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PubMed2002

Binding of polycyclic aromatic hydrocarbons (PAHs) to teleost aryl hydrocarbon receptors (AHRs).

Polycyclic aromatic hydrocarbons (PAHs) are ubiquitous, environmental contaminants that pose a potential risk to fish populations. Both field and laboratory studies suggest that exposure of the early life stages of fish to PAH can mimic the embryotoxic effects of the planar halogenated hydrocarbons (PHHs), the most potent of which is 2,3,7,8-tetrachlorodibenzo-p-dioxin. PHH toxicity is mediated by the aryl hydrocarbon receptor (AHR) and PHH potency is predicted by its AHR-binding affinity and CYP1A induction potency. However, the role of the AHR, if any, in mediating the developmental effects of PAH to fish remains unknown. In this study we looked at the AHR binding affinity of a test set of PAH that had been previously ranked for their potency for inducing teleost CYP1A. PAH that induced CYP1A inhibited [3H]TCDD binding to in vitro-expressed AHRs from rainbow trout and the AHR expressed in PLHC-1 fish hepatoma cells. Generally, the relative rank order for AHR binding affinity predicted the rank order of these same PAH for inducing CYP1A reported in other studies. There was a strong, positive relationship between binding to the PLHC-1 AHR (stimulus) and the EC50s for CYP1A induction (response) in whole juvenile trout and in RTL-W1 cells, but EC50s were much higher than expected for a 1:1 stimulus/response relationship. These data show that the ability of PAH to bind to teleost AHR predicts PAH potency for CYP1A induction. If PAH toxicity is receptor-mediated and predicted by induction potencies, we will have a powerful mechanistic-based tool for rapidly assessing the risk of toxicity to fish of PAH from any source.

Animals↗
PubMed1992

Three types of GABA-immunoreactive cone horizontal cells in teleost retina.

Peroxidase-anti-peroxidase immunocytochemistry, applied on serial semithin epoxy resin sections, was used to examine the localization of endogenous GABA in horizontal cells in the retina of a marine teleost, the dragonet (Callionymus lyra L.). The immunostaining shows that not only the external H1 cone horizontal cells label with antibodies against GABA, but also the H2 and H3 cone horizontal cells in the inner nuclear layer. The distribution of the H1 cells corresponds to that of the single cones. They are square-patterned and in the dorsal retina their density equals 20,000 cells/mm2. The estimated density of the immunostained H2 and the H3 cells in the dorsal retina is 9500 and 1300 cells/mm2, respectively. The H2 and H3 cells are not geometrically arranged, but nearest-neighbor analysis shows that these horizontal cell types do have a very regular disposition. We suggest that GABA is the likely neurotransmitter substance used by all cone horizontal cell types in teleost retina.

Animals↗
PubMedDate not supplied

Biplexiform ganglion cells, characterized by dendrites in both outer and inner plexiform layers, are regular, mosaic-forming elements of teleost fish retinae.

Biplexiform ganglion cells were labelled by retrograde transport of HRP in five species of marine fish from the neoteleost acanthopterygian orders Perciformes and Scorpaeniformes. Their forms and spatial distributions were studied in retinal flatmounts and thick sections. Biplexiform ganglion cells possessed sparsely branched, often varicose, dendrites that ramified through the inner nuclear layer (INL) to reach the outer plexiform layer (OPL), as well as conventional arborizations in the most sclerad part of the inner plexiform layer (IPL). Their somata were of above-average size and were displaced into the vitread border of the INL. Mean soma areas ranged from 99 +/- 6 microns2 in Bathymaster derjugini (Perciformes) to 241 +/- 12 microns2 in Hexagrammos stelleri (Scorpaeniformes), but were similar in each species to those of the outer-stratified alpha-like ganglion cells, whose dendritic trees occupied the same IPL sublamina. In the best-labelled specimens, biplexiform cells formed clear mosaics with spacings and degrees of regularity much like those of other large ganglion cells, but spatially independent of them. Biplexiform mosaics were plotted in three species, and analyzed by nearest-neighbor distance and spatial correlogram methods. The exclusion radius, an estimate of minimum mosaic spacing, ranged from 113 microns in Hexagrammos stelleri, through 150 microns in Ernogrammus hexagrammus (Perciformes), to 240 microns in Myoxocephalus stelleri (Scorpaeniformes). A spatial cross-correlogram analysis of the distributions of biplexiform and outer-stratified alpha-like cells in Hexagrammos demonstrated the spatial independence of their mosaics. Similar cells were previously observed not only in the freshwater cichlid Oreochromis spilurus (Perciformes) but also in the goldfish Carassius auratus (Cypriniformes) which, being an ostariophysan teleost, is only distantly related. Thus, biplexiform ganglion cells may be regular elements of all teleost fish retinae. Their functional role remains unknown.

