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排序方式: 共有814条查询结果,搜索用时 15 毫秒
1.
Ethan R. Block Michael A. Tolino Jennifer S. Lozano Kira L. Lathrop Rebecca S. Sullenberger Abigail R. Mazie Jes K. Klarlund 《Molecular biology of the cell》2010,21(13):2172-2181
The ability of epithelia to migrate and cover wounds is essential to maintaining their functions as physical barriers. Wounding induces many cues that may affect the transition to motility, including the immediate mechanical perturbation, release of material from broken cells, new interactions with adjacent extracellular matrix, and breakdown of physical separation of ligands from their receptors. Depending on the exact nature of wounds, some cues may be present only transiently or insignificantly. In many epithelia, activation of the epidermal growth factor receptor (EGFR) is a central event in induction of motility, and we find that its continuous activation is required for progression of healing of wounds in sheets of corneal epithelial cells. Here, we examine the hypothesis that edges, which are universally and continuously present in wounds, are a cue. Using a novel culture model we find that their presence is sufficient to cause activation of the EGFR and increased motility of cells in the absence of other cues. Edges that are bordered by agarose do not induce activation of the EGFR, indicating that activation is not due to loss of any specific type of cell–cell interaction but rather due to loss of physical constraints. 相似文献
2.
Ethan P. White 《Ecology letters》2004,7(4):329-336
The species–time relationship (STR) is a macroecological pattern describing the increase in the observed species richness with the length of time censused. Understanding STRs is important for understanding the ecological processes underlying temporal turnover and species richness. However, accurate characterization of the STR has been hampered by the influence of sampling. I analysed STRs for 521 breeding bird survey communities. I used a model of sampling effects to demonstrate that the increase in richness was not due exclusively to sampling. I estimated the time scale at which ecological processes became dominant over sampling effects using a two‐phase model combining a sampling phase and either a power function or logarithmic ecological phase. These two‐phase models performed significantly better than sampling alone and better than simple power and logarithmic functions. Most community dynamics were dominated by ecological processes over scales <5 years. This technique provides an example of a rigorous, quantitative approach to separating sampling from ecological processes. 相似文献
3.
Sublocalization of an Ataxia-Telangiectasia Gene Distal to D11S384 by Ancestral Haplotyping In Costa Rican Families 总被引:8,自引:4,他引:4 下载免费PDF全文
Nancy Uhrhammer Ethan Lange Oscar Porras Arash Naeim Xiaoguang Chen Sepideh Sheikhavandi Sujata Chiplunkar Lan Yang Sugandha Dandekar Teresa Liang Nima Patel Sharon Teraoka Nitin Udar Nidia Calvo Patrick Concannon Kenneth Lange Richard A. Gatti 《American journal of human genetics》1995,57(1):103-111
In an effort to localize a gene for ataxia-telangiectasia (A-T), we have genotyped 27 affected Costa Rican families, with 13 markers, in the chromosome 11q22-23 region. Significant linkage disequilibrium was detected for 9/13 markers between D11S1816 and D11S1391. Recombination events observed in these pedigrees places A-T between D11S1819 and D11S1960. One ancestral haplotype is common to 24/54 affected chromosomes and roughly two-thirds of the families. Inferred (ancestral) recombination events involving this common haplotype in earlier generations suggest that A-T is distal to D11S384 and proximal to D11S1960. Several other common haplotypes were identified, consistent with multiple mutations in a single gene. When considered together with all other evidence, this study further sublocalizes the major A-T locus to ≈200 kb, between markers S384 and S535. 相似文献
4.
Summary Ammonia evolution and urease, phosphatase and protease activities were measured after field incubations of soil from 5 sites, differently influenced by penguin guano, from Cape Bird, Antarctica. Rates of NH3 production were low considering the large amounts of free NH3 in these soils. Enzyme activities were higher than expected and, under optimum conditions of temperature, moisture and substrate availability, were sufficient to degrade rapidly the accumulated organic matter in these soils. Laboratory incubations confirmed these high levels of activity; they also showed high dehydrogenase, but not sulphatase, activity. The surface horizon from the site that received continuous additions of fresh penguin excreta had considerably more enzyme activity than the other samples. The optimum activity of phosphatase in this sample was at pH 9.5-10. These enzyme activities are compared with those of New Zealand topsoils, and considered in relation to activities likely to occur under field conditions. Recommendations are made for further biochemical studies at Cape Bird. 相似文献
5.
