Aluminium in aquatic environments: abundance and ecotoxicological impacts

Aquatic Ecology - Aluminium (Al) is a common chemical element released into the aquatic environment from the Earth’s crust and many anthropogenic activities. It may be present in various...     

Clear-cutting impacts nutrient,carbon and water exchange parameters in woody plants in an east Fennoscandian pine forest

Plant and Soil - Clear-cut logging currently is a key factor transforming forest communities in many boreal regions. The dynamics of biogeochemical processes taking place in clear-cuts makes them a...     

IL-2 secretion by CD4+ T cells in vivo is rapid, transient, and influenced by TCR-specific competition

The secretion of IL-2 is a critical and early landmark in the activation program of CD4(+) T cells in vitro, but the lack of sensitive assays has limited its application for studying T cell activation in vivo. Using a mouse cytokine capture assay we were able to detect the rapid secretion of IL-2 after an in vivo stimulus by 1-2 h in naive T cells and as early as 30 min in memory T cells. Maximal secretion was achieved within 1-2 h for memory cells or 6-8 h for naive T cells. Surprisingly IL-2 production terminated quickly in vivo and secretion was undetectable by 20-24 h in either cell type. We further demonstrated that this short duration of secretion can be influenced by cellular competition between Ag-specific CD4(+) T cells. The consequences of competition were mimicked by reducing the strength of the antigenic stimulus. These data argue that early competition between T cells influences both the eventual frequency of IL-2 producers in the population and also the duration of their secretion, potentially by altering the strength or duration of the stimulus available to each T cell.     

c-myc oncogene expression inhibits the initiation of myogenic differentiation

The role of c-myc oncogene expression in myogenic differentiation has been established by transfecting rat myoblasts of the L6 cell line with plasmid pMT-myc, in which the c-myc coding sequences were under the control of the metallothionein I promoter. We observed that the constitutive expression of the exogenous c-myc gene inhibits muscular differentiation. A diminution of the endogenous c-myc gene expression occurs within the first 24 h after the transfer of the cells to a differentiating medium. This early decrease of c-myc expression is required for cell differentiation to occur. We have also observed that exogenous myc gene expression has no effect on endogenous myc expression.     

Field monitoring of onion maggot (Delia antiqua) fly through improved trapping

Onion maggot (Delia antiqua) is an economically important pest of Allium crops in temperate regions throughout the world. Management of this pest is necessary to achieve economic returns and depends on insecticide regimes and cultural management. Current cultural management especially altering planting date, field location and crop rotation depend on monitoring. We evaluated the effect of shape, size, colour and chemical attractants on trap catch of field populations of adult D. antiqua flies in upstate New York. White, large diameter, spherical traps in conjunction with Delia Lure attractant performed the best in attracting and catching D. antiqua adults. These results suggest an improved means of attracting and capturing D. antiqua populations which could be useful in monitoring efforts and development of attract and kill strategies for pest control.     

Molecular modeling of benzothiazepine binding in the L-type calcium channel

Benz(othi)azepine (BTZ) derivatives constitute one of three major classes of L-type Ca(2+) channel ligands. Despite intensive experimental studies, no three-dimensional model of BTZ binding is available. Here we have built KvAP- and KcsA-based models of the Ca(v)1.2 pore domain in the open and closed states and used multiple Monte Carlo minimizations to dock representative ligands. In our open channel model, key functional groups of BTZs interact with BTZ-sensing residues, which were identified in previous mutational experiments. The bulky tricyclic moiety occupies interface between domains III and IV, while the ammonium group protrudes into the inner pore, where it is stabilized by nucleophilic C-ends of the pore helices. In the closed channel model, contacts with several ligand-sensing residues in the inner helices are lost, which weakens ligand-channel interactions. An important feature of the ligand-binding mode in both open and closed channels is an interaction between the BTZ carbonyl group and a Ca(2+) ion chelated by the selectivity filter glutamates in domains III and IV. In the absence of Ca(2+), the tricyclic BTZ moiety remains in the domain interface, while the ammonium group directly interacts with a glutamate residue in the selectivity filter. Our model suggests that the Ca(2+) potentiation involves a direct electrostatic interaction between aCa(2+) ion and the ligand rather than an allosteric mechanism. Energy profiles indicate that BTZs can reach the binding site from the domain interface, whereas access through the open activation gate is unlikely, because reorientation of the bulky molecule in the pore is hindered.     