Animals↗
PubMedDate not supplied

Localization and expression of insulin-like growth factor in the teleost retina.

Teleost fish retinas continue to add neurons throughout life, and evidence from in vitro experiments have implicated insulin-like growth factors (IGFs) in this process. To discover whether these factors are expressed in vivo, we have examined their expression in the cichlid fish, Haplochromis burtoni. Three lines of evidence show that IGFs are present in the fish retina. An IGF-I specific antibody, sm 1.2, binds preferentially to the retinal outer plexiform layer, in areas of cone photoreceptor synaptic endings. Northern blots of mRNA hybridized with riboprobes from trout IGF-I and IGF-II genes revealed transcripts of approximately 6.5 and 4.9 kb, respectively. The IGF-I probe detected an additional transcript of 1.2 kb in liver but not in retinal mRNA. In situ hybridization with digoxigenin-labeled riboprobes revealed that the IGF gene product is localized in the cone photoreceptors. These results show that cone photoreceptors are the source of IGFs in the fish retina, consistent with the hypothesis that IGFs play a role in regulating production of new neurons in the teleost retina.

Animals↗
PubMed1992

Peptidergic neurons of teleost retinas.

In retinas of teleost fish, neuropeptides typically have subtle, modulatory actions. The peptide effects typically have long latencies and durations, and, in some instances, they are known to be mediated by second messengers. Peptidergic neurons in teleost retinas have certain morphological features in common that are consistent with their function. Most peptidergic neurons are stratified amacrine cells with long, varicose processes; the processes of peptidergic centrifugal axons are also narrowly stratified and ramify extensively in the retina. The peptidergic amacrine cells are relatively infrequent, and, likewise, the centrifugal axons originate from a small number of perikarya in the brain. Cells that are so sparsely distributed and whose processes overlap so extensively are better-suited for modulation than for conveying detailed representations of visual space.

Animals↗
PubMed2002

Filial cannibalism in teleost fish.

This review summarizes information on filial cannibalism (the act of eating one's own offspring) in teleost fish. Cannibalistic parents can either consume their whole brood (total filial cannibalism), or eat only some of the eggs in the nest (partial filial cannibalism). Offspring consumption has been argued to be adaptive under the assumption that offspring survival is traded against feeding, and that offspring can act as an alternative food source for the parents. The evidence supporting the basic predictions formulated under these assumptions is summarized for both total and partial filial cannibalism. These two forms of cannibalism differ significantly since the former represents an investment only in future reproductive success, whereas the latter can affect both present and future reproductive success. Despite a few inconsistencies in the data from laboratory and field studies, the energy-based explanation appears valid for both forms of cannibalism. Alternative non-energy-based explanations are considered, but they are unable to account for the wide distribution of this behaviour in teleosts. The intersexual conflict arising from attempts of the non-cannibal sex to minimize the cost of filial cannibalism is also discussed, together with the potential effect of this behaviour on the operational sex ratio at a population level.

Animals↗
PubMed1999

Have chondracanthid copepods co-speciated with their teleost hosts?

Chondracanthid copepods parasites many teleost species and have a mobile larval stage. It has been suggested that copepod parasites, with free-living infective stages that infect hosts by attaching to their external surfaces, will have co-evolved with their hosts. We examined copepods from the genus Chondracanthus and their teleost hosts for evidence of a close co-evolutionary association by comparing host and parasite phylogenies using TreeMap analysis. In general, significant co-speciation was observed and instances of host switching were rare. The prevalence of intra-host speciation events was high relative to other such studies and may relate to the large geographical distances over which hosts are spread.

