WNK1 and p38-MAPK distribution in ionocytes and accessory cells of euryhaline teleost fish implies ionoregulatory function.

W S Marshall,M Spieker,R R F Cozzi

doi:10.1242/bio.024232

W S Marshall, M Spieker + Show 1 more

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https://doi.org/10.1242/bio.024232

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Journal: Biology open	Publication Date: Jan 1, 2017
Citations: 8	License type: CC BY 3.0

Affiliation: St. Francis Xavier University, University of Kassel

Abstract

ABSTRACTIonocytes of euryhaline teleost fish secrete NaCl, under regulation by serine and threonine kinases, including with-no-lysine kinase (WNK1) and p38 mitogen-activated protein kinase (MAPK). Mummichogs (Fundulus heteroclitus L.) were acclimated to freshwater (FW), full strength seawater (SW) and hypersaline conditions (2SW). Immunocytochemistry of ionocytes in opercular epithelia of fish acclimated to SW and 2SW revealed that WNK1-anti-pT58 phosphoantibody localized strongly to accessory cells and was present in the cytosol of ionocytes, close to cystic fibrosis transmembrane conductance regulator (CFTR) in the apical membrane and the sodium potassium 2 chloride cotransporter (NKCC) in the basolateral membrane. In FW acclimated fish, WNK1 localized to a sub-apical zone, did not colocalize with apical membrane-located sodium chloride cotransporter (NCC), and typically was present in one cell of paired ionocytes and in some single ionocytes. Forskolin treatment (10 μM, 30 min) increased WNK1 immunofluorescence in SW ionocytes only, while hypertonicity had little effect, compared to controls. Anti-p38-MAPK antibody localized to the cytosolic compartment. The distribution of WNK1 and p38MAPK is consistent with a proximal position in regulatory cascades, rather than directly affecting transporters. The strong staining of accessory cells by WNK1 phosphoantibody infers an osmoregulatory function for WNK.

Highlights

The ionocytes of teleost fishes are a focus of research into osmoregulation and ion balance (Edwards and Marshall, 2013;Evans et al, 2005)
Immunocytochemistry of ionocytes in opercular epithelia of fish acclimated to SW and 2SW revealed that WNK1-antipT58 phosphoantibody localized strongly to accessory cells and was present in the cytosol of ionocytes close to, cystic fibrosis transmembrane conductance regulator (CFTR) in the apical membrane and sodium, potassium, 2 chloride cotransporter (NKCC) in basolateral membrane
In marine teleost fish and euryhaline teleost fish acclimated to SW, ion secretion is accomplished by ionocytes via a basolateral-located NKCC1, which drives Cl- into the cell, in series with the anion channel, CFTR in the apical membrane, by which Cl- leaves down its electrochemical gradient

Summary

Introduction

The ionocytes (formerly known as mitochondrion-rich cells and chloride cells) of teleost fishes are a focus of research into osmoregulation and ion balance (Edwards and Marshall, 2013;Evans et al, 2005). In marine teleost fish and euryhaline teleost fish acclimated to SW, ion secretion is accomplished by ionocytes via a basolateral-located NKCC1, which drives Cl- into the cell, in series with the anion channel, CFTR in the apical membrane, by which Cl- leaves down its electrochemical gradient. Regulation of the transcellular ion transport pathway involves hormone and neurotransmitter regulation, principally via Ca2+-mediated inhibition of Cl- secretion and cAMPmediated stimulation of Cl- secretion via activation of NKCC and CFTR. FAK apparently can regulate CFTR at the apical membrane (Marshall et al., 2009), and in mammalian airway epithelial cells (Calu-3) the related tyrosine kinase, PYK2, activates CFTR (Billet et al, 2015). Y WNK1 is involved in ion transport regulation (see below), and the present research attempts to connect WNK1 to transport regulation in teleost ionocytes by localizing this regulatory enzyme to the ion transporting cells

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