The recovery of soil biochemical properties under grazed, grass-clover pasture, after simulated lignite mining, was studied over a 5-year period in a mesic Typic Dystrochrept soil at Waimumu, Southland, New Zealand. The restoration procedures involved four replacement treatments, after A, B, and C horizon materials had been separately removed, from all except the control, and stockpiled for 2–3 weeks. In each replacement treatment, the effects of ripping to 1.8 m depth, mole drainage, and the use of fertilizer nitrogen were also investigated.Replacement treatment markedly influenced the recovery of herbage production and soil organic C and total N contents, N mineralization, microbial biomass (as indicated by mineral-N flush) and invertase and sulphatase activities. The effectiveness of replacement treatments decreased in the order: 1. control (no stripping or replacement). 2 A, B, and C horizon materials replaced in the same order. 3. A, B, and C horizon materials each mixed with an equal amount of siltstone overburden and replaced in order, 4. A and B horizon materials mixed before replacing over C horizon material.Ripping increased herbage production, net N mineralization, and to some extent microbial biomass. Drainage had little, if any, effect.Fertilizer N also stimulated herbage production, but depressed clover growth. Over 2.5 years, it had little detectable effect on the soil properties.Increases in soil invertase and, to a lesser extent, sulphatase activity during the trial were closely related to changes in herbage production. Microbial biomass increased more rapidly than did soil organic C in the early stages of the trial.Rates of net N mineralization strongly suggest that N availability would have limited pasture growth, especially in the treatments with mixed soil materials. 相似文献
6.
Ethan Akin 《Mathematical biosciences》1980,50(3-4):239-250
In the dynamics of an evolutionary game an equilibrium in which all strategy types occur is called an interior equilibrium. Interior equilibria fail to exist only when there is domination among the strategy types. 相似文献
7.
Linkage of the gene controlling the synthesis of the fourth component of complement to the major histocompatibility complex of the guinea pig 总被引:1,自引:1,他引:0
C4-deficient (C4D) guinea pigs are lacking in C4 synthesis, a condition that appears to be caused by a structural gene defect. This defect is inherited as a simple autosomal recessive trait. We have demonstrated linkage between C4D and the major histocompatibility complex of the guinea pig (GPLA). Inbred C4D and inbred strain 13 guinea pigs appear to have the same GPLA haplotype. The use of these two strains should provide an animal model for reconstitution studies of C4 synthesis and for studied exploring the possible role of C4 in cellular and humoral immune responses.Abbreviations used in this paper are C4D
deficiency of the fourth component of complement
- MHC
major histocompatibility complex
- GPLA
major histocompatibility complex of the guinea pig
- MLC
mixed lymphocyte culture 相似文献
8.
Correlation of changes in cardiac calcium channels with hemodynamics in Syrian hamster cardiomyopathy and heart failure 总被引:2,自引:0,他引:2
M S Finkel E S Marks R E Patterson E H Speir K A Steadman H R Keiser 《Life sciences》1987,41(2):153-159
We compared hemodynamics with [3H]nitrendipine (calcium channel) binding to cardiac membranes from Bio 14.6 cardiomyopathic Syrian hamsters at 4 and 10 months with their F1B controls. A 50% increase in the number (Bmax) of nitrendipine binding sites (calcium channels) was seen only in the 4 month old myopathic vs controls (Bmax = 468 +/- 11 vs 309 +/- 10 fmol/mg prot with no change in affinity (KD) (KD = .65 +/- .12 vs .75 +/- .14 nM), while no differences in Bmax or KD were seen at 10 months (Bmax = 375 +/- 9 vs 362 +/- 7 fmol/mg prot/KD = .82 +/- .18 vs .89 +/- .17 nM) myopathic vs control respectively. Hemodynamic studies revealed no significant differences in cardiac output, cardiac index, stroke volume, heart rate, mean arterial pressure, peripheral resistance, body weight, heart weight at 4 months, but a significant decrease in peripheral resistance (1120 +/- 360 vs 2080 +/- 240) increase in body weight (118 +/- 2 vs 94 +/- 2 grams) and heart weight (97 +/- 5 vs 78 +/- 2 gms/100 gms body weight) in 10 month myopathic vs control animals. We conclude that the onset of cardiomyopathy at 4 months is associated with a selective increase in calcium channel binding sites and heart failure at 10 months is associated with a relative decrease in these sites. 相似文献
9.
