Molecular cloning and expression of hepatopancreas glutamine synthetase in the Pacific white shrimp, Litopenaeus vannamei, induced by acute hypo-osmotic stress

Glutamine synthetase (GS) is a key enzyme involved in nitrogen metabolism and glutamine synthesis. A 1455 bp cDNA clone encoding GS was isolated from Litopenaeus vannamei (LvGS, JN620540.1). The sequence consists of a 75 bp 5′ untranslated region followed by a 1101 bp open reading frame corresponding to 366 amino acids. The encoded protein has a 67% to 93% overall amino acid sequence identity with its counterparts in other various species. A phylogenetic analysis of the GS sequence showed that LvGS clustered with the invertebrate group as expected. qRT-PCR analysis indicated that LvGS was expressed in the stomach, gill, intestine, hepatopancreas, muscle, heart, and eyestalk. The profile of LvGS was up-regulated in the stomach, gills, intestines, and hepatopancreas after 48 h of exposure to dilute seawater (4 ppt). The mRNA levels of LvGS in the hepatopancreas significantly increased 2.9-fold after 3 h to 3 d of exposure to dilute seawater (P < 0.05). The LvGS activity and glutamine in the hepatopancreas increased after 3 h to 3 d and then decreased after 7 d to 20 d of exposure to dilute seawater. However, the hemolymph total protein and ammonia decreased after 3 h to 3 d, and then increased after 7 d to 20 d. The hemolymph urea and uric acid significantly increased after 3 h to 12 h of exposure to dilute seawater. L. vannamei fully acclimated to a low salinity environment within a week. LvGS can participate in physiological osmotic adaptation to hypo-osmotic water and aid L. vannamei in resisting acute salinity changes via the manipulation of nitrogen metabolism.