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Molecular characterization and mRNA expression of Na+/K+-ATPase in the gills of the mudskipper, Boleophthalmus boddarti, on exposure to salinity and/or ammonia stress
Author
Tan, Min Han
Supervisor
Chew, Shit Fun
Abstract
The mudskipper, Boleophthalmus boddarti, is commonly found on the mudflats of estuaries in South East Asia. They are amphibious, euryhaline and highly adaptable to different environmental conditions, including salinity changes, aerial exposure, hypoxia and exposure to ammonia, cyanide and sulfide. Boleophthalmus boddarti is capable of tolerating environmental NH3 concentrations of 36 μM (8 mM NH4Cl) with hardly any mortality. Both osmoregulation and active excretion of NH4+ in mudskippers involved Na+/K+-ATPase (Nka; please refer to http://www.ssr.org/NomenBullets.html on the nomenclature of protein and gene in fish) present on the basolateral membrane of the gill epithelium. This study was undertaken to elucidate if there exist different isoforms of α-subunit of nka in the gills of B. boddarti and to obtain their full cDNA sequences. The functional role of Nka in both osmoregulation and active ammonia excretion was also examined by measuring the mRNA expression of nka in the gills of B. boddarti after exposure to low salinity (3 ppt), low salinity with sublethal concentrations of ammonia (3 ppt + 8 mM NH4Cl), high salinity (25 ppt) and high salinity with sublethal concentrations of ammonia (25 ppt + 8 mM NH4Cl) for 1 day, 4 and 6 days. One isoform of the nka α-subunit has been identified in the gills of B. boddarti. Phylogenetic analyses conducted showed that the isoform shares the highest sequence identity with the Nka α1 present in other teleosts. The mRNA expression of nka α1 was upregulated only after 6 days of exposure to 3 ppt + 8 mM NH4Cl. Interestingly, the mRNA expression of nka α1 was upregulated after 1 day of exposure to 25 ppt + 8 mM NH4Cl and downregulated after 4 days of exposure to the same condition. Thus this study showed for the first time that nka α1 is involved in NH4+ excretion in B. boddarti.
Date Issued
2012
Call Number
QL638.G7 Tan
Date Submitted
2012