Chronic Salinity Adaptation Modulates Hepatic Heat Shock Protein and Insulin-like Growth Factor I Expression in Black Sea Bream Eddie E. Deane, Scott P. Kelly, James C.Y. Luk, and Norman Y.S. Woo* Department of Biology, The Chinese University of Hong Kong, Shatin, NT, Hong Kong SAR, China Abstract: Black sea bream (Mylio macrocephalus) hepatic heat shock proteins hsp90, hsp70, and hsp60 were found to be thermally and reversibly inducible as they were elevated 2.0, 3.2, and 2.1 fold, respectively, on acute heat shock and returned to pre-heat-shock levels after a 40-hour recovery period. To establish whether salinity plays a role in regulating heat shock protein (hsp) and insulin-like growth factor-I (IGF-I) expression in a euryhaline marine fish, we adapted groups of juvenile black sea bream to salinities of 50 ppt (hypersaline), 33 ppt (seawater), 12 ppt (isoosmotic), and 6 ppt (hypoosmotic) for 8 months. The lowest levels of hsps were found in fish reared in an isoosmotic salinity and the highest in those adapted to hypersaline and hypoosmotic salinities. Hepatic -actin messenger RNA abundance remained unchanged in all groups during salinity ad- aptation, whereas IGF-I mRNA abundance was highest in isoosmotic adapted black sea bream. This study is the first report of an effect of salinity ranging from hypersaline to hypoosmotic on the expression of different hsp forms and IGF-I in fish, and the possible relationship between environmental salinity, hepatic IGF-I expression, and hsp regulation is discussed. Key words: fish, salinity, hsp90, hsp70, hsp60, IGF-I. I NTRODUCTION Salinity fluctuations within the environment can occur naturally as tidal movements fluctuate, or it can change as a result of anthropogenic influences. Alterations in salinity can result in aquatic organisms becoming osmotically stressed, and as a result cellular ion regulation mechanisms can be adversely affected, which in turn can cause alter- ations in cellular protein structure. When normal cellular processes are adversely affected, a suite of proteins belong- ing to the heat shock protein (hsp) families are rapidly synthesized. These hsps are commonly called stress proteins as their up-regulation is often observed when organisms are subjected to an array of abiotic stressors including osmotic and heat stress (Hightower, 1991; Iwama et al., 1998). This rapid up-regulation of hsp is known as the heat shock re- sponse and serves a protective function for stressed animals. In addition, the salinity of the aquatic environment may itself determine whether the heat shock response of an or- ganism is augmented or attenuated on exposure to other abiotic or biotic stressors. A recent study on the golden brown algae Isochrysis Received July 18, 2001, accepted November 21, 2001 *Corresponding author: telephone (852) 26096148; fax (852) 26035646; e-mail normanwoo@cuhk.edu.hk Mar. Biotechnol. 4, 193–205, 2002 DOI: 10.1007/s1012602-0091-5 © 2002 Springer-Verlag New York Inc.