Evolution of Hox Clusters in Salmonidae: A Comparative Analysis Between Atlantic Salmon (Salmo salar) and Rainbow Trout (Oncorhynchus mykiss)

We studied the genomic organization of Hox genes in Atlantic salmon (Salmo salar) and made comparisons to that in rainbow trout (Oncorhynchus mykiss), another member of the family Salmonidae. We used these two species to test the hypothesis that the Hox genes would provide evidence for a fourth round of duplication (4R) of this gene family given the recent polyploid ancestry of the salmonid fish. Thirteen putative Hox clusters were identified and 10 of these complexes were localized to the current Atlantic salmon genetic map. Syntenic regions with the rainbow trout linkage map were detected and further homologies and homeologies are suggested. We propose that the common ancestor of Atlantic salmon and rainbow trout possessed at least 14 clusters of Hox genes, and additional clusters cannot be ruled out. Salmonid Hox cluster complements seem to be more similar to those of zebrafish (Danio rerio) than medaka (Oryzias latipes) or pufferfish (Sphoeroides nephelus and Takifugu rubripes), as both Atlantic salmon and rainbow trout have retained HoxCb ortholog, which has been lost in medaka and pufferfish but not in zebrafish. However, our data suggest that phylogenetically, the homologous genes within each cluster express mosaic relationships among the teleosts tested and, thus, leave unresolved the interfamilial relationships among these taxa. Sequence data from this article have been deposited within the EMBL/GenBank Data Libraries under the following accession numbers: AY677341, AY677342, AY677343, AY677344, AY677345, AY677346, AY677347, AY677348, AY677349, AY677350, AY677351, AY677352, AY677353, AY677354, AY677355, AY677356, AY677357, AY677358, AY677359, AY677360, AY677361, AY677362, AY677363, AY677364 and AY677365. [Reviewing Editor: Dr. Axel Meyer]     

Effect of Cytochalasin B on the Development of Membrane Transports in Sea Urchin Eggs after Fertilization

Investigations were made on the role of the cytoskeleton in the onset of ionic events following fertilization of sea urchin eggs. Events which depend upon phosphoinositide metabolism, such as the cortical reantion and acid release are affected by cytochalasin B (CB) after fertilization but not after activation of eggs with the ionophore A23187. These findings suggest that the sequence of events following sperm-egg attachment depends on the cytoskeleton. CB also inhibits the Na⁺ pump and alanine uptake when added before insemination and during the following 30 min. These results argue for a role of the egg cortex cytoskeleton in activation of the Na⁺ pump by fertilization. We propose that the inhibitory effect of CB on the development of amino-acid uptake after fertilization may result from an increase in the Na⁺ content of the egg resulting from Na⁺ pump suppression rather than from direct blockage of the carrier.     

细胞松弛素B对鲍受精卵超微结构的影响

细胞松弛素B（CB）作为一种微丝解聚剂,可用于诱导贝类三倍体,但由于其毒副作用导致了受精卵死亡和发育异常。通过透射电镜观察比较了皱纹盘鲍（Haliotis discus hannai)正常受精卵与CB处理后的受精卵亚显微结构的变化,结果显示,CB对线粒体等细胞器的破坏,造成了受精卵的代谢缺陷,是导致鲍受精卵孵化率低的原因之一。     

