What processes shape early-successional vegetation in fly ash and mine tailings?

Local abiotic filters and regional processes (i.e., regional pools of species that are dispersal-limited to varying degrees) interactively structure the development of vegetation in human-disturbed habitats, yet their relative contributions to this process are still to be determined. In this study conducted in the Czech Republic, we related plant species diversity and composition of 10 fly ash and 7 mine tailings to local edaphic conditions, and to vegetation from a 100-m perimeter (regional species pool). We found that the species richness and composition on the tailings were significantly associated with diversity and composition of vegetation in the surroundings, but not with the local edaphic conditions. Species from adjacent vegetation that were more abundant and those producing lighter seeds were more likely to establish on the tailings. The same characteristics also enhanced species abundance on the tailings, but the two predictors explained less than 10% in variation of establishment success or of species abundance. A non-significant relationship between species number and tailings size, but a significant association between diversity and time of vegetation development indicate that the study systems are still far from equilibrium. Our study provides evidence for a strong effect of regional processes, with a limited influence of measured edaphic conditions on plant communities developing de novo. It also highlights the necessity to consider the broader spatial context in the analysis of vegetation succession in human-disturbed habitats.     

Conservation of wildlife populations: factoring in incremental disturbance

Progressive anthropogenic disturbance can alter ecosystem organization potentially causing shifts from one stable state to another. This potential for ecosystem shifts must be considered when establishing targets and objectives for conservation. We ask whether a predator–prey system response to incremental anthropogenic disturbance might shift along a disturbance gradient and, if it does, whether any disturbance thresholds are evident for this system. Development of linear corridors in forested areas increases wolf predation effectiveness, while high density of development provides a safe‐haven for their prey. If wolves limit moose population growth, then wolves and moose should respond inversely to land cover disturbance. Using general linear model analysis, we test how the rate of change in moose (Alces alces) density and wolf (Canis lupus) harvest density are influenced by the rate of change in land cover and proportion of land cover disturbed within a 300,000 km² area in the boreal forest of Alberta, Canada. Using logistic regression, we test how the direction of change in moose density is influenced by measures of land cover change. In response to incremental land cover disturbance, moose declines occurred where <43% of land cover was disturbed; in such landscapes, there were high rates of increase in linear disturbance and wolf density increased. By contrast, moose increases occurred where >43% of land cover was disturbed and wolf density declined. Wolves and moose appeared to respond inversely to incremental disturbance with the balance between moose decline and wolf increase shifting at about 43% of land cover disturbed. Conservation decisions require quantification of disturbance rates and their relationships to predator–prey systems because ecosystem responses to anthropogenic disturbance shift across disturbance gradients.     

Whole cell cryo-electron tomography reveals distinct disassembly intermediates of vaccinia virus

At each round of infection, viruses fall apart to release their genome for replication, and then reassemble into stable particles within the same host cell. For most viruses, the structural details that underlie these disassembly and assembly reactions are poorly understood. Cryo-electron tomography (cryo-ET), a unique method to investigate large and asymmetric structures at the near molecular resolution, was previously used to study the complex structure of vaccinia virus (VV). Here we study the disassembly of VV by cryo-ET on intact, rapidly frozen, mammalian cells, infected for up to 60 minutes. Binding to the cell surface induced distinct structural rearrangements of the core, such as a shape change, the rearrangement of its surface spikes and de-condensation of the viral DNA. We propose that the cell surface induced changes, in particular the decondensation of the viral genome, are a prerequisite for the subsequent release of the vaccinia DNA into the cytoplasm, which is followed by its cytoplasmic replication. Generally, this is the first study that employs whole cell cryo-ET to address structural details of pathogen-host cell interaction.     