Diversity of plants in cocoa agroforests in the humid forest zone of Southern Cameroon

In the humid forest zone of Southern Cameroon, farmers generally associate cocoa with native and exotic trees in complex agroforestry systems. Despite the socio-economic and ecological importance of these systems, few studies have investigated their plant composition. We investigated tree composition of cocoa agroforests along a gradient of market access, population density and resource use intensity in the humid forest zone of southern Cameroon, comprising (i) the sub-region of Yaoundé, (ii) the sub-region of Mbalmayo, and (iii) the sub-region of Ebolowa. Market access, population density and resource use intensity all decreased from the first to the third sub-region. We quantified the diversity of tree species associated with cocoa within individual agroforests, among agroforests in the same region, and among the three sub-regions, and classified the tree species according to their main uses. A total of 9.1 ha belonging to 60 cocoa agroforests were inventoried in 12 villages. We encountered a total of 206 tree species with an average of 21 tree species per agroforest. In the more urbanized area around Yaoundé, agroforests were less diverse than in the other sub-regions. In all of the agroforests, food producing tree species tended to be more frequent than other species. Two thirds of the food trees were native forest species and one third was introduced. From Ebolowa to Yaoundé, the density of food producing trees doubled and the density of exotic food-producing species increased relative to native species. Some local species producing high-value non-timber forest products were found in the agroforests, but their density was far lower than that of exotic tree species. The agroforests also provide medicine, charcoal and other products for household consumption and sale. We conclude that unless there are specific efforts to promote local forest tree species in cocoa agroforests, these will progressively lose importance with increasing market access, population pressure and land use intensity.     

Determining environmental covariates which explain genotype environment interaction in winter wheat through probe genotypes and biadditive factorial regression

Genotype-environment interaction has been analyzed in a winter-wheat breeding network using bi-additive factorial regression models. This family of models generalizes both factorial regression and biadditive (or AMMI) models; it fits especially well when abundant external information is available on genotypes and/or environments. Our approach, focused on environmental characterization, was performed with two kinds of covariates: (1) deviations of yield components measured on four probe genotypes and (2) usual indicators of yield-limiting factors. The first step was based on the analysis of a crop diagnosis on four probe genotypes. Difference of kernel number to a threshold number (DKN) and reduction of thousand-kernel weight from a potential value (RTKW) were used to characterize the grain-number formation and the grain-filling periods, respectively. Grain yield was analyzed according to a biadditive factorial regression model using eight environmental covariates (DKN and RTKW measured on each of four probe genotypes). In the second step, the usual indicators of yield-limiting factors were too numerous for the analysis of grain yield. Thus a selection of a subset of environmental covariates was performed on the analysis of DKN and RTKW for the four probe genotypes. Biadditive factorial regression models involved environmental covariates related to each deviation and included environmental main effect, sum of water deficits, an indicator of nitrogen stress, sum of daily radiation, high temperature, pressure of powdery mildew and lodging. The correlations of each environmental covariate to the synthetic variates helped to discard those poorly involved in interaction (with | correlation | <0.3). The grain yield of 12 genotypes was interpreted with the retained covariates using biadditive factorial regression. The models explained about 75% of the interaction sums of squares. In addition, the biadditive factorial regression biplot gave relevant information about the interaction of the genotypes (interaction pattern and sensitivities to environmental covariates) with respect to the environmental covariates and proved to be interesting for such an approach. Received: 8 March 1999 / Accepted: 29 July 1999     

Ht31, a protein kinase A anchoring inhibitor, induces robust cholesterol efflux and reverses macrophage foam cell formation through ATP-binding cassette transporter A1

Macrophage foam cell is the predominant cell type in atherosclerotic lesions. Removal of excess cholesterol from macrophages thus offers effective protection against atherosclerosis. Here we report that a protein kinase A (PKA)-anchoring inhibitor, st-Ht31, induces robust cholesterol/phospholipid efflux, and ATP-binding cassette transporter A1 (ABCA1) greatly facilitates this process. Remarkably, we found that st-Ht31 completely reverses foam cell formation, and this process is ABCA1-dependent. The reversal is also accompanied by the restoration of well modulated inflammatory response to LPS. There is no detectable toxicity associated with st-Ht31, even when cells export up to 20% cellular cholesterol per hour. Using FRET-based PKA biosensors in live cells, we provide evidence that st-Ht31 drives cholesterol efflux by elevating PKA activity specifically in the cytoplasm. Furthermore, ABCA1 facilitates st-Ht31 uptake. This allows st-Ht31 to effectively remove cholesterol from ABCA1-expressing cells. We speculate that de-anchoring of PKA offers a novel therapeutic strategy to remove excess cholesterol from lipid-laden lesion macrophages.