Glutamate and glutamine transporter genes in grass carp (Ctenopharyngodon idellus): Molecular cloning, characterization and expression in response to different stocking densities

Abstract

Active transporters play a central role in the uptake and efflux of glutamate by cells and organelles. We aimed to assess the effects of crowding stress on the efficiency of active glutamate and glutamine transport in fish. We cloned intestinal-related transporters and investigated their transcriptional changes in grass carp Ctenopharyngodon idellus exposed to different stocking densities. The full-length cDNA sequences of slc1a1, slc1a3 and slc7a6 cloned by rapid amplification of cDNA ends were 2,869, 2,508 and 2,141 base pairs respectively. Based on homology modelling, we derived three-dimensional models of SLC1A1, SLC1A3, SLC7A6 and SLC7A7 and noted their transmembrane domains. The expression profiles of slc1a1, slc1a3 and slc7a7 demonstrated tissue specificity, with section-dependent expression patterns along the intestine. Moreover, segmental mRNA expression patterns of slc1a3, slc7a6 and slc7a7 were affected by stocking density. Crowding stress notably altered the segment-specific mRNA expression of slc7a6. The results of this study showed that increased stocking density increased mRNA expression levels of glutamine transporters (slc7a6 and slc7a7) but decreased mRNA expression of the glutamate transporter (slc1a3). These results furthered our understanding of the relationship between crowding stress and intestinal glutamate/glutamine transport in fish.