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International Journal Of Bilogical Sciences

.: Home > International Journal Of Bilogical Sciences > 2015 > Volume 11 Number 10 > Yi-Fang Wang1,2, Jia-Jiun Yan2, Yung-Che Tseng3, Ruo-Dong Chen2 and Pung-Pung Hwang1,2

Molecular Physiology of an Extra-renal Cl- Uptake Mechanism for Body Fluid Cl- Homeostasis

Yi-Fang Wang1,2, Jia-Jiun Yan2, Yung-Che Tseng3, Ruo-Dong Chen2 and Pung-Pung Hwang1,2
1. Institute of Fishery Science, National Taiwan University, Taipei city, Taiwan 2. Institute of Cellular and Organismic Biology, Academia Sinica, Taipei city, Taiwan 3. Department of Life Science, National Taiwan Normal University, Taipei city, Taiwan Corresponding author: pphwang@gate.sinica.edu.tw
Abstract :

The development of an ion regulatory mechanism for body fluid homeostasis was an important trait for vertebrates during the evolution from aquatic to terrestrial life. The homeostatic mechanism of Cl- in aquatic fish appears to be similar to that of terrestrial vertebrates; however, the mechanism in non-mammalian vertebrates is poorly understood. Unlike in mammals, in which the kidney plays a central role, in most fish species, the gill is responsible for the maintenance of Clhomeostasis via Cl- transport uptake mechanisms. Previous studies in zebrafish identified Na+ -Clcotransporter (NCC) 2b-expressing cells in the gills and skin as the major ionocytes responsible for Cl- uptake, similar to distal convoluted tubular cells in mammalian kidney. However, the mechanism by which basolateral ions exit from NCC cells is still unclear. Of the in situ hybridization signals of twelve members of the clc Cl- channel family, only that of clc-2c exhibited an ionocyte pattern in the gill and embryonic skin. Double in situ hybridization/immunocytochemistry confirmed colocalization of apical NCC2b with basolateral CLC-2c. Acclimation to a low Cl- environment increased mRNA expression of both clc-2c and ncc2b, and also the protein expression of CLC-2c in embryos and adult gills. Loss-of-function of clc-2c resulted in a significant decrease in whole body Clcontent in zebrafish embryos, a phenotype similar to that of ncc2b mutants; this finding suggests a role for CLC-2c in Cl- uptake. Translational knockdown of clc-2c stimulated ncc2b mRNA expression and vice versa, revealing cooperation between these two transporters in the context of zebrafish Cl- homeostasis. Further comparative genomic and phylogenetic analyses revealed that zebrafish CLC-2c is a fish-specific isoform that diverged from a kidney-predominant homologue, in the same manner as NCC2b and its counterparts (NCCs). Several lines of molecular and cellular physiological evidences demonstrated the cofunctional role of apical NCC2b and basolateral CLC-2c in the gill/skin Cl- uptake pathway. Taking the phylogenetic evidence into consideration, fish-specific NCC2b and CLC-2c may have coevolved to perform extra-renal Cl- uptake during the evolution of vertebrates in an aquatic environment.

Keywords :
ionocyte, CLC chloride channel, NCC, coevolution, zebrafish

Date Deposited : 08 Mar 2016 10:39

Last Modified : 08 Mar 2016 10:39

Official URL: http://www.ijbs.com/v11i10

Volume 11, Number 10, - 2015 , ISSN 1449-2288

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