Decreasing cytosolic translation is beneficial to yeast and human Tafazzin-deficient cells

Cardiolipin (CL) optimizes diverse mitochondrial processes, including oxidative phosphorylation (OXPHOS). To function properly, CL needs to be unsaturated, which requires the acyltransferase Tafazzin (TAZ). Loss-of-function mutations in the TAZ gene are responsible for the Barth syndrome (BTHS), a rare X-linked cardiomyopathy, presumably because of a diminished OXPHOS capacity. Herein we show that a partial inhibition of cytosolic protein synthesis, either chemically with the use of cycloheximide or by specific genetic mutations, fully restores biogenesis and the activity of the oxidative phosphorylation system in a yeast BTHS model (taz1Δ). Interestingly, the defaults in CL were not suppressed, indicating that they are not primarily responsible for the OXPHOS deficiency in taz1Δ yeast. Low concentrations of cycloheximide in the picomolar range were beneficial to TAZ-deficient HeLa cells, as evidenced by the recovery of a good proliferative capacity. These findings reveal that a diminished capacity of CL remodeling deficient cells to preserve protein homeostasis is likely an important factor contributing to the pathogenesis of BTHS. This in turn, identifies cytosolic translation as a potential therapeutic target for the treatment of this disease

Intracellular Phospholipase A1 and Acyltransferase, Which Are Involved in Caenorhabditis elegans Stem Cell Divisions, Determine the sn-1 Fatty Acyl Chain of Phosphatidylinositol

Phosphatidylinositol (PI) is unique in the abundance of stearic acid at the sn-1 position. This fatty acid is thought to be incorporated through fatty acid remodeling. Here, we identified a phospholipase and acyltransferases involved in the fatty acid remodeling at the sn-1 position of PI and provide a link between the sn-1 fatty acid of PI and asymmetric cell division

Metabolism and Regulation of Glycerolipids in the Yeast Saccharomyces cerevisiae

Due to its genetic tractability and increasing wealth of accessible data, the yeast Saccharomyces cerevisiae is a model system of choice for the study of the genetics, biochemistry, and cell biology of eukaryotic lipid metabolism. Glycerolipids (e.g., phospholipids and triacylglycerol) and their precursors are synthesized and metabolized by enzymes associated with the cytosol and membranous organelles, including endoplasmic reticulum, mitochondria, and lipid droplets. Genetic and biochemical analyses have revealed that glycerolipids play important roles in cell signaling, membrane trafficking, and anchoring of membrane proteins in addition to membrane structure. The expression of glycerolipid enzymes is controlled by a variety of conditions including growth stage and nutrient availability. Much of this regulation occurs at the transcriptional level and involves the Ino2–Ino4 activation complex and the Opi1 repressor, which interacts with Ino2 to attenuate transcriptional activation of UASINO-containing glycerolipid biosynthetic genes. Cellular levels of phosphatidic acid, precursor to all membrane phospholipids and the storage lipid triacylglycerol, regulates transcription of UASINO-containing genes by tethering Opi1 to the nuclear/endoplasmic reticulum membrane and controlling its translocation into the nucleus, a mechanism largely controlled by inositol availability. The transcriptional activator Zap1 controls the expression of some phospholipid synthesis genes in response to zinc availability. Regulatory mechanisms also include control of catalytic activity of glycerolipid enzymes by water-soluble precursors, products and lipids, and covalent modification of phosphorylation, while in vivo function of some enzymes is governed by their subcellular location. Genome-wide genetic analysis indicates coordinate regulation between glycerolipid metabolism and a broad spectrum of metabolic pathways

Identification et caractérisation de quatre lysolipide acyltransférases de S. cerevisiae (études in silico, in vitro et in vivo)

BORDEAUX2-BU Santé (330632101) / SudocSudocFranceF

Mutations des éléments cis-régulateurs de l'épissage (rôle en pathologie humaine)

