RESEARCH ARTICLE Unraveling the Molecular Signatures of Oxidative Phosphorylation to Cope with the Nutritionally Changing Metabolic Capabilities of Liver and Muscle Tissues in Farmed Fish

Mitochondrial oxidative phosphorylation provides over 90 % of the energy produced by aero-bic organisms, therefore the regulation of mitochondrial activity is a major issue for coping with the changing environment and energy needs. In fish, there is a large body of evidence of adaptive changes in enzymatic activities of the OXPHOS pathway, but less is known at the transcriptional level and the first aim of the present study was to define the molecular identity of the actively transcribed subunits of the mitochondrial respiratory chain of a live-stock animal, using gilthead sea bream as a model of farmed fish with a high added value for European aquaculture. Extensive BLAST searches in our transcriptomic database (www.nutrigroup-iats.org/seabreamdb) yielded 97 new sequences with a high coverage of catalytic, regulatory and assembly factors of Complex I to V. This was the basis for the de-velopment of a PCR array for the simultaneous profiling of 88 selected genes. This new ge-nomic resource allowed the differential gene expression of liver and muscle tissues in a model of 10 fasting days. A consistent down-regulated response involving 72 genes was made by the liver, whereas an up-regulated response with 29 and 10 differentially express