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61.
Leinonen T Herczeg G Cano JM Merilä J 《Evolution; international journal of organic evolution》2011,65(10):2916-2926
The transition from marine to freshwater life in the threespine stickleback (Gasterosteus aculeatus) is accompanied by complex morphological changes-including reduction in bony armor and change in body shape-but experimental evidence for the selective agents behind these evolutionary transitions is sparse. We investigated whether selection by predatory fish affects threespine stickleback morphology differentially when refuge is absent (pelagic lifestyle-ancestral condition) or present (benthic lifestyle-derived condition). Our results show that selection favors low numbers of lateral plates in habitats with refuge, whereas fully plated individuals have a selective advantage in habitats without refuge. We also found that a decrease in the length of the caudal peduncle increased survival probability, irrespective of habitat. The effect of spine lengths on survival was evident only in a multivariate analysis of selection, implying that it is essential to account for phenotypic and genetic correlations between traits before drawing conclusions about the effects of selection on single traits. Apart from uncovering targets and patterns of predator-induced selection on threespine stickleback morphology, our results provide direct evidence to support the hypothesis that differences in antipredator strategies in pelagic versus benthic sticklebacks could play a role in the repeated, independent cases of plate number reduction following freshwater colonization in this species. 相似文献
62.
King J Unterkofler K Teschl G Teschl S Koc H Hinterhuber H Amann A 《Journal of mathematical biology》2011,63(5):959-999
Recommended standardized procedures for determining exhaled lower respiratory nitric oxide and nasal nitric oxide (NO) have
been developed by task forces of the European Respiratory Society and the American Thoracic Society. These recommendations
have paved the way for the measurement of nitric oxide to become a diagnostic tool for specific clinical applications. It
would be desirable to develop similar guidelines for the sampling of other trace gases in exhaled breath, especially volatile
organic compounds (VOCs) which may reflect ongoing metabolism. The concentrations of water-soluble, blood-borne substances
in exhaled breath are influenced by: (i) breathing patterns affecting gas exchange in the conducting airways, (ii) the concentrations
in the tracheo-bronchial lining fluid, (iii) the alveolar and systemic concentrations of the compound. The classical Farhi
equation takes only the alveolar concentrations into account. Real-time measurements of acetone in end-tidal breath under
an ergometer challenge show characteristics which cannot be explained within the Farhi setting. Here we develop a compartment
model that reliably captures these profiles and is capable of relating breath to the systemic concentrations of acetone. By
comparison with experimental data it is inferred that the major part of variability in breath acetone concentrations (e.g.,
in response to moderate exercise or altered breathing patterns) can be attributed to airway gas exchange, with minimal changes
of the underlying blood and tissue concentrations. Moreover, the model illuminates the discrepancies between observed and
theoretically predicted blood-breath ratios of acetone during resting conditions, i.e., in steady state. Particularly, the
current formulation includes the classical Farhi and the Scheid series inhomogeneity model as special limiting cases and thus
is expected to have general relevance for a wider range of blood-borne inert gases. The chief intention of the present modeling
study is to provide mechanistic relationships for further investigating the exhalation kinetics of acetone and other water-soluble
species. This quantitative approach is a first step towards new guidelines for breath gas analyses of volatile organic compounds,
similar to those for nitric oxide. 相似文献
63.
Error-prone rolling circle amplification (RCA) is a promising alternative to error-prone PCR for random mutagenesis. The main disadvantage of error-prone RCA is the low transformation efficiency of the DNA concatemer produced in the amplification reaction. We improved the method by introducing loxP recombination site of bacteriophage P1 Cre recombinase into the target plasmid and reducing the concatemer by Cre recombinase to plasmid-sized units, increasing the number of transformants 50-fold in non-error-prone and 13-fold in error-prone conditions. The efficiency improvement was verified by obtaining 115 ± 57 ceftazidime resistant colonies per recombined RCA reaction from randomly mutated TEM-1 β-lactamase gene library whereas only 9 ± 11 colonies were gained without recombination. Supplementation of the error-prone RCA with Cre/loxP recombination is a simple and useful tool to increase the transformable library size. 相似文献
64.
Relationship between prion propensity and the rates of individual molecular steps of fibril assembly
Wang YQ Buell AK Wang XY Welland ME Dobson CM Knowles TP Perrett S 《The Journal of biological chemistry》2011,286(14):12101-12107
Peptides and proteins possess an inherent propensity to self-assemble into generic fibrillar nanostructures known as amyloid fibrils, some of which are involved in medical conditions such as Alzheimer disease. In certain cases, such structures can self-propagate in living systems as prions and transmit characteristic traits to the host organism. The mechanisms that allow certain amyloid species but not others to function as prions are not fully understood. Much progress in understanding the prion phenomenon has been achieved through the study of prions in yeast as this system has proved to be experimentally highly tractable; but quantitative understanding of the biophysics and kinetics of the assembly process has remained challenging. Here, we explore the assembly of two closely related homologues of the Ure2p protein from Saccharomyces cerevisiae and Saccharomyces paradoxus, and by using a combination of kinetic theory with solution and biosensor assays, we are able to compare the rates of the individual microscopic steps of prion fibril assembly. We find that for these proteins the fragmentation rate is encoded in the structure of the seed fibrils, whereas the elongation rate is principally determined by the nature of the soluble precursor protein. Our results further reveal that fibrils that elongate faster but fracture less frequently can lose their ability to propagate as prions. These findings illuminate the connections between the in vitro aggregation of proteins and the in vivo proliferation of prions, and provide a framework for the quantitative understanding of the parameters governing the behavior of amyloid fibrils in normal and aberrant biological pathways. 相似文献
65.
