Heating of a Local Region of a Branching Streamer as a Starting Point of a Space Leader and a Negative-Leader Step

Plasma Physics Reports - Localized plasma formations called space leaders are observed in streamer coronas of negative leaders of long laboratory sparks. The main leader completes a step when the...     

Geminiviruses: a tale of a plasmid becoming a virus

Background  

Geminiviruses (family Geminiviridae) are small single-stranded (ss) DNA viruses infecting plants. Their virion morphology is unique in the known viral world – two incomplete T = 1 icosahedra are joined together to form twinned particles. Geminiviruses utilize a rolling-circle mode to replicate their genomes. A limited sequence similarity between the three conserved motifs of the rolling-circle replication initiation proteins (RCR Reps) of geminiviruses and plasmids of Gram-positive bacteria allowed Koonin and Ilyina to propose that geminiviruses descend from bacterial replicons.     

Problems of being a cell in a soft body

Many soft bodied coelenterates are highly deformable or contractile. In the absence of hard skeletal elements, the epithelia are subjected to mechanical forces which cause a wide range of structural changes in the component epithelial cells. What kinds of structural change occur and how are the cells adapted to them? These questions are addressed with reference to cell surface area, cell membranes, cell junctions and epithelial cilia.

     

Mechanisms of coexistence of a bacteria and a bacteriophage in a spatially homogeneous environment

When bacteriophage are added to laboratory bacteria populations, bacteria mutants that are resistant to the phage quickly dominate the population. The phage will only persist in the long‐term if there are sufficient bacteria in the population that show susceptibility to the phage. We investigated the mechanisms allowing for coexistence by adding the virulent bacteriophage φ6 to cultures of the bacterium Pseudomonas syringae pv. phaseolicola in a spatially homogeneous environment. We saw large differences between replicate cultures, in particular when one or both of the species persisted. These differences can be explained by variation in the timing of the appearance of various resistant phenotypes in the bacteria populations before the phage were added, which determines their relative frequencies within the populations. Although these resistant phenotypes have similar fitnesses in the presence and in the absence of the phage, they have a profound effect on the persistence of the phage. Our results give a clearer understanding of the ecological mechanisms that lead to the coexistence of bacteria and virulent phage in environments where there are no spatial refuges available to the bacteria population.     

Analysis of a model of a vertically transmitted disease

A model is presented of a disease that can be transmitted directly from parent to offspring (vertical transmission) as well as through contact with infectives. A global stability analysis is given for the basic model and the epidemiological effects of vertical transmission are discussed. The effects of the addition of maturation and incubation delays as well as spatial diffusion are analyzed in some special cases.     

Terminology of a computer network: notes of a non-epidemiologist

In the development of discussion on epidemiological terms containing definitions "epidemic" and "epidemiological" variants of these terms as used in electronic documents placed on Internet sites are considered. Both most common combinations and contradictions in the use of some terminological constructions are presented.     

Dynamics of a neural system with a multiscale architecture

The architecture of the brain is characterized by a modular organization repeated across a hierarchy of spatial scales-neurons, minicolumns, cortical columns, functional brain regions, and so on. It is important to consider that the processes governing neural dynamics at any given scale are not only determined by the behaviour of other neural structures at that scale, but also by the emergent behaviour of smaller scales, and the constraining influence of activity at larger scales. In this paper, we introduce a theoretical framework for neural systems in which the dynamics are nested within a multiscale architecture. In essence, the dynamics at each scale are determined by a coupled ensemble of nonlinear oscillators, which embody the principle scale-specific neurobiological processes. The dynamics at larger scales are 'slaved' to the emergent behaviour of smaller scales through a coupling function that depends on a multiscale wavelet decomposition. The approach is first explicated mathematically. Numerical examples are then given to illustrate phenomena such as between-scale bifurcations, and how synchronization in small-scale structures influences the dynamics in larger structures in an intuitive manner that cannot be captured by existing modelling approaches. A framework for relating the dynamical behaviour of the system to measured observables is presented and further extensions to capture wave phenomena and mode coupling are suggested.     

