Presence of Na‐K‐ATPase in Mitochondria‐Rich Cells in the Yolk‐Sac Epithelium of Larvae of the TeleostOreochromis mossambicus

Abstract

The purpose of this study is to provide biochemical evidence for the functions of the mitochondria-rich cell (MR cell) in the yolk-sac epithelium of the developing larvae of tilapia Oreochromis mossambicus. Western blotting with the antibody (6F) raised against avian Na-K-ATPase alpha1 subunit demonstrated the presence of Na-K-ATPase in yolk-sac epithelium of tilapia larvae and about 1. 46-fold more of the enzyme in seawater larvae than in freshwater ones. The yolk-sac MR cells were immunoreacted to the antibody (alpha5) against the alpha subunit of avian Na-K-ATPase and were double-labeled with anthroylouabain and dimethylaminostyrylethyl-pyridiniumiodine, suggesting the existence and activity of Na-K-ATPase in these cells. Binding of 3H-ouabain in the yolk sac of seawater larvae was much higher than in that of freshwater larvae (4.183+/-0.143 pmol/mg protein versus 1.610+/-0. 060 pmol/mg protein or 0.0508+/-0.0053 pmol/yolk sac versus 0. 0188+/-0.0073 pmol/yolk sac). These biochemical results are further evidence that yolk-sac MR cells are responsible for a major role in the osmoregulatory mechanism of early developmental stages before the function of gills is fully developed.

Epithelial Ca2+channel expression and Ca2+uptake in developing zebrafish

“…MR cells, which were identified with the signal of the Na ϩ /K ϩ -ATPase protein (a marker for fish MR cells; Ref. 20), occurred initially in the body skin including the yolk sac skin of zebrafish embryos at 24 hpf (data not shown). The number of MR cells in the skin covering both somites and the yolk sac rapidly increased after embryonic development (Fig.…”

Regulation of glycogen metabolism in gills and liver of the euryhaline tilapia (Oreochromis mossambicus) during acclimation to seawater

“…These results indicate that the antibody recognizes different iosforms of the tGS and, thus, can be used to detect the tGS protein in gills and liver. (Tseng et al, 2007;Hwang et al, 1999). Double immunohistochemical labeling was conducted to localize GS, GP, glycogen and MR cells.…”

Mechanism of development of ionocytes rich in vacuolar-type H+-ATPase in the skin of zebrafish larvae

“…The latter process is carried out mainly by specialized cells called mitochondrion-rich cells (MRCs, also referred to as ionocytes or chloride cells), which are located in the gill and characterized by abundant mitochondria and ion transporters and extensive basolateral membrane infoldings that form a tubular system (Evans et al, 2005). In embryonic and larval stages where functional gills are not yet well developed, MRCs are present in the skin covering the yolk and its nearby regions (Ayson et al, 1994; Guggino, 1980; Hiroi et al, 1998; Hiroi et al, 1999; Hwang and Sun, 1989; Hwang et al, 1999; Kaneko et al, 2002; Varsamos et al, 2005). These extrabranchial MRCs are becoming attractive for osmoregulatory research since (1) they are easily accessible for manipulation and visualization and (2) their activities and developmental processes can be studied by knockdown experiments using antisense morpholino oligonucleotides (MOs) whose inhibitory effects are generally maintained until 4 days postfertilization (dpf); at this stage, gills are not formed and therefore the skin MRCs are the main site responsible for the active transport of ions.…”