66.
Heidi Hintsala Tuomas V. Kentt? Mikko Tulppo Antti Kiviniemi Heikki V. Huikuri Matti M?ntysaari Sirkka Kein?nen-Kiukaannemi Risto Bloigu Karl-Heinz Herzig Riitta Antikainen Hannu Rintam?ki Jouni J. K. Jaakkola Tiina M. Ik?heimo 《PloS one》2014,9(7)
Objectives
The aim of our study was to assess the effect of short-term cold exposure, typical in subarctic climate, on cardiac electrical function among untreated middle-aged hypertensive men.Methods
We conducted a population-based recruitment of 51 hypertensive men and a control group of 32 men without hypertension (age 55–65 years) who underwent whole-body cold exposure (15 min exposure to temperature −10°C, wind 3 m/s, winter clothes). Conduction times and amplitudes, vectorcardiography, arrhythmias, and heart rate variability (autonomic nervous function) were assessed.Results
Short-term cold exposure increased T-peak to T-end interval from 67 to 72 ms (p<0.001) and 71 to 75 ms (p<0.001) and T-wave amplitude from 0.12 to 0.14 mV (p<0.001) and from 0.17 to 0.21 mV (p<0.001), while QTc interval was shortened from 408 to 398 ms (p<0.001) and from 410 to 401 ms (p<0.001) among hypertensive men and controls, respectively. Cold exposure increased both low (from 390 to 630 ms2 (p<0.001) and 380 to 700 ms2 (p<0.001), respectively) and high frequency heart rate variability (from 90 to 190 ms2 (p<0.001) and 150 to 300 ms2 (p<0.001), respectively), while low-to-high frequency-ratio was reduced. In addition, the frequency of ventricular ectopic beats increased slightly during cold exposure. The cold induced changes were similar between untreated hypertensive men and controls.Conclusions
Short-term cold exposure with moderate facial and mild whole body cooling resulted in prolongation of T-peak to T-end interval and higher T-wave amplitude while QTc interval was shortened. These changes of ventricular repolarization may have resulted from altered cardiac autonomic regulation and were unaffected by untreated hypertension.Trial Registration
ClinicalTrials.gov NCT02007031相似文献67.
68.
69.
EZH2 is downstream of the pRB-E2F pathway, essential for proliferation and amplified in cancer 总被引:29,自引:0,他引:29 下载免费PDF全文
Recent experiments have demonstrated that the Polycomb group (PcG) gene EZH2 is highly expressed in metastatic prostate cancer and in lymphomas. EZH2 is a component of the PRC2 histone methyltransferase complex, which also contains EED and SUZ12 and is required for the silencing of HOX gene expression during embryonic development. Here we demonstrate that both EZH2 and EED are essential for the proliferation of both transformed and non-transformed human cells. In addition, the pRB-E2F pathway tightly regulates their expression and, consistent with this, we find that EZH2 is highly expressed in a large set of human tumors. These results raise the question whether EZH2 is a marker of proliferation or if it is actually contributing to tumor formation. Significantly, we propose that EZH2 is a bona fide oncogene, since we find that ectopic expression of EZH2 is capable of providing a proliferative advantage to primary cells and, in addition, its gene locus is specifically amplified in several primary tumors. 相似文献
70.
Selenium as an anti-oxidant and pro-oxidant in ryegrass 总被引:12,自引:1,他引:12
Selenium is an essential element for antioxidation reactions in human and animals. In order to study its biological role in
higher plants, ryegrass (Lolium perenne) was cultivated in a soil without Se or amended with increasing dosages of H2SeO4 (0.1, 1.0, 10.0 and 30.0 mg Se kg−1). Ryegrass was harvested twice and the yields were analyzed for antioxidative systems and growth parameters. Selenium exerted
dual effects: At low concentrations it acted as an antioxidant, inhibiting lipid peroxidation, whereas at higher concentrations,
it was a pro-oxidant, enhancing the accumulation of lipid peroxidation products. The antioxidative effect was associated with
an increase in glutathione peroxidase (GSH-Px) activity, but not with superoxide dismutase (SOD) and αα-tocopherol, which
was the only tocopherol detected. In the second yield, the diminished lipid peroxidation due to a proper Se addition coincided
with promoted plant growth. The oxidative stress found at the Se addition level ≥ 10 mg kg−1 resulted in drastic yield losses. This result indicates that the toxicity of Se can be attributed, in addition to metabolic
disturbances, to its pro-oxidative effects. Neither the growth-promoting nor the toxic effect of Se could be explained by
the changes in the total chlorophyll concentration.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献