Characterizing the Role of Glutamine synthetase Gene on Ammonia Nitrogen Detoxification Metabolism of the Razor Clam Sinonovacula constricta

Abstract

Ammonia nitrogen is a common toxic substance in the aquatic system, which seriously threatens the survival and growth of clams. However, less is known about the ammonia metabolism and detoxification strategy in razor clam. In this study, the polymorphism of the Glutamine synthetase gene from Sinonovacula constricta (Sc-GS) was found to be related to ammonia tolerance. By comparing the coding sequence (CDS) region of Sc-GS from two geographical populations, a total of 14 and 12 single nucleotide polymorphisms (SNPs) were identified, respectively, of which 10 loci were shared between the two populations. Among them, the locus c.1133T > G exhibited an extremely significant and strong association with ammonia tolerance in both populations (P < 0.01), and it was missense mutation, which led to the amino acid change from leucine (Leu) to arginine (Arg). Furthermore, the results about H&E staining and immunohistochemistry of Sc-GS protein in gills and hepatopancreas revealed that it was specifically localized in the lateral cilia of gill filaments and the endothelial cells of hepatocytes. After inhibiting the Sc-GS expression by RNA interference (RNAi) technology, the transcript levels of Sc-GS were extremely significantly downregulated at 24, 48, 72, and 96 h (P < 0.01) in the hepatopancreas. Taken together, these results indicated that the Sc-GS gene may participate in ammonia metabolism. In addition, these results will help to demonstrate the role of Sc-GS in ammonia nitrogen metabolism and provide markers related to ammonia nitrogen tolerance for molecular marker-assisted selection (MAS) of the razor clam.

Transcriptomic Analysis of Gill and Hepatopancreas in Razor Clam (Sinonovacula constricta) Exposed to Acute Ammonia

“…In addition, an unnegligible pathway of detoxifying ammonia into urea, which had been commonly found in the liver of ureogenic animals, maintained low concentration of ammonia. It occurs principally through ornithine-urea cycle involving catalysis of crucial enzymes, including arginase (ARG), argininosuccinate synthetase (ASS), and GS (Mommsen and Walsh, 1989;You et al, 2018;Sun et al, 2021). Although the study on molecular mechanism underlying regulation expose to ammonia in molluscs is still at its infancy, preliminary studies have been reported.…”

“…Of the top 10 sensitive genera, eight genera belong to molluscs (USEPA, 2013). However, the clam-fish/shrimps polyculture makes razor clam to face to high concentration of ambient ammonia (Sun et al, 2021). Therefore, S. constricta is a suitable model species to explore the molecular mechanism of higher tolerance to ammonia in molluscs.…”

Expression and Functional Analysis of AMT1 Gene Responding to High Ammonia Stress in Razor Clam (Sinonovacula constricta)

“…Remarkably, as benthic animals are often faced with higher ammonia concentrations compared with pelagic animals, they have evolved several mechanisms to adapt to high ambient ammonia [19]. In fact, excellent ammonia tolerance has been found in many marine bivalves, especially S. constricta, which lives under 30-40 cm of mud in ponds with an extreme high ammonia concentration [22,29]. A majority of aquatic invertebrates are ammonotelic and excrete ammonia primarily in the form of NH 3 or NH 4 + , rather than relying on ammonia metabolism [19,30].…”