Modelling population redistribution in a leaf beetle: an evaluation of alternative dispersal functions

1. Dispersal is a fundamental ecological process, so spatial models require realistic dispersal kernels. We compare five different forms for the dispersal kernel of the tansy beetle Chrysolina graminis moving between patches of its host-plant (tansy Tanacetum vulgare) in a riparian landscape. 2. Multi-patch mark-recapture data were collected every 2 weeks over 2 years within a large network of patches and from 2226 beetles. Dispersal was common (28.4% of 880 recaptures after a fortnight) and was more likely over longer intervals, out of small patches, for females and during flooding. Interpatch movement rates did not differ between years and exhibited no density dependence. Dispersal distances were similar for males and females, in both years and over all intervals, with a median dispersal distance of just 9.8 m, although a maximum of 856 m was recorded. 3. A model of dispersal, where patches competed for dispersers based on their size and distance from the beetle's source patch (scaled by the dispersal kernel) was fitted to the field data with a maximum likelihood procedure and each of five alternative kernels. The best fitting had relatively extended tails of long-distance dispersal, while Gaussian and negative exponential kernels performed worst. 4. The model suggests that females disperse more commonly than males and that both are strongly attracted to large patches but do not differ between years, which are consistent with the empirical results. Model-predicted emigration and immigration rates and dispersal phenologies match those observed, suggesting that the model captured the major drivers of tansy beetle dispersal. 5. Although negative exponential and Gaussian kernels are widely used for their simplicity, we suggest that these should not be the models of automatic choice, and that fat-tailed kernels with relatively higher proportions of long-distance dispersal may be more realistic.     

Dynamics of Th17 cells and their role in Schistosoma japonicum infection in C57BL/6 mice

Background

The current knowledge of immunological responses to schistosomiasis, a major tropical helminthic disease, is insufficient, and a better understanding of these responses would support vaccine development or therapies to control granuloma-associated immunopathology. CD4⁺ T cells play critical roles in both host immune responses against parasitic infection and immunopathology in schistosomiasis. The induction of T helper (Th)1, Th2 and T regulatory (Treg) cells and their roles in schistosome infections are well-illustrated. However, little in vivo data are available on the dynamics of Th17 cells, another important CD4⁺ T cell subset, after Schistosoma japonicum infection or whether these cells and their defining IL-17 cytokine mediate host protective responses early in infection.

Methodology

Levels of Th17 and the other three CD4⁺ T cell subpopulations and the cytokines related to induction or repression of Th17 cell generation in different stages of S. japonicum infection were observed. Contrary to reported in vitro studies, our results showed that the Th17 cells were induced along with the Th1, Th2, Treg cells and the IFN-γ and IL-4 cytokines in S. japonicum infected mice. The results also suggested that S. japonicum egg antigens but not adult worm antigens preferentially induced Th17 cell generation. Furthermore, decreasing IL-17 with a neutralizing anti-IL-17 monoclonal antibody (mAb) increased schistosome-specific antibody levels and partial protection against S. japonicum infection in mice.

Conclusions

Our study is the first to report the dynamics of Th17 cells during S. japonicum infection and indicate that Th17 cell differentiation results from the integrated impact of inducing and suppressive factors promoted by the parasite. Importantly, our findings suggest that lower IL-17 levels may result in favorable host protective responses. This study significantly contributes to the understanding of immunity to schistosomiasis and may aid in developing interventions to protect hosts from infection or restrain immunopathology.     

A structural limitation on enzyme activity: the case of HMG-CoA synthase

Recent structural studies of the HMG-CoA synthase members of the thiolase superfamily have shown that the catalytic loop containing the nucleophilic cysteine follows the phi and psi angle pattern of a II' beta turn. However, the i + 1 residue is conserved as an alanine, which is quite unusual in this position as it must adopt a strained positive phi angle to accommodate the geometry of the turn. To assess the effect of the conserved strain in the catalytic loop, alanine 110 of Enterococcus faecalis 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) synthase was mutated to a glycine. Subsequent enzymatic studies showed that the overall reaction rate of the enzyme was increased 140-fold. An X-ray crystallographic study of the Ala110Gly mutant enzyme demonstrated unanticipated adjustments in the active site that resulted in additional stabilization of all three steps of the reaction pathway. The rates of acetylation and hydrolysis of the mutant enzyme increased because the amide nitrogen of Ser308 shifts 0.4 A toward the catalytic cysteine residue. This motion positions the nitrogen to better stabilize the intermediate negative charge that develops on the carbonyl oxygen of the acetyl group during both the formation of the acyl-enzyme intermediate and its hydrolysis. In addition, the hydroxyl of Ser308 rotates 120 degrees to a position where it is able to stabilize the carbanion intermediate formed by the methyl group of the acetyl-S-enzyme during its condensation with acetoacetyl-CoA.     

