Interrogation of the Gulf toadfish intestinal proteome response to hypersalinity exposure provides insights into osmoregulatory mechanisms and regulation of carbonate mineral precipitation

Marine bony fish live in a hyperosmotic environment and maintain osmotic homeostasis by drinking seawater, and absorbing salt and water across their gastrointestinal tract. Although the ion and water transport mechanisms in the intestine have been the subject of much study, numerous questions remain unanswered. To address some of these questions, a shotgun proteomics methodology employing isobaric tandem mass tags (TMT) was used to interrogate the anterior intestine, posterior intestine, and intestinal fluid proteomes of Gulf toadfish (Opsanus beta) acclimated to normal (35 ppt) or hypersaline (60 ppt) seawater. Relative protein abundance between tissues was also investigated using label free quantitation. Protein products from nearly 3000 unique toadfish loci were identified and quantified between the tissues, and pathway analysis was performed to gain insight into biological significance. Numerous proteins potentially involved in ion transport, digestion, nutrient absorption, and intestinal CaCO3 precipitation were found to respond to changing salinity, providing additional insight into the molecular mechanisms behind these processes. Intestinal protein heterogeneity was also observed with proteins involved in ion transport responding to hypersalinity exposure primarily in the anterior intestine, and proteins involved in digestion and nutrient absorption showing higher abundance in the anterior intestine, regardless of salinity.