Cerebellar Granule Neurons are More Vulnerable to Transient Transport-Mediated Glutamate Release than to Glutamate Uptake Blockade. Correlation with Excitatory Amino Acids Levels

The extracellular concentration of glutamate is highly regulated due to its excitotoxic nature. Failure of glutamate uptake or reversed activation of its transporters contributes to neurodegeneration related to some pathological conditions. We have compared the neurotoxicity of the substrate glutamate uptake inhibitor, l-trans-pyrrolidine-2,4-dicarboxylate (PDC), which promotes glutamate release by heteroexchange, with that of DL-threo-beta-benzyloxyaspartate (DL-TBOA), a non-substrate inhibitor, in cerebellar granule cell cultures. PDC substantially increases the extracellular concentration of glutamate during 30 min exposure and causes neuronal death at high concentrations, while DL-TBOA neurotoxicity is only observed after long-term exposure (8–24 h). During mitochondrial inhibition by 3-nitropropionic acid (3-NP), PDC-induced neuronal death is facilitated, but not that of DL-TBOA. In cultures containing a higher population of astrocytes DL-TBOA-induced increase in glutamate levels is more pronounced, but neuronal death is only triggered in the presence of 3-NP. Results suggest that cerebellar granule neurons are more vulnerable to acute transport-mediated glutamate release than to uptake blockade, which correlates with the extracellular excitatory amino acids levels.     

Sequence evolution of the major satellite DNA of the genus Ctenomys (Octodontidae, Rodentia)

Sequence variability of RPCS (repetitive PuvII Ctenomys sequence), the major satellite DNA of octodontid Ctenomys rodents, was analysed in species belonging to three groups of species representing the two patterns of karyotypic evolution in the genus: stable and dynamic karyotypes among closely related species. The studied species represent the overall range of RPCS copy number (2000--6.6x10(6) copies per haploid genome) in the genus. RPCS sequence was characterised by PCR amplification of the genomic consensus sequence and cloned monomers. Our results suggest that RPCS genomic consensus sequence variability correlates with RPCS copy number stability and karyotypic stastis, but not with high or low RPCS copy number values. In contrast, the RPCS gcs shows a mutational profile that is similar across all analysed species. Our data suggest that an RPCS ancestral library of variants was maintained through the cladogenesis of the genus. There is also evidence pointing to the simultaneous contribution of processes of concerted evolution that resulted in a reduced representation of some ancestral variants and their partial replacement for new ones. In addition, analysis of distribution of the variability along the monomer suggests that subsequences of the RPCS are subject to some degree of constraint, probably driven by the recent replicative activity of RPCS in species with high copy number.     

Analysis of differentially expressed genes in response to bacterial stimulation in hemocytes of the carpet-shell clam Ruditapes decussatus: identification of new antimicrobial peptides

Suppression subtractive hybridization was used to identify differentially expressed genes in hemocytes from carpet-shell clam Ruditapes decussatus stimulated with a mixture of dead bacterial strains. Putative function could be assigned to 100 of the 253 sequenced cDNAs. Based on sequence homologies, 3.16% of the total identified genes were possibly related to immune functions. Clam myticin isoforms 1, 2 and 3, and clam mytilin, with similarity with myticins and mytilins previously reported on Mytilus galloprovincialis were identified and characterized for the first time in clams. The analysis of their expression levels by quantitative PCR showed that they were induced by bacterial challenge. The results obtained in this work could be the first step leading to the understanding of molecular mechanisms by which these economically important marine bivalves respond to pathogens.     

Spatial modelling of brief and long interactions between T cells and dendritic cells

In the early phases of an immune response, T cells of appropriate antigen specificity become activated by antigen-presenting cells in secondary lymphoid organs. Two-photon microscopy imaging experiments have shown that this stimulation occurs in distinct stages during which T cells exhibit different motilities and interactions with dendritic cells (DCs). In this paper, we utilize the Cellular Potts Model, a model formalism that takes cell shapes and cellular interactions explicitly into account, to simulate the dynamics of, and interactions between, T cells and DCs in the lymph node paracortex. Our three-dimensional simulations suggest that the initial decrease in T-cell motility after antigen appearance is due to "stop signals" transmitted by activated DCs to T cells. The long-lived interactions that occur at a later stage can only be explained by the presence of both stop signals and a high adhesion between specific T cells and antigen-bearing DCs. Furthermore, our results indicate that long-lasting contacts with T cells are promoted when DCs retract dendrites that detect a specific contact at lower velocities than other dendrites. Finally, by performing long simulations (after prior fitting to short time scale data) we are able to provide an estimate of the average contact duration between T cells and DCs.     

Sucrose-mediated priming of plant defense responses and broad-spectrum disease resistance by overexpression of the maize pathogenesis-related PRms protein in rice plants

Expression of pathogenesis-related (PR) genes is part of the plant's natural defense response against pathogen attack. The PRms gene encodes a fungal-inducible PR protein from maize. Here, we demonstrate that expression of PRms in transgenic rice confers broad-spectrum protection against pathogens, including fungal (Magnaporthe oryzae, Fusarium verticillioides, and Helminthosporium oryzae) and bacterial (Erwinia chrysanthemi) pathogens. The PRms-mediated disease resistance in rice plants is associated with an enhanced capacity to express and activate the natural plant defense mechanisms. Thus, PRms rice plants display a basal level of expression of endogenous defense genes in the absence of the pathogen. PRms plants also exhibit stronger and quicker defense responses during pathogen infection. We also have found that sucrose accumulates at higher levels in leaves of PRms plants. Sucrose responsiveness of rice defense genes correlates with the pathogen-responsive priming of their expression in PRms rice plants. Moreover, pretreatment of rice plants with sucrose enhances resistance to M. oryzae infection. Together, these results support a sucrose-mediated priming of defense responses in PRms rice plants which results in broad-spectrum disease resistance.     

Cytoprotective properties of alpha-tocopherol are related to gene regulation in cultured D-galactosamine-treated human hepatocytes

Vitamin E (alpha-tocopherol) has demonstrated antioxidant activity and gene-regulatory properties. d-Galactosamine (D-GalN)-induced cell death is mediated by nitric oxide in hepatocytes, and it is associated with hepatic steatosis. The beneficial properties of alpha-tocopherol and their relation to oxidative stress and gene regulation were assessed in D-GalN-induced cell death. Hepatocytes were isolated from human liver resections by a collagenase perfusion technique. alpha-Tocopherol (50 microM) was administered at the advanced stages (10 h) of D-GalN-induced cell death in cultured hepatocytes. Cell death, oxidative stress, alpha-tocopherol metabolism, and NF-kappaB-, pregnane X receptor (PXR)-, and peroxisome proliferator-activated receptor (PPAR-alpha)-associated gene regulation were estimated in the hepatocytes. D-GalN increased cell death and alpha-tocopherol metabolism. alpha-Tocopherol exerted a moderate beneficial effect against apoptosis and necrosis induced by D-GalN. Induction (rifampicin) or inhibition (ketoconazole) of alpha-tocopherol metabolism and overexpression of PXR showed that the increase in PXR-related CYP3A4 expression caused by alpha-tocopherol enhanced cell death in hepatocytes. Nevertheless, the reduction in NF-kappaB activation and inducible nitric oxide synthase expression and the enhancement of PPAR-alpha and carnitine palmitoyl transferase gene expression by alpha-tocopherol may be relevant for cell survival. In conclusion, the cytoprotective properties of alpha-tocopherol are mostly related to gene regulation rather than to antioxidant activity in toxin-induced cell death in hepatocytes.