Consequences of genome duplication

Polyploidy has been widely appreciated as an important force in the evolution of plant genomes, but now it is recognized as a common phenomenon throughout eukaryotic evolution. Insight into this process has been gained by analyzing the plant, animal, fungal, and recently protozoan genomes that show evidence of whole genome duplication (a transient doubling of the entire gene repertoire of an organism). Moreover, comparative analyses are revealing the evolutionary processes that occur as multiple related genomes diverge from a shared polyploid ancestor, and in individual genomes that underwent several successive rounds of duplication. Recent research including laboratory studies on synthetic polyploids indicates that genome content and gene expression can change quickly after whole genome duplication and that cross-genome regulatory interactions are important. We have a growing understanding of the relationship between whole genome duplication and speciation. Further, recent studies are providing insights into why some gene pairs survive in duplicate, whereas others do not.     

A large new subset of TRIM genes highly diversified by duplication and positive selection in teleost fish

Background  

In mammals, the members of the tripartite motif (TRIM) protein family are involved in various cellular processes including innate immunity against viral infection. Viruses exert strong selective pressures on the defense system. Accordingly, antiviral TRIMs have diversified highly through gene expansion, positive selection and alternative splicing. Characterizing immune TRIMs in other vertebrates may enlighten their complex evolution.     

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.     

Evolution of CC chemokines in teleost fish: a case study in gene duplication and implications for immune diversity

Chemokines are a superfamily of cytokines responsible for regulating cell migration under both inflammatory and physiological conditions. CC chemokines are the largest subfamily of chemokines, with 28 members in humans. A subject of intense study in mammalian species, the known functional roles of CC chemokines ligands in both developmental and disease conditions continue to expand. They are also an important family for the study of gene copy number variation and tandem duplication in mammalian species. However, little is known regarding the evolutionary origin and status of these ligands in primitive vertebrates such as teleost fish. In this paper, we review the evolution of the teleost fish CC chemokine gene family, noting evidence of widespread tandem gene duplications and examining the implications of this phenomenon on immune diversity. Through extensive phylogenetic analysis of the CC chemokine sets of four teleost species, zebrafish, catfish, rainbow trout, and Atlantic salmon, we identified seven large groups of CC chemokines. It appeared that several major groups of CC chemokines are highly related including the CCL19/21/25 group, the CCL20 group, CCL27/28 group, and the fish-specific group. In the three remaining groups that contained the largest number of members, the CCL17/22 group, the MIP group, and the MCP group, similarities among species members were obscured by rapid, tandem duplications that may contribute to immune diversity.     

Hox gene duplication in fish

The study of Hox gene clusters continues to serve as a paradigm for those interested in vertebrate genome evolution. Recent exciting discoveries about Hox gene composition in fishes challenges conventional views about vertebrate Hox gene evolution, and has initiated lively debates concerning the evolutionary events making the divergence of the major vertebrate lineages. Comparative analyses indicate that Hox cluster duplications occurred in early vertebrate evolution, and again within the order Cypriniformes of teleost fish. Loss of Hox genes was more widespread than duplication during fish evolution.     

Enameloid in the teleost fish Lophius

Summary The ultrastructural and chemical differences between mature enameloid and dentine in the teleost fish Lophius were demonstrated using transmission (TEM) and scanning (SEM) electron microscopy, X-ray diffraction analysis, electron diffraction analysis and electron microprobe analysis. An enameloid cap (about 50 m thick) and a thin layer (1 m thick) of collar enameloid were revealed in the scanning (SEM) and transmission (TEM) electron microscopes. Collar enameloid, structurally different from dentine both in SEM and TEM, proved to be less mineralized than the cap as revealed by electron microprobe analysis. The enameloid cap was seen to differ from dentine by (i) its electron density in TEM; (ii) the structural arrangement perpendicular to the underlying dentine, observed in SEM and TEM and corroborated by electron diffraction data, which showed a preferred orientation of enameloid crystallites; (iii) its higher F content decreasing gradually from the apex of the tooth to the junction with dentine and falling suddenly below this junction; and (iv) its lower Mg content. Establishment of a classification of enameloids is proposed, similar to that for dentines, in which selachian enameloid would be a reference standard.

