Expression of brush border enzymes and transporters in the intestine of European sea bass (Dicentrarchus labrax) following food deprivation

Studies on aquacultured fish nutrition have focused solely on performance and the activity of the brush-border enzymes, while the molecular aspects have barely been addressed. Nevertheless, the expression of genes encoding enzymes and transporters of the brush-border membrane is crucial for the final stages of digestion and absorption of nutrients through the epithelial luminal membrane of the intestine. To establish a molecular tool for such studies, primers for the European sea bass intestinal genes were designed utilizing evolutionarily conserved DNA sequences for the following intestinal enzymes and transporters: maltase, APN, PepT1 and Na+/K+-ATPase. The derived European sea bass cDNA fragments showed 64–92% homology to other animal species and enabled us to study the differences in their expression. The mRNA expression of these genes in pyloric caeca and the upper and lower intestinal sections were compared in fed fish vs conditions of food deprivation for 3, 7, 14 and 21 days. The mRNA expression examined using real time PCR of APN, maltase and PepT1 in all the intestinal tract sections, was the highest after 7 days of food deprivation. Na+/K+-ATPase showed a different pattern of expression in each section of the intestine. Significant positive linear correlations between APN, maltase and PepT1 mRNA expression were detected in all but day 3 post food deprivation. The cDNA fragments isolated in this study provide a novel molecular tool for revealing new aspects in fish nutrition and can provide additional information regarding the pattern of expression of intestinal genes following long-term fasting in fish.