Isolation and characterization of Vibrio parahaemolyticus causing infection in Iberian toothcarp Aphanius iberus.
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High mortality among laboratory cultured Iberian toothcarp Aphanius iberus occurred in February 1997 in Valencia (Spain). The main signs of the disease were external haemorrhage and tail rot. Bacteria isolated from internal organs of infected fish were biochemically homogeneous and identified as Vibrio parahaemolyticus. The bacteria were haemolytic against erythrocytes from eel Anguilla anguilla, amberjack Seriola dumerili, toothcarp A. iberus and humans, and were Kanagawa-phenomenon-negative. Infectivity tests showed that the virulence for A. iberus was dependent on salinity. Finally, all strains were virulent for amberjack and eel. (+info)
Multiple binding sites in the growth factor receptor Xmrk mediate binding to p59fyn, GRB2 and Shc.
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Melanoma formation in Xiphoporus is initiated by overexpression of the EGFR-related receptor tyrosine kinase Xmrk (Xiphoporus melanoma receptor kinase). This receptor is activated in fish melanoma as well as in a melanoma-derived cell line (PSM) resulting in constitutive Xmrk-mediated mitogenic signaling. In order to define the underlying signaling pathway(s), triggered by the activated Xmrk receptor, we attempted to identify its physiological substrates. Examination of the Xmrk carboxyterminus for putative tyrosine autophosphorylation sites revealed the presence of potential binding motifs for GRB2 as well as for Shc. Binding of these adaptor proteins to the Xmrk receptor was detected in vitro and in cells expressing the mrk kinase. The GRB2 and Shc interactions with the receptor could be disrupted individually by phosphotyrosine peptides containing putative Xmrk autophosphorylation sites, indicating direct binding of both proteins. Recruitment of GRB2 by the constitutively activated Xmrk receptor led to strong MAP kinase activation in Xiphoporus melanoma cells. We also identified a high-affinity binding site for src-kinases (pYEDL) in the Xmrk carboxyterminus. Competition experiments with phosphopeptides comprising this site confirmed that it is used for high-affinity binding of Xiphoporus fyn (Xfyn) to Xmrk in melanoma cells. Thus, Xmrk can initiate different signaling pathways by using multiple substrate-binding sites to trigger proliferation of pigment cells. (+info)
Female preferences in a fish genus without female mate choice.
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The evolution and the adaptive logic (if any) of female mate choice are subjects of lively debate. Whereas most researchers believe that females have evolved to recognize signs of male 'quality' (the ability to provide females or their offspring with direct or indirect genetic or material benefits), there is intriguing evidence that males can evolve to appeal to pre-existing female preferences. Evidence for these pre-existing biases is often ambiguous because phylogenetic reconstructions have usually failed to establish conclusively whether the female preference or the favored male traits evolved first. This potential difficulty is minimal in the mosquitofish genus Gambusia, none of whose 45 species appears to have a female-choice mating system in the wild, and none of which shows the male behavioral and morphological traits that are characteristic of female choice. Nevertheless, in an experimental situation in the laboratory, female Gambusia holbrooki readily chose between models of males and demonstrated significant and reliable preferences for a variety of exaggerated male traits that are not seen in their species or their genus. Other morphological alterations were not preferred. The latent willingness of females to choose traits in a genus without such traits and without evident female choice in the wild is remarkable and may indicate a pre-existing bias in females that is ready to drive male evolution, should the social system or the ecological variables that control it change. (+info)
Model ecosystem evaluation of the environmental impacts of the veterinary drugs phenothiazine, sulfamethazine, clopidol, and diethylstilbestrol.
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Four veterinary drugs of dissimilar chemical structures were evaluated for environmental stability and penchant for bioaccumulation. The techniques used were (1) a model aquatic ecosystem (3 days) and (2) a model feedlot ecosystem (33 days) in which the drugs were introduced via the excreta of chicks or mice. The model feedlot ecosystem was supported by metabolism cage studies to determine the amount and the form of the drug excreted by the chicks or mice. Considerable quantities of all the drugs were excreted intact or as environmentally short-lived conjugates. Diethylstilbestrol (DES) and Clopidol were the most persistent molecules, but only DES bioaccumulated to any appreciable degree. Phenothiazine was very biodegradable; sulfamethazine was relatively biodegradable and only accumulated in the organisms to very low levels. Data from the aquatic model ecosystem demonstrated a good correlation between the partition coefficients of the drugs and their accumulation in the fish. (+info)
Comparative structure and characterization of a CDKN2 gene in a Xiphophorus fish melanoma model.