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Résumé La microscopie électronique à transmission, la microscopie électronique à balayage, la diffraction X, la diffraction électronique et l'analyse par microsonde ont prouvé l'existence d'un émailoïde, ultrastructuralement et chimiquement différent de la dentine, chez la baudroie. La microscopie électronique à balayage et la microscopie électronique à transmission ont mis en évidence un chapeau d'émailoïde, d'environ 50 m d'épaisseur, et une couche fine (1 m) d'émailoïde du collet. L'émailoïde du collet, dont l'ultrastructure différente de celle de la dentine a été mise en évidence en microscopie électronique à transmission et en microscopie électronique à balayage, apparaît, après analyse par microsonde, moins minéralisé que le chapeau. Le chapeau d'émailoïde diffère de la dentine par (i) sa densité aux électrons en microscopie électronique à transmission; (ii) sa structure perpendiculaire à celle de la dentine sous-jacente, visible en microscopie électronique à transmission et en microscopie électronique à balayage et confirmée par la diffraction électronique, qui montre une orientation préférentielle des cristaux; (iii) son contenu en fluor plus élevé, qui diminue progressivement de l'apex à la jonction avec la dentine et chute brutalement au-dessous de cette jonction; (iv) sa teneur plus basse en magnésium. Les auteurs proposent que soit établie une classification des émailoïdes analogue à celle des dentines et dans laquelle l'émailoïde de Sélaciens constituerait un standard de référence.

     

Neuropharmacology of adrenergic neurons in teleost fish

Although this brief review is based on relatively few types of experiments in few species of teleosts, it is possible to summarize some points of interest regarding the similarities and differences in the mechanisms of adrenergic neurotransmission in fish compared to the higher vertebrates. 1. There is a substantial mixing of cranial autonomic ("parasympathetic") and spinal autonomic ("sympathetic") pathways in the cranial nerves. This close relationship between the two systems and the differences in the nature of the neurons of cranial origin (cholinergic, and non-adrenergic, non-cholinergic) and spinal origin (adrenergic, cholinergic and mixed "polynergic") gives a basis in fish also for a complex pattern of innervation of the various organs. 2. Adrenaline is the major transmitter substance in the adrenergic neurons of most teleosts studied, but there are exceptions within the same species. For instance, in the swimbladder mucosa of the cod, noradrenaline dominates, while adrenaline is the major catecholamine in most other organs innervated by adrenergic neurons. The reasons for the regional differences are not known and further studies of the rate of catecholamine turn-over in the adrenergic neurons of fish are clearly indicated. 3. Adrenoceptors of both the alpha- and the beta-type show great similarities with those of mammals. Some differences in the potencies of certain compounds (e.g., clonidine and methoxamine) exist and receptor binding studies should add valuable information about the adrenoceptors of teleosts. The existence of a subtype of beta-adrenoceptor (beta 2) has been proposed and further work is needed to confirm or deny the applicability of the beta 1/beta 2 adrenoceptor terminology in fish. 4. There appears to be some differences in the mode of action of the so called "indirectly acting amines", such as tyramine, between teleosts and mammals. While the uptake of tyramine into the nerve terminals in mammals appears to take place via the cocaine-sensitive neuronal uptake system which is also responsible for catecholamine uptake (uptake 1), tyramine uptake in cod neurons appears to be via a separate pathway. 5. Presynaptic supersensitivity of the type seen in mammals has also been demonstrated in teleost adrenergic neurons. Both denervation (chemical or surgical) and blockade of the neuronal uptake mechanism by cocaine or desipramine produce this type of supersensitivity, while post-synaptic supersensitivity has so far not been described in teleosts. The effects of removal of the uptake system shows that the uptake process may be as important in teleosts as in mammals in the removal of adrenergic transmitter from the synaptic cleft. 6. In the total picture of adrenergic functions in fish, the circulating catecholamines take a special role...     

