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21.
T. Fatima Mitterboeck Sarah J. Adamowicz 《Proceedings. Biological sciences / The Royal Society》2013,280(1767)
The loss of flight ability has occurred thousands of times independently during insect evolution. Flight loss may be linked to higher molecular evolutionary rates because of reductions in effective population sizes (Ne) and relaxed selective constraints. Reduced dispersal ability increases population subdivision, may decrease geographical range size and increases (sub)population extinction risk, thus leading to an expected reduction in Ne. Additionally, flight loss in birds has been linked to higher molecular rates of energy-related genes, probably owing to relaxed selective constraints on energy metabolism. We tested for an association between insect flight loss and molecular rates through comparative analysis in 49 phylogenetically independent transitions spanning multiple taxa, including moths, flies, beetles, mayflies, stick insects, stoneflies, scorpionflies and caddisflies, using available nuclear and mitochondrial protein-coding DNA sequences. We estimated the rate of molecular evolution of flightless (FL) and related flight-capable lineages by ratios of non-synonymous-to-synonymous substitutions (dN/dS) and overall substitution rates (OSRs). Across multiple instances of flight loss, we show a significant pattern of higher dN/dS ratios and OSRs in FL lineages in mitochondrial but not nuclear genes. These patterns may be explained by relaxed selective constraints in FL ectotherms relating to energy metabolism, possibly in combination with reduced Ne. 相似文献
22.
Han Zhang 《Autophagy》2017,13(3):627-628
Macroautophagy/autophagy is a well-established process involved in maintaining cellular homeostasis, but its role in cancer is complex and even controversial. Many studies have reported a correlative relationship between increased autophagy and evolving cancer cells under stress conditions such as nutrient or oxygen deprivation; however, there has been a lack of a plausible mechanistic link to properly target the autophagy process in the context of this microenvironment. We recently unveiled a positive regulatory loop involving TGM2 (transglutaminase 2)-NFKB/NF-κB signaling, IL6 and autophagy in cancer using mantle cell lymphoma (MCL) as a model system. These pathways are functionally connected to each other, thereby promoting malignant B cell survival and leading to enhanced lymphoma progression both in mice and in patients. Disruption of this network could provide an opportunity to increase the efficacies of current therapies and to reduce MCL drug resistance. 相似文献
23.
24.
María Prados-Privado Juan Carlos Prados-Frutos José Luis Calvo-Guirado José Antonio Bea 《Computer methods in biomechanics and biomedical engineering》2016,19(15):1583-1591
To measure fatigue in dental implants and in its components, it is necessary to use a probabilistic analysis since the randomness in the output depends on a number of parameters (such as fatigue properties of titanium and applied loads, unknown beforehand as they depend on mastication habits). The purpose is to apply a probabilistic approximation in order to predict fatigue life, taking into account the randomness of variables. More accuracy on the results has been obtained by taking into account different load blocks with different amplitudes, as happens with bite forces during the day and allowing us to know how effects have different type of bruxism on the piece analysed. 相似文献
25.
Automated determinations of 5-hydroxytryptamine and its main metabolite, 5-hydroxyindoleacetic acid, have been described (Technicon autoanalyzer). The determinations are based on an extraction procedure from deproteinized tissue extracts or cerebrospinal fluid by means of butanolheptane mixtures. The indoles are transferred from the organic phase to a water phase and determined fluormetrically with the cysteine-o-phthaldialdehyde method. The method is highly sensitive: solutions containing 1 ng/ml can be reproducibly determined. Twenty samples per hour can be passed through the system. The determination of both 5-hydroxyindoles is performed with the same manifold. 相似文献
26.
The dielectrophoretic (DEP) crossover method has been applied to the detection of cell responses to toxicants. Time and dose responses of the human cultured leukemia (HL-60) line were measured for paraquat, styrene oxide (SO), N-nitroso-N-methylurea (NMU) and puromycin. These toxicants were chosen because of their different predominant mechanisms of action, namely membrane free radical attack, simultaneous membrane and nucleic acid attack, nucleic acid alkylation, and protein synthesis inhibition, respectively. For all treatments, the specific membrane capacitance (Cmem) of the cells decreased while the specific membrane conductance (Gmem) increased in dose- and time-dependent manners. The DEP responses correlated sensitively with alterations in cell surface morphology, especially folds, microvilli, and blebs, observed by scanning electron microscopy. The DEP method was more sensitive to agents that had a direct action on the membrane than to agents for which membrane alterations were secondary. The responses to paraquat and SO, which directly damaged the cell membrane, could be detected 15 min after exposure, while those for puromycin and NMU, which acted on intracellular targets, could be detected after 30 min. The detection times and dose sensitivity results showed that the DEP method is much faster and more sensitive than conventional cell and higher organism viability testing techniques. The feasibility of producing small instruments for toxicity detection and screening based on cellular dielectric responses is discussed. 相似文献
27.
