receptor (ER) subtypes designated alpha and beta. As a step to understanding the mechanisms of estrogen action during natural and induced sex reversal in seabream, we have isolated two cDNAs encoding distinct forms of ER homologous to mammalian ERalpha and ERbeta. The seabream ERalpha clone (sbERalpha1), which was truncated in the A/B domain, corresponded to a variant differing in five amino acids from another recently cloned sbERalpha. The ERbeta clone (sbERbeta) encoded a protein 559 amino acids long and showed only 40% identity to sbERalpha. Northern blot analysis of liver and ovary mRNA indicated the presence of several transcripts of the two receptor subtypes. PCR analysis showed that the two receptors differed in their expression pattern. sbERalpha had a more restricted distribution, occurring mainly in testis, liver and heart, and sbERbeta was present in most tissues, being more abundant in ovary, testis, liver, intestine and kidney. The presence in seabream of two ERs with several ER transcripts and their pattern of distribution are consistent with the widespread effects of estrogen in different tissues.

Identification of betaIII- and betaIV-tubulin isotypes in cold-adapted microtubules from Atlantic cod (Gadus morhua): antibody mapping and cDNA sequencing

Isolated microtubule proteins from the Atlantic cod (Gadus morhua) assemble at temperatures between 8 and 30 degrees C. The cold-adaptation is an intrinsic property of the tubulin molecules, but the reason for it is unknown. To increase our knowledge of tubulin diversity and its role in cold-adaptation we have further characterized cod tubulins using alpha- and beta-tubulin site-directed antibodies and antibodies towards posttranslationally modified tubulin. In addition, one cod brain beta-tubulin isotype has been sequenced. In mammals there are five beta-tubulins (betaI, betaII, betaIII, betaIVa and betaIVb) expressed in brain. A cod betaIII-tubulin was identified by its electrophoretic mobility after reduction and carboxymethylation. The betaIII-like tubulin accounted for more than 30% of total brain beta-tubulins, the highest yield yet observed in any animal. This tubulin corresponds most probably with an additional band, designated beta(x), which was found between alpha- and beta-tubulins on SDS-polyacrylamide gels. It was found to be phosphorylated and neurospecific, and constituted about 30% of total cod beta-tubulin isoforms. The sequenced cod tubulin was identified as a betaIV-tubulin, and a betaIV-isotype was stained by a C-terminal specific antibody. The amount of staining indicates that this isotype, as in mammals, only accounts for a minor part of the total brain beta-tubulin. Based on the estimated amounts of betaIII- and betaIV-tubulins in cod brain, our results indicate that cod has at least one additional beta-tubulin isotype and that beta-tubulin diversity evolved early during fish evolution. The sequenced cod betaIV-tubulin had four unique amino acid substitutions when compared to beta-tubulin sequences from other animals, while one substitution was in common with Antarctic rockcod beta-tubulin. Residues 221, Thr to Ser, and 283, Ala to Ser, correspond in the bovine tubulin dimer structure to loops that most probably interact with other tubulin molecules within the microtubule, and might contribute to cold-adaptation of microtubules.

Expression of cold-adapted beta-tubulins confer cold-tolerance to human cellular microtubules

Isolated microtubule proteins from the cold-adapted fish, Atlantic cod (Gadus morhua), assemble at temperatures between 8 and 30 degrees C, while avian and mammalian microtubules normally do not assemble at temperatures below 20 degrees C. Tubulin, the main component in microtubules, is expressed as many isotypes. Microtubules with different isotype composition have been shown to have different dynamic properties in vitro. Our hypothesis was that cold-tolerance of microtubules is caused by tubulin isotypes that differ in the primary sequence compared to mammalian tubulins. Here we show that transfection of human HepG2 cells with cod beta-tubulin induced cold-adaptation of the endogenous microtubules. Incorporation of one single tubulin isotype can induce cold-tolerance to cold-intolerant microtubules. Three cod beta-tubulin isotypes were tested and two of these (beta1 and beta2) transferred cold-tolerance to HepG2 microtubules, thus not all cod beta-tubulins were able to confer cold-stability.

