Salinity‐Dependent Expression of ncc‐like 2 in the Gill and Opercular Epithelium of Euryhaline Killifish

Abstract

Atlantic killifish (Fundulus heteroclitus) can tolerate abrupt changes in environmental salinity because of their ability to rapidly adjust the activities of ionocytes in the gill and opercular epithelium. Salinity acclimation responses often entail the coordinated and dynamic expression of genes encoding effectors of ion transport. For example, exposure to seawater (SW) induces elevated gene transcription of Na+/K+/2Cl− cotransporter (nkcc) and cystic fibrosis transmembrane regulator (cftr) in support of the ion‐extrusion capacities of SW‐type ionocytes. On the other hand, it has not been fully resolved how freshwater (FW)‐type ionocytes in teleosts, including F. heteroclitus, actually mediate ion uptake at the sub‐cellular level. A recently characterized Na+/Cl− cotransporter (Ncc) has been proposed as a conduit for the uptake of Na+ and Cl− across the apical surface of FW‐type ionocytes in a subset of teleosts. To examine whether killifish employ an Ncc‐dependent ion‐uptake pathway, we first identified a putative ncc‐like 2 in F. heteroclitus that was highly expressed in the gill and opercular epithelium. Transfer of killifish from SW to FW elicited an increase in ncc‐like 2 levels in both gill and opercular epithelium in parallel with reductions in nkcc and cftr levels. On the other hand, transfer from FW to SW resulted in a marked reduction in ncc‐like 2 levels concurrent with increases in nkcc and cftr. We will describe the distribution of Ncc‐like 2 immunoreactivity in the gill and operculum epithelium by employing an anti‐killifish Ncc‐like 2 antibody. We propose that ncc‐like 2‐expressing ionocytes support the capacity of F. heteroclitus to acclimate to freshwater environments.Support or Funding InformationSupported by Start‐Up funds to J.P.B.