Ivy Liu 《Biometrical journal. Biometrische Zeitschrift》2003,45(6):730-750
For an r × ctable with ordinal responses, odds ratios are commonly used to describe the relationship between the row and column variables. This article shows two types of ordinal odds ratios where local‐global odds ratios are used to compare several groups on a c‐category ordinal response and a global odds ratio is used to measure the global association between a pair of ordinal responses. When there is a stratification factor, we consider Mantel‐Haenszel (MH) type estimators of these odds ratios to summarize the association from several strata. Like the ordinary MH estimator of the common odds ratio for several 2 × 2 contingency tables, the estimators are used when the association is not expected to vary drastically among the strata. Also, the estimators are consistent under the ordinary asymptotic framework in which the number of strata is fixed and also under sparse asymptotics in which the number of strata grows with the sample size. Compared to the maximum likelihood estimators, simulations find that the MH type estimators perform better especially when each stratum has few observations. This article provides variances and covariances formulae for the local‐global odds ratios estimators and applies the bootstrap method to obtain a standard error for the global odds ratio estimator. At the end, we discuss possible ways of testing the homogeneity assumption. 相似文献
28.
Ethylene production of habituated and auxin-requiring tobacco ( Nicotiana tabacum L. cv. Xanthi) callus cultures were compared. More ethylene was produced by auxinrequiring i.e. auxin-heterotrophic cultures than by habituated ones. Treatment with 2,4-dichlorophenoxyacetic acid increased the ethylene evolution of habituated cultures over the range 10−7 to 10−4 M , which suggests that the higher ethylene production of auxin-dependent callus is caused by the 2,4-D in the medium. The IAA levels depended on the age of both types of callus cultures. 相似文献
29.
I. Papastylianou 《Plant and Soil》1987,104(1):23-29
The increasing need for protein at low cost has created a need to evaluate the biological nitrogen fixing potential of legumes
in Cyprus. In field studies which were conducted over the growing years of 1982–3 and 1983–4, legumes which are traditionally
grown in the country were evaluated for dry matter and nitrogen yield and biological nitrogen fixation (BNF). The legumes
studied were medic (Medicago truncatula Gearth), ochrus vetch (Lathyrus ochrus L.), bitter vetch (Vicia ervilia L.) and faba bean (Vicia faba L. var major) in the first year and in addition chickpea (Cicer arietinum L.), woollypod vetch (Vicia dasycarpa Ten.) and tickbean (Vicia faba L. var minor) in the second year.
Using the A-value method with barley and oats as reference crops, nitrogen (N) fixed by the various legumes in the first year
was 30–50% and from 55–67% of total N yield for the two reference crops, respectively. In the second year the estimates of
N fixed ranged from 70 to 80% with similar results obtained for the two reference crops barley and ryegrass. However, in the
second year chickpea, which had limited nodulation, fixed only 40% of its N yield.
Estimates of nitrogen from the atmosphere (Ndfa) obtained by the difference method (DM) were 10 to 14% lower than those from
the A-value method. These results were obtained after correcting for the amount of N derived from the applied fertilizer.
The two methods were highly correlated (r=0.98) for estimates of amount of BNF. The rates of N2 fixation of uninoculated legumes which are nodulated by the indigenous populations of Rhizobium in Cyprus are comparable
to those of legumes inoculated with selected strains of Rhizobium in other countries. An exception was the amount of N fixed
by chickpea. The appearance of the first nodules at late stages of growth may be the reason for the low BNF of this crop. 相似文献
30.
Alvaro García-Tejedor A. Raul Castaño Federico Morán Francisco Montero 《Journal of molecular evolution》1987,26(4):294-300
Summary The most relevant properties of hypercycles were previously studied mainly from a theoretical point of view. We have developed a Monte Carlo method simulating hypercyclic organization to obtain information about the dynamics of this prebiotic organization. Nucleation, growth, and selective properties have been tested and the results obtained are in good agreement with those of the theoretical predictions. The influence of hypercyclic organization of the error threshold has also been studied. As a consequence of the emergence of a hypercycle, the value of this threshold decreases. The amount of this decrease depends on the population size. Moreover, for some interval of quality factor values, either the hypercycle organization or an error catastrophe can be produced, depending on the initial conditions. The influence of these phenomena on both the dynamic behavior and evolutionary advantages of the hypercycle, as well as their decisive roles on genome size, are discussed.Presented at the FEBS Symposium on Genome Organization and Evolution, held in Crete, Greece, September 1–5, 1986 相似文献