Cloning, expression, and nutritional regulation of the glutamine synthetase gene in Ctenopharyngodon idellus

Glutamine synthetase (GS) is considered a master enzyme that catalyzes ATP-dependent biosynthesis of glutamine from glutamate. In the present study, the GS gene was cloned from the intestine of grass carp (Ctenopharyngodon idellus). The full-length cDNA sequence of GS encodes a 371-amino-acid polypetide. Phylogenetic analysis of the C. idellus GS sequence reveals common carp (Cyprinus carpio) as its closest neighbor. GS mRNA was differentially expressed in different tissues, with high to low gradient expression the intestine, brain, muscle, heart, gill, liver, pituitary gland, and spleen. Additionally, GS exhibited a dynamic pattern of expression during embryonic development, reaching maximal and minimal levels in the organ and hatching stages, respectively, and constant low levels from 7 to 28 days post-hatching. We also assessed dietary protein levels and feed sources in diet-regulated fish, and the results suggested that low crude protein (CP) and fish meal stimulate GS gene expression. Furthermore, intestinal GS mRNA expression was significantly increased by 0.2, 0.4, 0.6, 0.8 mM concentrations of glutamine dipeptide in vitro. This study provides valuable knowledge about the regulation of GS expression in teleosts.