Éditeur(s) : HAL CCSD Elsevier
Résumé : Understanding the pattern in spatial distribution of soil microbial processes is critical to understand the environmental factors that regulate them as well as to scale up these processes to ecosystem. Soil samples from a I ha tropical rainforest plot (Paracou, French Guiana) were analyzed according a nested sampling approach using different separation distances ranging from 0.4 to 40 m. The variability of substrate induced respiration (SIR) and of denitrification enzyme activity (DEA) was characterized in relation to various soil properties (total C and N contents, NIRS related index of soil organic matter quality, SOMQ and index of tree influence potential, IP). The variability of SIR and DEA was higher than that of environmental properties. The patterns of accumulated variance as a function of distance varied among the soil properties. The variability of SIR and DEA mainly occurred at small (1 m) scale (and at the 10-40 m-scales for SIR), probably reflecting the quality of litter input that results of the influence of local assemblage of different tree species, though changes in the soil N and C contents. Indeed, total soil C and N contents explained the microbial properties at every scale. Coefficients of codispersion showed that neither SOMQ nor IP did correlate with SIR and DEA, and confirmed that total C and N contents explained microbial properties in a scale dependent and complex manner. Such spatial dependency underlines the importance of soil heterogeneity in this tropical forest with implications for sampling strategies when studying the microbial processes and their response to disturbances. (C) 2012 Elsevier B.V. All rights reserved.
ISSN: 0016-7061

hal-01032409
https://hal.archives-ouvertes.fr/hal-01032409
DOI : 10.1016/j.geoderma.2012.12.009

Éditeur(s) : HAL CCSD
Résumé : Travaux Pratiques de Biochimie, IUT 2e année. Mise en place d'un réacteur enzymatique. Beta galactosidase. Transformation de l'oNPG en orthonitrophénol et galactose.
https://medihal.archives-ouvertes.fr/medihal-00459244
Terre Sainte, France

Droits : http://creativecommons.org/licenses/by-nc/
medihal-00459244
https://medihal.archives-ouvertes.fr/medihal-00459244
https://medihal.archives-ouvertes.fr/medihal-00459244/image
https://medihal.archives-ouvertes.fr/medihal-00459244/file/tp_biochimie_iut11.jpg

Éditeur(s) : HAL CCSD American Society for Biochemistry and Molecular Biology
Résumé : International audience
The budding yeast Saccharomyces cerevisiae is a major model organism for important biological processes such as mitotic growth and meiotic development, it can be a human pathogen, and it is widely used in the food-, and biotechnology industries. Consequently, the genomes of numerous strains have been sequenced and a very large amount of RNA profiling data is available. Moreover, it has recently become possible to quantitatively analyze the entire yeast proteome; however, efficient and cost-effective high-throughput protein profiling remains a challenge. We report here a new approach to direct and label-free large-scale yeast protein identification using a tandem buffer system for protein extraction, two-step protein prefractionation and enzymatic digestion, and detection of peptides by iterative mass spectrometry. Our profiling study of diploid cells undergoing rapid mitotic growth identified 86% of the known proteins and its output was found to be widely concordant with genome-wide mRNA concentrations and DNA variations between yeast strains. This paves the way for comprehensive and straightforward yeast proteome profiling across a wide variety of experimental conditions.
ISSN: 1535-9476

hal-00682837
https://hal.archives-ouvertes.fr/hal-00682837
DOI : 10.1074/mcp.M111.012682
PUBMED : 21997732

Éditeur(s) : HAL CCSD Nature Publishing Group
Résumé : International audience
The shallow water bivalve Codakia orbicularis lives in symbiotic association with a sulfur-oxidizing bacterium in its gills. The endosymbiont fixes CO2 and thus generates organic carbon compounds, which support the host's growth. To investigate the uncultured symbiont's metabolism and symbiont-host interactions in detail we conducted a proteogenomic analysis of purified bacteria. Unexpectedly, our results reveal a hitherto completely unrecognized feature of the C. orbicularis symbiont's physiology: the symbiont's genome encodes all proteins necessary for biological nitrogen fixation (diazotrophy). Expression of the respective genes under standard ambient conditions was confirmed by proteomics. Nitrogenase activity in the symbiont was also verified by enzyme activity assays. Phylogenetic analysis of the bacterial nitrogenase reductase NifH revealed the symbiont's close relationship to free-living nitrogen-fixing Proteobacteria from the seagrass sediment. The C. orbicularis symbiont, here tentatively named `Candidatus Thiodiazotropha endolucinida', may thus not only sustain the bivalve's carbon demands. C. orbicularis may also benefit from a steady supply of fixed nitrogen from its symbiont-a scenario that is unprecedented in comparable chemoautotrophic symbioses.
ISSN: 2058-5276

hal-01545904
https://hal.archives-ouvertes.fr/hal-01545904
DOI : 10.1038/nmicrobiol.2016.193

