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排序方式: 共有215条查询结果,搜索用时 202 毫秒
1.
2.
Cecilie Boysen Christopher Carlson Eran Hood Leroy Hood Deborah A. Nickerson 《Immunogenetics》1996,44(2):121-127
The T-cell receptor (TCR) is a highly variable molecule composed of two polypeptide chains that recognize antigenic peptides
in the context of major histocompatibility complex (MHC) molecules. In this study, we describe a sequence-based search for
germline polymorphisms in the variable (V) gene segments of the human TCRA/D locus. Thirty different V gene segments were amplified from six to eight unrelated individuals and sequenced from low melting point agarose. Twenty-seven
polymorphisms were identified in 15 V gene segments. These polymorphisms are mainly single nucleotide substitutions, but an insertion/deletion polymorphism and
a single dinucleotide repeat with variable length were also seen. Of the 15 sequence variations found in the coding regions,
six are silent and nine encode amino acid changes. All of the amino acid changes are found at non-conserved residues, frequently
in the hypervariable regions, where they may influence MHC and/or peptide recognition. Therefore, it is possible that germline
variations in TCR genes could influence an individual’s immune response, and may also contribute to susceptibility to diseases such as autoimmunity.
Received: 9 January 1996 / Revised: 22 February 1996 相似文献
3.
Örjan Totland 《American journal of botany》1996,83(4):452-458
Some plants in arctic and alpine habitats have heliotropic flowers that track the sun. This results in a heating of the flower's interior, which may improve the possibilities for insect pollination and seed production. Here, I examine whether flower heliotropism in an alpine population of the self-incompatible Ranunculus acris L. (Ranunculaceae) enhances pollinator visitation and seed production. Flowers of Ranunculus acris tracked the sun during the day. Tracking accuracy was greatest during the middle of the day. The temperature elevation in flowers was negatively correlated with the flower's angle of deviation from the sun. Despite the increased temperature, insects did not discriminate among flowers on the basis of their angle of deviation from the sun, or tend to stay longer in the flowers aligned closest towards the sun. A tethering experiment was conducted on three groups of plants flowering at different times in the 1993 season and on one group the following season. Manipulation plants were constrained not to track the sun, whereas control plants tracked the sun naturally. Solar tracking had no effect on seed:ovule ratio, seed mass, or abortion rate in any of the groups. There is probably a very narrow range of weather conditions (cold, sunny, and calm) where flower heliotropism may enhance visitation rate to flowers and their seed production. 相似文献
4.
Factors influencing inter-population variation in Ranunculus acris seed production in an alpine area of southwestern Norway 总被引:1,自引:0,他引:1
There have been few attempts to examine the relationship between mean seed production of populations and the environmental conditions experienced by these populations. This study uses redundancy, analysis (RDA) to explore which environmental factors influence the patterns of inter-population variation in mean seed production (seed:ovule ratio and seed weight) and mean plant height in 25 alpine populations of Ranunculus acris L at Finse, southwestern Norway. The mean seedrovule ratio and height of the plants differed more than three-fold among populations situated close to each other, whereas mean seed weight showed less variation. In two RDAs differences in site elevation and pH accounted for a substantial part of the among-population variation in mean plant height, seed:ovule ratio, and seed weight. Mean plant height and seed weight were negatively correlated with the altitude of the populations, whereas mean seed:ovule ratio showed a high positive correlation with pH. When pooling all data from the populations, simple linear regressions showed that seed weight was positively correlated with plant height, whereas plant height had little influence on seed:ovule ratio. Seed weight was positively correlated with the numbers of seeds that a flower produced. The results indicate that mean seediovule ratio of a population is influenced primarily by the pH-conditions at the site, whereas mean seed weight and plant height are more strongly influenced by altitude which largely reflects the climatic severity at the site. Inter-population variation in average reproductive success in R. acris at Finse appears to be determined by several environmental and intrinsic factors that interact in a complex fashion. 相似文献
5.
