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排序方式: 共有327条查询结果,搜索用时 15 毫秒
61.
Mario Calomme Jean Vanderpas Baudouin François Micheline Van Caillie-Bertrand Nicole Vanovervelt Christian Van Hoorebeke Dirk Vanden Berghe 《Biological trace element research》1995,47(1-3):349-353
Type I 5′-deiodinase was recently characterized as a selenocysteine-containing enzyme in humans and other mammals. Up to now,
the effect of selenium (Se) supplementation on thyroid hormone metabolism in humans has only been reported in the very peculiar
nutritional environment of Central Africa, where combined severe iodine and Se deficiency occurs. In this study, a group of
phenylketonuria subjects with a low selenium status, but a normal iodine intake were supplemented with selenium to investigate
changes in their thyroid hormone metabolism. After 3 wk of selenium supplementation (1 μg/kg/d), both the concentrations of
the prohormone thyroxine (T4) and the metabolic inactive reverse triiodothyronine (rT3) decreased significantly. Clinically,
the phenylketonuria subjects remained euthyroid before and after selenium supplementation. The individual changes of plasma
Se and glutathione peroxidase activity were closely associated with individual changes of plasma T4 and rT3. 相似文献
62.
63.
Fine-Structure Analysis of Intercellular and Intracellular Mitochondrial Diversity in Saccharomyces cerevisiae 总被引:1,自引:0,他引:1 下载免费PDF全文
Crosses were made between haploid wild-type and suppressive petite strains of bakers' yeast to obtain zygotes for analysis of mitochondrial heterogeneity. Wild-type x petite zygotes contained about 40% noncristate mitochondria when immediate mating mixtures were examined. The frequency of defective mitochondria had decreased to an average of 9.2% in 1-week-old zygote isolate cultures, and to 4.4% in slant cultures 1.5 years after initial zygote isolation. The latter value was not significantly different from values obtained with wild x wild zygotes of either age. The noncristate mitochondria were of two types: one lacking inner membrane invaginations or elaborations and the other containing concentrically arranged loops of inner membrane. The significance of these two types of respiration-deficient mitochondria is unknown. The gradual decrease in frequency of noncristate mitochondria, perhaps due to selection pressures in mixed chondriomes, was discussed as a further indication of the semiautonomous nature of the yeast organelle. 相似文献
64.
65.
Catherine R. M. Attard Luciano B. Beheregaray K. Curt S. Jenner Peter C. Gill Micheline‐Nicole Jenner Margaret G. Morrice Kelly M. Robertson Luciana M. Möller 《Molecular ecology》2012,21(23):5715-5727
Understanding the degree of genetic exchange between subspecies and populations is vital for the appropriate management of endangered species. Blue whales (Balaenoptera musculus) have two recognized Southern Hemisphere subspecies that show differences in geographic distribution, morphology, vocalizations and genetics. During the austral summer feeding season, the Antarctic blue whale (B. m. intermedia) is found in polar waters and the pygmy blue whale (B. m. brevicauda) in temperate waters. Here, we genetically analyzed samples collected during the feeding season to report on several cases of hybridization between the two recognized blue whale Southern Hemisphere subspecies in a previously unconfirmed sympatric area off Antarctica. This means the pygmy blue whales using waters off Antarctica may migrate and then breed during the austral winter with the Antarctic subspecies. Alternatively, the subspecies may interbreed off Antarctica outside the expected austral winter breeding season. The genetically estimated recent migration rates from the pygmy to Antarctic subspecies were greater than estimates of evolutionary migration rates and previous estimates based on morphology of whaling catches. This discrepancy may be due to differences in the methods or an increase in the proportion of pygmy blue whales off Antarctica within the last four decades. Potential causes for the latter are whaling, anthropogenic climate change or a combination of these and may have led to hybridization between the subspecies. Our findings challenge the current knowledge about the breeding behaviour of the world's largest animal and provide key information that can be incorporated into management and conservation practices for this endangered species. 相似文献
66.
Landscape genetic analyses are typically conducted at one spatial scale. Considering multiple scales may be essential for identifying landscape features influencing gene flow. We examined landscape connectivity for woodland caribou (Rangifer tarandus caribou) at multiple spatial scales using a new approach based on landscape graphs that creates a Voronoi tessellation of the landscape. To illustrate the potential of the method, we generated five resistance surfaces to explain how landscape pattern may influence gene flow across the range of this population. We tested each resistance surface using a raster at the spatial grain of available landscape data (200 m grid squares). We then used our method to produce up to 127 additional grains for each resistance surface. We applied a causal modelling framework with partial Mantel tests, where evidence of landscape resistance is tested against an alternative hypothesis of isolation-by-distance, and found statistically significant support for landscape resistance to gene flow in 89 of the 507 spatial grains examined. We found evidence that major roads as well as the cumulative effects of natural and anthropogenic disturbance may be contributing to the genetic structure. Using only the original grid surface yielded no evidence for landscape resistance to gene flow. Our results show that using multiple spatial grains can reveal landscape influences on genetic structure that may be overlooked with a single grain, and suggest that coarsening the grain of landcover data may be appropriate for highly mobile species. We discuss how grains of connectivity and related analyses have potential landscape genetic applications in a broad range of systems. 相似文献
67.