A Comparison Between a Parametric and a Non-Parametric Method of Estimating the Percentiles of a Difference

A parametric and a nonparametric method of estimating the percentiles of a difference are compared. The parametric method assumes an underlying normal distribution and the nonparametric method estimates the distribution from the residuals. Applications to immunology are discussed.     

Identification of a SmD3 epitope with a single symmetrical dimethylation of an arginine residue as a specific target of a subpopulation of anti-Sm antibodies

Anti-Sm antibodies, identified in 1966 by Tan and Kunkel, are highly specific serological markers for systemic lupus erythrematosus (SLE). Anti-Sm reactivity is found in 5-30% of SLE patients, depending on the autoantibody detection system and the racial background of the SLE population. The Sm autoantigen complex comprises at least nine different polypeptides. All of these core proteins can serve as targets of the anti-Sm B-cell response, but most frequently the B and D polypeptides are involved. Because the BB'Sm proteins share cross-reactive epitopes (PPPGMRPP) with U1 specific ribonucleoproteins, which are more frequently targeted by antibodies that are present in patients with mixed connective tissue disease, the SmD polypeptides are regarded as the Sm autoantigens that are most specific to SLE. It was recently shown that the polypeptides D1, D3 and BB' contain symmetrical dimethylarginine, which is a component of a major autoepitope within the carboxyl-terminus of SmD1. In one of those studies, a synthetic dimethylated peptide of SmD1 (amino acids 95-119) exhibited significantly increased immunoreactivity as compared with unmodified SmD1 peptide. Using immobilized peptides, we confirmed that the dimethylated arginine residues play an essential role in the formation of major SmD1 and SmD3 autoepitopes. Moreover, we demonstrated that one particular peptide of SmD3 represents a more sensitive and more reliable substrate for the detection of a subclass of anti-Sm antibodies. Twenty-eight out of 176 (15.9%) SLE patients but only one out of 449 (0.2%) control individuals tested positive for the anti-SmD3 peptide (SMP) antibodies in a new ELISA system. These data indicate that anti-SMP antibodies are exclusively present in sera from SLE patients. Thus, anti-SMP detection using ELISA represents a new serological marker with which to diagnose and discriminate between systemic autoimmune disorders.     

Identification of miRNAs in a Liver of a Human Fetus by a Modified Method

Background

miRNAs are 17–25 nucleotides long RNA molecules that have been found to regulate gene expression in human cells. There are studies showing that different groups of miRNAs are involved in development of different tissues. In hepatocytes there are reported particular types of miRNAs that regulate gene expression.

Methods

We established a human fetal liver cDNA library by a modified cloning protocol. Then plasmid isolation from the colonies was performed. After sequencing and database searching, the miRNAs were recognized. RT-PCR and sequencing were carried out to validate the miRNAs detected. Real-time PCR was used to analyze the expression of each miRNA.

Results

One novel miRNA was discovered, together with another 35 previously-known miRNAs in the fetal liver. Some of them existed in variants. The miRNAs identified were validated by RT-PCR and sequencing. Quantitative analysis showed that they have variable expression.

Conclusion

Our results indicate that a special group of miRNAs may play an important role in fetal liver development in a synergistic manner.     

On the propagation of a disturbance through a viscous liquid flowing in a distensible tube of appreciable mass

The velocity of propagation of a disturbance wave in a liquid flowing in a distensible tube is computed. The mathematical model is more general than those used in previous analyses: the tube wall properties are realistic; the convective part of the axial inertia forces is taken into account; radial inertia forces of both the fluid and tube wall are present; viscous stresses are present. Four parameters influencing the velocity of propagation are obtained and discussed. Curves are plotted illustrating the effects of the parameters. Contrary to the results of previous analyses, viscous effects are shown to be appreciable in blood flow. It is also shown that radial inertia effects can be important in laboratory set-ups. The material presented in this paper was adapted from the Ph.D. thesis written by the author at Harvard University.     

