Acclimation of the threshold induction temperatures for 70-kDa and 90-kDa heat shock proteins in the fish Gillichthys mirabilis.

The characteristic heat shock or stress response is induced upon exposure of an organism (cell) to a number of environmental stressors, e.g. heat, anoxia and heavy metals (reviewed in Morimoto et al. 1990; Ellis and van der Vies, 1991). The heat shock or stress proteins are the most broadly distributed class of proteins known and amongst the most highly conserved. These stress proteins and their cognates (non-stress-inducible forms of the proteins) play key roles in the proper folding, oligomerization, compartmentalization, translocation and activation of other cellular proteins. They have additionally been implicated in the process of acquired thermotolerance (Bosch et al. 1988; Mosser and Bols, 1988; McLennan and Miller, 1990; Sanchez and Lindquist, 1990) and in restoring aberrant proteins to their native state subsequent to thermal denaturation (Morimoto et al. 1990). Although a widely studied phenomenon in cultured cells and isolated tissues, few studies of the stress response have investigated adaptation of the transcriptional regulatory process in organisms adapted or acclimated to different thermal conditions (Whyard et al. 1986; Koban et al. 1987; Oda et al. 1991; Sanders et al. 1991; Dietz and Somero, 1992, 1993; Ulmasov et al. 1992). Previously we have shown that the eurythermal fishes Gillichthys mirabilis and G. seta (family Gobiidae) shifted their threshold induction temperature for enhanced synthesis of heat shock protein (HSP) 90 in brain by at least 4 ̊C on a seasonal basis (Dietz and Somero, 1992). These data are evidence that the recent thermal history of an organism can affect HSP threshold induction temperatures and that stress protein gene induction set points are not genetically hard-wired. The present study extends this type of analysis by determining the effect of acclimation temperature on the threshold induction temperatures of HSP70 and HSP90, two readily heat inducible proteins, in the brain, gill and liver tissues of G. mirabilis. Acclimation of G. mirabilis to approximately its preferred temperature and temperatures close to its high and low tolerance extremes allowed the ability of thermal