Options
Molecular characterization and mRNA expression of Na+/K+-ATPase in the gills of the giant mudskipper, Periophthalmodon schlosseri, on exposure to salinity and/or ammonia stress
Author
Lam, Sock Peng
Supervisor
Chew, Shit Fun
Abstract
The giant mudskipper, Periophthalmodon schlosseri, an amphibious fish found living on the mudflats has evolved osmoregulatory mechanisms to enable it to survive in low and high salinity. It has the highest tolerance towards ammonia and is able to actively excrete NH4+. Both osmoregulation and active excretion of NH4+ involve Na+/K+-ATPase (NKA denotes protein symbol used for invertebrates and vertebrates except Fish; Nka denotes protein symbol used for Fish) present on the basolateral membrane of the gill epithelium. This study was undertaken to elucidate if there exist different isoforms of the α-subunit of Nka in the gills of P. schlosseri and to obtain their full cDNA sequences. The functional roles of Nka in both osmoregulation and active ammonia excretion were also examined by measuring the mRNA expression of the Na+/K+-ATPase isoforms (nka denotes gene symbol used for Fish) in the gills of P. schlosseri after exposure to 5 ppt water (low salinity), 5 ppt water plus 75 mM NH4Cl, 30 ppt water (seawater) and 30 ppt water plus 75 mM NH4Cl for 1 day. Two isoforms of the cDNA of nka α-subunit have been identified in the gills of P. schlosseri. Phylogenetic analyses conducted showed that these two isoforms when translated into amino acid sequences share the highest sequence identities with Nka α1 and Nka α3 from teleosts, respectively. The mRNA expression of nka α1 in gill arch 1 was up-regulated after the fish was exposed to seawater for 1 day indicating that it could be a seawater-isoform involved in NaCl extrusion to enable the mudskipper to adapt to high salinity during high tide. The mRNA expression of nka α1 was up-regulated only in gill arch 1 while that of nka α3 was up-regulated only in gill arch 4 when P. schlosseri was exposed to 75 mM NH4Cl in 5 ppt water for 1 day. However, the mRNA expressions of both nka α1 and nka α3 were up-regulated in gill arches 1 and 4 when P. schlosseri was exposed to 75 mM NH4Cl in seawater for 1 day. Thus, this study showed for the first time that nka α1 which is necessary for adaptation of the fish to high salinity is also involved in NH4+ excretion while nka α3 is mainly involved in active NH4+ excretion in P. schlosseri.
Date Issued
2011
Call Number
QL638.G7 Lam
Date Submitted
2011