Einar Lystad Arne T. Høstmark Cecilie Kiserud Aage Haugen 《In vitro cellular & developmental biology. Animal》1994,30(9):568-573
Summary The protective influence of bovine serum albumin against growth inhibition caused by fatty acids was studied in human hepatoma
(HepG2) and immortalized human kidney epithelial (IHKE) cells. In general, growth inhibition by unsaturated fatty acids (0.15
mmol/liter) increased with increasing number of double bonds. For HepG2 cells crude albumin (1g/100 ml) did not greatly modify growth inhibition by arachidonic, eicosapentaenoic, and docosahexaenoic acid. With oleic,
linoleic, and linolenic acids, crude and defatted albumin stimulated cell growth. In contrast, for IHKE cells both albumins
counteracted growth inhibition by unsaturated fatty acids to approximately the same extent. When HepG2 cells were cultured
in the presence of saturated fatty acids (0.3 mmol/liter), C2, C6, and C8 had no or little inhibitory effect. C10 and C12
inhibited cell growth appreciably, whereas C14, and especially C16, had poor inhibitory effects. Crude albumin counteracted
growth inhibition by all these fatty acids. In contrast, defatted albumin had little or no effect (except against C10 and
C12), and even increased the growth inhibition by C14 and C16. With unsaturated fatty acids there seemed to be an inverse
relationship between cell growth and the concentration of thiobarbituric acid reactive substances (TBARS) in media. Vitamin
E abolished growth inhibition (and the increase in TBARS concentration) by unsaturated fatty acids. The complex interaction
between fatty acids and albumins calls for great caution when interpreting data on growth effects. 相似文献
6.
Ørjan Totland 《Oikos》2004,106(3):558-564
The preference for certain floral phenotypes by flower visiting animals may fuel the evolution of floral traits because variation in flower visitation rates may lead to fitness variation within a population. Here, I examine the importance of flower size for pollinator visitation rate, seed set, and seed mass in two alpine populations of the insect-pollinated herb Ranunculus acris L. during two seasons. There was no pollen limitation of seed set or mass. Pollinators discriminated strongly against flowers experimentally reduced in size. Despite this, there were no signs of any significant impact of flower size on female reproductive success. The results show that although pollinators discriminate strongly among floral phenotypes, this may not always result in female fitness differences within a population because seed set or mass is not limited by pollen availability alone. Probably abiotic environmental constraints prevent plants with high pollinator visitation from capitalizing on the high pollen deposition. 相似文献
7.
Woody plant encroachment alters the structure and function of rangeland ecosystems. The objective of this study was to explore the association between woody plant encroachment and various ecosystem properties (i.e. vascular plant species diversity, richness, evenness, soil organic matter, herbaceous biomass, leaf litter and bare ground cover) in a semiarid savanna rangeland, and also to test whether the relationships were influenced by woody species composition, elevation and site. We carried out a vegetation survey in four rangeland sites in the lower Omo region of southwestern Ethiopia, and regressed each one of the ecosystem properties, separately, against woody plant density, elevation and site using multiple linear regressions. We found that vascular plant species diversity, richness and evenness increased with woody plant density, most likely due to increased spatial heterogeneity and soil microclimate improvement. Bare ground cover increased significantly, whereas herbaceous biomass and soil organic matter did not respond to woody encroachment. In a subsequent investigation, we used a redundancy analysis to assess whether ecosystem properties were influenced by the identity of encroaching woody plant species. Species diversity and richness responded positively to Lannea triphylla, whereas leaf litter responded positively to Grewia tenax and G. villosa. Our findings suggest that woody plant encroachment in a semiarid rangeland does alter ecosystem properties. However, its impact is highly variable, influenced by a set of factors including the level of encroachment and identity of encroaching woody species. 相似文献
8.
