Glutamate related osmoregulation of guanine nucleotide-binding protein G (I) α2 from giant freshwater prawn (Macrobrachium rosenbergii) during molting and salinity stress

Giant freshwater prawn (Macrobrachium rosenbergii) is one of the most important cultured freshwater prawn species. Although giant freshwater prawn lives in freshwater, brackish water environment is essential for their larval stage of development. M. rosenbergii has to regulate osmotic pressure through osmoregulation, no matter it lives in either brackish water in the course of their larval stage or during the consequential molting process. Comprehensive studies have revealed that Guanine nucleotide-binding protein G (i) subunit alpha (Gi) could counteract with the cAMP-dependent protein kinase and controlling the release of Glutamate (Glu). Being a key player as modulators or transducers in various transmembrane signaling systems, neither the effects of Gi nor their osmoregulatory functions has been investigated in M. rosenbergii under molting and osmotic stress conditions. In this report, we have cloned and characterized the Gi gene of M. rosenbergii (designated as Mr-Gi). The results showed that the open reading frame (ORF) of Gi from M. rosenbergii was 1023 bp, which encoded a putative protein of 340 amino acids that phylogenetically shared the highest identity with other crustaceans and predicted to contain a domain of coiled-coil and seven WD40 repeat proteins. The mRNA expressions of Gi from M. rosenbergii in healthy prawn have abundantly existed in muscle and other examined tissues in the following order hepatopancreas > heart > brain > stomach > muscle > intestines > gills > hemocytes. Besides, the Gi from M. rosenbergii transcription was significantly up-regulated in the muscle and gills tissues as a result of molting or challenges with either hyper (0 -> 13 part per thousand, ppt) or hypo (13 -> ppt) osmotic stress at 3, 6, 12, 24 and 48 h. Moreover, Glu levels exhibited similar patterns in the gills and muscle tissues after molting and post-treatments with hyper or hypo-osmotic stress. These findings indicated that Gi from M. rosenbergii potentially plays significant roles in Glu-related osmoregulation during molting and osmotic pressure. Moreover, the results provide a deeper understanding of Gi from M. rosenbergii molecular mechanisms and its relationship with the osmoregulatory functions in M. rosenbergii.