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Recent experimental work involving Dictyostelium discoideum seems to contradict several theoretical models. Experiments suggest that localization of the release of the chemoattractant
cyclic adenosine monophosphate to the uropod of the cell is important for stream formation during aggregation. Yet several
mathematical models are able to reproduce streaming as the cells aggregate without taking into account localization of the
chemoattractant. A careful analysis of the experiments and the theory suggests the two major features of the system which
are important to stream formation are random cell motion and chemotaxis to regions of higher cell density. Random cell motion
acts to reduce streaming, whereas chemotaxis to regions of higher cell density reinforces streaming. With this understanding,
the experimental results can be explained in a manner consistent with the theoretical results. In all the experiments, alterations
in the two main factors of random motion and chemotaxis to regions of higher cell density, not the localization of the release
of the chemoattractant, can explain the results as they relate to streaming. Additionally, a comparison of results from a
mathematical model that simulates cells which localize the chemoattractant and cells which do not shows little difference
in the streaming patterns. 相似文献
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Kelsey L. Fletcher Brittany N. Whitley Lisa A. Treidel David Thompson Annie Williams Jose C. Noguera Jennie R. Stevenson Mark F. Haussmann 《Biology letters》2015,11(7)
Organismal performance directly depends on an individual''s ability to cope with a wide array of physiological challenges. For social animals, social isolation is a stressor that has been shown to increase oxidative stress. Another physiological challenge, routine locomotor activity, has been found to decrease oxidative stress levels. Because we currently do not have a good understanding of how diverse physiological systems like stress and locomotion interact to affect oxidative balance, we studied this interaction in the prairie vole (Microtus ochrogaster). Voles were either pair housed or isolated and within the isolation group, voles either had access to a moving wheel or a stationary wheel. We found that chronic periodic isolation caused increased levels of oxidative stress. However, within the vole group that was able to run voluntarily, longer durations of locomotor activity were associated with less oxidative stress. Our work suggests that individuals who demonstrate increased locomotor activity may be better able to cope with the social stressor of isolation. 相似文献
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Thomas A. Coudron Kent S. Shelby Mark R. Ellersieck Brittany R. Winston Holly J.R. Popham 《Entomologia Experimentalis et Applicata》2011,139(3):235-241
We report here the effects of a range of ascorbic acid concentrations (0.07, 0.3, 3.0, and 30.0 g l?1) in artificial diets on growth rates, adult weights, fecundity, and survival over two generations of the predatory stink bug, Podisus maculiventris (Say) (Heteroptera: Pentatomidae). Overall, a dietary level of 3.0 g l?1 gave the shortest developmental times over two generations. The likelihood of egg hatch at one ascorbic acid concentration compared to another concentration suggested that egg hatch increased as the concentration of ascorbic acid increased from 0.07 to 3.0 g l?1 and then declined from 3.0 to 30.0 g l?1. The combination of the maximum egg oviposition at 0.3 and 3.0 g l?1, egg hatch at 3.0 g l?1, and survival at 0.07 and 0.3 g l?1 suggests an overall superior performance at a concentration between 0.3 and 3.0 g l?1. Depletion of ascorbic acid below 3.0 g l?1 or addition of ascorbic acid above 3.0 g l?1 lowered the likelihood of egg hatch, which became more pronounced in the second generation. This is consistent with previously published information for phytophagous insects. 相似文献