Background
Insulin resistance and type 2 diabetes are more prevalent in people of South Asian ethnicity than in people of Western European origin. To investigate the source of these differences, we compared insulin sensitivity, insulin secretion, glucose and lipid metabolism in South Asian and Nordic subjects with type 2 diabetes.Methods
Forty-three Nordic and 19 South Asian subjects with type 2 diabetes were examined with intra-venous glucose tolerance test, euglycemic clamp including measurement of endogenous glucose production, indirect calorimetry measuring glucose and lipid oxidation, and dual x-ray absorptiometry measuring body composition.Results
Despite younger mean ± SD age (49.7±9.4 vs 58.3±8.3 years, p = 0.001), subjects of South Asian ethnicity had the same diabetes duration (9.3±5.5 vs 9.6±7.0 years, p = 0.86), significantly higher median [inter-quartile range] HbA1c (8.5 [1.6] vs 7.3 [1.6] %, p = 0.024) and lower BMI (28.7±4.0 vs 33.2±4.7 kg/m2, p<0.001). The South Asian group exhibited significantly higher basal endogenous glucose production (19.1 [9.1] vs 14.4 [6.8] µmol/kgFFM⋅min, p = 0.003). There were no significant differences between the groups in total glucose disposal (39.1±20.4 vs 39.2±17.6 µmol/kgFFM⋅min, p = 0.99) or first phase insulin secretion (AUC0–8 min: 220 [302] vs 124 [275] pM, p = 0.35). In South Asian subjects there was a tendency towards positive correlations between endogenous glucose production and resting and clamp energy expenditure.Conclusions
Subjects of South Asian ethnicity with type 2 diabetes, despite being younger and leaner, had higher basal endogenous glucose production, indicating higher hepatic insulin resistance, and a trend towards higher use of carbohydrates as fasting energy substrate compared to Nordic subjects. These findings may contribute to the understanding of the observed differences in prevalence of type 2 diabetes between the ethnic groups. 相似文献9.
Maria Wik Markhus Siv Skotheim Ingvild Eide Graff Livar Fr?yland Hanne Cecilie Braarud Kjell Morten Stormark Marian Kjellevold Malde 《PloS one》2013,8(7)
Background
Depression is a common disorder affecting 10–15% women in the postpartum period. Postpartum depression can disrupt early mother-infant interaction, and constitutes a risk factor for early child development. Recently, attention has been drawn to the hypothesis that a low intake of seafood in pregnancy can be a risk factor for postpartum depression. Seafood is a unique dietary source of the marine omega-3 fatty acids and is a natural part of a healthy balanced diet that is especially important during pregnancy.Methods
In a community based prospective cohort in a municipality in Western Norway, we investigated both nutritional and psychological risk factors for postpartum depression. The source population was all women who were pregnant within the period November 2009 - June 2011. The fatty acid status in red blood cells was assessed in the 28th gestation week and participants were screened for postpartum depression using the Edinburgh Postnatal Depression Scale (EPDS) three months after delivery. The aim of the present study was to investigate if a low omega-3 index in pregnancy is a possible risk factor for postpartum depression.Results
In a simple regression model, the omega-3 index was associated with the EPDS score in a nonlinear inverse manner with an R square of 19. Thus, the low omega-3 index explained 19% of the variance in the EPDS score. The DPA content, DHA content, omega-3 index, omega-3/omega-6 ratio, total HUFA score, and the omega-3 HUFA score were all inversely correlated with the EPDS score. The EPDS scores of participants in the lowest omega-3 index quartile were significantly different to the three other omega-3 index quartiles.Conclusion
In this study population, a low omega-3 index in late pregnancy was associated with higher depression score three months postpartum. 相似文献10.
Einar Osland Vik-Mo Marta Nyakas Birthe Viftrup Mikkelsen Morten Carstens Moe Paulina Due-Tønnesen Else Marit Inderberg Suso Stein Sæbøe-Larssen Cecilie Sandberg Jan E. Brinchmann Eirik Helseth Anne-Marie Rasmussen Knut Lote Steinar Aamdal Gustav Gaudernack Gunnar Kvalheim Iver A. Langmoen 《Cancer immunology, immunotherapy : CII》2013,62(9):1499-1509