Coordinated Gene Expression of Na+/Cl−cotransporter 1 (ncc1) and Clc family Cl−channel 2 (clcn2c) in Kidney and Urinary Bladder of Euryhaline Tilapia

Abstract

Euryhaline fishes maintain hydromineral balance in a broad range of environmental salinities through the functional coordination of multiple tissues, including the gill, intestine, kidney, and urinary bladder. Fishes inhabiting freshwater (FW) environments are faced with the diffusive loss of ions and the osmotic gain of water. In turn, both kidney and urinary bladder support the reabsorption of Na+ and Cl− and the excretion of excess water. While functional responses by these two organs to FW conditions have been previously described, the subcellular pathways for Na+ and Cl− reabsorption are not well understood. We hypothesized that euryhaline tilapia (Oreochromis mossambicus), employ Na+/Cl− cotransporter 1 (Ncc1) and Clc family Cl− channel 2 (Clcn2c) for the active reabsorption of Na+ and Cl− and thus their respective gene transcripts are expressed under FW conditions. In the current study, we report ncc1 and clcn2c gene expression patterns in both steady‐state animals and animals abruptly transferred from seawater (SW) to FW. In kidney and urinary bladder, ncc1 and clcn2c gene expression was markedly enhanced (>30‐fold) in FW‐ versus SW‐acclimated tilapia. By 6 hours after transfer from SW to FW, ncc1 and clcn2c in both kidney and urinary bladder were coordinately elevated compared with controls continuously maintained in SW. These patterns in the kidney and urinary bladder occurred in concert with branchial processes supportive of Na+ and Cl− absorption from the external environment. Collectively, our results suggest that both Ncc1 and Clcn2c contribute to the functional plasticity of kidney and urinary bladder that underlies acclimation to variable environmental salinities.Support or Funding InformationSupported by the National Science Foundation (IOS‐1755131 and ‐1755016).