Interactions between ant species increase arrival rates of an ant parasitoid

Behaviours or traits associated with aggression and communication may increase an animal's conspicuousness to predators or parasitoids. Most examples of this come from instances of aggression or communication within a species. We tested whether interspecific encounters between ants enhance the host location success of a parasitoid (Diptera: Phoridae) that attacks ants in the genus Linepithema. At food resources recruited to by Linepithema, parasitoid discovery rates were lower when Linepithema was alone than when other ant species were present. In experimentally controlled encounters, parasitoid discovery rates were elevated when Linepithema confronted an ant species that elicited use of chemicals, but not when it confronted an ant species that primarily elicited physical aggression. These results indicate that phorid parasitoids of Linepithema use the ant's chemicals as host location cues. Because Linepithema is known to abandon food resources in the presence of its phorid parasitoids, its use of chemicals during interspecific encounters may diminish its competitive success when phorids are nearby. Copyright 2003 Published by Elsevier Science Ltd on behalf of The Association for the Study of Animal Behaviour.      

Erythroid differentiation and regulatory gene expression are modulated by adenosine derivatives interfering with S-adenosylmethionine metabolic pathway

The differentiation of murine erythroleukemia cells and the expression of SCL, Id1 and c-myc regulatory genes were studied. The first gene is a positive regulator of differentiation, while the other two are both negative regulators of differentiation and positive regulators of proliferation. Accordingly, our data show that when differentiation is stimulated SCL is upregulated while Id1 and c-myc are, coordinately, downregulated. The cultures were treated with two adenosine derivatives, 3-deazaadenosine and 3-deazaaristeromycin, known to act on the metabolic pathway of the methyl donor S-adenosylmethionin, in order to assess the possibility of a coordinated modulation, by these drugs, of regulatory gene expression and erythroid cell differentiation. 3-Deazaaristeromycin caused the simultaneous downregulation of Id1 and c-myc, whereas 3-deazaadenosine caused their upregulation; both drugs produced a transient increase in SCL expression. The use of these drugs evidenced a predominant regulatory effect of negative regulators in the control of erythroid differentiation. The distinct effects of the two drugs on regulatory gene expression led to an increased differentiation induced by 3-deazaaristeromycin and to a reduced differentiation induced by 3-deazaadenosine, if compared with controls. Southern analysis of DNA digested with methylation-specific restriction endonucleases showed that the administration of 3-deazaaristeromycin resulted in hypomethylation of SCL and c-myc, thus evidencing, in these cells, a clear correlation between DNA hypomethylation and differentiation but no straightforward correlation between DNA methylation and gene expression.     

A direct pyrophosphatase-coupled assay provides new insights into the activation of the secreted adenylate cyclase from Bordetella pertussis by calmodulin

Continuous recording of the activity of recombinant adenylate cyclase (CyaA) of Bordetella pertussis (EC ) by conductimetric determination of enzyme-coupled pyrophosphate cleavage has enabled us to define a number of novel features of the activation of this enzyme by calmodulin and establish conditions under which valid activation data can be obtained. Activation either in the presence or absence of calcium is characterized by a concentration-dependent lag phase. The rate of formation and breakdown of the activated complex can be determined from an analysis of the lag phase kinetics and is in good agreement with thermodynamic data obtained by measuring the dependence of activation on calmodulin concentration, which show that calcium increases k(on) by about 30-fold. The rate of breakdown of the activated complex, formed either in the presence or absence of calcium, has been determined by dilution experiments and has been shown to be independent of the presence of calcium. The coupled assay is established as a rapid, convenient and safe method which should be readily applicable to the continuous assays of most other enzymes that catalyze reactions in which inorganic pyrophosphate is liberated.     

A long CAG repeat in the mouse Sca1 locus replicates SCA1 features and reveals the impact of protein solubility on selective neurodegeneration

A single nicotine exposure increases dopamine levels in the mesolimbic reward system for hours, but nicotine concentrations experienced by smokers desensitize nAChRs on dopamine neurons in seconds to minutes. Here, we show that persistent modulation of both GABAergic and glutamatergic synaptic transmission by nicotine can contribute to the sustained increase in dopamine neuron excitability. Nicotine enhances GABAergic transmission transiently, which is followed by a persistent depression of these inhibitory inputs due to nAChR desensitization. Simultaneously, nicotine enhances glutamatergic transmission through nAChRs that desensitize less than those on GABA neurons. The net effect is a shift toward excitation of the dopamine reward system. These results suggest that spatial and temporal differences in nicotinic receptor activity on both excitatory and inhibitory neurons in reward areas coordinate to reinforce nicotine self-administration.     