The Effect of Ration on Acclimation to Environmental Acidity in Rainbow Trout

Freshwater salmonids exposed to low environmental pH typically suffer a net loss of ions, primarily Na⁺ and Cl^–, across the gills, resulting in reduced plasma and tissue ion concentrations. However, in recent experiments in our laboratory, juvenile rainbow trout, Oncorhynchus mykiss, fed a ration of 1% body weight d^–1 or greater showed no ionoregulatory disturbance during chronic, sublethal acidification. This raised the possibility that these fish had acclimated to low pH in that they would be better able to withstand further, more severe acidification than fish that had no prior experience of acid conditions: previous studies had concluded that such acclimation does not occur. This hypothesis was tested by measuring unidirectional ion fluxes during a 24h acute acid challenge (pH 4.2) in juvenile rainbow trout that had previously been exposed to either ambient pH 6.2 (naive fish) or sublethal low pH 5.2 (acid pre-exposed fish) for 90 days, and fed a ration of either 1.0 or 0.25% d^–1 (wet basis). No mortalities were observed during the acute acid challenge in the fish fed the higher ration and no differences between the two groups in the response of Na⁺ fluxes were observed. Sodium influx in both groups was significantly inhibited throughout the challenge and Na⁺ net flux was significantly stimulated over the first 6h. Prior to the acute acid challenge, the fish fed the lower ration that had previously been exposed to pH 5.2 had significantly lower plasma ion concentrations than those fish previously exposed to pH 6.2. Both groups suffered mortalities; those of the naive fish (22% by 24h) being markedly lower than those of the acid pre-exposed fish (68% by 24h). However, there were no significant differences in either Na⁺ or Cl^– fluxes between the two groups of fish during the acid challenge: both showed significant inhibition of ion influxes and significantly greater net ion losses, resulting in reduced plasma ion concentrations. These results indicate that rainbow trout are unable to acclimate to environmental acidification irrespective of the availability of dietary salts.     

Effect of Diet Change on Rheoreaction in Young Rainbow Trout Oncorhynchus mykiss

Journal of Ichthyology - The motivational component of rheoreaction has been determined in 4-month-old juvenile rainbow trout Oncorhynchus mykiss on different diets. It is shown that the diet...     

Homologous Viral Interference in Trout and Atlantic Salmon Cell Cultures Infected with Infectious Pancreatic Necrosis Virus

The occurrence of homologous interference in the replication of infectious pancreatic necrosis virus was demonstrated after successive passages of partially purified virus at high input multiplicities in trout and Atlantic salmon cell cultures. Pretreatment of cell cultures with interfering virus inhibited the replication of homologous standard infectious virus but not unrelated viruses. The ability of infectious pancreatic interfering virus to interfere with homologous virus was abolished with UV irradiation, immune serum, and freeze-thawing.     

A General Model of Distant Hybridization Reveals the Conditions for Extinction in Atlantic Salmon and Brown Trout

Interspecific hybridization is common in nature but can be increased in frequency or even originated by human actions, such as species introduction or habitat modification, which may threaten species persistence. When hybridization occurs between distantly related species, referred to as “distant hybridization,” the resulting hybrids are generally infertile or fertile but do not undergo chromosomal recombination during gametogenesis. Here, we present a model describing this frequent but poorly studied interspecific hybridization to assess its consequences on parental species and to anticipate the conditions under which they can reach extinction. Our general model fully incorporates three important processes: density-dependent competition, dominance/recessivity inheritance of traits and assortative mating. We demonstrate its use and flexibility by assessing population extinction risk between Atlantic salmon and brown trout in Norway, whose interbreeding has recently increased due to farmed fish releases into the wild. We identified the set of conditions under which hybridization may threaten salmonid species. Thanks to the flexibility of our model, we evaluated the effect of an additional risk factor, a parasitic disease, and showed that the cumulative effects dramatically increase the extinction risk. The consequences of distant hybridization are not genetically, but demographically mediated. Our general model is useful to better comprehend the evolution of such hybrid systems and we demonstrated its importance in the field of conservation biology to set up management recommendations when this increasingly frequent type of hybridization is in action.     

Hybridization between Atlantic Salmon Salmo salar L. and Brown Trout S. trutta L. upon Artificial Propagation

Samples of Salmo salar and S. trutta were examined in 12 Russian fish hatcheries. With protein markers, hybrids of the two species were found in three hatcheries of the Baltic Sea basin. Some fishes had a phenotype intermediate between theS. salar and S. trutta phenotypes by morphological traits, but did not differ genetically from one of the parental species. Possible consequences of hybridization and ways to prevent it are discussed.     

