Expression and regulation of gill ion transporters in Japanese medaka (Oryzias latipes) during SW acclimation
Date Issued
2008
Date
2008
Author(s)
Lai, Yun-Wei
Abstract
Euryhaline teleosts have to cope with the fluctuating salinities of the environments in which they inhabit during their life time. In current model of gill salt scecretion of seawater- (SW) adaptated teleosts, mitochondria-rich cells (MR cells) play the major roles in the active ion secretion mechanism. The ion secretion mechanism in SW gill MR cells is achieved by the balsolateral Na+/K+-ATPase (NKA) and Na+/K+/2Cl- cotransporter (NKCC), and an apical membrane located cystic fibrosis transmembrane conductance regulator (CFTR). However, this model still lacks sufficient molecular evidences and leaves some controversies in the previous studies. The present study used Japanese medaka (Oryzias latipes, OL) as the model species to provide molecular and physiological evidence to support the roles of the relevant transporters in the current NaCl secretion model of SW type MR cells. The mortality experiment showed that OL enhanced their salinity adaptability after a pre-acclimation to SW and even after back to FW for 1 wk. This study examined the mRNA expression patterns of 8 transporter isoforms, and found that 3 NKA isoforms (atp1a1a.1, atp1b1a and atp1b1b), 1 NKCC (slc12a1a) and 1 CFTR (abcc7) mRNA levels were up-regulated during SW exposure, suggesting that these genes may play critical roles in salt secretion. Interestingly, the elevated mRNA levels of atp1b1b and slc12a2a in SW medaka were prolonged even after transfer back to FW for 1 wk, indicating that occurrence of a latent salt secretion mechanism of these 2 genes may be necessary for the subsequent salinity challenge as we mentioned above. Furthermore, atp1a1a.1, atp1b1b, slc12a2a and abcc7 were found to be co-expressed in the same MR cell, providing the first molecular evidence for their isoform-specific identities. The cell number of proliferation (by PH3 stainning) and apoptosis (by TUNEL assay) in gill MR cells showed that the gill cell’s turnover rate is faster in SW than in FW. In addition, olfoxi3 expression indicated the differentiation of MR cells during SW acclimation. NKCC and CFTR mRNA expression levels highly related to the number of SW-type MR cells. According to these results, we proposed that the differentiation of immature cells into SW-type MR cells can be accelerated to enhance NaCl secretion pathway in SW. In summary, several isoforms were isolated from gill MR cells of OL, and in vivo molecular evidences demonstrated their roles in iono/osmo-regulation and cell differentiation mechanisms in fish gills. This supports the notion that the expressions of these ion transporters correlate with the NaCl secretion function in MR cells, and also offer new insights into the studies on salinity tolerance in euryhaline teleosts.
Subjects
medaka
ion transporter
MR cells
gill
seawater acclimation
File(s)![Thumbnail Image]()
Loading...
Name
ntu-97-R95b46005-1.pdf
Size
23.32 KB
Format
Adobe PDF
Checksum
(MD5):129d1cd1c945316dd6477dc226009c9a