L'épissage des ARN pre-messagers joue un rôle fondamental dans l'expression des gènes chez les eucaryotes supérieurs. La régulation de ce processus extrêmement complexe, qui permet l'excision des introns, repose sur la reconnaissance de multiples éléments, incluant les séquences consensus (sites accepteurs et donneurs) et cis-régulatrices auxiliaires, dont la combinaison définit un "code de l'épissage" propre à chaque exon. Les exemples de mutation associées à des anomalies d'épissage dans les maladies génétiques humaines sont de plus en plus nombreux, néanmoins leur contribution reste très probablement sous estimée. En effet, un nombre important de variants non classés (Unknown Variants, UVs) introniques ou exoniques est identifié par séquençage des gènes, dont une partie est susceptible d'altérer l'épissage. Quand les transcrits spécifiques des patients ne sont pas accessibles, l'utilisation combinée d'outils bio-informatiques et de tests fonctionnels basés sur l'utilisation de minigènes rapporteurs d'épissage permet d'évaluer l'impact de ces UVs sur l'épissage. Cette stratégie, appliquée aux variants identifiés dans les gènes responsables du syndrome de Usher, a montré que 76% des UVs localisés à des positions peu conservées des sites consensus avaient des conséquences majeures sur l'épissage. Au cours de ces travaux, nous avons confirmé l'importance de l'interdépendance des positions nucléotidiques dans la définition des sites d'épissage, et avons pu établir que les positions -1 et +4 du site donneur d'épissage permettaient de compenser un mésappariement en position +3 avec la protéine U1 snRNP. Les évènements d'épissage alternatifs jouent également un rôle important dans la modulation de sévérité du phénotype en pathologie humaine. On observe ainsi pour le gène DMD (Duchenne muscular Dystrophy) que des mutations non-sens (introduisant un codon stop prématuré) sont retrouvées dans des formes modérées de la maladie (Myopathie de Becker) lorsqu'elles sont à l'origine d'un épissage alternatif en phase de l'exon muté. L'identification des éléments cis-régulateurs de l'épissage impliqués (ou SREs, splicing regulatory elements), notamment les séquences activatrices de type ESE (Exonic Splicing Enhancer), représente un enjeu majeur pour la mise en place des stratégies thérapeutiques par saut d'exon dans la myopathie de DuchenneSplicing of pre-messenger RNAs to mature transcripts is a crucial step in eukaryotic gene expression. This highly regulated mechanism involves multiple signals, including the core splice site motifs (donor and acceptor splice sites) and auxiliary ci-regulatory elements, which are part of integrated "splicing code". More and more examples of splicing mutations resulting in genetic diseases are described in the literature, however their true contribution is probably underestimated. Indeed, sequence-based approach to study disease-causing genes in diagnostic procedures leads to the identification of an increasing number of variants of unknown significance (UVs). The biological consequences of the so-called UVs and notably their purative impact of splicing ar unknown. When specific analysis is not achievable in patients, in silico predictions associated with minigene studies are performed to determine the impact of these UVs on splicing. This strategy was applied to a set of UVs located in poorly conserved positions of acceptor and donor splice sites of Usher genes, and 76% of them were found to cause aberrant splicing. From our results, we further confirmed the importance of the overall nucleotidic environment in splice sites selection. In particular, we could establish that positions -1 and +4 in donor splice sites can compensate a mismatch at position +3 with the U1 snRNP and contribute to the correct recognition of such donor splice sites. Alernative splicing events play also a major role in modulation of disease severity. In the DMD gene, nonsense mutations introducing a premature stop codon are found in patients with a milder phenotype (Becker-like) than expected (Duchenne-like), and usually result from the elimination of the truncating mutation from dystrophin mRNA by skipping of an in-frame exon. This kind of disease-causing mutations can contribute to shed light on new cis-regulatory elements, in particular Exonic Splicing Enhancer (ESE) motifs, essential for splicing in the DMD gene, which may be important for the exon skipping therapeuric strategyMONTPELLIER-BU Médecine UPM (341722108) / SudocMONTPELLIER-BU Médecine (341722104) / SudocSudocFranceF

Les bioindicateurs pour la gestion des sites contaminés - Evaluation des risques de transfert dans les chaînes trophiques terrestres : résultats sur sites ateliers.