Résumé : Once fished, the shrimps must be cooled quickly in water cooled in order to slow down all chemical and bacteriological activities. In addition, in order to avoid blackening (mélanose) shrimps (céphalothorax and legs) it is necessary to treat those with an antioxydant product. The product currently used to inhibit this enzymatic change is the soda niétabisuifite (Na-> S7 O5), until now, after being fished. the shrimps were directly soaked in a cooled water tank, containing the pesticide. The solution of treatment was progressively prepared needs. The concentration of this one was approximately 2 to 3% of métabisulfite, that is to say 6 to 9 G of SO2 per liter for a starting product containing 320 G of SO2 approximately. In order to preserve a good quality of the liquid of treatment it was essential to often renew it (every 400 to 500 kg) what was not always the case, the métabisulfite being often added progressively with the liking of the appointed person with the treatment of shrimps. In order to cure this delicate problem of renewal of vat and uniformity of the treatment, the SODACAL obtained the system of treatment by sprinkling.
Une fois pêchées, les crevettes doivent être refroidies rapidement dans de l'eau réfrigérée afin de ralentir toutes activités chimiques et bactériologiques. D'autre part, afin d'éviter le noircissement (mélanose) des crevettes (céphalothorax et pattes) il est nécessaire de traiter celles-ci avec un produit anti-oxydant. Le produit actuellement utilisé pour inhiber cette altération enzymatique est le niétabisuifite de soude (Na-> S7 O5), jusqu'à maintenant, après avoir été pêchées. les crevettes étaient directement trempées dans une cuve d'eau réfrigérée, contenant le produit de traitement. La solution de traitement était préparée au fur et à mesure des besoins. La concentration de celle-ci était d'environ 2 à 3 % de métabisulfite, soit 6 à 9 g de SO2 par litre pour un produit de départ contenant 320 g de SO9 environ. Afin de conserver une bonne qualité du liquide de traitement il était indispensable de le renouveler souvent (tous les 400 à 500 kg) ce qui n'était pas toujours le cas, le métabisulfite étant souvent rajouté au fur et à mesure au gré de la personne préposée au traitement des crevettes. Afin de remédier à ce problème délicat de renouvellement de bac et d'uniformité du traitement, la SODACAL s'est dotée du système de traitement par aspersion.

Droits : info:eu-repo/semantics/openAccess
http://archimer.ifremer.fr/doc/1991/rapport-1648.pdf
http://archimer.ifremer.fr/doc/00000/1648/

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
The brain of the adult teleost fish exhibits intense neurogenic activity and an outstanding capability for brain repair. Remarkably, the brain estrogen-synthesizing enzyme, aromatase B, is strongly expressed, particularly in adult fishes, in radial glial cells, which act as progenitors. Using zebrafish, we tested the hypothesis that estrogens affect adult neurogenesis and brain regeneration by modulating the neurogenic activity of radial glial cells. To investigate this, the estrogenic environment was modified through inhibition of aromatase activity, blockade of nuclear estrogen receptors, or estrogenic treatments. Estrogens significantly decreased cell proliferation and migration at the olfactory bulbs/telencephalon junction and in the mediobasal hypothalamus. It also appears that cell survival is reduced at the olfactory bulbs/telencephalon junction. We also developed a model of telencephalic lesion to assess the role of aromatase and estrogens in brain repair. Proliferation increased rapidly immediately after the lesion in the parenchyma of the injured telencephalon, while proliferation at the ventricular surface appeared after 48 h and peaked at 7 days. At this time, most proliferative cells express Sox2, however, none of these Sox2 positive cells correspond to aromatase B-positive radial glial cells. Interestingly, aromatase B expression was significantly reduced 48 h and 7 days after the injury, but surprisingly, at 72 h after lesion, aromatase B expression appeared de novo expressed in parenchyma cells, suggesting a role for this ectopic expression of aromatase in brain repair mechanisms. Altogether these data suggest that estrogens modulate adult, but not reparative neurogenesis, in zebrafish.
ISSN: 0018-506X

inserm-00831715
http://www.hal.inserm.fr/inserm-00831715
DOI : 10.1016/j.yhbeh.2012.04.003
PUBMED : 22521210