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We have cloned, sequenced, and characterized the RNA expression properties of a fish CDKN2 gene from Xiphophorus helleri and X. maculatus. This gene, termed CDKN2X, shows a high degree of amino acid sequence similarity to members of the mammalian CDKN2 gene family, which includes the tumor suppressor loci CDKN2A (P16) and CDKN2B (P15). Comparative sequence analysis suggests that fish CDKN2X is similarly related to all four mammalian gene family members, and may represent a descendant of an ancestral prototypic CDKN2 gene. CDKN2X was mapped to a region on autosomal Xiphophorus linkage group V (LG V) known to contain the DIFF gene that acts as a tumor suppressor of melanoma formation in X. helleri/X. maculatus backcross hybrids. Thus, CDKN2X may be a candidate for the tumor suppressor DIFF gene. Here we have sequenced CDKN2X in both Xiphophorus species and have characterized its expression in normal and melanotic tissues within control and backcross hybrid fish. A simultaneous expressional analysis of the Xmrk-2 tyrosine kinase receptor gene, which is strongly implicated in melanomagenesis in this system, was also performed. RT - PCR analyses revealed that both genes were highly expressed in melanomas. For CDKN2X, this result contrasts numerous findings in human tumors including human melanoma in which either CDKN2A (P16) deactivation or LOH was observed. (+info)
Melanoma loss-of-function mutants in Xiphophorus caused by Xmrk-oncogene deletion and gene disruption by a transposable element.
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The overexpression of the Xmrk oncogene (ONC-Xmrk) in pigment cells of certain Xiphophorus hybrids has been found to be the primary change that results in the formation of malignant melanoma. Spontaneous mutant stocks have been isolated that have lost the ability to induce tumor formation when crossed with Xiphophorus helleri. Two of these loss-of-function mutants were analyzed for genetic defects in ONC-Xmrk's. In the lof-1 mutant a novel transposable element, TX-1, has jumped into ONC-Xmrk, leading to a disruption of the gene and a truncated protein product lacking the carboxyterminal domain of the receptor tyrosine kinase. TX-1 is obviously an active LTR-containing retrotransposon in Xiphophorus that was not found in other fish species outside the family Poeciliidae. Surprisingly, it does not encode any protein, suggesting the existence of a helper function for this retroelement. In the lof-2 mutant the entire ONC-Xmrk gene was found to be deleted. These data show that ONC-Xmrk is indeed the tumor-inducing gene of Xiphophorus and thus the critical constituent of the tumor (Tu) locus. (+info)
The non-LTR retrotransposon Rex3 from the fish Xiphophorus is widespread among teleosts.
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Rex3, the first reverse transcriptase (RT)-encoding retrotransposon isolated from the melanoma fish model Xiphophorus, is a non-long-terminal-repeat element related to the RTE family. The essential features of Rex3 are (1) an endonuclease and a reverse transcriptase, (2) 5' truncations of most of the copies, (3) a 3' tail consisting of tandem repeats of the sequence GATG, and (4) short target site sequence duplications of variable length. Compilation of Rex3 sequences from the pufferfish genome project suggested that, as observed for other members of the RTE family, no additional large open reading frame was present upstream of the endonuclease/reverse transcriptase open reading frame. There are about a thousand copies of Rex3 in the haploid genome of Xiphophorus, some of them probably resulting from recent retrotransposition events. Rex3 RNA was detected by RT-PCR in melanoma and in nontumorous tissues, as well as in melanoma-derived and embryonic cell lines. Rex3 is present in a broad panel of teleost species and was found in the promoter region and in introns of various genes. To our knowledge, Rex3 is the first autonomous retrotransposon described to date which is widespread in teleosts. This wide distribution and occasional association with coding sequences may confer on Rex3 a predisposition to play a role in genome evolution in teleosts. (+info)
Effects of nonylphenol and 17beta-estradiol on vitellogenin synthesis and testis morphology in male platyfish Xiphophorus maculatus.
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Nonylphenol has been found to exert estrogenic effects in fish and may influence the fertility of male fish. In the present study, the effects of nonylphenol and 17beta-estradiol on vitellogenin synthesis and testis morphology in platyfish Xiphophorus maculatus were investigated. Vitellogenin was observed in the plasma of all fish exposed to nonylphenol or 17beta-estradiol. Exposure to 17beta-estradiol resulted in a significant reduction in the gonadosomatic index. A tendency for a dose-dependent reduction in the gonadosomatic index in the nonylphenol exposed groups was observed. Histological examination revealed dose-dependent effects of nonylphenol on the testis structure. The testes of control fish contained numerous cysts with spermatogenetic cells. The testes of fish exposed to nonylphenol or 17beta-estradiol showed a decrease in the number of cysts concomitant with an increase in the amount of hypertrophied Sertoli cells present. Formation of spermatozeugmata is compulsory for this species, but free spermatozoa were observed in the efferent ducts of the treated fish. The study indicates that nonylphenol has estrogenic potency, and that both nonylphenol and 17beta-estradiol have marked effects on the testis morphology of X. maculatus. The ambient concentration of nonylphenol was measured by high pressure liquid chromatography during the experiment. The measurements revealed that the actual concentrations of nonylphenol in the water were about 30-40 % of the nominal concentrations. (+info)