Explaining and predicting patterns in stochastic population systems

Lattice effects in ecological time-series are patterns that arise because of the inherent discreteness of animal numbers. In this paper, we suggest a systematic approach for predicting lattice effects. We also show that an explanation of all the patterns in a population time-series may require more than one deterministic model, especially when the dynamics are complex.     

Carotenoid cleavage products modify respiratory burst and induce apoptosis of human neutrophils

Carotenoid supplementation in the treatment of diseases associated with oxidative stress has been recently questioned because of the cell damage and the increased risk of lung cancer in male smokers. Because of the complex role of neutrophils in lung diseases, we investigated whether carotenoid derivatives could affect respiratory burst and apoptosis of human neutrophils purified from peripheral blood. Stimulation of superoxide production was induced by nanomolar and micromolar concentrations of carotenoid cleavage products with aliphatic chains of different length, but not by carotenoids lacking the carbonyl moiety. The stimulatory effect of carotenoid cleavage products was observed in cells activated by phorbol myristate acetate (PMA), while a slight inhibition of superoxide production was noticed with cells activated by the chemotactic tripeptide N-formyl-Met-Leu-Phe (f-MLP). At higher concentrations, carotenoid cleavage products inhibited superoxide production in the presence of both PMA and f-MLP. In the presence of 20 microM carotenoid cleavage products, inhibition of superoxide production was accompanied by DNA fragmentation and increased level of intracellular caspase-3 activity.     

Isolation of oligosaccharides from a partial-acid hydrolysate of pneumococcal type 3 polysaccharide for use in conjugate vaccines

A series of well-defined oligosaccharide fragments of the capsular polysaccharide of Streptococcus pneumoniae type 3 has been generated. Partial-acid hydrolysis of the capsular polysaccharide, followed by fractionation of the oligosaccharide mixture by Sepharose Q ion-exchange chromatography yielded fragments containing one to seven [-->3)-beta-D-GlcpA-(1-->4)-beta-D-Glcp-(1-->] repeating units. The isolated fragments were analysed for purity by high-pH anion-exchange chromatography with pulsed amperometric detection (HPAEC-PAD) using an IonPac AS11 column, and their structures were verified by 1H NMR spectroscopy and nano-electrospray mass spectrometry. The oligosaccharides can be used to produce neoglycoprotein vaccines with a defined carbohydrate part.     

Oligogalacturonides inhibit the induction of late but not of early auxin-responsive genes in tobacco

Oligogalacturonides (OGs) released from the plant cell wall regulate several defense responses, as well as various aspects of plant growth and development. In these latter effects, OGs exhibit auxin-antagonist activity. To shed light on the mechanism by which OGs antagonise auxin, we analysed the ability of these oligosaccharides to inhibit the activity of four auxin-up-regulated promoters [pGm-GH3 of soybean (Glycine max L. Merr.), pNt114 of tobacco (Nicotiana tabacum L.), and prolB and prolD of Agrobacterium rhizogenes] driving the expression of the beta-glucuronidase reporter gene (GUS) in transgenic tobacco seedlings. Our results indicate that OGs at submicromolar concentrations inhibit the activation by auxin of pNt114, prolB and prolD, but not that of pGm-GH3. Comparative analysis of the kinetics of activation of the four promoters in response to the hormone shows that, while pGm-GH3 is rapidly activated, the other three promoters exhibit a delayed activation, with a lag of at least 4 h before the appearance of GUS activity. The lack of effect of the OGs on early auxin-responsive genes was confirmed by RNA gel blot analysis of the tobacco genes Nt-GH3 and Nt-iaa2.3/2.5. Our results suggest that the auxin-antagonist action of OGs affects the expression of late but not of early auxin-responsive genes.     

Effects of early dexamethasone therapy on pulmonary fibrogenic mediators and respiratory mechanics in preterm infants

Corticosteroid administration may prevent chronic lung disease in premature newborns, perhaps by modulating the synthesis of various cytokines, including those involved in fibrogenic processes. This study analyses the levels of three fibrogenic cytokines, namely vascular endothelial growth factor, transforming growth factor-beta 1 and basic fibroblast growth factor in tracheobronchial aspirate fluids collected from 20 premature newborns randomly assigned to the early dexamethasone group or to the control group. Furthermore, pulmonary function tests were performed on days 0 and 2 following the start of therapy. The results show that early corticosteroid administration reduces transforming growth factor-beta 1 and basic fibroblast growth factor levels, and abolishes the spontaneous vascular endothelial growth factor increase observed in untreated patients, concomitantly with significant improvement of dynamic lung compliance and shorter duration of the intubation period in the treated group of patients. Significant correlations were observed between the levels of transforming growth factor-beta 1 and vascular endothelial growth factor, indicating that the production of both these cytokines is coordinated. Finally, transforming growth factor-beta 1 ratios (day 2/day 0), representing early variations of the cytokine levels, were significantly different between treated and untreated subjects and correlated with the dynamic lung compliance ratios and the extubation day, suggesting that the downmodulation of some fibrogenic mediators may be involved in the mode of action of dexamethasone.     

Mutations in the Dof zinc finger genes DAG2 and DAG1 influence with opposite effects the germination of Arabidopsis seeds

We describe the Arabidopsis gene DAG2 encoding a Dof zinc finger protein and show that it is involved in the control of seed germination. An Arabidopsis mutant line with a T-DNA insertion in DAG2 isolated by reverse genetics produces seeds that are substantially more dependent than the wild type on the physical stimuli-light and cold treatment-that promote germination. Mutant dag2 seeds also are less sensitive to the germination-promotive effect of gibberellins, because a 10-fold higher amount of gibberellins is needed to restore germination when endogenous gibberellin biosynthesis is blocked. The seed germination characteristics of the dag2 mutant are opposite to those of dag1, a knockout mutant of another Dof gene (DAG1) that we showed previously to be involved in the control of seed germination, and are similar to those of plants that overexpress DAG1. The promoter of the DAG2 gene is active specifically in the vascular system of the mother plant but not in the embryo, and segregation analysis indicates that the effect of the dag2 mutation is maternal. Both characteristics are in common with DAG1; additionally, the DAG1 and DAG2 proteins share high sequence homology and an identical zinc finger domain. These data suggest, and the germination phenotype of the double mutant is compatible with, a model whereby the zinc finger proteins DAG1 and DAG2 act on a maternal switch that controls seed germination, possibly by regulating the same gene(s).     

Phase switching in population cycles

Oscillatory populations may exhibit a phase change in which, for example, a high–low periodic pattern switches to a low–high pattern. We propose that phase shifts correspond to stochastic jumps between basins of attraction in an appropriate phase space which associates the different phases of a periodic cycle with distinct attractors. This mechanism accounts for two-cycle phase shifts and the occurrence of asynchronous replicates in experimental cultures of Tribolium.