Éditeur(s) : HAL CCSD
Résumé : Travaux Pratiques de Biochimie, IUT 2e année. Mise en place d'un réacteur enzymatique. Beta galactosidase. Transformation de l'oNPG en orthonitrophénol et galactose.
https://medihal.archives-ouvertes.fr/medihal-00459242
Terre Sainte, France

Droits : http://creativecommons.org/licenses/by-nc/
medihal-00459242
https://medihal.archives-ouvertes.fr/medihal-00459242
https://medihal.archives-ouvertes.fr/medihal-00459242/image
https://medihal.archives-ouvertes.fr/medihal-00459242/file/tp_biochimie_iut09.jpg

Éditeur(s) : HAL CCSD BioMed Central
Résumé : International audience
Background: The meiotic developmental pathway in yeast enables both differentiation of vegetative cells into haploid spores that ensure long-term survival, and recombination of the parental DNA to create genetic diversity. Despite the importance of proper metabolic regulation for the supply of building blocks and energy, little is known about the reprogramming of central metabolic pathways in meiotically differentiating cells during passage through successive developmental stages. Results: Metabolic regulation during meiotic differentiation in budding yeast was analyzed by integrating information on genome-wide transcriptional activity, 26 enzymatic activities in the central metabolism, the dynamics of 67 metabolites, and a metabolic flux analysis at mid-stage meiosis. Analyses of mutants arresting sporulation at defined stages demonstrated that metabolic reprogramming is tightly controlled by the progression through the developmental pathway. The correlation between transcript levels and enzymatic activities in the central metabolism varies significantly in a developmental stage-dependent manner. The complete loss of phosphofructokinase activity at mid-stage meiosis enables a unique setup of the glycolytic pathway which facilitates carbon flux repartitioning into synthesis of spore wall precursors during the co-assimilation of glycogen and acetate. The need for correct homeostasis of purine nucleotides during the meiotic differentiation was demonstrated by the sporulation defect of the AMP deaminase mutant amd1, which exhibited hyper-accumulation of ATP accompanied by depletion of guanosine nucleotides. Conclusions: Our systems-level analysis shows that reprogramming of the central metabolism during the meiotic differentiation is controlled at different hierarchical levels to meet the metabolic and energetic needs at successive developmental stages.
ISSN: 1471-2180

inserm-01094132
http://www.hal.inserm.fr/inserm-01094132
http://www.hal.inserm.fr/inserm-01094132/document
http://www.hal.inserm.fr/inserm-01094132/file/s12915-014-0060-x.pdf
DOI : 10.1186/s12915-014-0060-x

Éditeur(s) : HAL CCSD Springer Verlag (Germany)
Résumé : International audience
The Michaelis-Menten enzymatic reaction is sufficient to perceive many subtleties of network modeling, including the concentration and time scales separations, the formal equivalence between bulk phase and single-molecule approaches, or the relationships between single-cycle transient probabilities and steady state rates. Seven methods proposed by different authors and yielding the same famous Michaelis-Menten equation, are selected here to illustrate the kinetic and probabilistic use of rate constants and to review basic techniques for handling them. Finally, the general rate of an ordered multistep reaction, of which the Michaelis-Menten reaction is a particular case, is deduced from a Markovian approach.
Journal of Mathematical Chemistry

hal-00920806
https://hal-univ-rennes1.archives-ouvertes.fr/hal-00920806
https://hal-univ-rennes1.archives-ouvertes.fr/hal-00920806/document
ARXIV : 1312.5468
DOI : 10.1007/s10910-013-0237-5

