Glucose transporters in pearl gentian grouper (Epinephelus fuscoguttatus ♀ × E. lanceolatus ♂): Molecular cloning, characterization, tissue distribution and their expressions in response to dietary carbohydrate level

The glucose transporters (GLUTs) play vital role in mediating the glucose uptake process, the movement of glucose across plasma membranes. In this study, three GLUTs, GLUT1, GLUT2 and GLUT4 were cloned and characterized form pearl gentian grouper, a hybrid grouper, and their expressions in response to dietary carbohydrate level (8.02%, 11.89% and 16.08%) were investigated after feeding. The full‐length cDNA of GLUT1, GLUT2 and GLUT4 were 2,104, 3,759 and 2,815 bp, respectively, encoding a putative protein of 491, 508 and 505 amino acids respectively. The results of sequence and phylogenetic analysis revealed that grouper GLUTs were highly conserved and clustered together with their corresponding teleost orthologues, rather than mammals. In addition, GLUT1 was ubiquitously expressed in all detected tissues with relative high expressions in heart and brain. GLUT2 is relatively abundant in some certain tissues that release glucose, such as liver and intestine, and GLUT4 was expressed primarily in muscle and eye. The elevated dietary carbohydrate level had no significant difference on the expression of GLUT1 in grouper liver. The expression of GLUT2 in grouper liver was significantly up‐regulated with the increasing dietary carbohydrate from 8.02% to 11.89%, and therefore down‐regulated significantly. Meanwhile, the expression of GLUT4 in grouper muscle increased significantly with increasing dietary carbohydrate. Results of this study indicate that the up‐regulation of GLUTs in fish contribute to maintain glucose equilibrium to some extent when fish were fed with high carbohydrate diets.