Genome-wide identification of the Na+/H+ exchanger gene family in Lateolabrax maculatus and its involvement in salinity regulation

Na+/H+ exchangers (NHEs) are one of the major groups of transmembrane proteins that play crucial roles in pH homeostasis, cell volume regulation and Na+ transport in animals. In our study, twelve NHEs were identified from transcriptomic and genomic databases of Lateolabrax maculatus. The evolutionary footprint of each NHE gene was revealed via the analysis of phylogenetic tree, copy numbers, exon-intron structures and motif compositions. NHEs harbored a high proportion of alpha-helices (54.7% to 67.0%) and a low proportion of beta-sheets (1.3%) and contained 9-13 transmembrane helices (TM). Results of tissue distribution detection revealed that L. maculatus NHE genes exhibited different expression profiles in a tissue-specific manner under normal physiological conditions. In the main osmoregulatory organ, gill, NHE2c and NHE3 showed significant higher expression comparing with other L. maculatus NHE genes. To gain insight into the potential function of L. maculatus NHE genes in response to salinity changes, we evaluated their expression variation after different salinity treatment (0 ppt, 12 ppt, 30 ppt, 45 ppt). During acute salinity stress experiment, L. maculatus NHE genes were regulated in a gene-specific and time-dependent manner. Most NHE genes were upregulated to different extent by low salinity (0 ppt) and exhibited the highest expression value in gills at 6 h, while NHE2c and NHE3 were the most strongly induced genes, suggesting they may play crucial roles in salinity and osmotic regulation. In addition, the expressions of several NHE genes were regulated by isotonic or high salinity treatments, indicating their potential involvements in response to salinity challenge. Our findings in this study provide a foundation for future studies about NHE gene deciphering stress physiology correlated to salinity and osmotic regulation in teleosts.