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Geek culture is a subculture of enthusiasts that is traditionally associated with obscure media (Japanese animation, science fiction, video games, etc.). However, geek culture is becoming increasingly mainstream; for example, in the past year alone, Dragon*Con, a major Geek convention in Atlanta, Georgia, attracted an attendance of over 57,000 members. The present article uses an individual differences approach to examine three theoretical accounts of geek culture. Seven studies (N = 2354) develop the Geek Culture Engagement Scale (GCES) to quantify geek engagement and assess its relationships to theoretically relevant personality and individual differences variables. These studies present evidence that individuals may engage in geek culture in order to maintain narcissistic self-views (the great fantasy migration hypothesis), to fulfill belongingness needs (the belongingness hypothesis), and to satisfy needs for creative expression (the need for engagement hypothesis). Geek engagement is found to be associated with elevated grandiose narcissism, extraversion, openness to experience, depression, and subjective well-being across multiple samples. These data lay the groundwork for further exploration of geek culture as well as provide a foundation for examining other forms of subculture participation. 相似文献
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Ariel Alperstein Brittany Ulrich Denise M. Garofalo Ruth Dreisbach Hannah Raff Kelly Sheppard 《PloS one》2014,9(10)
The predatory bacterium Bdellovibrio bacteriovorus preys on other Gram-negative bacteria and was predicted to be an asparagine auxotroph. However, despite encoding asparaginyl-tRNA synthetase and glutaminyl-tRNA synthetase, B. bacteriovorus also contains the amidotransferase GatCAB. Deinococcus radiodurans, and Thermus thermophilus also encode both of these aminoacyl-tRNA synthetases with GatCAB. Both also code for a second aspartyl-tRNA synthetase and use the additional aspartyl-tRNA synthetase with GatCAB to synthesize asparagine on tRNAAsn. Unlike those two bacteria, B. bacteriovorus encodes only one aspartyl-tRNA synthetase. Here we demonstrate the lone B. bacteriovorus aspartyl-tRNA synthetase catalyzes aspartyl-tRNAAsn formation that GatCAB can then amidate to asparaginyl-tRNAAsn. This non-discriminating aspartyl-tRNA synthetase with GatCAB thus provides B. bacteriovorus a second route for Asn-tRNAAsn formation with the asparagine synthesized in a tRNA-dependent manner. Thus, in contrast to a previous prediction, B. bacteriovorus codes for a biosynthetic route for asparagine. Analysis of bacterial genomes suggests a significant number of other bacteria may also code for both routes for Asn-tRNAAsn synthesis with only a limited number encoding a second aspartyl-tRNA synthetase. 相似文献
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David Dweck Marcos A. Sanchez-Gonzalez Audrey N. Chang Raul A. Dulce Crystal-Dawn Badger Andrew P. Koutnik Edda L. Ruiz Brittany Griffin Jingsheng Liang Mohamed Kabbaj Frank D. Fincham Joshua M. Hare J. Michael Overton Jose R. Pinto 《The Journal of biological chemistry》2014,289(33):23097-23111
The cardiac troponin I (cTnI) R21C (cTnI-R21C) mutation has been linked to hypertrophic cardiomyopathy and renders cTnI incapable of phosphorylation by PKA in vivo. Echocardiographic imaging of homozygous knock-in mice expressing the cTnI-R21C mutation shows that they develop hypertrophy after 12 months of age and have abnormal diastolic function that is characterized by longer filling times and impaired relaxation. Electrocardiographic analyses show that older R21C mice have elevated heart rates and reduced cardiovagal tone. Cardiac myocytes isolated from older R21C mice demonstrate that in the presence of isoproterenol, significant delays in Ca2+ decay and sarcomere relaxation occur that are not present at 6 months of age. Although isoproterenol and stepwise increases in stimulation frequency accelerate Ca2+-transient and sarcomere shortening kinetics in R21C myocytes from older mice, they are unable to attain the corresponding WT values. When R21C myocytes from older mice are treated with isoproterenol, evidence of excitation-contraction uncoupling is indicated by an elevation in diastolic calcium that is frequency-dissociated and not coupled to shorter diastolic sarcomere lengths. Myocytes from older mice have smaller Ca2+ transient amplitudes (2.3-fold) that are associated with reductions (2.9-fold) in sarcoplasmic reticulum Ca2+ content. This abnormal Ca2+ handling within the cell may be attributed to a reduction (2.4-fold) in calsequestrin expression in conjunction with an up-regulation (1.5-fold) of Na+-Ca2+ exchanger. Incubation of permeabilized cardiac fibers from R21C mice with PKA confirmed that the mutation prevents facilitation of mechanical relaxation. Altogether, these results indicate that the inability to enhance myofilament relaxation through cTnI phosphorylation predisposes the heart to abnormal diastolic function, reduced accessibility of cardiac reserves, dysautonomia, and hypertrophy. 相似文献