Éditeur(s) : HAL CCSD Nature Publishing Group
Résumé : International audience
CYLD is a tumour suppressor gene mutated in familial cylindromatosis, a genetic disorder leading to the development of skin appendage tumours. It encodes a deubiquitinating enzyme that removes Lys63- or linear-linked ubiquitin chains. CYLD was shown to regulate cell proliferation, cell survival and inflammatory responses, through various signalling pathways. Here we show that CYLD localizes at centrosomes and basal bodies via interaction with the centrosomal protein CAP350 and demonstrate that CYLD must be both at the centrosome and catalytically active to promote ciliogenesis independently of NF-κB. In transgenic mice engineered to mimic the smallest truncation found in cylindromatosis patients, CYLD interaction with CAP350 is lost disrupting CYLD centrosome localization, which results in cilia formation defects due to impairment of basal body migration and docking. These results point to an undiscovered regulation of ciliogenesis by Lys63 ubiquitination and provide new perspectives regarding CYLD function that should be considered in the context of cylindromatosis.
ISSN: 2041-1723

hal-01063915
https://hal.archives-ouvertes.fr/hal-01063915
DOI : 10.1038/ncomms5585
PUBMED : 25134987

Éditeur(s) : HAL CCSD Vsevolod Gurevich
Résumé : International audience
Chemotherapy is frequently used to treat primary or metastatic cancers, but intrinsic or acquired drug resistance limits its efficiency. Sphingolipids are important regulators of various cellular processes including proliferation, apoptosis, differentiation, angiogenesis, stress, and inflammatory responses which are linked to various aspects of cancer, like tumor growth, neoangiogenesis, and response to chemotherapy. Ceramide, the central molecule of sphingolipid metabolism, generally mediates antiproliferative and proapoptotic functions, whereas sphingosine-1-phosphate and other derivatives have opposing effects. Among the variety of enzymes that control ceramide generation, acid or neutral sphingomyelinases and ceramide synthases are important targets to allow killing of cancer cells by chemotherapeutic drugs. On the contrary, glucosylceramide synthase, ceramidase, and sphingosine kinase are other targets driving cancer cell resistance to chemotherapy. This chapter focuses on ceramide-based mechanisms leading to cancer therapy sensitization or resistance which could have some impacts on the development of novel cancer therapeutic strategies.
Handb Exp Pharmacol

inserm-00871347
http://www.hal.inserm.fr/inserm-00871347
PUBMED : 23563652
DOI : 10.1007/978-3-7091-1511-4_4

Éditeur(s) : Elsevier
Résumé : Previous studies conducted on the continental shelf in the Southeast Bay of Biscay influenced by Gironde waters (one of the two largest rivers on the French Atlantic coast) showed the occurrence of late winter phytoplankton blooms and phosphorus limitation of algal growth thereafter. In this context, the importance of dissolved organic phosphorus (DOP) for both algae and bacteria was investigated in 1998 and 1999 in terms of stocks and fluxes. Within the mixed layer, although phosphate decreased until exhaustion from winter to spring, DOP remained high and phosphate monoesters made up between I I to 65% of this pool. Total alkaline phosphatase activity (APA, V-max) rose gradually from winter (2-8 nM h(-1)) to late spring (100-400 nM h-1), which was mainly due to an increase in specific phytoplankton (from 0.02 to 3.0 nmol mu gC(-1) h(-1)) and bacterial APA (from 0.04 to 4.0 nmol mu gC(-1) h(-1)), a strategy to compensate for the lack of phosphate. At each season, both communities had equal competitive abilities to exploit DOP but, taking into account biomass, the phytoplankton community activity always dominated (57-63% of total APA) that of bacterial community (9-11%). The dissolved APA represented a significant contribution. In situ regulation of phytoplanktonic APA by phosphate (induction or inversely repression of enzyme synthesis) was confirmed by simultaneously conducted phosphate-enrichment bioassays. Such changes recorded at a time scale of a few days could partly explain the seasonal response of phytoplankton communities to phosphate depletion.
Journal of Experimental Marine Biology and Ecology (0022-0981) (Elsevier), 2005-05 , Vol. 318 , N. 2 , P. 213-225

Droits : 2005 Elsevier B.V. All rights reserved
http://archimer.ifremer.fr/doc/2005/publication-608.pdf
DOI:10.1016/j.jembe.2004.12.017
http://archimer.ifremer.fr/doc/00000/608/

