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The Recent volutids Cymbiola and Melo burrow in a forward direction. This agrees well with the spiral terrace pattern observed in Eocene Volutidae, thus strengthening the idea that they were forward burrowers as well. The presence of collabral terraces near the aperture in the Cassidae suggests an oblique burrowing direction, by convergence with the Nassariidae. This is confirmed by observations on living cassids. The sutural canals and associated structures of the Olividae and Seraphidae are functional in detecting whether the posterior region of the shell is buried. This confirms the idea that fossil Strombidae possessing similar features were burrowers. In contrast with these “predictable”; observations, burrowing was observed in a few gastropods the shell morphology of which would seem to exclude such behaviour, such as Architectonica, Cymatium, Volema and Bolinus. Thus, a few morphologic criteria appear to be reliable and of general applicability in inferring burrowing habits in gastropods. At the same time, the broad variety of burrowing mechanisms and life habits of gastropods makes it unlikely that general criteria will ever be found to exclude burrowing habits on the basis of shell morphology. 相似文献
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Delong Zhao Xuefeng Sun Li Yao Hongli Lin Jijun Li Jiuyang Zhao Zhimin Zhang Lide Lun Jianrong Zhang Mingxu Li Qi Huang Yang Yang Shimin Jiang Yong Wang Hanyu Zhu Xiangmei Chen 《PloS one》2013,8(4)
Background
Heparin-induced thrombocytopenia is an immune response mediated by anti-PF4/heparin antibody, which is clinically characterized by thrombocytopenia and thromboembolic events. In this study, a prospective and multi-center clinical investigation determined the positive rate of anti-PF4/heparin antibody in maintenance hemodialysis patients in China, identified the related risk factors, and further explored the effect of the anti-PF4/heparin antibody on bleeding, thromboembolic events, and risk of death in the patients.Methods
The serum anti-PF4/heparin antibody was measured in 661 patients from nine hemodialysis centers, detected by IgG-specific ELISA and followed by confirmation with excess heparin. Risk factors of these patients were analyzed. Based on a two-year follow-up, the association between the anti-PF4/heparin antibody and bleeding, thromboembolic events, and risk of death in the patients was investigated.Results
The positivity rate of the anti-PF4/heparin antibody in maintenance hemodialysis patients was 5.6%. With diabetes as an independent risk factor, the positivity rate of the anti-PF4/heparin antibody decreased in the patients undergoing weekly dialyses ≥3 times. The positivity rate of the anti-PF4/heparin antibody was not related to the occurrence of clinical thromboembolic events and was not a risk factor for death within two years in maintenance hemodialysis patients. Negativity for the anti-PF4/heparin antibody combined with a reduction of the platelet count or combined with the administration of antiplatelet drugs yielded a significant increase in bleeding events. However, the composite determination of the anti-PF4/heparin antibody and thrombocytopenia, as well as the administration of antiplatelet drugs, was not predictive for the risk of thromboembolic events in the maintenance hemodialysis patients.Conclusions
A single detection of the anti-PF4/heparin antibody did not predict the occurrence of clinical bleeding, thromboembolic events, or risk of death in the maintenance hemodialysis patients. 相似文献4.
The thermal denaturation of Lactobacillus confusus
l-2-Hydroxyisocaproate Dehydrogenase (l-HicDH) has been studied by Differential Scanning Calorimetry (DSC). The stability of this enzyme has been investigated at
different pH conditions. The results of this study indicate that the thermal denaturation of this enzyme is irreversible and
the T
m
is dependent on the scan-rate, which suggests that the denaturation process of l-HicDH is kinetically determined. The heat capacity function of l-HicDH shows a single peak with the T
m
values between 52.14°C and 55.89°C at pH 7.0 at different scan rates. These results indicate that the whole l-HicDH could unfold as a single cooperative unit, and intersubunit interactions of this homotetrameric enzyme must play a
significant role in the stabilization of the whole enzyme. The rate constant of the unfolding is analyzed as a first order
kinetic constant with the Arrhenius equation, and the activation energy has been calculated. The variation of the activation
energy values obtained with different methods does not support the validity of the one-step irreversible model. The denaturation
pathway was described by a three-state model, N → U → F, in which the dissociation of the tetramer takes place as an irreversible
step before the irreversible unfolding of the monomers. The calorimetric enthalpy associated with the irreversible dissociation
and the calorimetric enthalpy associated with the unfolding of the monomer were obtained from the best fitting procedure.