Details of Retropositional Genome Dynamics That Provide a Rationale for a Generic Division: The Distinct Branching of All the Pacific Salmon and Trout (Oncorhynchus) from the Atlantic Salmon and Trout (Salmo)

Salmonid species contain numerous short interspersed repetitive elements (SINEs), known collectively as the HpaI family, in their genomes. Amplification and successive integration of individual SINEs into the genomes have occurred during the evolution of salmonids. We reported previously a strategy for determining the phylogenetic relationships among the Pacific salmonids in which these SINEs were used as temporal landmarks of evolution. Here, we provide evidence for extensive genomic rearrangements that involved retropositions and deletions in a common ancestor of all the Pacific salmon and trout. Our results provide genetic support for the recent phylogenetic reassignment of steelhead and related species from the genus Salmo to the genus Oncorhynchus. Several other informative loci identified by insertions of HpaI SINEs have been isolated, and previously proposed branching orders of the Oncorhynchus species have been confirmed. The authenticity of our phylogenetic tree is supported both by the isolation of more than two informative loci per branching point and by the congruence of all our data, which suggest that the period between succesive speciations was sufficiently long for each SINE that had been amplified in the original species to become fixed in all individuals of that species.     

哈尔滨医科大学附属第一医院神经外科

血脑屏障的是人体自然屏障之一。其主要作用是阻止有害物质通过颅内血管进入脑实质,并同时辅助排出脑内代谢物质等。对相当多的颅内恶性肿瘤术后患者,血脑屏障在一定程度上阻碍了化疗药物进入脑实质,从而影响化疗效果。因此近年来越来越多的学者将研究重点放在如何开放血脑屏障这个问题上。血脑屏障构成主要为毛细血管的内皮细胞、基膜周细胞和星状胶质细胞的足突,其中血管内皮细胞处于最重要的地位。原因归结于它自身的一个特殊结构--紧密连接。紧密连接是否完整,功能是否可以正常发挥关系到内皮细胞的完整性,因此对血脑屏障的开放有着举足轻重的作用。维持紧密连接结构中功能蛋白功能的能量物质为葡萄糖。脑血管中的葡萄糖进入脑实质需载体或通道,脑组织负责此过程的物质为葡萄糖转运蛋白1(GLUT1)。本文作者通过松胞菌素B抑制葡萄糖转运蛋白1,降低能量供应从而影响紧密连接功能,最终引起血脑屏障开放角度做一综述。     

Computational Study of Evolutionary Selection Pressure on Rainbow Trout Estrogen Receptors

Molecular dynamics simulations were used to determine the binding affinities between the hormone 17-estradiol (E2) and different estrogen receptor (ER) isoforms in the rainbow trout, Oncorhynchus mykiss. Previous phylogenetic analysis indicates that a whole genome duplication prior to the divergence of ray-finned fish led to two distinct ER isoforms, ER and ER, and the recent whole genome duplication in the ancestral salmonid created two ER isoforms, ER and ER. The objective of our computational studies is to provide insight into the underlying evolutionary pressures on these isoforms. For the ER subtype our results show that E2 binds preferentially to ER over ER. Tests of lineage specific N/S ratios indicate that the ligand binding domain of the ER gene is evolving under relaxed selection relative to all other ER genes. Comparison with the highly conserved DNA binding domain suggests that ER may be undergoing neofunctionalization possibly by binding to another ligand. By contrast, both ER and ER bind similarly to E2 and the best fitting model of selection indicates that the ligand binding domain of all ER genes are evolving under the same level of purifying selection, comparable to ER.     

Effect of Hydrogen Peroxide on Immersion Challenge of Rainbow Trout Fry with Flavobacterium psychrophilum

An experimental model for immersion challenge of rainbow trout fry (Oncorhynchus mykiss) with Flavobacterium psychrophilum, the causative agent of rainbow trout fry syndrome and bacterial cold water disease was established in the present study. Although injection-based infection models are reliable and produce high levels of mortality attempts to establish a reproducible immersion model have been less successful. Various concentrations of hydrogen peroxide (H₂O₂) were evaluated before being used as a pre-treatment stressor prior to immersion exposure to F. psychrophilum. H₂O₂ accelerated the onset of mortality and increased mortality approximately two-fold; from 9.1% to 19.2% and from 14.7% to 30.3% in two separate experiments. Clinical signs observed in the infected fish corresponded to symptoms characteristically seen during natural outbreaks. These findings indicate that pre-treatment with H₂O₂ can increase the level of mortality in rainbow trout fry after exposure to F. psychrophilum.     

