A model of bacterial intestinal infections in Drosophila melanogaster

Serratia marcescens is an entomopathogenic bacterium that opportunistically infects a wide range of hosts, including humans. In a model of septic injury, if directly introduced into the body cavity of Drosophila, this pathogen is insensitive to the host's systemic immune response and kills flies in a day. We find that S. marcescens resistance to the Drosophila immune deficiency (imd)-mediated humoral response requires the bacterial lipopolysaccharide O-antigen. If ingested by Drosophila, bacteria cross the gut and penetrate the body cavity. During this passage, the bacteria can be observed within the cells of the intestinal epithelium. In such an oral infection model, the flies succumb to infection only after 6 days. We demonstrate that two complementary host defense mechanisms act together against such food-borne infection: an antimicrobial response in the intestine that is regulated by the imd pathway and phagocytosis by hemocytes of bacteria that have escaped into the hemolymph. Interestingly, bacteria present in the hemolymph elicit a systemic immune response only when phagocytosis is blocked. Our observations support a model wherein peptidoglycan fragments released during bacterial growth activate the imd pathway and do not back a proposed role for phagocytosis in the immune activation of the fat body. Thanks to the genetic tools available in both host and pathogen, the molecular dissection of the interactions between S. marcescens and Drosophila will provide a useful paradigm for deciphering intestinal pathogenesis.     

Effect of trehalose on a phospholipid membrane under mechanical stress

Explicit solvent molecular dynamics simulations were used to investigate at atomic resolution the effect of trehalose on a hydrated phospholipid bilayer under mechanical stress (stretching forces imposed in the form of negative lateral pressure). Simulations were performed in the absence or presence of trehalose at 325 K, and with different values for negative lateral pressure. In the concentration regime (2 molal) and range of lateral pressures (1 to −250 bar) investigated, trehalose was found to interact directly with the membrane, partially replacing water molecules in the formation of hydrogen bonds with the lipid headgroups. Similar to previous findings in the context of thermal stress, the number, degree of bridging, and reaching depth of these hydrogen bonds increased with the magnitude of perturbation. However, at the concentration considered, trehalose was not sufficient to preserve the integrity of the membrane structure and to prevent its extreme elongation (and possible disruption) under the effect of stretching forces.     

Influence of exogenous abscisic acid on germination and plantlet conversion frequencies of hybrid larch somatic embryos (Larix × leptoeuropaea)

The effect of exogenous abscisic acid, provided to somatic embryos during the maturation step, on endogenous abscisic acid and its main conjugated form (abscisic acid glucose ester), germination and conversion frequencies is presented in this paper. Abscisic acid measurements were obtained after a methanolic extraction, a fractionation through high performance liquid chromatography, quantitation with an immunoassay and identification of the quantitated compound using gas chromatography-mass spectrometry. Results show that endogenous abscisic acid and abscisic acid glucose ester levels are clearly correlated with the exogenous abscisic acid concentration provided to the embryos. Maturation was clearly enhanced by exogenous abscisic acid, but no correlation was found between abscisic acid concentration and germination frequency. Conversely, development of the aerial part of the germinated somatic embryos was dependent upon the abscisic acid concentration in the culture medium and results suggest that this dependence could be related to the endogenous abscisic acid content.     

Autocrine activation of adenosine A1 receptors blocks D1A but not D1B dopamine receptor desensitization

Adenosine is known to modulate dopamine responses in several brain areas. Here, we show that tonic activation of adenosine receptors is able to impede desensitization of D1 dopamine receptors. As measured by cAMP accumulation in transfected COS-7 cells, long-term exposure to dopamine agonists promoted desensitization of D1B receptor but not that of D1A receptor. The inability of D1A receptor to desensitize was a result of the adenosine present in culture medium acting through activation of adenosine A1 receptors. Cell incubation with either adenosine deaminase, CGS-15943, a generic adenosine receptor antagonist, or the A1 antagonist DPCPX restored the long-term desensitization time-course of D1A receptors. In Ltk cells stably expressing A1 adenosine receptors and D1A dopamine receptors, pre-treatment of cells with R(-)-PIA, a full A1 receptor agonist, did not significantly inhibit the acute increase in cAMP levels induced by D1 receptor agonists, but blocked desensitization of D1A receptors. However, simultaneous activation of A1 and D1A receptors promoted a delayed D1A receptor desensitization. This suggests that functional interaction between A1 and D1A receptors may depend on the activation kinetics of components regulating D1 receptor responses, acting differentially on D1A and D1B receptors.     