Development of a serum-free medium using computer-assisted factorial design and analysis

Stepwise screening of media supplements using factorial design and analysis was employed in the development of serum-free medium for a recombinant Chinese hamster ovary cell line. The effects (growth and target protein production) of different combinations were measured at two time points to ensure adequate response. The results were analysed by a computer program specialized in factorial analysis. The formulation deduced from the previous experiment was used as the new basal medium for the next screening. Certain significant nutrients were studied again in a more advanced formulation in order to analyse the potential synergistic effects with new media components. Compared to cells grown in serum-containing medium, cells adapted to the final formulation of the serum-free medium had a comparable growth rate but a four fold increase in the active protein production.Abbreviations ANOVA Analysis of variance - BSA bovine serum albumin - CHO Chinese hamster ovary - FBS fetal bovine serum - MTT 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide - PBS phosphate buffered saline - SFM serum-free medium     

Metabolic Adaptations of Azospirillum brasilense to Oxygen Stress by Cell-to-Cell Clumping and Flocculation

The ability of bacteria to monitor their metabolism and adjust their behavior accordingly is critical to maintain competitiveness in the environment. The motile microaerophilic bacterium Azospirillum brasilense navigates oxygen gradients by aerotaxis in order to locate low oxygen concentrations that can support metabolism. When cells are exposed to elevated levels of oxygen in their surroundings, motile A. brasilense cells implement an alternative response to aerotaxis and form transient clumps by cell-to-cell interactions. Clumping was suggested to represent a behavior protecting motile cells from transiently elevated levels of aeration. Using the proteomics of wild-type and mutant strains affected in the extent of their clumping abilities, we show that cell-to-cell clumping represents a metabolic scavenging strategy that likely prepares the cells for further metabolic stresses. Analysis of mutants affected in carbon or nitrogen metabolism confirmed this assumption. The metabolic changes experienced as clumping progresses prime cells for flocculation, a morphological and metabolic shift of cells triggered under elevated-aeration conditions and nitrogen limitation. The analysis of various mutants during clumping and flocculation characterized an ordered set of changes in cell envelope properties accompanying the metabolic changes. These data also identify clumping and early flocculation to be behaviors compatible with the expression of nitrogen fixation genes, despite the elevated-aeration conditions. Cell-to-cell clumping may thus license diazotrophy to microaerophilic A. brasilense cells under elevated oxygen conditions and prime them for long-term survival via flocculation if metabolic stress persists.     

The effects of temperature and ouabain on steady-state Na and K exchanges in human lymphocytes

The temperature-dependence of steady-state exchanges of K and Na were determined under conditions in which cell viability, ATP, water, Ca, and Mg were not confounding variables. Steady-state ion contents are near-normal between 37° and 10° C, Below 10° C K is replaced by Na in a mole-for-mole fashion with significant net K retention and Na exclusion occurring even below 3°C. The rates of steady-state Kand Na exchanges have markedly different temperature-dependences; between 37° and 10° C, for example, that of K decreases markedly while that of Na remains near-normal, and there is no consistent correlation between the steady-state exchanges and the ionic contents. Ouabain increases steady-state Na flux at 37° C and induces a more marked temperature-dependence over the entire temperature range. This effect is not due simply to inhibition of some processes and unmasking others; it mirrors a pronounced effect of ouabain on the intrinsic properties of Na self-exchange. These results are compatible with a model based on two simple concepts: (1) partial ionic exclusion from cellular water that is ordered by interaction with proteins; and (2) ionic accumulation mediated by adsorption onto and desorption from fixed macromolecular anionic sites, the majority of which interact with one another in a cooperative fashion. In this view, the sharp temperature transition in the net replacement of K by Na below 10° C is due to a critical transition in the selectivity of the cooperatively interacting adsorption sites. The rates of steady-state self-exchanges of K and Na are determined by parameters of ion-site interaction, and the major set of ion-adsorbing sites that interact cooperatively have a steep thermal activation energy of ionic self-exchange. When they are in the K-preferring state above 10° C, exchange of K has a steep temperature-dependence. When they are in the Na-preferring state below 10° C, exchange of Na has a steep temperature-dependence. When these sites are forced into a Na-preferring state at all temperatures by treatment with ouabain, exchange of Na acquires a steep temperature-dependence over the entire temperature range 37° to 0° C.     

Automated analysis of courtship suppression learning and memory in Drosophila melanogaster

Study of the fruit fly, Drosophila melanogaster, has yielded important insights into the underlying molecular mechanisms of learning and memory. Courtship conditioning is a well-established behavioral assay used to study Drosophila learning and memory. Here, we describe the development of software to analyze courtship suppression assay data that correctly identifies normal or abnormal learning and memory traits of individual flies. Development of this automated analysis software will significantly enhance our ability to use this assay in large-scale genetic screens and disease modeling. The software increases the consistency, objectivity, and types of data generated.