Éditeur(s) : HAL CCSD Springer Verlag
Résumé : International audience
Chromatin modification enzymes are important regulators of gene expression and some are evolutionarily conserved from yeast to human. Saccharomyces cerevisiae is a major model organism for genome-wide studies that aim at the identification of target genes under the control of conserved epigenetic regulators. Ume6 interacts with the upstream repressor site 1 (URS1) and represses transcription by recruiting both the conserved histone deacetylase Rpd3 (through the co-repressor Sin3) and the chromatin-remodeling factor Isw2. Cells lacking Ume6 are defective in growth, stress response, and meiotic development. RNA profiling studies and in vivo protein-DNA binding assays identified mRNAs or transcript isoforms that are directly repressed by Ume6 in mitosis. However, a comprehensive understanding of the transcriptional alterations, which underlie the complex ume6Δ mutant phenotype during fermentation, respiration, or sporulation, is lacking. We report the protein-coding transcriptome of a diploid MAT a/α wild-type and ume6/ume6 mutant strains cultured in rich media with glucose or acetate as a carbon source, or sporulation-inducing medium. We distinguished direct from indirect effects on mRNA levels by combining GeneChip data with URS1 motif predictions and published high-throughput in vivo Ume6-DNA binding data. To gain insight into the molecular interactions between successive waves of Ume6-dependent meiotic genes, we integrated expression data with information on protein networks. Our work identifies novel Ume6 repressed genes during growth and development and reveals a strong effect of the carbon source on the derepression pattern of transcripts in growing and developmentally arrested ume6/ume6 mutant cells. Since yeast is a useful model organism for chromatin-mediated effects on gene expression, our results provide a rich source for further genetic and molecular biological work on the regulation of cell growth and cell differentiation in eukaryotes.
ISSN: 1617-4615

hal-01151619
https://hal-univ-rennes1.archives-ouvertes.fr/hal-01151619
DOI : 10.1007/s00438-015-1051-5
PUBMED : 25957495

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
The last step of oestrogen biosynthesis is catalyzed by the enzyme aromatase, the product of the cyp19a1 gene. In vertebrates, cyp19a1 is expressed in the brain resulting in a local oestrogen production that seems important not only for the control of reproduction-related circuits and sexual behaviour, but also for the regulation of neural development, synaptic plasticity and cell survival. In adult amphibians, the precise sites of expression of cyp19a1 in the brain have not been investigated which prevents proper understanding of its potential physiological functions. The present study aimed at examining the precise neuroanatomical distribution of cyp19a1 transcripts in adult brains of both male and female Xenopus. We found that cyp19a1 expression is highly regionalized in the brains of both sexes. The highest expression was found in the anterior part of the preoptic area and in the caudal hypothalamus, but significant levels of cyp19a1 transcripts were also found in the supraoptic paraventricular and suprachiasmatic areas, and in brain regions corresponding to the septum, bed nucleus of the stria terminalis and amygdala. Importantly, no obvious difference between male and female Xenopus was detected at the level of cyp19a1 transcripts. Additionally, in the brain of adult Xenopus, cyp19a1 transcripts were detected in neurons, and not in glial cells. These data and those available in other vertebrates on cyp19a1/aromatase expression suggest that, with the intriguing exception of teleost fishes, cyp19a1 was under strong evolutionary conservation with respect to its sites of expression and the nature of the cells in which it is expressed
ISSN: 0016-6480

hal-01187140
https://hal-univ-rennes1.archives-ouvertes.fr/hal-01187140
DOI : 10.1016/j.ygcen.2015.08.008
PUBMED : 26255686