Field studies of hearing in teleost fish

Summary 1. Field measurements of hearing in haddock,Melanogrammus aeglefinus, pollack,Pollachius pollachius and ling,Molva molva, show that they are sensitive to sounds in the frequency range from 30 to 500 Hz, with greatest sensitivity from 100 to 300 Hz.2. At the most sensitive frequencies the thresholds varied between — 15 to — 25 dB relative to a sound pressure of 1µbar.3. In all three species, the thresholds at some frequencies were affected by the level of ambient sea noise. A direct correlation between the thresholds and the spectrum level of sea noise was obtained in haddock and pollack.4. The masking effect of sea noise was confirmed in some experiments on cod,Gadus morbua and haddock, where the background noise level was raised artificially. It was found that the masking of a tone signal was reduced by about 8 dB when the tone and noise were from different directions (85° apart), suggesting that directional discrimination may be well developed in these fish.

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Freilandversuche über das Hörvermögen bei Teleostiern

Kurzfassung Versuche über das Hörvermögen verschiedener mariner Fische — des Schellfischs(Melanogrammus aeglefinus), des Pollacks(Pollachius pollachius), des Kabeljaus(Gadus morhua) und des Lengs(Molva molva) — wurden im Biotop, und zwar in 20 m Tiefe bei Loch Torridon (Schottland) durchgeführt. Die Reaktionen der Fische wurden mit Hilfe einer besonderen Dressurtechnik getestet, wobei dem Tonreiz ein leichter elektrischer Schock folgte; wurde das akustische Signal wahrgenommen, traten Veränderungen im Elektrokardiogramm der Fische auf. Alle 4 Arten wiesen ein ähnliches Hörvermögen auf. Im Niederfrequenzbereich von etwa 60–300 Hz wurde die höchste Empfindlichkeit registriert. Bei höheren Frequenzen stellte sich eine Verminderung der Empfindlichkeit ein; nurMolva molva konnte zuverlässig auf einen Ton von 550 Hz abgerichtet werden. Im Bereich niederer Frequenzen waren alle Fische äußerst empfindlich; es ergaben sich Hinweise, daß die Hörschwellen vom Eigenrauschen des Meeres maskiert wurden. Dies wurde durch Versuche bestätigt, bei denen die Intensität des Eigenrauschens vergrößert wurde, die Mithörschwellen aber in konstantem Abstand zum Störpegel blieben. Ferner wurde festgestellt, daß die Verdeckung reiner Töne wesentlich vermindert wurde, wenn Ton und Störpegel aus verschiedenen Richtungen (im rechten Winkel zueinander) abgestrahlt wurden. Daraus ist zu schließen, daß die Fähigkeit, die Richtung der Schallquellen zu unterscheiden, gut entwickelt sein dürfte.

     

Iron acquisition by teleost fish

Iron is a vital micronutrient for teleost fish, being an integral component of proteins involved in cellular respiration and oxygen transfer. However, in excess iron is toxic, and fish need to balance uptake to prevent deficiency vs. potential toxicity. This review assesses the current physiological and molecular knowledge of the mechanisms of iron acquisition in the teleost fish. It focuses on freshwater teleost fish when assessing the gill as a possible site for iron acquisition, and includes a summary of geochemical processes that govern aquatic iron bioavailability. It focuses on marine teleost fish for assessing the mechanism of intestinal iron uptake. Physiological evidence indicates that iron preferentially crosses the apical membrane of both the gills and intestine in the ferrous (Fe2+) state. Molecular evidence supports this, demonstrating the presence of homologues in fish to the large Slc 11a family of evolutionary conserved proteins linked to Fe2+ transport. This symporter is probably linked to a reductase, which reduces either ferric (Fe3+) or organic complexed iron to Fe2+ prior to uptake.     