International audienceCette présentation synthétise les résultats obtenus avec des bio-indicateurs d'accumulation (plantes, escargots) et d'effet (teneurs des feuilles en acides gras) par plusieurs équipes dans le cadre du programme Bioindicateur conduit sur 13 sites en France. Il est également montré que la biodisponibilité (évaluée avec des méthodes biologiques) ne peut être estimée par l'évaluation de la disponibilité (évaluée avec des méthodes chimiques)

Sequence Contexts That Determine the Pathogenicity of Base Substitutions at Position+3 of Donor Splice-Sites

Variations at position +3 of 5' splice-sites (5'ss) are reported to induce aberrant splicing in some cases but not in others suggesting that the overall nucleotidic environment can dictate the extent to which 5'ss are correctly selected. Functional studies of three variations identified in donor splice-sites of USH2A and PCDH15 genes sustain this assumption. To gain insights into this question, we compared the nucleotidic context of U2-dependent 5'ss naturally deviated (+3G, +3C, or +3T) from the +3A consensus with 5'ss for which a +3 variation (A>G, A>C, or A>T) was shown to induce aberrant splicing. Statistical differences were found between the two datasets, highlighting the role of one peculiar position in each context (+3G/+4A; +3C/-1G; and +3T/-1G). We provided experimental support to the biostatistical results through the analysis of a series of artificial mutants in reporter minigenes. Moreover, different 5' end-mutated U1 snRNA expression plasmids were used to investigate the importance of the position +3 and of the two identified compensatory positions -1 and +4 in the recognition of 5'ss by the U1 snRNP Overall, our findings establish general properties useful to Molecular geneticists to identify nucleotide substitutions at position +3 that are more likely to alter splicin

Microbial communities in As contaminated agricultural soils – How PK fertiliser can influence As speciation

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Communautés microbiennes dans les sols agricoles pollués par l'arsenic - comment les engrais KP peuvent influencer la spéciation de l'arsenic

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The reductase activity of the Arabidopsis Caleosin RESPONSIVE TO DESSICATION20 mediates gibberellin-dependent flowering time, abscisic acid sensitivity, and tolerance to oxidative Stress

International audienceContrasting with the wealth of information available on the multiple roles of jasmonates in plant development and defense, knowledge about the functions and the biosynthesis of hydroxylated oxylipins remains scarce. By expressing the caleosin RESPONSIVE TO DESSICATION20 (RD20) in Saccharomyces cerevisiae, we show that the recombinant protein possesses an unusual peroxygenase activity with restricted specificity toward hydroperoxides of unsaturated fatty acid. Accordingly, Arabidopsis (Arabidopsis thaliana) plants overexpressing RD20 accumulate the product 13-hydroxy-9,11,15-octadecatrienoic acid, a linolenate-derived hydroxide. These plants exhibit elevated levels of reactive oxygen species (ROS) associated with early gibberellin-dependent flowering and abscisic acid hypersensitivity at seed germination. These phenotypes are dependent on the presence of active RD20, since they are abolished in the rd20 null mutant and in lines overexpressing RD20, in which peroxygenase was inactivated by a point mutation of a catalytic histidine residue. RD20 also confers tolerance against stress induced by Paraquat, Rose Bengal, heavy metal, and the synthetic auxins 1-naphthaleneacetic acid and 2,4-dichlorophenoxyacetic acid. Under oxidative stress, 13-hydroxy-9,11,15-octadecatrienoic acid still accumulates in RD20-overexpressing lines, but this lipid oxidation is associated with reduced ROS levels, minor cell death, and delayed floral transition. A model is discussed where the interplay between fatty acid hydroxides generated by RD20 and ROS is counteracted by ethylene during development in unstressed environments