Éditeur(s) : HAL CCSD American Society for Microbiology
Résumé : International audience
UNLABELLED: During visceral leishmaniasis, the control of hepatic parasite burden is mainly due to granuloma assembly in a microenvironment consisting of both Th1 and Th2 components. Using enzyme-linked immunosorbent assay (ELISA) dosages, quantitative PCR (qPCR), immunohistochemistry, and flow cytometry, we studied the role of interleukin-33 (IL-33), a recently described cytokine signaling through the ST2 receptor, during visceral leishmaniasis. We showed that a higher level of IL-33 was detected in the serum of patients with visceral leishmaniasis than in that from healthy donors and demonstrated the presence of IL-33(+) cells in a liver biopsy specimen from a patient. Similarly, in BALB/c mice experimentally infected with L. donovani, a higher level of IL-33 was detected in the serum, as well as the presence of IL-33(+) cells and ST2(+) cells in the mouse liver. In ST2(-/-) BALB/c mice, better control of the hepatic parasite burden and reduced hepatomegaly were observed. This was associated with strong induction of Th1 cytokines (gamma interferon [IFN-γ] and IL-12) compared to the level in wild-type (WT) mice and better recruitment of myeloid cells associated with strongly induced chemokines (CCL2 and CXCL2) and receptors (CCR2 and CXCR2). Conversely, BALB/c mice treated twice weekly with recombinant IL-33 showed a dramatically reduced induction of Th1 cytokines and delayed inhibition of monocyte and neutrophil recruitment in the liver, which was associated with reduced KC/CXCL1 and CXCR2 expression. Taken together, our results suggest that IL-33 could be a new deleterious regulator of the hepatic immune response against Leishmania donovani, via the repression of the Th1 response and myeloid cell recruitment. IMPORTANCE: Visceral leishmaniasis is a life-threatening systemic disease due to the Leishmania protozoa L. infantum and L. donovani and is ranked by the World Health Organization as the second most important protozoan parasitic disease after malaria for its grave morbidity, high mortality, and global distribution. Leishmania parasites subvert the host's immune response to propagate to target organs, including the spleen, the bone marrow, and the liver. Control of hepatic parasite burdens depends on a delicate and poorly understood Th1/Th2 immune balance. To better understand this complex immune response, new cytokines are interesting targets for research studies. IL-33 is a newly described cytokine usually associated with Th2 response and involved in different diseases, including infectious diseases and hepatitis. Our results suggest that IL-33 could be a new factor of susceptibility and a potential prognostic marker during visceral leishmaniasis.
ISSN: 2150-7511

inserm-00871493
http://www.hal.inserm.fr/inserm-00871493
http://www.hal.inserm.fr/inserm-00871493/document
http://www.hal.inserm.fr/inserm-00871493/file/mBio.00383-13.pdf
DOI : 10.1128/mBio.00383-13

Résumé : Chez la banane dessert, les saveurs sucrée et acide, caractéristiques importantes pour les consommateurs, sont pilotées par les teneurs en acides citrique et malique. Ce travail a donc porté sur l’étude des processus physiologiques qui pilotent l’accumulation de ces acides dans la pulpe de banane (Musa sp. AA) en combinant analyse expérimentale et modélisation écophysiologique. Nous nous sommes notamment intéressés à l’effet du génotype et des conditions de croissance du fruit en adoptant une approche intégrative liant les phases pré et post récolte.Les effets de la charge en fruit, de la fertilisation potassique, et du stade de récolte sur l’accumulation du citrate et du malate dans la pulpe ont été étudiés expérimentalement. La variabilité génotypique a été prise en compte en choisissant trois génotypes présentant des acidités contrastées à maturité. Des différences d’évolution des teneurs en acides, dues à des modifications métaboliques, ont été observées entre les génotypes pendant les phases pré et post récolte. Le stade de récolte a eu un effet significatif sur les teneurs en acides des fruits pendant la maturation post récolte. La charge en fruit et la fertilisation potassique n’en ont eu aucun. Des modèles écophysiologiques ont été développés pour prédire différents critères d’acidité de la banane en pré et post récolte. Le pH et l’acidité titrable ont été prédits par un modèle d’équilibres acido-basiques, la teneur en malate par un modèle de stockage vacuolaire, et la teneur en citrate par un modèle du cycle de Krebs. Ces modèles ont permis d’identifier les processus physiologiques clés qui pilotent l’acidité de la banane. Des paramètres génotypiques ont été identifiés liés à l’activité de l’enzyme malique mitochondriale et à celle des transporteurs mitochondriaux du malate pour le modèle citrate, et à l’activité des pompes à protons vacuolaire ATPases pour le modèle malate. Ces modèles ont également permis de disséquer l’effet des conditions de croissance du fruit sur l’acidité de la banane. L’intégration des modèles développés dans un modèle d’élaboration de l’acidité et son utilisation potentielle pour l’amélioration variétale sont discutées.
Citric and malic acids determine the sourness and sweetness of banana pulp, which are the two main determinants of consumer preferences. The present work focused on the physiological processes controlling the accumulation of citric and malic acids in banana pulp (Musa sp. AA) using experimental analysis and ecophysiological modeling. We chose an integrative approach linking the pre and post-harvest stages, and focused on the effect of genotype and fruit growing conditions. Experiments were conducted to study the effect of fruit load, potassium fertilization and fruit age at harvest on the accumulation of citrate and malate in banana pulp. To account for genotypic variability, three genotypes with contrasting acidity at the eating stage were studied. Major differences in the pattern of citrate and malate accumulation were found in the three cultivars both during growth and post-harvest ripening and were shown to be the result of metabolic changes. The harvest stage had a significant effect on the concentrations of acids during post-harvest ripening. Fruit load and potassium fertilization had no effect.Ecophysiological models were developed to predict several banana acidity criteria during the pre and post harvest stages. pH and titratable acidity were predicted by a model of acid-base reactions; malate content by a model of vacuolar storage; and citrate content by a model of the TCA cycle. These models led to the identification of the key physiological processes that control banana acidity. Genotypic parameters were identified, which were related to the activity of the mitochondrial malic enzyme and of the malate mitochondrial carriers in the citrate model, as well as to the activity of the vacuolar proton pump, ATPase, in the malate model. The two models were also used to analyze the effects of fruit growth conditions on banana acidity.Combining the three models in a global model of banana acidity, and the possible use of this model for varietal improvement are discussed.