Identification of a SmD3 epitope with a single symmetrical dimethylation of an arginine residue as a specific target of a subpopulation of anti-Sm antibodies

Anti-Sm antibodies, identified in 1966 by Tan and Kunkel, are highly specific serological markers for systemic lupus erythrematosus (SLE). Anti-Sm reactivity is found in 5–30% of SLE patients, depending on the autoantibody detection system and the racial background of the SLE population. The Sm autoantigen complex comprises at least nine different polypeptides. All of these core proteins can serve as targets of the anti-Sm B-cell response, but most frequently the B and D polypeptides are involved. Because the BB'Sm proteins share cross-reactive epitopes (PPPGMRPP) with U1 specific ribonucleoproteins, which are more frequently targeted by antibodies that are present in patients with mixed connective tissue disease, the SmD polypeptides are regarded as the Sm autoantigens that are most specific to SLE. It was recently shown that the polypeptides D1, D3 and BB' contain symmetrical dimethylarginine, which is a component of a major autoepitope within the carboxyl-terminus of SmD1. In one of those studies, a synthetic dimethylated peptide of SmD1 (amino acids 95–119) exhibited significantly increased immunoreactivity as compared with unmodified SmD1 peptide. Using immobilized peptides, we confirmed that the dimethylated arginine residues play an essential role in the formation of major SmD1 and SmD3 autoepitopes. Moreover, we demonstrated that one particular peptide of SmD3 represents a more sensitive and more reliable substrate for the detection of a subclass of anti-Sm antibodies. Twenty-eight out of 176 (15.9%) SLE patients but only one out of 449 (0.2%) control individuals tested positive for the anti-SmD3 peptide (SMP) antibodies in a new ELISA system. These data indicate that anti-SMP antibodies are exclusively present in sera from SLE patients. Thus, anti-SMP detection using ELISA represents a new serological marker with which to diagnose and discriminate between systemic autoimmune disorders.     

The risk of a mosquito-borne infection in a heterogeneous environment

A common assumption about malaria, dengue, and other mosquito-borne infections is that the two main components of the risk of human infection—the rate at which people are bitten (human biting rate) and the proportion of mosquitoes that are infectious—are positively correlated. In fact, these two risk factors are generated by different processes and may be negatively correlated across space and time in heterogeneous environments. Uneven distribution of blood-meal hosts and larval habitat creates a spatial mosaic of demograPhic sources and sinks. Moreover, mosquito populations fluctuate temporally, forced by environmental variables such as rainfall, temperature, and humidity. These sources of spatial and temporal heterogeneity in the distribution of mosquito populations generate variability in the human biting rate, in the proportion of mosquitoes that are infectious, and in the risk of human infection. To understand how heterogeneity affects the epidemiology of mosquito-borne infections, we developed a set of simple models that incorporate heterogeneity in a stepwise fashion. These models predict that the human biting rate is highest shortly after the mosquito densities peak, near breeding sites where adult mosquitoes emerge, and around the edges of areas where humans are aggregated. In contrast, the proportion of mosquitoes that are infectious reflects the age structure of mosquito populations; it peaks where old mosquitoes are found, far from mosquito breeding habitat, and when mosquito population density is declining. Finally, we show that estimates for the average risk of infection that are based on the average entomological inoculation rate are strongly biased in heterogeneous environments.     

Comparison of a potentiometric and a micromechanical triglyceride biosensor

Sensitive biosensors for detection of triglyceride concentration are important. In this paper we report on two types of silicon based triglyceride sensors: an electrolyte-insulator-semiconductor capacitor (EISCAP) which is a potentiometric device and a polysilicon microcantilever. The detection principle for both sensors is based on the enzymatic hydrolysis of triglyceride though the sensing mechanisms are different: electronic for the EISCAP and mechanical for the microcantilever. The characteristics and performances of the two sensors are critically compared. The EISCAP sensor necessitates the presence of a buffer for stable measurements which limits the sensitivity of the sensor at low concentrations of the bioanalyte to 1mM. The cantilever sensor works without a buffer which improves the lower level of sensitivity to 10 microm. Both sensors are found to give reproducible and reliable results.     

