Functional classification of gill ionocytes and spatiotemporal changes in their distribution after transfer from seawater to fresh water in Japanese seabass

Abstract

Spatiotemporal changes in branchial ionocyte distribution were investigated following transfer from seawater (SW) to freshwater (FW) in Japanese seabass. The mRNA expression levels of cystic fibrosis transmembrane conductance regulator (CFTR) and Na/K/2Cl cotransporter 1a (NKCC1a) in the gills rapidly decreased after transfer to FW, whereas Na/H exchanger 3 (NHE3) and Na/Cl cotransporter 2 (NCC2) expression were upregulated following the transfer. Using quadruple-color whole-mount immunofluorescence staining with anti-Na/K-ATPase, anti-NHE3, anti-CFTR and T4 (anti-NKCC1a/NCC2) antibodies, we classified ionocytes into one SW type and two FW types: NHE3 cell and NCC2 cell. Time course observation after transfer revealed an intermediate type between SW-type and FW-type NHE3 ionocytes, suggesting functional plasticity of ionocytes. Finally, on the basis of the ionocyte classification of Japanese seabass, we observed the location of ionocyte subtypes on frozen sections of the gill filaments stained by triple-color immunofluorescence staining. Our observation indicated that SW-type ionocytes transformed into FW-type NHE3 ionocytes and at the same time shifted their distribution from filaments to lamellae. However, FW-specific NCC2 ionocytes appeared mainly in the filaments. Taken together, these findings indicate that ionocytes originated from undifferentiated cells in the filaments and expanded their distribution to the lamellae during FW acclimation.

Ion uptake pathways in European sea bass Dicentrarchus labrax

“…Immunolocalization of NHE3 shows an apical localization in a subset of ionocytes that also express Na + /K + -ATPase as previously shown in rainbow trout PNA+ MRC, zebrafish HR cells and Mozambique tilapia type-III ionocytes Hwang, 2011;Inokuchi et al, 2008). We have not detected NHE3 in apical membranes of gill ionocytes from SW fish unlike previous data obtained in other species like Japanese sea bass (Inokuchi et al, 2017). NH 4 + -dependent Na + uptake has been identified in medaka, trout and zebrafish (Shih et al, 2012;Wright and Wood, 2009;Wu et al, 2010).…”

“…immunostaining which suggests the presence of NKCC1 in these cells as shown recently in the Japanese sea bass Lateolabrax japonicus (Inokuchi et al, 2017). In NHE3-expressing cells from the FW condition, T4 staining intensity is clearly lower than in ionocytes from fish maintained in SW condition.…”

“…Na + /Clcotransporters are called ncc1 (slc12a3) or ncc2 (or ncc-like) (slc12a10). The latter have been analyzed in different teleost species (Breves et al, 2014;Hiroi et al, 2008;Hsu et al, 2014;Inokuchi et al, 2017;Takei et al, 2014;Wang et al, 2009). Among different paralogs belonging to the ncc2 family, zebrafish slc12a10.2 was specifically expressed in the gills and its expression is stimulated in a low-Clenvironment and not in a low-Na + environment (Wang et al, 2009).…”

An intestinal cell type in zebrafish is the nexus for the SARS-CoV-2 receptor and the Renin-Angiotensin-Aldosterone System that contributes to COVID-19 comorbidities

“…3F) and in an unidentified type of mesenchyme (c135), likely vascular precursors. In mammals, the kidney controls ion and water balance and expresses Agtr1 (Miyata et al, 1999), but in fish, ionocytes in the skin control ion and water balance (Dymowska et al, 2012;Guh et al, 2015;Inokuchi et al, 2017;Kwong et al, 2016) although they did not have detectable agtr1a or agtr1b expression in the Atlas despite the fact that eel ionocytes express a protein that binds a mouse antibody to Agtr1 (Marsigliante et al, 1997). Expression of agtr1a was not detected in the Atlas.…”

Effect of dendritic organ ligation on striped eel catfish Plotosus lineatus osmoregulation

“…The staining pattern of the T4 antibody indicates NKCC1 immunoreactivty based on the cytosolic staining pattern. As noted earlier the T4 antibody also crossreacts with NCC and NKCC2 but these can be distinguished based on their apical distribution [ 60 , 61 ]. The sparsity of immunoreactive cells indicates that the tissue protein expression levels were likely well below the sensitivity of the Western blotting technique.…”