Cytochalasin B and water transport

Summary A morpho-functional study of the effects of cytochalasin B (CB) on Na and water transport was made in amphibian epithelia. The functional studies confirmed the dissociation of the natriferic and hydrosmotic effects of vasopressin in toad urinary bladders exposed to CB and showed in addition that the block of the hydrosmotic effect was reversible and could still be induced in epithelia maximally stimulated with the hormone. Scanning electron microscopy revealed that CB, per se, did not alter the apical surface of the bladders. An almost total loss of microvilli of granular cells was seen, however, if CB was associated with vasopressin and an osmotic gradient. The results suggest two points: a) the block of the hydrosmotic flow induced by CB is due to factors beyond the apical membrane; b) microfilaments may be important mechanochemical transducers in the chain of events leading to the hydrosmotic effect of vasopressin.Supported by the grants Nos 3.1300.73 and 3.043-0.76 of the Swiss National Science FoundationThe authors are grateful to Miss C. Brücher, SEM operator of the Department of Physics, Ciba-Geigy, for skillful collaboration, to Mr. R. Mira for the illustrations and to Mrs. A. Cergneux for secretarial assistance     

Genetics of Growth Reaction Norms in Farmed Rainbow Trout

Rainbow trout is farmed globally under diverse uncontrollable environments. Fish with low macroenvironmental sensitivity (ES) of growth is important to thrive and grow under these uncontrollable environments. The ES may evolve as a correlated response to selection for growth in one environment when the genetic correlation between ES and growth is nonzero. The aims of this study were to quantify additive genetic variance for ES of body weight (BW), defined as the slope of reaction norm across breeding environment (BE) and production environment (PE), and to estimate the genetic correlation (r _{g(int, sl)}) between BW and ES. To estimate heritable variance of ES, the coheritability of ES was derived using selection index theory. The BW records from 43,040 rainbow trout performing either in freshwater or seawater were analysed using a reaction norm model. High additive genetic variance for ES (9584) was observed, inferring that genetic changes in ES can be expected. The coheritability for ES was either -0.06 (intercept at PE) or -0.08 (intercept at BE), suggesting that BW observation in either PE or BE results in low accuracy of selection for ES. Yet, the r _{g(int, sl)} was negative (-0.41 to -0.33) indicating that selection for BW in one environment is expected to result in more sensitive fish. To avoid an increase of ES while selecting for BW, it is possible to have equal genetic gain in BW in both environments so that ES is maintained stable.     

Regional Response to Cytochalasin B of the Equatorial Cell Cortex in Sea-Urchin Eggs during the First Mitosis

Sea-urchin eggs treated with cytochalasin B (CB) during the first mitosis were examined for topography of the cell surface and the cortical microfilaments. Scanning electron microscopy revealed microvillar elongation and clumping on the whole cell surface of interphase and prophase eggs, but such changes were restricted to the equatorial surface in eggs treated with CB after metaphase up to the end of telophase. The clumping occurred also all over the cell surface of binuclear eggs after prolonged treatment up to the following interphase. These indicate localization of a target structure(s) of CB during mid- and late mitotic stages. Extraction with Triton X-100 allowed detection of CB-induced alterations in cortical microfilaments: The microvillar microfilaments were transformed into short filaments with random orientation. The submembranous meshwork and the contractile ring microfilaments were transformed into a network of shorter filaments. The prolonged CB treatment led to incorporation of the network microfilaments into the basal portions of the microvillar clumps. Thus, CB application during mid- and late mitotic stages induced (a) local microvillar changes and (b) alterations in the meshwork and the contractile ring. The present results suggest that the microvillar changes are caused by alterations of underlying cortical microfilamentous structures.