Immunohistochemical characterization and change in location of branchial ionocytes after transfer from freshwater to sea
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ORIGINAL PAPER
Immunohistochemical characterization and change in location of branchial ionocytes after transfer from freshwater to seawater in the euryhaline obscure puffer, Takifugu obscurus Tie Ding1 · Yan Shi1 · Wen Duan1 · Sufei Hu1 · Zhe Zhao1 Received: 30 April 2020 / Revised: 21 June 2020 / Accepted: 10 July 2020 © Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract The obscure puffer Takifugu obscurus is a euryhaline fish species suitable for studying the molecular mechanism of osmoregulation. The distributional changes of branchial ionocytes were detected following the transfer from freshwater (FW) to seawater (SW) based on two main ion transporters, Na+/K+-ATPase (NKA) and Na+/K+/ 2Cl− cotransporter 1 (NKCC1). The mRNA and protein expression levels of NKA and NKCC1 in the gills all increased rapidly in the first four days after transfer to SW. Double immunofluorescence staining showed that NKCC1 and NKA were colocalized in the branchial ionocytes and the immunoreaction of NKCC1 was stronger after transfer. Moreover, following transfer to SW, the number of lamellar ionocytes in the gills is reduced and the number of filament ionocytes is increased significantly. Taken together, these findings indicated that SW transfer of obscure puffer promotes the changes of distribution, function and size of branchial ionocytes. Keywords Ionocyte · Gill · Osmoregulation · Takifugu obscurus · Na+/K+-ATPase · Na+/K+/2Cl− cotransporter 1
Introduction Osmoregulation is necessary for fish to retain their body fluid ionic and osmotic homeostasis (Yancey 2005). Euryhaline fishes can live in waters with a wide range of salinities and maintain their plasma osmolality within narrow ranges (Henry et al. 2012). The osmoregulation of euryhaline fishes takes place mainly in the gills, kidney, and intestine which are osmoregulatory organs responsible for ion and water transports (Seo et al. 2013). The gills carry out the majority of ionoregulation tasks (Hwang and Lee 2007). Branchial ionocytes are the major cells of ion absorption and ion secretion in euryhaline fishes. Ionocytes secretions in seawater (SW) and absorb ions in freshwater (FW) through multiple ion pumps, transporters, and channels in apical and basolateral membranes (Kang et al. 2008). The function of ionocytes is usually identified by detecting the expression Communicated by Bernd Pelster. * Yan Shi [email protected] 1
Department of Marine Biology, College of Oceanography, Gulou District, Hohai University, No.1 Xikang Road, Nanjing 210098, People’s Republic of China
and localization of various ion transporters, such as Na+/K+ATPase (NKA), Na+/K+/ 2Cl− cotransporter 1 (NKCC1). The NKA is a key membrane-bound enzyme for osmoregulation in fish, creating ionic and electrical gradient to drive the ion transport system. The NKA enzyme consists of two major subunits. The α subunit is the main catalytic subunit and contains all of the critical binding sites for ATP, Na+, K+. The NKA β subunit is a glycosylated polypeptide, and its main functio
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