Animals↗
PubMed2000

Nonradiometric detection of cytotoxicity of teleost nonspecific cytotoxic cells.

The development of a sensitive, rapid and reliable nonradiometric cytotoxicity assay would significantly facilitate studies of teleost nonspecific cytotoxic cells. Such an assay would not require handling and disposal of radionuclides and it would not depend on secondary enzyme or colorimetric determinations. The requirements for this assay would consist of a one-step binding protocol which could detect early target cell membrane lesions and at very low effector:target cell ratios. In this chapter, we have developed a flow cytometry based cytotoxicity assay utilizing the uptake of propidium iodide (PI) into cells containing damaged (i.e. permeabilized) cell membranes. The basis of detection of cellular damage depended on flow discrimination of targets from effector cells by establishing 'scatter' gates from these mixtures. Teleost (catfish) anterior kidney NCC were mixed with human transformed targets (IM-9 and HL-60 cells) at effector:target cell ratios of 1, 5 and 10 and PI uptake was determined at 3 and 14 hours post-incubation. Percent specific uptake (PSU) was calculated by determining total binding capacity (TBC) (i.e. uptake of PI by cold acetone permeabilized target cells) and spontaneous binding capacity (SBC) (i.e. PI uptake by target cells incubated in media w/o effectors). This was represented by the formula PSU = [T - SBC/TBC - SBC] x 100 where T is the PI uptake of targets following addition of effector cells. Using this technique, NCC initiated target cell permeabilization as early as 30 minutes co-incubation (25:1 E:T ratio) and damaged membranes were detected in mixtures containing as few as 1:1 effector:target cell ratios. At 5:1 E:T ratios, greater than 50 PSU was determined following 14 hours co-incubation. Using these criteria, a new and sensitive cytotoxicity assay has been developed to determine NCC activity.

Animals↗
PubMed2000

Prolactin signaling in erythrophores and xanthophores of teleost fish.

Prolactin directly affects erythrophores and xanthophores of teleost fish, resulting in pigment dispersion. In the present study, signal transduction elicited by prolactin was examined using split-tail fin preparations of the rose bitterling and Nile tilapia, and cultured erythrophores and xanthophores from the paradise goby and rose bitterling. When antibodies to the prolactin receptor were added to an ovine prolactin (oPRL) solution, pigment dispersion within cultured cells was significantly inhibited, suggesting the existence of a prolactin receptor in the cell membrane. In mammals and birds, prolactin receptors belong to a cytokine receptor superfamily and signal through a tyrosine kinase-mediated pathway. Therefore, we examined the effects of three kinds of protein tyrosine kinase inhibitors on pigment dispersion elicited by oPRL. None of those inhibitors depressed the response. On the other hand, lithium ions (an inhibitor of adenylate cyclase) and H-88 and H-89 (inhibitors of protein kinase A) decreased the levels of oPRL-induced pigment dispersion in a dose-dependent manner. In cultured cells treated with cholera toxin for 3 hrs, the effect of oPRL was irreversible, indicating the possible involvement of Gs protein in the prolactin action. From these results, we conclude that cAMP may be a second messenger in the dispersion of pigment induced by prolactin and that a novel protein receptor coupled with a Gs protein may be present in the membrane of erythrophores and xanthophores of teleost fish.

Animals↗
PubMedDate not supplied

Centrifugal fibres synapse on dopaminergic interplexiform cells in the teleost retina.

In teleost fish, centrifugal fibres originating in the olfactory bulb and containing FMRFamide-like and luteinizing hormone releasing hormone (LHRH)-like peptides project to the retina and terminate along the border of the inner nuclear and inner plexiform layers. Using a novel simultaneous two-colour immunolabelling technique, we have found that these centrifugal fibres are often closely apposed to the dopaminergic interplexiform cells. Contacts between centrifugal fibres and dopaminergic interplexiform cells were observed by electron microscopy to be conventional type synaptic junctions. Since the dopaminergic interplexiform cells make synapses on horizontal and bipolar cells, providing an intraretinal centrifugal pathway for information flow from the inner to the outer plexiform layers, we conclude that every neuron in the teleost retina is potentially susceptible to central influences via these centrifugal fibres and dopaminergic interplexiform cells.