Lebreton A Saveanu C Decourty L Jacquier A Fromont-Racine M 《The Journal of biological chemistry》2006,281(37):27099-27108
In Saccharomyces cerevisiae, a large variety of pre-ribosomal factors have been identified recently, a number of which are still of unknown function. The essential pre-ribosomal 30-kDa protein, Nsa2, was characterized as one of the most conserved proteins from yeast to human. We show here that the expression of the human orthologue TINP1 complements the repression of NSA2 in yeast. Nsa2 was co-purified in several pre-ribosomal complexes and found to be essential for the large ribosomal subunit biogenesis. Like several other factors of the pre-60 S particles, the absence of Nsa2 correlated with a decrease in the 25 S and 5.8 S ribosomal RNA levels, and with an accumulation of 27 SB pre-ribosomal RNA intermediates. We show that Nsa2 is a functional partner of the putative GTPase Nog1. In the absence of Nsa2, Nog1 was still able to associate with pre-ribosomal complexes blocked in maturation. In contrast, in the absence of Nog1, Nsa2 disappeared from pre-60 S complexes. Indeed, when ribosome biogenesis was blocked upstream of Nsa2, this short half-lived protein was largely depleted, suggesting that its cellular levels are tightly regulated. 相似文献
68.
Monocyte/macrophage dysfunctions do not impair the promotion of myelofibrosis by high levels of thrombopoietin 总被引:2,自引:0,他引:2
Wagner-Ballon O Chagraoui H Prina E Tulliez M Milon G Raslova H Villeval JL Vainchenker W Giraudier S 《Journal of immunology (Baltimore, Md. : 1950)》2006,176(11):6425-6433
Several lines of evidence indicate that the megakaryocyte/platelet lineage is crucial in myelofibrosis induction. The demonstration that NOD/SCID mice with functionally deficient monocytes do not develop fibrotic changes when exposed to thrombopoietin (TPO) also suggests an important role for monocyte/macrophages. However, in this animal model, the development of myelofibrosis is dependent on the level of TPO. This study was conducted to investigate whether NOD/SCID mice exposed to high TPO levels mediated by a retroviral vector would be refractory to the development of bone marrow fibrosis. We show that TPO and TGF-beta1 in plasma from NOD/SCID and SCID mice engrafted with TPO-overexpressing hemopoietic cells reach levels similar to the ones reached in immunocompetent mice, and all animals develop a myeloproliferative disease associated with a dense myelofibrosis at 8 wk posttransplantation. Monocytes in NOD/SCID mice are functionally deficient to secrete cytokines such as IL-1alpha in response to stimuli, even under TPO expression. Surprisingly, the plasma of these mice displays high levels of IL-alpha, which was demonstrated to originate from platelets. Together, these data suggest that completely functional monocytes are not required to develop myelofibrosis and that platelets are able, under TPO stimulation, to synthesize inflammatory cytokines, which may be involved in the pathogenesis of myelofibrosis and osteosclerosis. 相似文献
69.
Saïd Achamlale Bernadette Rezzonico Micheline Grignon-Dubois 《Journal of applied phycology》2009,21(3):347-352
Detritus of the seagrasses Zostera noltii and Z. marina collected on the beaches of Arcachon Lagoon (France) over a 3-year period was screened as a new source of zosteric acid (ZA).
This natural sulphated phenolic acid is a high value-added product capable of preventing settlement of marine organisms and
protecting crops from fungal diseases. The seasonal variation of the ZA content was quantified in methanolic and aqueous crude
extracts using high-performance liquid chromatography. The concentration found ranged from 65 to 456 μg g−1 dry wt for Z. noltii and 51–692 μg g−1 dry wt for Z. marina, respectively. This is the first report of ZA in Zostera noltii. Detrital leaves of Zostera have never before been screened for their bioactive substances. These results show that this low cost, very abundant and
renewable, but heretofore unused, marine resource has potential as a source of a rare and naturally occurring bioactive product. 相似文献
70.
Hepatic ABC efflux transporters control the cellular uptake (in basolateral membranes) and excretion (in apical membranes) of many substrates. Since type‐1 diabetes mellitus (T1DM) is associated with altered hepatobiliary excretion of many endogenous and exogenous substances, we examined key hepatic ABC transporters and levels of the endogenous substrate glutathione in rats with acute streptozotocin‐induced T1DM. Renal transporters and inflammatory markers were also examined. Abcb1, Abcc1–4, and Abcg2 were measured using qRT‐PCR. Glutathione was measured in liver tissue, plasma, and urine. Inflammatory markers, including C‐reactive protein (CRP), were measured in plasma via ELISA. In diabetic rats, Abcb1a, Abcc2, and Abcg2 (apical) were decreased, while Abcc4 (basolateral) was increased. Abcb1a and Abcc2 inversely correlated with plasma CRP. Diabetic and control rats exhibited similar hepatic glutathione, but levels in diabetic plasma were lower. When standardized to urinary output, diabetic rats excreted 6.7‐fold more glutathione in urine than controls. Renal transporter levels were normal in diabetic rats. Results show apical transporters involved in hepatobiliary excretion are downregulated in T1DM, possibly through an inflammation‐mediated process. Findings suggest that there may be a vectorial shift from hepatic to renal excretion for some substrates in T1DM. 相似文献