Teleosts inhabiting fresh water (FW) depend upon ion-absorptive ionocytes to counteract diffusive ion losses to the external environment. A Clc Cl−channel family member, Clc-2c, was identified as a conduit for basolateral Cl−transport by Na+/Cl−cotransporter 2 (Ncc2)-expressing ionocytes in stenohaline zebrafish (Danio rerio). It is unresolved whether Clc-2c/clc-2cis expressed in euryhaline species and how extrinsic and/or intrinsic factors modulate branchialclc-2cmRNA. Here, we investigated whether environmental salinity, prolactin (Prl) and osmotic conditions modulateclc-2cexpression in euryhaline Mozambique tilapia (Oreochromis mossambicus). Branchialclc-2candncc2mRNAs were enhanced in tilapia transferred from seawater (SW) to FW, whereas both mRNAs were attenuated upon transfer from FW to SW. Next, we injected hypophysectomized tilapia with ovine prolactin (oPrl) and observed a marked increase inclc-2cfrom saline-injected controls. To determine whether Prl regulatesclc-2cin a gill-autonomous fashion, we incubated gill filaments in the presence of homologous tilapia Prls (tPrl177and tPrl188). By 24 h, tPrl188stimulatedclc-2cexpression ~5-fold from controls. Finally, filaments incubated in media ranging from 280 to 450 mosmol/kg for 3 and 6 h revealed that extracellular osmolality exerts a local effect onclc-2cexpression;clc-2cwas diminished by hyperosmotic conditions (450 mosmol/kg) compared with isosmotic controls (330 mosmol/kg). Our collective results suggest that hormonal and osmotic control of branchialclc-2ccontributes to the FW adaptability of Mozambique tilapia. Moreover, we identify for the first time a regulatory link between Prl and a Clc Cl−channel in a vertebrate.
Aquaporin-3 expressed in the basolateral membrane of gill chloride cells in Mozambique tilapia Oreochromis mossambicus adapted to freshwater and seawater