Dynamics of a mutualism in a multi-species context

Despite recent findings that mutualistic interactions between two species may be greatly affected by species external to the mutualism, the implications of such multi-species interactions for the population dynamics of the mutualists are virtually unexplored. In this paper, we ask how the mutualism between the shoot-base boring weevil Apion onopordi and the rust fungus Puccinia punctiformis is influenced by the dynamics of their shared host plant Cirsium arvense, and vice versa. In particular, we hypothesized that the distribution of the weevil's egg load between healthy and rust-infected thistles may regulate the abundance of the mutualists and their host plant. In contrast to our expectations we found that the dynamics of the mutualists are largely determined by the dynamics of their host. This is, to our knowledge, the first demonstration that the dynamics of a mutualism are driven by a third, non-mutualistic species.     

Genetic Structure of a Population Occupying a Circular Habitat

The geographical structure of a finite population distributed continuously and homogeneously along a circular habit is explored. Selection is supposed to be absent, and the analysis is restricted to a single locus with discrete, non-overlapping generations. Assuming every mutant is new to the population, the rate of decay of genetic variability is obtained, and the probability that two homologous genes separated by a given distance are different alleles is calculated. If moments of the migration function higher than second are neglected, the eigenvalue equation is shown to be a simple trigonometric one, and the Fourier series giving the transient and stationary probabilities of allelism are summed in terms of elementary functions. The proportion of homozygotes, the effective number of alleles maintained in the population, and the amount of local differentiation of gene frequencies are discussed.     

Phase diagrams for a model of a lipid monolayer

A microscopic model of a lipid monolayer is proposed. It includes, within a single scheme, the following factors which are considered to be essential in phase transitions in lipid systems: formation of gauche rotamers, interactions between polar heads, interactions between hydrocarbon chains (depending on their conformation) and changes in the energy of the system due to a directional ordering of the chains. Phase diagrams are constructed and discussed and it is shown how the phase diagrams are modified by alterations of these parameters and the length of the hydrocarbon chains.     

Scraping a living: a review of littorinid grazing

Littorinid snails are predominantly herbivorous and the versatility of their radulae enables them to feed on a variety of macroscopic and microscopic plants in a diversity of habitats. Some are selective feeders preferring some species of algae to others, and rejecting some even after a prolonged period of starvation. Different species of snail exhibit different preferences. The factors affecting the attractiveness and edibility of food plants are discussed and food value considered.Foraging behaviour of littorinids is briefly reviewed in relation to the influence of chemical cues from the algae. Littorinids appear to be able to select or reject algae without having ingested them, having perceived the plants from a distance, moving towards favoured foods (or habitat-providing plants) and away from those that it rejects. The nature of the chemical cues emitted by the algae is discussed. Temporal patterns of foraging activity show some evidence of an endogenous component which can be overridden by responses to environmental conditions. These patterns place restraints on energy intake.The structural and chemical defences used by algae against littorinid grazing are considered. The importance of polyphenolic compounds is evaluated. The effects of grazing as a selective agency and a factor influencing algal populations are discussed. There is some evidence that life history patterns are a response to grazing. The influence of external physical factors, such as salinity on grazing pressure is demonstrated.Finally, the impact of littorinid snails on intertidal communities is assessed in relation to their abundance and biogeographical distribution. The relative importance of littorinids is contrasted on shores possessing or lacking limpets.     

Elimination of a group II intron from a plastid gene causes a mutant phenotype

Group II introns are found in bacteria and cell organelles (plastids, mitochondria) and are thought to represent the evolutionary ancestors of spliceosomal introns. It is generally believed that group II introns are selfish genetic elements that do not have any function. Here, we have scrutinized this assumption by analyzing two group II introns that interrupt a plastid gene (ycf3) involved in photosystem assembly. Using stable transformation of the plastid genome, we have generated mutant plants that lack either intron 1 or intron 2 or both. Interestingly, the deletion of intron 1 caused a strong mutant phenotype. We show that the mutants are deficient in photosystem I and that this deficiency is directly related to impaired ycf3 function. We further show that, upon deletion of intron 1, the splicing of intron 2 is strongly inhibited. Our data demonstrate that (i) the loss of a group II intron is not necessarily phenotypically neutral and (ii) the splicing of one intron can depend on the presence of another.