Assessment of PCBs and hydroxylated PCBs as potential xenoestrogens: In vitro studies based on MCF-7 cell proliferation and induction of vitellogenin in primary culture of rainbow trout hepatocytes

In the present study, four structurally diverse polychlorinated biphenyls (PCBs) were chosen from a set of 20 PCBs selected to represent the 154 tetra- through hepta-chlorinated biphenyls. The purpose was to determine estrogenic activities of the chosen PCBs and five of their hydroxylated derivatives (OH-PCBs). A human breast cancer cell line (MCF-7) and primary cultures of rainbow trout (Oncorhyncus mykiss) hepatocytes were used to determine estrogenic effects. The PCBs 2,2',4,6,6'-pentachlorobiphenyl (104) and 2,2',3, 4', 5,6,6'-heptachlorobiphenyl (188), and the hydroxylated PCBs 2,2', 4',6'-tetrachloro-4-biphenylol (4'-50), 2',4', 6'-trichloro-4-biphenylol (4'-30), 2',3,5, 5'-tetrachloro-4-biphenylol (4'-72), 2',3,3',5', 6'-pentachloro-4-biphenylol (4'-112), and 2',3,4',5, 6'-pentachloro-4-biphenylol (4'-121) significantly increased MCF-7 cell proliferation. The coaddition of hydroxytamoxifen, an estrogen antagonist, inhibited increased cell proliferation. The activity of the hydroxylated PCBs 4'-50 and 4'-30 was significantly higher at all nominal concentrations tested as compared to the corresponding PCB, viz., PCB 104. The hydroxylated PCBs 4'-50, 4'-30, 4'-72 and 4'-112 induced vitellogenin synthesis in rainbow trout hepatocytes. Significant differences were found in the MCF-7 system between the parent PCB and its hydroxylated derivative, viz., for 4'-50/4'-30 and 104, and in the rainbow trout hepatocyte assay between 4'-112 and 112, respectively. No activity was observed for PCB 58 in any of the two assays in the present study. Even though cells from two different species (human and fish) are used in the present study, the results obtained by the two methods agree fairly well. In both studies the hydroxylated PCBs were more active than the PCBs, and 4'-30 was the most active compound second only to 17beta-estradiol. http://link.springer-ny. com/link/service/journals/00244/bibs/37n2p145.html

Functional comparison of the metal-regulated transcriptional control regions of metallothionein genes from cadmium-sensitive and tolerant fish species

The promoter region of teleost metallothioneins (MTs) contains multiple metal-responsive elements (MREs) organized in proximal and distal clusters which together mediate gene induction by heavy metals. This arrangement of MREs is found both in cadmium-sensitive species, such as the rainbow trout, and in cadmium-tolerant species such as the pike and the stone loach. On comparison of the putative regulatory elements identified within the 5'-flanking region of these genes the major differences are that the number of MREs differ between the different species and that, while both the stone loach and rainbow trout MT genes contain TATA boxes, the pike MT gene has a TTTA box. In order to investigate if the metal sensitivity of a species is correlated to the regulatory potential of the putative MT detoxification system the promoter regions of MT genes from all three species were assessed for their ability to enhance transcription in response to the heavy metals Zn, Cd and Cu. The polymerase chain reaction was used to produce nested deletion sets of each promoter region and these were cloned into the mammalian expression vector pGL-2 upstream of the firefly luciferase gene. The inducibility of the different constructs in response to heavy metal challenge was tested in two cell lines, one fish cell line (homologous to rainbow trout and heterologous to the two other species), the rainbow trout hepatoma, RTH-149, cell line and one cell line that was heterologous to all studied species, the human hepatoblastoma; HepG2, cell line. Maximum inducibility of each gene was achieved with constructs containing both the proximal and the distal MRE clusters. Both the rainbow trout and the stone loach MT genes showed inducibility of comparable amplitude whilst the pike MT gene on the other hand was less inducible, partly due to fewer MREs and partly due to the TTTA box. These data indicate that more than one mechanism is responsible for the differences in cadmium sensitivity of these three teleost species. Although MT is the main heavy-metal detoxifying system in most vertebrates and appears to be contributing to the differences seen between rainbow trout and pike, the present study shows that the relative sensitivity of these species is not primarily due to MT.

