Functional Differences Among Benthic Macroinvertebrate Communities in Reference Streams of Same Order in a Given Biogeographic Area

Ecological theory (Southwood, 1977. Journal of Animal Ecology 46: 337–365, 1988. Oikos 52: 3–18; Townsend, 1989. Journal of the North American Benthological Society 8: 36–50; Townsend & Hildrew, 1994. Freshwater Biology 31: 265–275) considers that spatio-temporal variations in habitats act as evolutionary forces on organisms, selecting for traits that maximize fitness. As a consequence, communities developed under same environmental conditions should present the same combination of species bio-ecological characteristics. The objective was to verify, using data from the same biogeographical zone, (1) if there was a unique suite of bio-ecological profiles for reference macrobenthic communities of `comparable' rivers or (2) if the distribution of bio-ecological traits within reference communities was significantly influenced by geology. The variability of 22 bio-ecological traits in 12 different sites was tested to evaluate the potential influence of geological substrate on biological and ecological features of reference stream communities. Observed patterns suggested that communities displayed highly stable bio-ecological profiles among sites (within a given biogeographical zone) whatever the substrate was, even if communities on clayey substrate exhibited slightly different bio/ecological characteristics than on others geologies. Nevertheless, the functional structure of macrobenthic communities in reference sites was quite stable in this biogeographical area. This study was restricted to the selected stream types and its results may not directly be transferred to other biogeographical areas and stream types. However, the perspective of a unique functional reference for streams of the same order in a given biogeographical area, improve functional comparison between observed vs. reference communities. This could simplify and objectively define the ecological status of a given site.     

Influence of chain length and polymer concentration on the gelation of (amidated) low-methoxyl pectin induced by calcium

The gelation of low-methoxyl pectin (LMP) induced by addition of Ca2+ was studied by measuring the storage modulus as a function of temperature during cooling. Samples with different molar masses were prepared by mechanical degradation. The effect of the molar mass and the pectin concentration on the gelation properties was investigated. The effect of partial amidation was studied by comparing LMP and partially amidated LMP with the same molar mass and degree of methylation. The results are compared to those from a model developed for Ca2+-induced pectin gelation, and good agreement is found except at low concentrations and low molar masses where the gels are weaker than predicted. At low concentrations intrachain bonding weakens the gel, while the presence of small pectin chains weakens the gel because it neutralizes binding sites on larger chains.     

The endoproteolytic processing of alphavbeta5 integrin is involved in cytoskeleton remodelling and cell migration

We previously showed that the post-translational cleavage of alphav subunit is essential for integrin-dependent signalling and cell adhesion. Here, we report that blocking alphav subunit cleavage by expression of alpha1-PDX, a convertase inhibitor, modified the capacity of cells to change shape, via a remodelling of the actin cytoskeleton upon cell attachment. These changes are associated with cell scattering and with a dramatic increase in cell migration to vitronectin. The alphav subunit cleavage is thus essential for integrin function and has a considerable impact on integrin-dependent events, especially those leading to cell migration.     

Acetyl:succinate CoA-transferase in procyclic Trypanosoma brucei. Gene identification and role in carbohydrate metabolism

Acetyl:succinate CoA-transferase (ASCT) is an acetate-producing enzyme shared by hydrogenosomes, mitochondria of trypanosomatids, and anaerobically functioning mitochondria. The gene encoding ASCT in the protozoan parasite Trypanosoma brucei was identified as a new member of the CoA transferase family. Its assignment to ASCT activity was confirmed by 1) a quantitative correlation of protein expression and activity upon RNA interference-mediated repression, 2) the absence of activity in homozygous Deltaasct/Deltaasct knock out cells, 3) mitochondrial colocalization of protein and activity, 4) increased activity and acetate excretion upon transgenic overexpression, and 5) depletion of ASCT activity from lysates upon immunoprecipitation. Genetic ablation of ASCT produced a severe growth phenotype, increased glucose consumption, and excretion of beta-hydroxybutyrate and pyruvate, indicating accumulation of acetyl-CoA. Analysis of the excreted end products of (13)C-enriched and (14)C-labeled glucose metabolism showed that acetate excretion was only slightly reduced. Adaptation to ASCT deficiency, however, was an infrequent event at the population level, indicating the importance of this enzyme. These studies show that ASCT is indeed involved in acetate production, but is not essential, as apparently it is not the only enzyme that produces acetate in T. brucei.     

