Among the 41 differentially expressed genes, some were
involved in genetic information and environmental processing (mainly for membrane transporters of nutrients), the others having active roles in intermediary metabolism. The decrease lipid intake in trout fed diet LL was associated with apparent lower capacity of fatty acid transport as confirmed by real time RT-PCR analysis with the FABL gene expression. Original data obtained here on other differentially expressed genes involved in amino acid/ion transport, cell motility, transcription, signal transduction suggest for example an increased apoptosis and a decreased hepatic cell proliferation: further studies are needed to explain these observations.
The post-transcriptomic analysis on hepatic intermediary metabolism shows that the major part of the differentially expressed genes between HL and LL fish are involved in intermediary metabolism: fatty acid metabolism, protein metabolism and energy metabolism. We confirmed some of these data using specific real time PCR with a higher number of individuals per dietary groups. Decreased gene expression for proteins involved Table 6 Selected genes analysed by real time PCR: effect of dietary fish oil removal.
Statistical differences in gene expression between samples were evaluated in group means by randomisation tests (Pfaffl et al., 2002) using REST© software: down and up regulation means that the target gene is expressed at a lower or higher level, respectively Gene Foldregulation P-values CV HL (%) CV LL (%) Up-expressed genes in microarrays Fatty acid synthase +3.8 P= 0.001 1.4 0.7
Elongation of very long fatty acid protein +2.0 P= 0.001 1.0 1.1 Long-chain fatty acid-CoA ligase +1.8 P= 0.005 1.9 0.2 Down-expressed genes in microarrays Acyl-CoA oxidase −1.7 P= 0.003 0.2 0.3 Fatty acid-binding protein −1.3 P= 0.03 0.7 0.7 Cytochrome c oxidase polypeptide II −1.3 P= 0.006 0.9 1.2 Ubiquitin-E2-protein
ligase −1.5 P= 0.004 1.2 0.7 Proteasome-subunit α3 −1.5 P= 0.02 1.5 1.9 Transcript level of target genes normalised with EF1α expressed transcripts. S. Panserat et al. / Aquaculture 275 (2008) 235–241 239 in energy metabolism such as cytochrome c oxidase polypeptide II in fish fed without fish oil is in agreement with data by Salem et al. (2007) who showed this protein to be highly dependent on nutritional status, being induced in refed rainbow trout compared
to fasted trout