Bradykinins and their precursor cDNAs from the skin of the fire-bellied toad (Bombina orientalis)

Bradykinin and (Thr(6))-bradykinin have been identified in the defensive skin secretion of the fire-bellied toad, Bombina orientalis. The homologous cDNAs for both peptides were cloned from a skin library using a 3'- and 5'-RACE strategy. Kininogen-1 (BOK-1) contained an open-reading frame of 167 amino acid residues encoding four repeats of bradykinin, and kininogen-2 (BOK-2) contained an open-reading frame of 161 amino acid residues encoding two repeats of (Thr(6))-bradykinin. Alignment of both precursor nucleotide and amino acid sequences revealed a high degree of structural similarity. These amphibian skin kininogens/preprobradykinins are not biologically analogous to mammalian kininogens.     

Detection of isoniazid and rifampin resistance in Mycobacterium tuberculosis strains by single-strand conformation polymorphism analysis and restriction fragment length polymorphism

Anti-Mycobacterium tuberculosis drug-resistance, mainly multi-drug resistance (MDR-TB), represents an important public health problem in several countries. Aim of our study is to identify the presence of these mutations in M. tuberculosis isoniazid- and rifampin-resistant strains isolated in our Institute; to evaluate linkage between type of mutation and level of resistance; to determine the usefulness of easy molecular techniques for rapid detection of such mutations on body specimens. Isoniazid- and rifampin-resistance was tested on 67 M. tuberculosis strains by Single-Strand Conformation Polymorphism (SSCP) and Polymerase Chain Reaction-Restriction Fragment Length Polymorphism (PCR-RFLP) assays, using HaeIII, PstuI, BsteII, BstuI enzymes. Drug-resistance of control strains was determined by cultural techniques (fluorimetry- BACTEC 9120). Cultural assay showed isoniazid- and rifampin-resistance in 6.12 and 2%, respectively (data confirmed by SSCP assay). Mutation of katG, linked to isoniazid resistance, was detected using BstuI enzyme, and mutation of rpoB, expression of reduced sensitivity to rifampin, using HaeIII. 15 body specimens, M. tuberculosis-positive to conventional assays, were tested by SSCP technique. Epidemiologic reports of numerous cases of tuberculosis due to MDR strains induce to detect quickly both Mycobacteria and drug-resistance, in order to start prompt effective therapy. On this basis, molecular assays are useful for a rapid therapeutic decision.     

An estimate of the fraction of belugas (<Emphasis Type="Italic">Delphinapterus leucas</Emphasis>) in the Canadian high Arctic that winter in West Greenland

Five belugas, or white whales (Delphinapterus leucas), were tracked by satellite from Creswell Bay, Somerset Island, in the Canadian high Arctic towards West Greenland in autumn 2001. After 1 October, three of the whales stayed in the North Water polynya and the other two whales moved to West Greenland. One of the whales that moved to Greenland migrated south along the west coast, following a route and timing similar to another beluga tracked in 1996. The belugas that moved towards West Greenland from Canada did so before or near 1 October. The movements of both these whales followed a similar timing and assumed migratory route of belugas hunted in autumn in West Greenland. In Greenland, the hunt begins in September, where the first whales are taken in the northernmost community of Qaanaaq. Hunting takes place farther south in Upernavik in October, and finally in November and December, belugas are taken even farther south in Uummannaq and Disko Bay. The whales that remain in the North Water after 1 October most likely do not contribute to the harvest in West Greenland. Based on the total number of belugas satellite-tracked in Canada between 1995 and 2001 with tags that lasted beyond 1 October, approximately 0.15 (95% CI 0.06-0.35; n=26) of the summering stock of belugas in the Canadian high Arctic move to West Greenland for the winter. Genetic studies have indicated that belugas moving east through Lancaster Sound are significantly differentiated from belugas taken in the autumn hunt in West Greenland. These conflicting results suggest molecular genetics cannot be solely relied on to reveal the stock identity of these belugas.     

Rapid method for measuring ScFv thermal stability by yeast surface display

We have characterized a simplified method to determine the relative thermal stability of single-chain antibodies by following the irreversible denaturation of scFv fusions on the surface of yeast by flow cytometry. The method was highly reproducible and correlated well with other methods used to monitor thermal denaturation of the soluble proteins. We found a range of thermal stabilities for wild-type single-chain antibodies with half-maximum denaturation temperatures between 43 and 61 degrees C. The ability to quantitate thermal stability of antibodies or other proteins that are immobilized on the surface of yeast allows rapid comparisons of primary structural information with stability. Thermal denaturation could be a useful parameter to consider in the choice of scFv fragments for various applications.