Proteomic analysis on the alteration of protein expression in gills of ayu (Plecoglossus altivelis) associated with salinity change

Gill is the primary osmoregulatory organ for euryhaline fish to acclimate salinity change. The effect of salinity on gill proteome in ayu, Plecoglossus altivelis, was investigated by two-dimensional gel electrophoresis (2-DE) and matrix assisted laser desorption ionization time-of-flight tandem mass spectrometry (MALDI-TOF-MS/MS). Eight of eighteen altered proteins were successfully identified. They are involved in osmoregulation, cytoskeleton, energy metabolism, and stress response. Our results showed that vinculin, echinoderm microtubule-associated protein like protein 1, pyruvate kinase, betaine–homocysteine methyltransferase (BHMT), transaldolase, glyceraldehyde 3-phosphate dehydrogenase, and heat shock protein 70 (HSP70) were down-regulated, whereas cofilin was up-regulated when ayu transferred from fresh water (FW) to brackish water (BW). Partial cDNA sequences of BHMT, HSP70, Na+/K+ ATPase (NKA) α-subunit and 18S rRNA genes were subsequently determined and used for 2-DE data verification by real-time PCR. Gill BHMT and HSP70 mRNAs decreased significantly in BW-transferred ayu, while NKA α-subunit mRNA had no significant change. It was suggested that cell volume-regulatory response, especially the protection by the BHMT/betaine system might play an important role in ayu acclimation to salinity change.