http://www.theses.fr/2014AGUY0777/document

Éditeur(s) : Academic Press Ltd- Elsevier Science Ltd
Résumé : Extracellular products (ECPs) of the pathogenic Vibrio aestuarianus 01/32 were previously reported to display lethality in Crassostrea gigas oysters and to cause morphological changes and immunosuppression in oyster hemocytes. To identify the source of this toxicity, biochemical and genetic approaches were developed. ECP protease activity and lethality were shown to be significantly reduced following incubation with metal chelators, suggesting the involvement of a zinc metalloprotease. An open reading frame of 1836 bp encoding a 611-aa metalloprotease (designated yam) was identified. The deduced protein sequence showed high homology to other Vibrio metalloproteases reported to be involved in pathogenicity. To further confirm the role of this enzyme in ECP toxicity, a plasmid carrying the yarn gene under the control of an araC-P-BAD expression cassette was transferred to a Vibrio splendidus related strain, LMC20012(T), previously characterized as non-pathogenic to oysters. Expression of Vam conferred a toxic phenotype to LMG20012(T) ECPs in vivo and cytotoxicity to oyster hemocytes in vitro. Collectively, these data suggest that the Vam metalloprotease is a major contributor to the toxicity induced by V aestuarianus ECPs and is involved in the impairment of oyster hemocyte functions. (C) 2010 Elsevier Ltd. All rights reserved.
Fish & Shellfish Immunology (1050-4648) (Academic Press Ltd- Elsevier Science Ltd), 2010-11 , Vol. 29 , N. 5 , P. 753-758

Droits : 2010 Elsevier Ltd All rights reserved.
http://archimer.ifremer.fr/doc/00015/12649/9588.pdf
DOI:10.1016/j.fsi.2010.07.007
http://archimer.ifremer.fr/doc/00015/12649/

Éditeur(s) : HAL CCSD Wiley
Résumé : International audience
Recent reports suggest that extracellular signal-regulated kinase (ERK1) and ERK2 mitogen-activated protein kinases (MAPK) may direct specific biological functions under certain contexts. In this study, we investigated the role of early and sustained epidermal growth factor (EGF) stimulation on long-term hepatocyte differentiation and the possible role of ERK1 and ERK2 in this process. We demonstrate a long-term survival and an elevated level of differentiation up to 3 weeks. The differentiation state of hepatocytes is supported by sustained expression of aldolase B, albumin, and the detoxifying enzymes CYP1A2, 2B2, and 3A23. Similarly to freshly isolated cells, cultured hepatocytes also retain the ability to respond to 3-methylcholanthrene (3MC) and phenobarbital (PB), two known CYP inducers. In addition, we show evidence that continuous MAPK/ERK kinase (MEK) inhibition enhances the level of differentiation. Using RNA interference approaches against ERK1 and ERK2, we demonstrate that this effect requires both ERK1 and ERK2 activity, whereas the specific ERK1 knockdown promotes cell survival and the specific ERK2 knockdown regulates cell proliferation. In conclusion, we demonstrate that early and sustained EGF stimulation greatly extends long-term hepatocyte survival and differentiation, and that inhibition of the ERK1/2 MAPK pathway potentiates these pro-survival/pro-differentiation phenotypes. We clearly attest that specific ERK1 and ERK2 MAPKs determine hepatocyte survival and proliferation, respectively, whereas dual inhibition is required to stabilize a highly differentiated state.
ISSN: 0021-9541

hal-00681056
https://hal.archives-ouvertes.fr/hal-00681056
DOI : 10.1002/jcp.22742
PUBMED : 21437905