Brachypodium distachyon: making hay with a wild grass

Brachypodium distachyon is a wild grass with a short life cycle. Although it is related to small grain cereals such as wheat, its genome is only a fraction of the size. A draft genome sequence is currently available, and molecular and genetic tools have been developed for transformation, mutagenesis and gene mapping. Accessions collected from across its ancestral range show a surprising degree of phenotypic variation in many traits, including those implicated in domestication of the cereals. Thus, given its rapid cycling time and ease of cultivation, Brachypodium will be a useful model for investigating problems in grass biology.     

Nuclear Localization Signals Enhance Germline Transmission of a Transgene in Zebrafish

We report that cytoplasmic injection into zebrafish eggs of 104 copies of plasmid DNA complexed to nuclear localization signal (NLS) peptides, as compared to 106 copies of naked DNA, increased nuclear uptake of transgene DNA early during embryo development and enhanced transgene integration frequency into the germline of founders. Monitoring the dynamics of nuclear uptake of DNA-NLS complexes by fluorescence in situ hybridization (FISH) of interphase nuclei indicates that NLS enhances both the proportion of nuclei importing DNA during early embryo development, and the amount of DNA imported by individual nuclei. The use of NLS increases the proportion of germline transgenic founders from 14 to 43% (P < 0.01) as assessed by polymerase chain reaction analysis of F1s. From germline transgenic DNA-NLS-injected founders, 47% transgenic F1s are obtained in wild-type crosses, as opposed to 6% from naked DNA-injec...     

In vivo simulation of human pharmacokinetics in the rabbit

The evaluation of drugs in vivo is often based on experimental models using small animals such as mice, rats and rabbits. However, these models could be improved to correspond more closely to the human situation if the pharmacokinetics of the drugs tested in animals were similar to that observed in humans. The use of a computer-controlled pump allowing an adequate flow of tobramycin and amikacin to be infused into rabbits enabled us to simulate the human pharmacokinetics of these antibiotics in vivo in this study. The function defining the rate of infusion required to perform the simulation of an intravenous bolus was first determined generally and symbolically for linear pharmacokinetic models independently from the number of compartments involved. The practical simulation of a decreasing monoexponential serum profile with a half-life of 2 h (one-compartment model for the human pharmacokinetics of aminoglycosides) was then studied for tobramycin and amikacin on the basis of a two-compartment model in the animal. The kinetics obtained had an apparent elimination half-life of 1.97 and 1.86 h, respectively. Linearity of the semilogarithmic regressions of the profiles obtained was quite sound. Finally, an a posteriori analysis of the pharmacokinetic model and its parameters is proposed on the basis of the results obtained after simulation.     

Effects of testosterone on Reelin expression in the brain of male European starlings

Reelin, a large glycoprotein defective in reeler mice, is assumed to determine the final location of migrating neurons in the developing brain. We studied the expression of Reelin in the brain of adult male European starlings that had been treated or not with exogenous testosterone. Reelin-immunoreactive cells and fibers were widely distributed in the forebrain including areas in and around the song control nucleus, HVC. No labeling was detected in other song control nuclei with the exception of nucleus uvaeformis, which was delineated by a dense cluster of Reelin-immunoreactive perikarya. Reelin is thus expressed in areas incorporating new neurons in adulthood, such as HVC. Reelin expression was sharply decreased by testosterone in HVC, nucleus uvaeformis and dorsal thalamus but not in other brain regions. These results are consistent with the idea that seasonal changes in Reelin expression modulate the incorporation of neurons within HVC. The presence of Reelin in other brain areas that do not incorporate new neurons in adulthood indicates, however, that this protein must play other unrelated roles in the adult brain. Additional studies should now be carried out to determine the specific role played by this protein in the seasonal plasticity of the songbird brain.