Chimeric Fc receptors identify ligand binding regions in human glycoprotein VI

Glycoprotein (GP) VI, a key receptor for collagen-induced platelet activation, recently emerged as a major target for developing new antithrombotics. However, little is known about its functional domains, which is a disadvantage for the rational development of antagonists. Our aim was to identify the structures determining GPVI specificity. GPVI presents homologies with members of the Ig superfamily (in particular with FcalphaRI) whose extracellular parts present two domains, D1 and D2 linked by a hinge interdomain. To identify the respective role of these domains in GPVI, we have substituted D1 and D2 by their FcalphaRI homologue in a soluble GPVI fusion protein (GPVI-Fc) and have modified the linker motif by mutagenesis. Proteins were tested for their binding to ligands and antibodies specific for GPVI and FcalphaRI. We demonstrate for the first time that D2 plays a specific and significant role in GPVI binding to collagen and that the hinge interdomain is critical for the binding to convulxin. Furthermore, binding to CRP requires elements of D1 and of the linker motif. Our results indicate that GPVI is unique amongst the receptors of its family as it uses different structural domains to interact with several agonists and provide evidence that different sites on GPVI constitute targets to develop antagonists of GPVI.     

Geographical gradients of species richness: a test of the water‐energy conjecture of Hawkins et al. (2003) using European data for five taxa

Aims We present an analysis of grid‐based species‐richness data for European plants, mammals, birds, amphibians and reptiles, designed to test the proposition of Hawkins et al. (2003a ) that the single best factor describing richness variation switches from the water regime to the energy regime in the mid‐latitudes and that the ‘breakpoint’ is related to the physiological character of the taxa. We go on to develop subregional models showing the extent to which regional model fits vary as a function of the extent of the study system, and compare the relative performance of ‘water’, ‘energy’ and ‘water–energy’ models of richness for southern, northern and pan‐European models. Location Western Europe. Methods We use atlas data comprising species range data for 187 species of mammals, 445 species of breeding birds, 58 amphibians, 91 reptiles and 2362 plant species, inserted into a c. 50 × 50 km grid cell system. We used 11 modelled climate variables, averaged for the period 1961–90. Statistical analyses were carried out using generalized additive models (GAMs), with splines simplified to a maximum of four degrees of freedom, and we tested for spatial autocorrelation using Moran's I values obtained at 10 different distance intervals. We selected favoured models on the grounds of deviance explained combined with a simple parsimony criterion, such that we selected either: (1) the best two‐variable energy, water or water–energy model, or (2) a four‐variable water–energy model, where the latter improved on the best two‐variable model by a minimum of 5% deviance explained. Results Threshold energy values, at which richness shows a transition from an increasing to a decreasing function of annual solar radiation, were identified for all taxa apart from reptiles. We found conditional support for the switch from dominance of water variables (southern models) to energy variables (northern models). Our favoured models switched between ‘water’ and ‘energy’ for mammals, and between ‘energy’ and ‘water–energy’ for birds, depending on whether we used data of pan‐European extent, southern or northern subsets. Deviance explained in our favoured models varied from 15% (birds, southern Europe) to 72% (amphibians, northern Europe), i.e. ranging from very poor to good fits with the data. Comparison with previous work indicates that our models are generally consistent with (if sometimes weaker than) previous findings. Main conclusions Our models are incomplete representations of factors influencing macro‐scale richness patterns across Europe, taking no explicit account of, for example, topographic variation, human influences or long‐term climatic variation. However, with the exception of birds, for which only the northern model attains over one‐third deviance explained, the models show that climate can account for meaningful proportions of the deviance. We find general support for considering water and energy regimes together in modelling species richness, and for the proposition that water is more limiting in southern Europe and energy in the north. Our analyses demonstrate the sensitivity of model outcomes to the geographical location and extent of the study system, illustrating that simple curve‐fitting exercises like these, particularly if based on regions with the complex history and geography characteristic of Europe, are unlikely to provide the basis for global, predictive models. However, such exercises may be of value in detecting which aspects of water and energy regimes may be of most importance in refining independently generated global models for regional application.     

镉胁迫对金银花生理生态特征的影响

采用水培试验方法,研究了不同浓度镉(Cd)(0、5、10、25和50 mg·L^-1) 胁迫条件下藤本植物金银花的生长和生理特性.结果表明: 与对照相比,Cd胁迫对金银花的生长未造成明显影响,在5～50 mg·L^-1 Cd处理下,其生物量无明显差异(P>0.05),在低浓度Cd(5 mg·L^-1)处理下生物量有所增加,叶、根生物量和总生物量分别增加了2.88%、2.33%和1.25%,说明金银花对Cd具有较强的抗性.在低浓度Cd胁迫下,植物各器官的含水量和可溶性蛋白含量均有所降低,而根系和叶片的丙二醛含量分别增加51.90%和23.07%,叶绿素和类胡萝卜素含量则增加15.87%和24.89%,超氧化物歧化酶活性也显著增强.随着Cd浓度的增高,金银花体内的叶绿素和类胡萝卜素含量,以及超氧化物歧化酶活性均有所降低.     