Widely distributed native and alien plant species differ in arbuscular mycorrhizal associations and related functional trait interactions

It is debated whether alien plants in new environments benefit from being mycorrhizal and whether widely distributed natives and aliens differ in their associations with mycorrhizal fungi. Here, we compared whether species differing in their origin status, i.e. natives, archaeophytes (alien species introduced before the year 1500) and neophytes (introduced after the year 1500), and arbuscular mycorrhizal (AM) status (obligate, facultative, non‐mycorrhizal) differ in their area of occupancy in Germany (i.e. number of occupied grid cells, each ~130 km²). We used generalized linear models, incorporating main effects and up to three‐way interactions combining AM status, origin status and plant functional traits. The latter were chosen to describe the possible trade‐off in carbon allocation either towards the symbiosis or to other plant structures, such as storage organs (significant interactions involving traits were assumed to indicate the existence of such trade‐offs). AM status significantly explained the area of occupancy of natives and neophytes – with facultative mycorrhizal species occupying the largest area in both groups – but was less pronounced among archaeophytes. Archaeophytes may have reduced dependency on AM fungi, as they are generally agricultural weeds and the symbiosis potentially becomes obsolete for plants growing in habitats providing a steady provision of nutrients. Trait interactions between AM status and other functional traits were almost exclusively detected for neophytes. While facultative mycorrhizal neophytes benefit from trade‐offs with other traits related to high C cost in terms of area of occupancy, such trade‐offs were almost absent among natives. This indicates that natives and neophytes benefit differently from the symbiosis and suggests that native AM fungal partners might be less important for neophytic than for native plant species or that more time is required to establish similar relationships between neophytes and native fungal symbionts.     

The genetic control of natural killer cell activity and its association with in vivo resistance against a moloney lymphoma isograft

Spleens of normal young mice of certain strains contain lymphocytes that can kill strain A-derived YAC-1 lymphoma cells in a⁵¹Cr release cytotoxic assay in vitro. We have previously classified mouse genotypes as high or low reactors, according to their responses in this test. In vivo resistance to small numbers of YAC ascites lymphoma cells is correlated with in vitro cytolytic activity. In vitro and in vivo tests were carried out on the same individual (A x C57BL)F₁ x A backcross mice. Natural in vitro killer cell activity appeared to be under polygenic control, including a strong H-2-linked factor. No linkage was found with five different isozyme loci, with theIg-l locus or with C5 serum activity. Also in vivo resistance showed strong linkage with theH-2 complex. In (A x CBA)F₁ x A backcross mice, a weak linkage was found with the coat color locusC. There was a correlation between in vitro killer activity and in vivo resistance in the same backcross mice. In vivo resistance was particularly strong in mice that combined theH-2 ^b -linked resistance factor with a high cytolytic activity in vitro.     

The fine-scale utilization of forest edges by mammalian mesopredators related to patch size and conservation issues in Central European farmland

The marked negative impact of habitat fragmentation and the edge effect on many populations of bird species is a recent major concern in conservation biology. Here, we focus on the edge effect in different sized forest patches in Central European farmland. In particular, we tested whether the distribution of mammalian mesopredators is related to fragment size and distance to habitat edge, and whether the contribution of these factors is additive or interactive. To assess fine-scale utilization of forest edges, we established transects of four scent stations at different distances from forest edges into the interior (0, 25, 50, 100 m) in 146 forest fragments of variable patch size (3.2–5099.6 ha) from May to June, 2008–2009. This large sample size allowed us to perform detailed analyses separately for all detected species. Our findings confirm that mammalian mesopredators strongly prefer habitat edges and small forest fragments. The probability of occurrence tended to decrease with increasing distance from the edge for all seven carnivore species detected. The carnivores’ occurrence was also negatively correlated with forest fragment area. All detected species tended to prefer small fragments, with the exception of the Eurasian badger (showing the reverse but non-significant pattern) and the red fox (no effect of fragment size). In addition, the non-significant interaction between fragment size and distance to edge suggests that both of these factors contribute independently and additively to mesopredator-mediated effects on biota in a fragmented landscape.     

Variability measures of positive random variables

During the stationary part of neuronal spiking response, the stimulus can be encoded in the firing rate, but also in the statistical structure of the interspike intervals. We propose and discuss two information-based measures of statistical dispersion of the interspike interval distribution, the entropy-based dispersion and Fisher information-based dispersion. The measures are compared with the frequently used concept of standard deviation. It is shown, that standard deviation is not well suited to quantify some aspects of dispersion that are often expected intuitively, such as the degree of randomness. The proposed dispersion measures are not entirely independent, although each describes the interspike intervals from a different point of view. The new methods are applied to common models of neuronal firing and to both simulated and experimental data.     

