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191.
P.C. Wilkinson 《FEMS microbiology letters》1990,64(5-6):303-311
Abstract Chemoattractants determine not only the direction of leucocyte locomotion (chemotaxis) but also its speed (chemokinesis). Various mechanisms by which leucocytes may detect chemotactic gradients, including spatial and temporal detection, are briefly reviewed. These mechanisms as originally proposed did not address the question how attractants cause leucocytes to migrate in persistent random paths in the absence of a gradient. Stochastic models have recently been presented in which leucocytes either respond by polarizing and migrating in the direction from which they receive their first signal, or respond to random flucuations in the perceived attractant concentration. Stochastic models allow an explanation for the persistent random walk shown by cells in uniform concentrations of attractant as well as for directional locomotion in gradients. They suggest that, at the biochemical level, the mechanisms by which attractants stimulate chemotaxis and chemokinesis are probably the same. 相似文献
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Yolanda Schaerli Alba Jiménez José M Duarte Ljiljana Mihajlovic Julien Renggli Mark Isalan James Sharpe Andreas Wagner 《Molecular systems biology》2018,14(9)
Phenotypic variation is the raw material of adaptive Darwinian evolution. The phenotypic variation found in organismal development is biased towards certain phenotypes, but the molecular mechanisms behind such biases are still poorly understood. Gene regulatory networks have been proposed as one cause of constrained phenotypic variation. However, most pertinent evidence is theoretical rather than experimental. Here, we study evolutionary biases in two synthetic gene regulatory circuits expressed in Escherichia coli that produce a gene expression stripe—a pivotal pattern in embryonic development. The two parental circuits produce the same phenotype, but create it through different regulatory mechanisms. We show that mutations cause distinct novel phenotypes in the two networks and use a combination of experimental measurements, mathematical modelling and DNA sequencing to understand why mutations bring forth only some but not other novel gene expression phenotypes. Our results reveal that the regulatory mechanisms of networks restrict the possible phenotypic variation upon mutation. Consequently, seemingly equivalent networks can indeed be distinct in how they constrain the outcome of further evolution. 相似文献
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Jantina Toxopeus Brent J. Sinclair 《Biological reviews of the Cambridge Philosophical Society》2018,93(4):1891-1914
Freeze tolerance – the ability to survive internal ice formation – has evolved repeatedly in insects, facilitating survival in environments with low temperatures and/or high risk of freezing. Surviving internal ice formation poses several challenges because freezing can cause cellular dehydration and mechanical damage, and restricts the opportunity to metabolise and respond to environmental challenges. While freeze‐tolerant insects accumulate many potentially protective molecules, there is no apparent ‘magic bullet’ – a molecule or class of molecules that appears to be necessary or sufficient to support this cold‐tolerance strategy. In addition, the mechanisms underlying freeze tolerance have been minimally explored. Herein, we frame freeze tolerance as the ability to survive a process: freeze‐tolerant insects must withstand the challenges associated with cooling (low temperatures), freezing (internal ice formation), and thawing. To do so, we hypothesise that freeze‐tolerant insects control the quality and quantity of ice, prevent or repair damage to cells and macromolecules, manage biochemical processes while frozen/thawing, and restore physiological processes post‐thaw. Many of the molecules that can facilitate freeze tolerance are also accumulated by other cold‐ and desiccation‐tolerant insects. We suggest that, when freezing offered a physiological advantage, freeze tolerance evolved in insects that were already adapted to low temperatures or desiccation, or in insects that could withstand small amounts of internal ice formation. Although freeze tolerance is a complex cold‐tolerance strategy that has evolved multiple times, we suggest that a process‐focused approach (in combination with appropriate techniques and model organisms) will facilitate hypothesis‐driven research to understand better how insects survive internal ice formation. 相似文献
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Patrick K. Durkee Aaron T. Goetz Aaron W. Lukaszewski 《Evolution and human behavior》2018,39(2):170-178
Throughout vertebrate evolution, asymmetries in the ability to inflict costs on others (i.e., formidability) have determined the outcomes of contests over limited resources. Therefore, natural selection would have favored mechanisms designed to efficiently and accurately estimate the formidability of conspecifics. Although previous research has provided evidence for the existence of adaptations for formidability assessment, the design features of these mechanisms have not been fully examined. In the current study, participants underwent a battery of tasks to test hypotheses regarding the speed and automaticity of formidability assessment mechanisms. Results suggest that formidability is automatically and rapidly tracked and assessed from visual cues. With a few interesting exceptions, characteristics of the raters (N = 187) and targets (N = 64) did not influence these assessments. Additionally, we present eye–tracking data to highlight the salience of upper–body musculature as a cue to physical strength. Taken together, these findings bolster and extend evidence for formidability assessment mechanisms in humans. 相似文献
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In the search for MBP phosphorylating activities in Dictyostelium discoideum, we have found a proteolysis-activated protein kinase. This activity which is distributed between the soluble and the particulate fractions of the cell, uses MBP and histone as substrate and has a molecular mass of 140 kDa as detected in an in situ' assay.This protein kinase has several features shared by the protein kinase C family, such as substrate specificity and sensitivity to proteolysis, but its molecular mass is much larger than that described for the known protein kinase C isoforms.To better characterize this activity we have studied its sensitivity to several protein kinase C inhibitors and activators. This protein kinase is activated neither by phorbol ester nor by phosphatidylserine or Ca2+. The activity is inhibited by staurosporine and PKC pseudosubstrate, but is not affected by the specific protein kinase C inhibitor bisindolylmaleimide.These data lead us to propose that proteolytically activated Dictyostelium protein kinase belongs to the recently described protein kinase C-related family. 相似文献
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