Phenobarbital induction of CYP1A1 gene expression in a primary culture of rainbow trout hepatocytes

In mammals, phenobarbital (PB) is an in vivo inducer of the cytochrome P4502B (CYP2B) family, whereas in teleosts PB induction of cytochrome P450 is unclear. We show that teleost cytochrome P4502K1 (CYP2K1) protein levels and 7-pentoxyresorufin-O-deethylase activity were not induced by exposure of primary cultures of rainbow trout hepatocytes to PB. Instead, cytochrome P4501A1 (CYP1A1) gene expression was strongly induced by PB, based upon observations of marked increases in CYP1A1 mRNA, CYP1A1 protein, and 7-ethoxyresorufin-O-deethylase activity. In accordance with these data we provide a temporal study employing antibodies for the aromatic hydrocarbon (Ah) receptor that showed an increase in Ah receptor in nuclear extracts prepared from cells exposed to PB. Employment of the electrophoretic mobility shift assay (EMSA) showed PB to cause activation or "transformation" of the Ah receptor in nuclear extracts. Studies employing actinomycin D and cycloheximide indicated that PB induction of CYP1A1 was regulated at both the transcriptional and post-transcriptional levels. Nuclear run-off experiments confirm that PB causes an increase in CYP1A1 transcription. Inhibition of protein synthesis led to the superinduction of CYP1A1 mRNA, suggesting the regulation of teleost CYP1A1 may involve a labile repressor protein. These findings suggest that PB induction of the CYP1A1 gene involves the Ah receptor and is via transcriptional activation.

Structural and functional analysis of the rainbow trout (Oncorhyncus mykiss) metallothionein-A gene

In the present study, the distal part of the 5'-flanking region of the rainbow trout metallothionein-A promoter was sequenced in order to identify cis-acting regulatory elements. Analysis of this sequence combined with that previously reported for the 5'-flanking region directly proximal to the start of transcription revealed several putative regulatory sequences. In total, six metal-responsive elements (MREs) were identified; these sequences were organised into two clusters, one containing two copies of MRE and located close to the predicted TATA box sequence, and a second consisting of four MREs and lying 500-700 bp upstream from the start of transcription. In addition, the 5'-flanking region contained sequences sharing high similarity with the activator protein 1 consensus sequence as well as one nuclear-factor-interleukin-6-responsive element. Functional analysis of the promoter was performed by introducing deletion mutants of the 5'-flanking region into the vector pGL-2, directly upstream from the luciferase reporter gene. Both MRE clusters were needed for maximal metal inducibility in both rainbow trout hepatoma (RTH-149) and human hepatoblastoma (Hep G2) cell lines. Furthermore, the distal region was found to be functional in promoting gene transcription following exposure of RTH-149 cells to hydrogen peroxide.

Interaction of cadmium and oestradiol-17 beta on metallothionein and vitellogenin synthesis in rainbow trout (Oncorhynchus mykiss)

The induction of metallothionein and vitellogenin synthesis in rainbow trout liver was studied after injection of oestradiol-17 beta alone or in combination with cadmium or zinc. Intraperitoneal injection of oestradiol-17 beta increased the liver somatic index, with subsequent induction of vitellogenin synthesis. Oestradiol-17 beta did not induce metallothionein synthesis. Injection of cadmium induced the synthesis of metallothionein mRNA and metallothionein. Injection of oestradiol-17 beta in combination with cadmium resulted in inhibition of transcription and translation of both vitellogenin and metallothionein. Chromatography of liver cytosols revealed that cadmium, when co-injected with oestradiol-17 beta, did not bind to metallothionein but would initially bind to high-molecular-mass (HMr) cytosolic proteins. In fish injected with cadmium in combination with oestradiol-17 beta, cadmium was gradually redistributed from HMr proteins to metallothionein. This resulted in induction of metallothionein synthesis and in binding of most of the cadmium to metallothionein. Induction of vitellogenin mRNA was observed 15 days after injection, as cadmium was being redistributed to newly synthesized metallothionein. These findings indicate that cadmium inhibits the transcription of vitellogenin. The binding of cadmium to these non-metallothionein proteins represses the induction of metallothionein and results in increased toxicity of the metal. Preinduction of metallothionein by zinc injections resulted in decreased cadmium sensitivity of the fish and a decrease in the repression of vitellogenin mRNA. Furthermore, a role for metallothionein in the detoxification of cadmium is indicated by the induction of vitellogenin synthesis that occurs once metallothionein has begun sequestering cadmium.

