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Adaptation du métabolisme respiratoire de l'huître creuse Crassostrea gigas

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ABSTRACT Summer mortality of the oyster result from the interaction of many factors. A respiratory assumption proposes a link between the supposed causes of the energy state, the cultivation methods and the medium. This work is focused towards the search for specific metabolic markers of environmental stresses. The cDNA of genes coding for PK and PEPCK were cloned and sequenced in order to detect their regulation level. The sediment nearness affects the state of energy reserves, the metabolic pathways of energy production implying a regulation of the PK. Face to the dissolved oxygen decline, oysters were oxyregulator but with a low regulation ability. In hypoxia, glycolysis was slowed down. PK activity was inhibited resulting from an increase in alanine sensitivity whereas ETS activity of the respiratory chain was stimulated. When exposed to sulphides, filtration of oyster was affected from 20μM whereas the oxygen consumption persisted. At short term, an anaerobic metabolic pathway associated to the inhibition of the respiratory chain and the fall of CEA took place. Muscular PK and PEPCK had different regulation levels: PEPCK appeared controlled at the transcriptional level and PK was first allosterically regulated before to be lately regulated at transcriptional level. Lastly, this study revealed new specificities of the oysters R and S. In normoxia, the more important stock of carbohydrate of the S oysters was correlated to a higher production of ATP via a more intense PK activity. In hypoxia, the expression of the muscular PEPCK was stimulated in S oyster. In all the situations, the oysters R produce more alanine. Les mortalités estivales des huîtres résultent de l'interaction de nombreux facteurs. Une hypothèse respiratoire propose de lier les causes présumées de la baisse énergétique, les pratiques culturales et le milieu. Le présent travail a pour objectif de d'identifier des marqueurs métaboliques de stress. Les ADNc des gènes codant pour la PK et la PEPCK ont été clonés et séquencés pour en détecter les niveaux de régulation. La proximité du sédiment affecte les réserves énergétiques et les voies métaboliques de production d'énergie impliquant une régulation de la PK. Face à la chute d'oxygène, le comportement des huîtres est de type oxyrégulateur, avec une faible capacité de régulation. En hypoxie, la glycolyse est ralentie. La PK est inhibée via une augmentation de la sensibilité à l'alanine alors que l'activité ETS de la chaîne respiratoire est stimulée. La filtration est affectée dès 20μM de sulfures alors que la consommation d'oxygène persiste. A court terme, un métabolisme anaérobie avec inhibition de la chaîne respiratoire et baisse de la charge énergétique se met en place. Les niveaux de régulation des PK et PEPCK musculaires sont différents : la PEPCK apparaît régulée au niveau transcriptionnel alors que la PK subit une régulation allostérique, avant une régulation transcriptionelle tardive. Cette étude révèle de nouvelles spécificités des huîtres R et S. En normoxie, le stock plus important des glucides des huîtres S est associé à une production d'ATP plus élevée via une activité PK plus intense. En hypoxie, l'expression de la PEPCK musculaire est stimulée chez les S. Dans toutes les situations respiratoires, les huîtres R produisent plus d'alanine.

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