Animals↗
PubMed1999

Expression of murine early embryonic antigens, SSEA-1 and antigenic determinant of EMA-1, in embryos and ovarian follicles of a teleost medaka (Oryzias latipes).

Stage-specific embryonic antigen-1 (SSEA-1) and the antigenic determinant of monoclonal antibody EMA-1 are expressed in a stage-specific manner in mouse early embryos. To study whether these antigens generally exist in fish, expression of the antigens was examined in embryos, ovarian follicles, and adult tissues of a teleost medaka (Oryzias latipes), using immunohistochemical techniques. In 1-cell-stage embryos, these carbohydrate antigens were found in numerous cytoplasmic granules in the blastodisc and the cortical cytoplasm. These granules gradually decreased in number as the embryos developed. In 4-cell-stage embryos, the antigens appeared on the cleavage planes and were located on the cleavage planes within the blastoderm in the following cleavage stages. In blastula-stage embryos, the expression was ubiquitously found on the cell surface of blastomeres. At the mid-gastrula stage, the antigens were restricted to the enveloping layer, yolk syncytial layer, and cortical cytoplasm, but were rarely found in deep cells that contribute to formation of the embryonic body. In later-stage embryos and adult fish, the antigens were located in various tissues. In ovarian follicles, the antigens were found in granules of oocytes and granulosa cells. These observations were basically consistent with those in mice; however, expression in 1-cell-stage embryos and ovarian follicles has not been observed in mice. This unexpected finding suggests that the antigens are produced in granulosa cells and transferred to 1-cell-stage embryos via oocytes, and that the antigens involved in the early developmental process are maternally prepared in teleosts.

Animals↗
PubMed1995

Evidence for D4 receptor regulation of retinomotor movement in isolated teleost cone inner-outer segments.

In the retinas of teleost fish, cone photoreceptors change shape in response to light and circadian signals. They elongate in the dark, contract in the light, and under conditions of constant darkness undergo appropriate movements at expected dusk and dawn. Dopamine induces cones to contract, thus mimicking the effect of light or expected dawn. To identify the receptor subtype responsible for mediating dopamine regulation of cone retinomotor movements, we have carried out pharmacological studies using isolated fragments of teleost cones consisting of cone inner segments-cone outer segments (CIS-COS). Isolated CIS-COS retain the ability to elongate in dark culture and contract when subsequently exposed to light or dopamine. We report that dark-induced elongation of CIS-COS was inhibited by dopamine and its agonists with an effectiveness ranking of dopamine = quinpirole > bromocriptine >>> SKF-38393. After 60 min of elongation in dark culture, CIS-COS myoids contracted when subsequently cultured in the dark with dopamine or quinpirole. Quinpirole-induced inhibition of elongation and quinpirole-induced contraction were completely blocked by clozapine at 1 microM or by sulpiride at 100 microM. These effectiveness profiles for dopamine agonists and antagonists suggest that dopamine regulation of cone retinomotor movement is mediated by a D4-like receptor.

Animals↗
PubMedDate not supplied

Teeth outside the mouth in teleost fishes: how to benefit from a developmental accident.

Evolution proceeds by the selection of characters that enhance survival rates so that the long-term outcome for a species is better adaptation to its environment. These new characters are "accidentally" acquired, mostly through mutations leading to modifications of developmental events. However, changes that lead to the ectopic expression of an organ are rare and, whereas their subsequent selection for a new role is even more rare, such a scenario has apparently occurred for denticles in some teleost fish. Small, conical denticles are present, mainly on the dermal bones of the head, in a few, unrelated lineages of living teleosts. Here, I show that the morphology and structure of the denticles in Atherion elymus, an atheriniform, is similar to those of teeth inside the oral cavity. These denticles are not derived evolutionarily from odontodes of early vertebrates, nor do they represent a re-expression as such (i.e., a long-lasting ability to make odontodes outside the oral cavity). Teeth and odontodes are homologous organs but the origin of the denticles is to be found in teeth, not in odontodes. The denticles are simply teeth that form outside the mouth, probably derived from a sub-population of odontogenically pre-specified neural crest cells. These "accidental" extra-oral teeth have arisen independently in these lineages and were selectively advantageous in a hydrodynamic context.

