| Heat shock proteins are molecular chaperones. Atlantic salmon is a major aquaculture species in the world, their anadromous nature made them encounter osmotic shock twice in the life cycle. Salmon prior treated with a mild thermal shock observed a significantly higher survival rate upon transfer to hyperosmotic seawater than control fish. Heat shock protein 70 was prominently induced and persisted up to 24 hours after initial heat shock. Fish with prior heat shock treatment exhibited significant higher rate of protein synthesis over control after transfer to seawater. Hsp90 is known to enhance the fidelity of glucocorticoid hormone and receptors. Northern blot analysis showed that hsp90 messenger level was up regulated by osmotic stress in branchial lamellae, but not kidney both in isolated tissues and whole animal.; To identify osmotic response genes, differential display was used to generate the probe to screen an osmotic shock cDNA library. Four cDNA fragments with a range from 150 to 250 nucleotides were isolated. The cDNA library was screened using two of the cDNA probes, and two clones were identified with insert sizes of 1.3 and 2.0 kb, designated to osp1.1 and osp4.0. Sequence analysis suggest that osp1.1 contains an ORF of 262 amino acids, with a molecular weight of 27.5 kDa, and shares 70% identity with a human cold inducible RNA binding protein. However, osp4.0 contains an ORF of 189 amino acids, with a molecular weight of 20.9 kDa, contains a peroxisomal targeting signal. A 108 amino acid region of osp4.0 shares 98% of identity with a human protein Rbx1. Further characterization suggested that upregulation of both osp1.1 and osp4.0 was dose dependent, extreme hyperosmotic shock inhibited expression. Osp1.1 most prominently expressed in liver, while osp4.0 in heart. Both transcripts increased expression over the course of hyperosmotic treatment. The solute replacement study revealed both osp1.1 and osp4.0 were upregulated by addition of mannitol but not glycerol. Osp1.1 did not respond to heat shock, while osp4.0 increased 2 fold, suggests it is also a heat shock protein. Interestingly, both osp1.1 and osp4.0 were down regulated by sodium arsenite. |