Climatic Control on Forests and Tree Species Distribution in the Forest Region of Northeast China

North-east （NE） China covers considerable climatic gradients and all major forests types of NE Asia. in the present study, 10 major forest types across the forest region of NE China were sampled to Investigate forest distribution in relation to climate. Canonical correspondence analysis （CCA） revealed that growing season precipitation and energy availability were primary climatic factors for the overall forest pattern of NE China, accounting for 66% of the explanatory power of CCA. Conversely, annual precipitation and winter coldness had minor effects. Generalized additive models revealed that tree species responded to climatic gradients differently and showed three types of response curve： （i） monotonous decline; （ii） monotonous Increase; and （iii） a unimodai pattern. Furthermore, tree species showed remarkable differences in limiting climatic factors for their distribution. The power of climate in explaining species distribution declined significantly with decreasing species dominance, suggesting that the distribution of dominant species was primarily controlled by climate, whereas that of subordinate species was more affected by competition from other species.     

黄土残塬沟壑区流域次生植被物种分布的地形响应

研究流域次生植被物种对地形因子的响应规律,识别影响次生植被物种分布的主要地形因子,是流域近自然植被生态恢复和重建的基础。采用ArcGIS空间分析模块和地形分析模块TauDEM,并与统计软件SPLUS2000中的GRASP工具相结合,建立了位于黄土高原残垣沟壑区山西省吉县蔡家川流域次生植被各个物种分布基于地形因子的广义相加模型(GAM)。模型中的地形因子包括:海拔、坡向、坡度、平面曲率、坡位指数(SPI)、地形湿度指数(TWI)、单宽汇水面积(SCA)等。受试者操作特征曲线(ROC)测试中AUC值表明:大部分测试物种(约62%)拟合模型效果较好,且模型较为稳定。总体来看,研究流域次生植被物种分布体现了水分限制的空间分异特征:阴坡各物种分布概率较大,且随海拔升高而减小。影响研究流域次生植被物种空间分布的潜在重要因子为海拔和坡向,而单宽汇水面积(SCA)和地形湿度指数(TWI)虽然是多个物种响应模型的预测因子,但受高一级尺度海拔的影响,SCA与TWI对物种分布的影响作用较小;坡度影响作用最小。据此,在流域植被恢复和防护林建设目标区选择及立地条件划分时应首先以海拔和坡向为依据,单宽汇水面积(SCA)和地形湿度指数(TWI)则可以作为次一级立地分类依据,而坡度则仅能作为最后一级的分类依据。     

The population trend of southern elephant seals (<Emphasis Type="Italic">Mirounga leonina</Emphasis> L.) at Macquarie Island (1952–2004)

Total numbers of adult female southern elephant seals (cows) breeding at Macquarie Island were determined for 19 of the 52 year period between 1952 and 2004. Totals for 1952–1987 (exc. 1959 and 1985) were estimated from the relationship between censuses of the isthmus study area and concurrent censuses for the whole island. Totals for 1987–2004 were obtained by direct census of the entire island in mid-October. Cow numbers decreased from a maximum of about 40,000 in the 1950s to a minimum of 18,300 in 2000, but then increased slightly to 19,200 in 2004. Nonlinear and post-hoc linear analysis of the count data identified 1999 as the year when the exponential rate of change (r) slowed from −1.4% per annum to near zero. The rate of change was not uniform for each census sub-area counted (1987–2004), suggesting that certain terrestrially based density-dependent mechanisms were influencing the annual distribution of cows.     

Habitat modelling of <Emphasis Type="Italic">Electrona antarctica</Emphasis> (Myctophidae,Pisces) in Kerguelen by generalized additive models and geographic information systems

Electrona antarctica is one of the most abundant mesopelagic fishes in the oceanic zone surrounding the Kerguelen Archipelago in the Indian sector of the Southern Ocean. Generalized additive models (GAM) combined with geographical information systems (GIS) were used to predict and map the abundance of this species according to three environmental variables: sea surface temperature, bathymetry and surface chlorophyll a. The model was applied on the Antarctic Polar Front in the eastern part of Kerguelen Archipelago. E. antarctica seems to be linked to areas presenting low chlorophyll a concentrations, depths greater than 500 m and temperatures lower than 5°C. The model was then applied to the Kerguelen’s plateau for three different years: 1998, 1999 and 2000. The position of Antarctic Polar Front and the intensity of an upwelling play an important role in the abundance variability of E. antarctica. Furthermore, the model allows the understanding of the habitat of E. antarctica and its trophic place in the pelagic ecosystem.