Animals↗
PubMed2005

Discovery of a unique Ig heavy-chain isotype (IgT) in rainbow trout: Implications for a distinctive B cell developmental pathway in teleost fish.

During the analysis of Ig superfamily members within the available rainbow trout (Oncorhynchus mykiss) EST gene index, we identified a unique Ig heavy-chain (IgH) isotype. cDNAs encoding this isotype are composed of a typical IgH leader sequence and a VDJ rearranged segment followed by four Ig superfamily C-1 domains represented as either membrane-bound or secretory versions. Because teleost fish were previously thought to encode and express only two IgH isotypes (IgM and IgD) for their humoral immune repertoire, we isolated all three cDNA isotypes from a single homozygous trout (OSU-142) to confirm that all three are indeed independent isotypes. Bioinformatic and phylogenetic analysis indicates that this previously undescribed divergent isotype is restricted to bony fish, thus we have named this isotype "IgT" (tau) for teleost fish. Genomic sequence analysis of an OSU-142 bacterial artificial chromosome (BAC) clone positive for all three IgH isotypes revealed that IgT utilizes the standard rainbow trout V(H) families, but surprisingly, the IgT isotype possesses its own exclusive set of D(H) and J(H) elements for the generation of diversity. The IgT D and J segments and tau constant (C) region genes are located upstream of the D and J elements for IgM, representing a genomic IgH architecture that has not been observed in any other vertebrate class. All three isotypes are primarily expressed in the spleen and pronephros (bone marrow equivalent), and ontogenically, expression of IgT is present 4 d before hatching in developing embryos.

Amino Acid Sequence↗
PubMed2006

Evolutionary constraint on Otx2 neuroectoderm enhancers-deep conservation from skate to mouse and unique divergence in teleost.

Otx2 is a paired type homeobox gene that plays essential roles in each step and site of head development in vertebrates. In the mouse, Otx2 expression in the anterior neuroectoderm is regulated primarily by two distinct enhancers: anterior neuroectoderm (AN) and forebrain/midbrain (FM) enhancers at 92 kb and 75 kb 5'of the Otx2 locus, respectively. The AN enhancer has activity in the entire anterior neuroectoderm at headfold and early somite stages, whereas the FM enhancer is subsequently active in the future caudal forebrain and midbrain ectoderm. In tetrapods, both AN and FM enhancers are conserved, whereas the AN region is missing in teleosts, despite overt Otx2 expression in the anterior neuroectoderm. Here, we show that zebrafish and fugu FM regions drive expression not only in the forebrain and midbrain but also in the anterior neuroectoderm at headfold stage. The analysis of coelacanth and skate genomic Otx2 orthologues suggests that the utilization of the two enhancers, AN and FM, is an ancestral condition. In contrast, the AN enhancer has been specifically lost in the teleost lineage with a compensatory establishment of AN activity within the FM enhancer. Furthermore, the AN activity in the fish FM enhancer was established by recruiting upstream factors different from those that direct the tetrapod AN enhancer, yet zebrafish FM enhancer is active in both mouse and zebrafish anterior neuroectoderm at the headfold stage.

