Characterization of the heat shock protein response of Atlantic salmon (Salmo salar)

The heat shock protein (hsp) response of juvenile Atlantic salmon, Salmo salar was investigated in isolated tissues subjected to various degrees of thermal shock. Distinct but overlapping arrays of proteins from the major hsp families (hsps 100, 90, 70, 60 and small hsps) were induced in branchial lamellae, hepatic tissue and erythrocytes. The two most prominent proteins induced by heat shock (MW ≅ 65 and 66 kDa) were found to be antigenic homologues of mammalian hsps72/73. A 2.6 kb transcript upregulated by the same conditions hybridized with cDNA probes to both human and salmon hsp70. Branchial lamellae exhibited the greatest degree of thermotolerance and mounted the most significant heat shock response. Moderate thermal shock induced more species of proteins in branchial lamellae than in hepatic tissue or erythrocytes, with the rate of hsp65/66 synthesis increased by as much as five fold. Thermal shock induced hsp65/66 eight fold in erythrocytes. In contrast, hepatic tissue which was least tolerant of thermal shock, lacked the inducible hsp65 and exhibited minimal induction of hsp66. Persistence of hsps was tested in erythrocytes, where elevated levels remained in the cells for at least 48 h after heat shock. The temporal pattern and magnitude of the hsp response in the stenothermal Atlantic salmon differed from that previously reported for eurythermal species. Also notable was the limited hsp response mounted by salmon tissues exposed to sodium arsenite, a known inducer of hsps. The characteristics of the hsp response to thermal shock support the significance of these proteins in adaptation of Atlantic salmon to environmental insult.