Photokinesis in the teleost fish Danio malabaricus

Summary Photokinesis as shown by the rapidly moving fish Danio malabaricus was examined in two experiments.In Experiment I, which involved sequences of short periods of light and darkness, the Ss for the most part showed a positive relationship between light intensity and level of activity. This reaction included a well differentiated response to abrupt intensity change, the effect of the transition from darkness to light being marked. Level of activity in both light and dark periods tended to fall; after a certain point, however, it rose again in the light but continued to fall in the darkness.In Experiment II, successive increases in the total area of lighted space available were matched by increases in the total length of time spent there by the Ss. The overall reaction, however, was initially photonegative and became more so as the experiment progressed. The range of most frequent periods of time spent in the lighted area increased gradually, while the length of entries into the shaded area gradually decreased, in the course of the experiment. But for a lighted area the Ss' length of entry was shorter than for the corresponding dark area, the choice of period was more precise, there were fewer longer periods, and the range was less. In the last condition, the Ss divided their time approximately equally between the lighted 7/8 and the shaded 1/8 of the area available. The number of times the Ss crossed from one area to the other almost doubled during the experiment.The author wishes to express his gratitude to Prof. G. Thinès for his help and encouragement. He was supported by a research grant from N. A. T. O., administered through the Science Research Council, London. The findings reported formed part of a study submitted as a doctoral dissertation at the Université de Louvain. The raw data is tabulated in this study and may be consulted at the Institut de Psychologie et des Sciences Pédagogiques. Address after 1 October: Department of Psychology, Bryn Mawr College, Bryn Mawr, Pennsylvania, U.S.A.     

The interferon system of teleost fish

Interferons (IFNs) are secreted proteins, which induce vertebrate cells into an antiviral state. In mammals, three families of IFNs (type I IFN, type II IFN and IFN-lambda) can be distinguished on the basis of gene structure, protein structure and functional properties. Type I IFNs, which include IFN-alpha and IFN-beta, are encoded by intron lacking genes and have a major role in the first line of defense against viruses. The human IFN-lambdas have similar biological properties as type I IFNs, but are encoded by intron containing genes. Type II IFN is identical to IFN-gamma, which is produced by T helper 1 cells in response to mitogens and antigens and has a key role in adaptive cell mediated immunity. IFNs, which show structural and functional properties similar to mammalian type I IFNs, have recently been cloned from Atlantic salmon, channel catfish, pufferfish, and zebrafish. Teleost fish appear to have at least two type I IFN genes. Phylogenetic sequence analysis shows that the fish type I IFNs form a group separated from the avian type I IFNs and the mammalian IFN-alpha, -beta and -lambda groups. Interestingly, the fish IFNs possess the same exon/intron structure as the IFN-lambdas, but show most sequence similarity to IFN-alpha. Recently, IFN-gamma genes have also been cloned from several fish species and shown to have the same exon/intron structure as mammalian IFN-gamma genes. The antiviral effect of mammalian type I IFN is exerted through binding to the IFN-alpha/beta-receptor, which triggers signal transduction through the JAK-STAT signal transduction pathway resulting in expression of Mx and other antiviral proteins. Putative IFN receptor genes have been identified in pufferfish. Several interferon regulatory factors and members of the JAK-STAT pathway have also been identified in various fish species. Moreover, Mx and several other interferon stimulated genes have been cloned and studied in fish. Furthermore, antiviral activity of Mx protein from Atlantic salmon and Japanese flounder has recently been demonstrated.     

Sexual determination and differentiation in teleost fish

The present work reviews the latest information on the cellular, molecular and physiological aspects of sexual determination and differentiation in teleost fish. The group exhibits a large variety of mechanisms of sexual determination. These may be genetic, or depend on environmental conditions such as temperature, pH, and social factors, all of which can influence the proportion of the sexes. Additionally, sex steroids play an important role in the regulation of sexual differentiation. The patterns of gonadal sexual differentiation are diverse, and species may be hermaphroditic or gonochoristic, some of the latter displaying juvenile hermaphroditism. In recent years, several genes involved in the sexual determination and differentiation pathways in vertebrates, particularly in mammals, have also been characterized in teleosts. Conserved as well as diversified functions have been proposed.     