Ascorbate-2-sulfate as a dietary vitamin C source for Atlantic salmon (Salmo salar): 2. Effects of dietary levels and immunization on the metabolism of trace elements

Atlantic salmon fingerlings were fed a vitamin C deficient diet for four months. The fish were then provided a dry, practical fishmeal based diet supplemented with 0, 500 or 5000 mg vitamin C/kg as L-ascorbic acid or equivalent amounts of ascorbate-2-sulfate. After six weeks on these diets ten fish in each group were injected with a soluble antigen (NIP11-LPH). Six weeks thereafter blood, liver, kidney, spleen and vertebrae were examined for trace elements. The livers were also analysed for metallothionein.The vitamin C deficient fish were anemic despite the significantly elevated iron concentrations in the liver. Vitamin C had no positive effect in lowering tissue levels of cadmium. The highest level of dietary vitamin C given as ascorbic acid reduced the liver selenium concentrations. In response to antigen injection, the fish in all groups showed increased levels of hepatic metallothionein, copper, zinc and cadmium, while hepatic selenium and iron levels were less affected. The elemental composition in other organs was affected by the antigen injection to a minor extent.

Developmental regulation of metallothionein mRNA, zinc and copper levels in rainbow trout, Salmo gairdneri

The metallothionein (MT) gene expression profile was followed in rainbow trout during early embryo development and in liver and gonads during the period of sexual maturation. The hepatic MT mRNA levels increase at the end of sexual maturation in both male and female rainbow trout. Although both isoforms of MT mRNA accumulate in the liver, there is a preferential increase in MT-A in the female liver. Concomitantly with this increase in MT there is a redistribution of zinc and copper to MT. In the juvenile female there is an abundance of MT mRNA in the ovaries. This is correlated to high levels of zinc in the MT fraction upon Sephadex G-75 chromatography. During ovary development the MT mRNA levels and the MT-bound zinc levels drop, with an increase in zinc being bound to high-molecular-mass proteins. At ovulation most of the zinc is found in the membrane portion upon centrifugation. In contrast to the ovaries, there are no apparent changes in either trace metal distribution or MT mRNA levels during testis development. In the developing embryo there is an increase in MT-bound copper at gastrulation. This is accompanied by an increase in both isoforms of MT mRNA. At hatch both the copper and zinc levels increase in the MT fraction, with a concomitant increase in mainly MT-A mRNA. These findings indicate that the variations in MT mRNA levels during development are closely associated with metal regulation.

Differential regulation of metallothionein genes in rainbow trout fibroblasts, RTG-2

Exposure of a trout gonadal fibroblast (RTG-2) cell line to ZnCl2, CdCl2 and CuCl2 resulted in differential levels of accumulation of metallothionein (MT) mRNA. ZnCl2 being the most effective agent induced MT mRNA in 3 h, with 172-fold induction after 48 h and continued accumulation up to 144 h. Following CdCl2 treatment, mRNA could be detected after 24 h, reaching peak levels at 72 h. Furthermore, trout MT mRNA could be detected up to 8 days after withdrawal of extraneous ZnCl2. Using a novel technique of primer extension and DNA sequencing with total RNA as template, specificity of the trout MTa and MTb gene-specific primers was established. Primer extension studies revealed a higher response of MTa to ZnCl2 and CdCl2 compared to MTb. Insensitivity of MT mRNA induction to cycloheximide suggested that induction by the metals was independent of de novo protein synthesis. However, simultaneous exposure of cells to actinomycin D and metals completely inhibited MT mRNA synthesis implying control at the transcriptional level.