Biochemical and spectroscopic characterization of the covalent binding of heme to cytochrome b6

The three-dimensional structure of the cytochrome b(6)f complex disclosed the unexpected presence of a new heme c(i) [Stroebel, D., Choquet, Y., Popot, J.-L., and Picot, D. (2003) Nature 426, 413-418; Kurisu, G., Zhang, H., Smith, J. L., and Cramer, W. A. (2003) Science 302, 1009-1014]. Here we present a biochemical, spectroscopic, and mutagenesis study of this unusual heme binding in Chlamydomonas reinhardtii. As predicted by the structure data, we identify a Cys(35)-containing proteolytic fragment (Tyr(25)-Lys(111)) from cytochrome b(6) as a peptide that covalently binds a heme. Resonance Raman spectra of cyt b(6)f complexes show particular frequencies in nu(2), nu(3), nu(4), and nu(8) regions that identify this extra heme as a ferrous c'-like heme under a five-coordinated high-spin state. The set of frequencies is consistent with a coordination by either a water molecule or a hydroxide ion. Other changes in resonance Raman bands, observed in the mid- and low-frequency regions, point to a modification in conformation and/or environment of at least one b heme methyl and/or propionate group. Site-directed mutagenesis of apocytochrome b(6), leading to a Cys(35)Val substitution, generates Chlamydomonas strains that are unable to assemble cytochrome b(6)f complexes. On the basis of the mutant phenotype, we discuss the participation, in the covalent binding of heme c(i), of the nuclear CCB factors that we identified previously as controlling the apo to holo conversion of cytochrome b(6) [Kuras, R., de Vitry, C., Choquet, Y., Girard-Bascou, J., Culler, D., Büschlen, S., Merchant, S., and Wollman, F.-A. (1997) J. Biol. Chem. 272, 32427-32435].     

Intracellular trafficking of Gag and Env proteins and their interactions modulate pseudotyping of retroviruses

Glycoproteins derived from most retroviruses and from several families of enveloped viruses can form infectious pseudotypes with murine leukemia virus (MLV) and lentiviral core particles, like the MLV envelope glycoproteins (Env) that are incorporated on either virus type. However, coexpression of a given glycoprotein with heterologous core proteins does not always give rise to highly infectious viral particles, and restrictions on pseudotype formation have been reported. To understand the mechanisms that control the recruitment of viral surface glycoproteins on lentiviral and retroviral cores, we exploited the fact that the feline endogenous retrovirus RD114 glycoprotein does not efficiently pseudotype lentiviral cores derived from simian immunodeficiency virus, whereas it is readily incorporated onto MLV particles. Our results indicate that recruitment of glycoproteins by the MLV and lentiviral core proteins occurs in intracellular compartments and not at the cell surface. We found that Env and core protein colocalization in intracytoplasmic vesicles is required for pseudotype formation. By investigating MLV/RD114 Env chimeras, we show that signals in the cytoplasmic tail of either glycoprotein differentially influenced their intracellular localization; that of MLV allows endosomal localization and hence recruitment by both lentiviral and MLV cores. Furthermore, we found that upon membrane binding, MLV core proteins could relocalize Env glycoproteins in late endosomes and allow their incorporation on viral particles. Thus, intracellular colocalization, as well as interactions between Env and core proteins, may influence the recruitment of the glycoprotein onto viral particles and generate infectious pseudotyped viruses.     

Expression and function of NPSR1/GPRA in the lung before and after induction of asthma-like disease

A genetic contribution to asthma susceptibility is well recognized, and linkage studies have identified a large number of genes associated with asthma pathogenesis. Recently, a locus encoding a seven-transmembrane protein was shown to be associated with asthma in founder populations. The expression of the protein GPRA (G protein-coupled receptor for asthma susceptibility) in human airway epithelia and smooth muscle, and its increased expression in a mouse model of asthma, suggested that a gain-of-function mutation in this gene increased the disease risk. However, we report here that the development of allergic lung disease in GPRA-deficient mice is unaltered. A possible explanation for this finding became apparent upon reexamination of the expression of this gene. In contrast to initial studies, our analyses failed to detect expression of GPRA in human lung tissue or in mice with allergic lung disease. We identify a single parameter that distinguishes GPRA-deficient and wild-type mice. Whereas the change in airway resistance in response to methacholine was identical in control and GPRA-deficient mice, the mutant animals showed an attenuated response to thromboxane, a cholinergic receptor-dependent bronchoconstricting agent. Together, our studies fail to support a direct contribution of GPRA to asthma pathogenesis. However, our data suggest that GPRA may contribute to the asthmatic phenotype by altering the activity of other pathways, such as neurally mediated mechanisms, that contribute to disease. This interpretation is supported by high levels of GPRA expression in the brain and its recent identification as the neuropeptide S receptor.