The hapten-carrier effect in teleost fish.

The sea robin (Prionotus evolans), a representative teleost fish, was found to undergo the hapten-carrier effect, suggestive of T-B cell cooperativity, in vivo with dinitrophenyl as the hapten and bovine gamma-globulin or bovine serum albumin as carriers. In contrast to mammalian systems, the secondary anti-hapten response in the sea robin was found to involve exclusively high molecular weight antibody.     

Genome evolution and biodiversity in teleost fish

Teleost fish, which roughly make up half of the extant vertebrate species, exhibit an amazing level of biodiversity affecting their morphology, ecology and behaviour as well as many other aspects of their biology. This huge variability makes fish extremely attractive for the study of many biological questions, particularly of those related to evolution. New insights gained from different teleost species and sequencing projects have recently revealed several peculiar features of fish genomes that might have played a role in fish evolution and speciation. There is now substantial evidence that a round of tetraploidization/rediploidization has taken place during the early evolution of the ray-finned fish lineage, and that hundreds of duplicate pairs generated by this event have been maintained over hundreds of millions of years of evolution. Differential loss or subfunction partitioning of such gene duplicates might have been involved in the generation of fish variability. In contrast to mammalian genomes, teleost genomes also contain multiple families of active transposable elements, which might have played a role in speciation by affecting hybrid sterility and viability. Finally, the amazing diversity of sex determination systems and the plasticity of sex chromosomes observed in teleost might have been involved in both pre- and postmating reproductive isolation. Comparison of data generated by current and future genome projects as well as complementary studies in other species will allow one to approach the molecular and evolutionary mechanisms underlying genome diversity in fish, and will certainly significantly contribute to our understanding of gene evolution and function in humans and other vertebrates.     

The role of aquaporin 3 in teleost fish

The aquaporin isoform, AQP3 has now been identified in a number of different teleost fish species, with additional DNA sequence information on AQP3 genes in further fish species available in genome databases. In zebrafish (Danio rerio), the AQP3 gene is present as two duplicate isoforms resulting from a teleostean fish genome-wide duplication. A further splicoform/isoform has also been identified in rainbow trout (Oncorhynchus mykiss). The identification of these AQP3 isoforms in other fish species is consequently explored. The role of AQP3 in physiological/osmoregulatory processes, in various teleost organs is then described. In teleost gill, AQP3 is expressed in 'chloride' cells, and in some species, in other epithelial cell types, where it may have a number of different functions including the prevention of dehydration. In eel esophagus, immunohistochemistry shows that AQP3 is expressed in surface epithelial cells in the anterior esophagus, but in mucus cells within the epithelium of the posterior esophagus. In eel intestine, AQP3 is found in macrophage-like cells and probably plays no part in osmoregulatory processes. In the rectum, as in the posterior esophagus AQP3 is expressed in mucus cells. In eel kidney, AQP3 is expressed in a subset of renal tubules, and localizes to the apical pole of tubule cells. There is no apparent change in the location or protein abundance of renal AQP3 following the acclimation of eels from freshwater to seawater.     

Sacciform cells in the skin of teleost fish

The fine structure of sacciform gland cells of the epidermis is described in the number of species of teleost fish. In some of these the cell type had either not been found, or not recognized as such, before. Some histological and histochemical results are also reported. Despite considerable differences in the histochemistry and in the morphology of the sacciform cells over the range of species studied, some features of the fine structure are constant and can be used as diagnostic characters. The nucleus is peripheral, and there is a large membrane-limited lumen, into which the secretion is released from membrane-bounded vacuoles at the margin of the cytoplasm. It is probable that the secretion originates mainly in channels of endoplasmic reticulum which become swollen to form the vacuoles. Most sacciform cells open at the surface of the skin by an apical pore, but some have not been seen to open. The classification of the various unicellular glands of teleosts is discussed and it is concluded that attempts to categorise them by the nature of the secretion alone are unsatisfactory.