Differences in metallothionein gene expression in primary cultures of rainbow trout hepatocytes and the RTH-149 cell line

Primary cultures of rainbow trout, Salmo gairdneri, hepatocytes were used to study the expression of metallothionein (MT) genes in response to steroid hormone treatment. The expression pattern was compared to that of an immortal cell line (RTH-149). MT mRNA accumulated in both cell cultures after exposure to zinc while 17 beta-oestradiol had no effect in either system. Treatment with cortisol and corticosterone resulted in a 2-fold increase of metallothionein mRNA levels in the primary cultures but had no effect in the RTH-149 cell culture. Primary cultures that were exposed to zinc or cortisol showed a high temporal correlation (r = 0.974) between MT mRNA and MT protein levels. The basal level expression was 3-4-fold higher in primary cultures than in RTH-149 cells. The present study demonstrates the inducibility of rainbow trout MT genes in response to glucocorticoids. It further indicates that primary cultures are to be preferred to immortal cell lines when investigating the inducibility of MT mRNA.

Endogenous and heavy-metal-ion-induced metallothionein gene expression in salmonid tissues and cell lines

Endogenous levels of metallothionein (MT) mRNA were detected by RNA probes in several somatic and germ-line tissues of rainbow trout, such as eggs, ovaries and immature testis. These levels may be related to metal-ion homeostasis in the observed tissues. The induction kinetics of trout MT isoform B (MT-B) mRNA were studied after single intraperitoneal injections of CdCl2, CuCl2 and ZnCl2. MT-B mRNA was induced within 12 h in liver, kidney, spleen and gills. However, over the 48-h experimental period, the kinetics of MT-B mRNA accumulation differed in response to the three metal salts, possibly due to differential handling of the salts by these tissues. Multiple metal-salt injections induced high levels of MT-B mRNA in the four tissues studied. In the rainbow trout hepatoma cell line, ZnCl2 was a better inducer of the MT-B gene, as compared to CdCl2 and CuCl2. The expression of the exogenous trout MT-B promoter in Chinook salmon embryonic cell line indicates the presence of MT regulatory factors. In contrast, the endogenous MT genes in these cells are quiescent, possibly due to the methylation of their promoter region.

Calcium phosphate-mediated transfection alters metallothionein gene expression in response to Cd2+ and Zn2+

The level of expression of a transfected metallothionein (MT)-IGcat fusion gene in response to cadmium differed from that of the endogenous MT-IG gene. Atomic absorption analysis indicated that the total cellular content of cadmium and zinc increased upon calcium phosphate-mediated transfection. Thus, changes in the influx/efflux of metals may regulate the level of MT gene expression.

Induction of metallothionein synthesis in rainbow trout,Salmo gairdneri, during long-term exposure to waterborne cadmium

Rainbow trout were exposed to 200 μg cadmium/l in the water during four months at 6-10°C. The liver, kidney and gills were analyzed for cadmium, copper, zinc, metallothionein and metallothionein mRNA. Cadmium accumulated in all three organs and reached the highest concentration in the kidney. The tissue zine and copper concentrations showed no major alterations during the experiment. The cytosolic distribution of cadmium, copper and zinc was followed during four months of exposure by Sephadex G-75 chromatography. It was found that cadmium was predominantly associated with proteins of an apparent molecular vieght of 10,000 daltons. These proteins were further identified as metallothioneins after fast protein liquid chromatography on a Mono-Q column. The metallothionein concentration was significantly higher in liver of exposed fish than in control fish after only one month. The kidneys reached significantly elevated levels of metallothionein in the exposed group after three months. In the gills, elevated metallothionein concentrations were observed after four months of exposure. After four months of exposure, the metallothionein mRNA content of liver and kidney was analyzed using a rainbow trout anti-sense RNA probe. Elevated MT mRNA levels were observed in both kidney and liver. These results demonstrate thatde novo synthesis of metallothionein is induced by cadmium in rainbow trout after exposure to the metalvia water.