Thermal unfolding of l-HicDH was also studied using Circular Dichroism (CD) spectroscopy. Both methods yielded comparable values. 相似文献
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Differential regulation of beta-defensin expression in human skin by microbial stimuli 总被引:6,自引:0,他引:6
Sørensen OE Thapa DR Rosenthal A Liu L Roberts AA Ganz T 《Journal of immunology (Baltimore, Md. : 1950)》2005,174(8):4870-4879
In response to infection, epithelia mount an innate immune response that includes the production of antimicrobial peptides. However, the pathways that connect infection and inflammation with the induction of antimicrobial peptides in epithelia are not understood. We analyzed the molecular links between infection and the expression of three antimicrobial peptides of the beta-defensin family, human beta-defensin (hBD)-1, hBD-2, and hBD-3 in the human epidermis. After exposure to microbe-derived molecules, both monocytes and lymphocytes stimulated the epidermal expression of hBD-1, hBD-2, and hBD-3. The induced expression of hBD-3 was mediated by transactivation of the epidermal growth factor receptor. The mechanisms of induction of hBD-1 and hBD-3 were distinct from each other and from the IL-1-dependent induction of hBD-2 expression. Thus during inflammation, epidermal expression of beta-defensins is mediated by at least three different mechanisms. 相似文献
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The identity-by-descent (IBD) based variance component analysis is an important method for mapping quantitative trait loci (QTL) in outbred populations. The interval-mapping approach and various modified versions of it may have limited use in evaluating the genetic variances of the entire genome because they require evaluation of multiple models and model selection. In this study, we developed a multiple variance component model for genome-wide evaluation using both the maximum likelihood (ML) method and the MCMC implemented Bayesian method. We placed one QTL in every few cM on the entire genome and estimated the QTL variances and positions simultaneously in a single model. Genomic regions that have no QTL usually showed no evidence of QTL while regions with large QTL always showed strong evidence of QTL. While the Bayesian method produced the optimal result, the ML method is computationally more efficient than the Bayesian method. Simulation experiments were conducted to demonstrate the efficacy of the new methods. 相似文献
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The α1‐adrenergic receptor is involved in hepcidin upregulation induced by adrenaline and norepinephrine via the STAT3 pathway
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石羊河下游民勤绿洲退耕地植被自然演替特征及物种多样性分析 总被引:3,自引:0,他引:3
采用重要值、Margalef物种丰富度指数、Shannon-wiener和Simpson多样性指数、Pielou和Alatalo均匀度指数对石羊河下游民勤绿洲不同年限退耕地自然恢复的植物群落进行了研究。结果表明:(1)石羊河下游民勤绿洲退耕地在50a自然恢复过程中共出现植物34种,14科,其中灌木6种,草本28种,分别占总物种数的17.65%和82.35%;藜科(8种)、禾本科(6种)、蒺藜科(4种)植物占总物种数的52.94%。(2)研究区退耕后50a植物群落演替经历为:田旋花→藜→苦苣菜→骆驼蒿→骆驼蓬→盐生草→黑果枸杞→红砂→盐爪爪的演替过程。(3)群落物种丰富度和多样性指数均随退耕时间的延长而呈现出波动式下降的变化趋势,而均匀度指数则呈现出在退耕初期(1~5a)先下降然后呈波动式上升的变化趋势。研究表明,随着退耕年限的增加,群落物种组成逐渐减少,植物群落演替向前发展的大致经历分为4个阶段:退耕1~5a为一年生草本和宿根植物迅速恢复阶段,退耕5~15a为一年生草本植物向多年生草本演替阶段,退耕15~30a为多年生草本向多年生灌木演替阶段,退耕30~50a为多年生灌木植物稳定阶段。 相似文献