Osmoregulation of glutamine synthetase from Giant freshwater prawn (Macrobrachium rosenbergii) under osmotic stress
Glutamine synthetase is a key enzyme that catalyzes the biosynthesis of glutamine (Gln) from glutamate and ammonia. Gln a vital amino acid acts as a precursor for protein synthesis and also assist in ammonia repressor and a key osmoregulators in aquatics. Here, we report the cloning and characterization of the GS gene from Macrobrachium rosenbergii (Mr-GS). The complete nucleotide and deduced amino acid sequences were determined that phylogenetically shared highest identity with other crustaceans. GS mRNA was differentially expressed in 6 different tissues, with high to low order as muscle > gills > heart > stomach > brain > haemolymph. Mr-GS expression and the glutamine concentrations were analyzed in the gills and muscle tissues of prawn under hyper/hypo-osmotic stress conditions. Under hyper-osmotic stress, the mRNA expression of Mr-GS was significantly increased in both gills and muscle at 3, 6 and 12 h post-treatment with 2.54, 4.21 and 10.83 folds, and 11.66, 17.97 and 45.92 folds, respectively. Protein analysis by western blot (WB) and Immunohistochemistry (IHC) further confirmed the Mr-GS expression was increased at 12 h post treatment. On the other hand, under hypo-osmotic stress, the mRNA expression of Mr-GS was also significantly increased in both gills and muscle at 3, 6 and 12 h post treatment with 1.63, 3.30 and 3.52 folds, and 4.06, 42.99 and 26.69 folds, respectively. Furthermore, under hyperosmotic stress, Gln concentration was increased in both gills and muscle at 6 and 12 h post treatment with 1.83, 2.02 folds, and 1.41, 1.29 folds, respectively. While, under hypo-osmotic stress, Gln concentration was increased in both gills and muscle at 3, 6 and 12 h post treatment with 3.99, 3.40, 2.59 folds, and 1.72, 1.83, 1.80 folds, respectively. Taken together, these results suggest that Mr-GS might play a key role in osmoregulation in M. rosenbergii.