Cortisol induction of metallothionein in primary culture of rainbow trout hepatocytes

In the present experiment, metabolically active primary cultures of rainbow trout hepatocytes were utilized to study the inducibility of metallothionein after cortisol treatment. Glucocorticoid induction of metallothionein has previously only been demonstrated in mammalian systems. We now demonstrate the inducibility of rainbow trout metallothionein by cortisol treatment of primary hepatocytes. A 90% elevation above control levels was achieved within 8 days of treatment. Zinc treatment was performed to evaluate the system, and 100 microns zinc in the culture medium resulted in a 350% increase of the metallothionein levels. We conclude that primary culture of rainbow trout hepatocytes constitutes an efficient system for studies of MT induction kinetics.

A role of metallothionein in zinc regulation after oestradiol induction of vitellogenin synthesis in rainbow trout, Salmo gairdneri

The regulation of metallothionein (MT) biosynthesis in rainbow-trout liver was studied after a single intraperitoneal injection of oestradiol-17 beta. Sampling was performed after 2, 7, 14, 21, 28 and 35 days. Following induction of vitellogenin synthesis in the liver, liver somatic index (LSI) rose from 1.25 to 2.00 in 14 days. Associated with the increase in LSI was an elevation of hepatic vitellogenin mRNA and zinc concentrations. The vitellogenin mRNA concentrations peaked at 7 days after treatment. The zinc concentrations increased to a peak at day 14. MT was analysed by using differential pulse polarography and a rainbow-trout MT RNA probe. The MT mRNA concentrations rose after 14 days and remained elevated at 21 and 28 days. The MT concentrations increased after 14 days and remained elevated throughout the experimental period. The concentrations of MT-bound zinc increased in association with the elevation in MT concentrations in the oestradiol-treated rainbow trout. These findings indicate that MT is involved in the regulation of zinc during the period of vitellogenin induction and that MT may function by maintaining the pool of available zinc at an appropriate concentration.

Improved separation of perch liver metallothionein by fast protein liquid chromatography

The separation of metallothionein isoforms by Mono-Q column chromatography by fast protein liquid chromatography is described and compared to separation on a DEAE-Sephadex A-25 ion-exchange column. The separation of two isoforms of rainbow trout (Salmo gairdneri) metallothionein was possible by DEAE-Sephadex A-25 chromatography, while only one form of perch (Perca fluviatilis) metallothionein was obtained with this method. However, by applying FPLC on a Mono-Q column it was possible to separate two isoforms of perch metallothionein. When comparing the chromatographic behaviour of rainbow trout and perch metallothioneins it was found that the two isoforms of perch metallothionein were eluted closer together than the two rainbow trout metallothioneins. Both forms of perch and rainbow trout metallothioneins lacked aromatic amino acids and histidine, and had a high cystein content (30 mol%). The molecular weight was estimated to be 6000 for the apothioneins. The results from this study demonstrate the usefulness of FPLC to improve the resolution of metallothionein separations.

Partial development of a radioimmunoassay for horse metallothionein

The partial development and evaluation of a radioimmunoassay for horse metallothionein (MT) with low amounts of antigen is described. Factors that affect the yield of the conjugation reaction between horse MT and bovine IgG are discussed. Dot-blot has been used as a simple, rapid and inexpensive test for antibody screening.

Variations in hepatic metallothionen, zinc and copper levels during an annual reproductive cycle in rainbow trout,Salmo gairdneri

The normal variations in hepatic levels of metallothionein, zinc and copper were studied during an annual reproductive cycle in rainbow trout of both sexes. In female fish, the total hepatic zinc levels closely followed the estradiol-17β and the LSI levels. Hence, the zinc levels rose in September, peaked in December and dropped in January. No distinct peaks were, however, observed in the whole-liver copper content. The hepatic metallothionein levels in female fish began to increase at the onset of exogenous vitellogenesis. Maximum levels were reached after estradiol-17β and LSI levels had dropped in January. In male fish no distinct peaks in either zinc or copper levels were observed. The metallothionein levels increased somewhat during the time of spermatogenesis. It is suggested that metallothionein may regulate the hepatic zinc distribution during the annual reproductive cycle in female rainbow trout, thereby ensuring the organism of a control mechanism to keep the pool of available zinc at an appropriate level.