Endothelial expression of endoglin in normocholesterolemic and hypercholesterolemic C57BL/6J mice before and after atorvastatin treatment

Endoglin (CD105) is a homodimeric transmembrane glycoprotein strongly related to transforming growth factor (TGF)-beta signaling and many pathological states. In this study, we wanted to evaluate whether endoglin is expressed in normocholesterolemic and hypercholesterolemic C57BL/6J mice as well as whether it is affected by atorvastatin treatment in these mice. C57BL/6J mice were fed with chow diet or an atherogenic diet for 12 weeks after weaning. In 2 atorvastatin-treated groups, mice were fed the same diets (chow or atherogenic) as described above except atorvastatin was added at the dosage of 10 mg x kg(-1) x day(-1) for the last 8 weeks before euthanasia. Biochemical analysis of blood samples revealed that administration of atherogenic diet significantly increased levels of total cholesterol, VLDL, LDL, and decreased levels of HDL. Atorvastatin treatment resulted in a significant decrease in total cholesterol and VLDL only in mice fed by atherogenic diet. Quantitative stereological analysis revealed that atorvastatin significantly decreased endothelial expression of endoglin in C57BL/6J mice fed the atherogenic diet. In conclusion, we demonstrated that endothelial expression of endoglin is upregulated by hypercholesterolemia and decreased by the hypolipidemic effect of atorvastatin in C57BL/6J mice, suggesting that endoglin expression could be involved in atherogenesis.     

Preferential Binding of Hot Spot Mutant p53 Proteins to Supercoiled DNA In Vitro and in Cells

Hot spot mutant p53 (mutp53) proteins exert oncogenic gain-of-function activities. Binding of mutp53 to DNA is assumed to be involved in mutp53-mediated repression or activation of several mutp53 target genes. To investigate the importance of DNA topology on mutp53-DNA recognition in vitro and in cells, we analyzed the interaction of seven hot spot mutp53 proteins with topologically different DNA substrates (supercoiled, linear and relaxed) containing and/or lacking mutp53 binding sites (mutp53BS) using a variety of electrophoresis and immunoprecipitation based techniques. All seven hot spot mutp53 proteins (R175H, G245S, R248W, R249S, R273C, R273H and R282W) were found to have retained the ability of wild-type p53 to preferentially bind circular DNA at native negative superhelix density, while linear or relaxed circular DNA was a poor substrate. The preference of mutp53 proteins for supercoiled DNA (supercoil-selective binding) was further substantiated by competition experiments with linear DNA or relaxed DNA in vitro and ex vivo. Using chromatin immunoprecipitation, the preferential binding of mutp53 to a sc mutp53BS was detected also in cells. Furthermore, we have shown by luciferase reporter assay that the DNA topology influences p53 regulation of BAX and MSP/MST1 promoters. Possible modes of mutp53 binding to topologically constrained DNA substrates and their biological consequences are discussed.     

DNA2 drives processing and restart of reversed replication forks in human cells

Accurate processing of stalled or damaged DNA replication forks is paramount to genomic integrity and recent work points to replication fork reversal and restart as a central mechanism to ensuring high-fidelity DNA replication. Here, we identify a novel DNA2- and WRN-dependent mechanism of reversed replication fork processing and restart after prolonged genotoxic stress. The human DNA2 nuclease and WRN ATPase activities functionally interact to degrade reversed replication forks with a 5′-to-3′ polarity and promote replication restart, thus preventing aberrant processing of unresolved replication intermediates. Unexpectedly, EXO1, MRE11, and CtIP are not involved in the same mechanism of reversed fork processing, whereas human RECQ1 limits DNA2 activity by preventing extensive nascent strand degradation. RAD51 depletion antagonizes this mechanism, presumably by preventing reversed fork formation. These studies define a new mechanism for maintaining genome integrity tightly controlled by specific nucleolytic activities and central homologous recombination factors.