Éditeur(s) : HAL CCSD Wiley
Résumé : International audience
Cytochrome P450 aromatase (P450arom; aromatase) is a microsomal enzyme involved in the production of endogeneous sex steroids by converting testosterone into oestradiol. Aromatase is the product of the cyp19a1 gene and plays a crucial role in the sexual differentiation of the brain and in the regulation of reproductive functions. In the brain of mammals and birds, expression of cyp19a1 has been demonstrated in neuronal populations of the telencephalon and diencephalon. By contrast, a wealth of evidence established that, in teleost fishes, aromatase expression in the brain is restricted to radial glial cells. The present study investigated the precise neuroanatomical distribution of cyp19a1 mRNA during brain development in Xenopus laevis (late embryonic to juvenile stages). For this purpose, we used in situ hybridisation alone or combined with the detection of a proliferative (proliferating cell nuclear antigen), glial (brain lipid binding protein, Vimentin) or neuronal (acetylated tubulin; HuC/D; NeuroβTubulin) markers. We provide evidence that cyp19a1 expression in the brain is initiated from the very early larval stage and remains strongly detected until the juvenile and adult stages. At all stages analysed, we found the highest expression of cyp19a1 in the preoptic area and the hypothalamus compared to the rest of the brain. In these two brain regions, cyp19a1-positive cells were never detected in the ventricular layers. Indeed, no co-labelling could be observed with radial glial (brain lipid binding protein, Vimentin) or dividing progenitors (proliferating cell nuclear antigen) markers. By contrast, cyp19a1-positive cells perfectly matched with the distribution of post-mitotic neurones as shown by the use of specific markers (HuC/D, acetylated tubulin and NeuroβTubulin). These data suggest that, similar to that found in other tetrapods, aromatase in the brain of amphibians is found in post-mitotic neurones and not in radial glia as reported in teleosts.
ISSN: 0953-8194

hal-00994513
https://hal-univ-rennes1.archives-ouvertes.fr/hal-00994513
DOI : 10.1111/jne.12142
PUBMED : 24612124

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
The transcription factor nuclear factor-erythroid 2-related-2 (Nrf2) controls cellular redox homeostasis and displays immunomodulatory properties. Nrf2 alters cytokine expression in murine T cells, but its effects in human T lymphocytes are unknown. This study investigated the expression and activity of Nrf2 in human activated CD4(+) T helper lymphocytes (Th cells) that mediate the adaptive immune response. Th cells were isolated from peripheral blood mononuclear cells and activated with antibodies against CD3 and CD28, mimicking physiologic Th cell stimulation by dendritic cells. Nrf2 is hardly detectable in unstimulated Th cells. Activation of Th cells rapidly and strongly increases the levels of Nrf2 protein by increasing NRF2 gene transcription. Th cell activation also enhances mRNA and protein levels of Nrf2 target genes encoding antioxidant enzymes. Blocking Nrf2 expression using chemical inhibitors or siRNAs prevents these gene inductions. Pretreatment with inorganic arsenic, a Nrf2 inducer that does not alter NRF2 gene expression, increases protein level and transcriptional activity of Nrf2 induced by Th cell stimulation. Inorganic arsenic enhances nuclear translocation of Nrf2, its interaction with the coactivator protein p300, and its DNA binding activity. Inhibition of Nrf2 expression abrogates the effects of inorganic arsenic on mRNA levels of antioxidant genes, but does not alter the expression of IL-2, TNF-α, interferon-γ, or IL-17 in Th cells activated in the absence or presence of the metalloid. In conclusion, this study demonstrates for the first time that stimulation of human Th cells increases transcription of the NRF2 gene and activity of the Nrf2 protein. However, modulation of Nrf2 levels does not modify the secretion of inflammatory cytokines from these T lymphocytes.
ISSN: 0891-5849

hal-01018643
https://hal-univ-rennes1.archives-ouvertes.fr/hal-01018643
https://hal-univ-rennes1.archives-ouvertes.fr/hal-01018643/document
https://hal-univ-rennes1.archives-ouvertes.fr/hal-01018643/file/Nrf2_expression_and_activity_in_human_T_lymphocytes_accepted.pdf
DOI : 10.1016/j.freeradbiomed.2014.03.006