Animals↗
PubMed1993

cDNA cloning of the beta subunit of teleost thyrotropin.

cDNA clones encoding the beta subunit of thyrotropin (thyroid-stimulating hormone; TSH) were isolated from a cDNA library made from the pituitaries of immature rainbow trout and sequenced. The precursor of rainbow trout TSH beta consists of 147 aa, which can be cleaved into a signal peptide (20 aa) and a mature protein (127 aa) containing one potential N-glycosylation site and 12 cysteine residues. The protein showed highest homology with human TSH beta (51%) and lesser homology with human follitropin (42%), human lutropin (32%), and salmon gonadotropin (31-33%) beta subunits. The identification of TSH in addition to two gonadotropins (gonadotropins I and II) in the teleost fish suggests that the divergence of three kinds of glycoprotein hormones from an ancestral molecule took place earlier than the time of divergence of teleosts from the main line of evolution leading to tetrapods. Northern blot analysis showed that the expression of the rainbow trout TSH beta gene is specific to the pituitary gland and is significantly higher in immature fish than in mature fish, suggesting that TSH plays some role in the biological processes of immature fish.

Age Factors↗
PubMed1994

Structure, function, and phylogeny of [Arg8]vasotocin receptors from teleost fish and toad.

[Arg8]Vasotocin (AVT) is considered to be the most primitive known vertebrate neurohypophyseal peptide of the vasopressin/oxytocin hormone family and may thus be ancestral to all the other vertebrate peptide hormones. The molecular evolution of the corresponding receptor family has now been studied by cloning an AVT receptor, consisting of 435 amino acid residues, from the teleost fish, the white sucker Catostomus commersoni. Frog oocytes injected with the AVT receptor-encoding cRNA respond to the application of AVT, but not to its structural and functional counterpart isotocin, by an induction of membrane chloride currents indicating the coupling of the AVT receptor to the inositol phosphate/calcium pathway. The pharmacological properties of the expressed AVT receptor show that it represents, or is closely related to, an ancestral nonapeptide receptor: oxytocin, aspargtocin, mesotocin, and vasopressin activated the receptor, but other members of the vasopressin/oxytocin family tested showed little or no potency; antagonists of the mammalian vasopressin V1 and oxytocin receptors blocked the AVT response. Comparison of AVT receptor sequences spanning transmembrane domains two to five, deduced by cloning cDNAs from the Pacific salmon Oncorhynchus kisutch, the cave-dwelling fish Astyanax fasciatus, and the anuran Xenopus laevis, with those of their mammalian counterparts emphasizes amino acid residues that are involved in hormone binding. The presence of a 5.0-kb transcript in various teleost tissues (pituitary, liver, gills, swim bladder, and lateral line) points to a physiological role for the fish AVT receptor in metabolic, osmoregulatory, and sensory processes.

Amino Acid Sequence↗
PubMed1997

Somatotropic actions of the homologous growth hormone and prolactins in the euryhaline teleost, the tilapia, Oreochromis mossambicus.

It is increasingly clear that growth hormone (GH) has growth-promoting effects in fishes, which are mediated in part by the insulin-like growth factor (IGF)-I. Growth-promoting actions of prolactin (PRL) have been reported in higher vertebrates, but are less well established in teleosts. We examined the effects of injecting homologous GH or the two homologous tilapia PRLs (tPRL177 and tPRL188) on the in vitro incorporation of [35S] sulfate (extracellular matrix synthesis) and [3H]thymidine (DNA synthesis) by ceratobranchial cartilage explants and on IGF-I mRNA levels in tilapia liver. Tilapia GH (tGH) and tPRL177 stimulated sulfate uptake at the highest doses examined. Thymidine incorporation was stimulated by tPRL177. tPRL188 was without these effects. Consistent with its somatotropic actions, tGH elevated IGF-I mRNA levels in the liver. tPRL177 also elevated liver IGF-I levels. Consistent with the previously described osmoregulatory actions of GH and PRL in teleosts, we observed that tGH elevated and tPRL177 and tPRL188 lowered levels of gill Na+,K+-ATPase activity. High-affinity, low-capacity binding sites for tGH in the tilapia liver were identified. tPRL177 binds with lower affinity than tGH to these sites but can displace 125I-labeled tGH from its receptor. The ability of tPRL177 to displace tGH was similar to that of ovine GH. tPRL188 did not displace 125I-labeled tGH binding. Collectively, this work suggests that tPRL177 may possess somatotropic actions similar to tGH, but only in freshwater tilapia where tPRL177 levels are sufficiently high for it to act as a competitive ligand for GH receptors.

Animals↗