Impact of feed availability on PepT1 mRNA expression levels in sea bass (Dicentrarchus labrax)

The expression and regulation of oligopeptide transporter (PepT)-1 in relation to dietary treatments has not yet been explored in fish. In the present study, as part of our ongoing work on elucidating genes involved in compensatory growth induced by refeeding, we have now isolated a full-length cDNA representing the PepT1 in the European sea bass (Dicentrarchus labrax). A total of 3014 bases including a 5′-untranslated region (101 bp), an open reading frame (ORF) (2184 bp), and a 3′-untranslated region (729 bp) were detected. The predicted 12 transmembrane domains of the protein (728 amino acids) are presented. A phylogenetic treewas constructed on the PepT1 sequences of sea bass and those of other teleost, avian, and mammalian species. We also analyzed fasting- and refeeding-induced changes in the expression of PepT1 mRNA, using a one-tube two-temperature real-time RT-PCR with which the gene expression can be absolutely quantified using the standard curve method. Our results revealed that PepT1 was highly expressed in the proximal intestine with much lower levels of expression in the gill, brain, heart, liver and spleen. Nutritional status significantly influenced PepT1 mRNA copy number in the proximal intestine, inducing a down-regulation during prolonged fasting (35 days) and an up-regulation during the recovery from fasting. These findings offer new information about the dietary regulation of PepT1 mRNA level in sea bass, and support a role of this membrane transporter protein in promoting sea bass compensatory growth induced by refeeding.