In vitro blood-brain barrier (BBB) models often consist of brain microvascular endothelial cells (BMECs) that are co-cultured with other cells of the neurovascular unit, such as astrocytes and neurons, to enhance BBB properties. Obtaining primary astrocytes and neurons for co-culture models can be laborious, while yield and heterogeneity of primary isolations can also be limiting. Neural progenitor cells (NPCs), because of their self-renewal capacity and ability to reproducibly differentiate into tunable mixtures of neurons and astrocytes, represent a facile, readily scalable alternative. To this end, differentiated rat NPCs were co-cultured with rat BMECs and shown to induce BBB properties such as elevated trans-endothelial electrical resistance, improved tight junction continuity, polarized p-glycoprotein efflux, and low passive permeability at levels indistinguishable from those induced by primary rat astrocyte co-culture. An NPC differentiation time of 12 days, with the presence of 10% fetal bovine serum, was found to be crucial for generating NPC-derived progeny capable of inducing the optimal response. This approach could also be extended to human NPC-derived astrocytes and neurons which similarly regulated BBB induction. The distribution of rat or human NPC-derived progeny under these conditions was found to be a roughly 3 : 1 mixture of astrocytes to neurons with varying degrees of cellular maturity. BMEC gene expression analysis was conducted using a BBB gene panel, and it was determined that 23 of 26 genes were similarly regulated by either differentiated rat NPC or rat astrocyte co-culture while three genes were differentially altered by the rat NPC-derived progeny. Taken together, these results demonstrate that NPCs are an attractive alternative to primary neural cells for use in BBB co-culture models. 相似文献
10.
Clotfelter ED Pedersen AB Cranford JA Ram N Snajdr EA Nolan V Ketterson ED 《Oecologia》2007,154(3):493-503
Resource pulses can have cascading effects on the dynamics of multiple trophic levels. Acorn mast is a pulsed resource in
oak-dominated forests that has significant direct effects on acorn predators and indirect effects on their predators, prey,
and pathogens. We evaluated changes in acorn mast, rodent abundance, raptor abundance, and reproductive success of a ground-nesting
songbird over a 24-year period (1980–2004) in the southern Appalachian Mountains in an effort to determine the relationships
among the four trophic levels. In particular, we examined the following: acorn mast from red oaks (Quercus rubra) and white oaks (Q. alba), abundance of white-footed mice (Peromyscus leucopus) and deer mice (P. maniculatus), population estimates of seven raptor species from three feeding guilds, and nest failure and number of juveniles of dark-eyed
juncos (Junco hyemalis). Finally, we recorded seasonal temperature and precipitation to determine the effects of weather on each trophic level.
We found that weather patterns had delayed effects of up to 3 years on these trophic interactions. Variation in acorn mast,
the keystone resource in this community, was explained by weather conditions as far back as 2 years before the mast event.
Acorn mast, in turn, was a strongly positive predictor of rodent abundance the following year, whereas spring and summer temperature
and raptor abundance negatively affected rodent abundance. Dark-eyed junco nests were more likely to fail in years in which
there were more rodents and raptors. Nest failure rate was a strong predictor of the number of juvenile juncos caught at the
end of the summer. Our results improve our understanding of the complex ecological interactions in oak-dominated forests by
illustrating the importance of abiotic and biotic factors at different trophic levels.
Ethan D. Clotfelter and Amy B. Pedersen contributed equally to the writing of this paper. 相似文献