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The cellular heat shock response and thermotolerance of fishes Nakano, Kazumi

Abstract

The relationship between the cellular heat shock response and thermotolerance was examined in fishes. The first series of experiments was conducted on fishes from various latitudes whose body and water temperatures range from -1.7 °C in Antarctica to 37 °C in the sub-tropical ocean. Although all fishes synthesized 70-kDa heat shock protein (hsp70) under a heat stress, the induction temperature for hsp70 was strongly correlated with the habitat temperature of the species. A higher hsp70 mRNA level at a near-lethal temperature in the Antarctic fish, Trematomus bernacchii, was not associated with a higher level of hsp70. A part of the translational pathway from hsp70 mRNA to hsp70 might have been modified in this species during adaptation to extreme cold. Thus, they might not be able to increase the level of hsp70, at least, immediately after heat shock. I chose the intertidal cottids as model animals to examine the relationship between the level of hsp70 and the thermotolerance of fish in more detail. The tidepool sculpin (Oligocottus maculosus) is known to be distributed over a wide range of the intertidal zone including upper tidepools where it can experience wider temperature extremes than in lower tidepools that are usually occupied by the fluffy sculpin (O. snyderi). The lethal temperature and the induction temperature for liver hsp70 were higher in the tidepool sculpin, while changes in hsp70 levels were more thermally sensitive in the fluffy sculpin. The relationship between hsp70 mRNA and hsp70 levels in those sculpins under heat shock imply that the cellular concentration of hsp70 may be controlled at the translational level in the tidepool sculpin, and at the transcriptional level in the fluffy sculpin. Higher viability under a severe heat shock at 28 °C was observed in the tidepool sculpin in its natural habitat than in the same species which was acclimated at constant 10 °C for 2 weeks in the laboratory. This result indicates that the fluctuating environment in the intertidal zone may enhance the resistance to heat in this species. Overall results from this study indicate that, although the cellular heat shock response is conserved in various species of fishes, its function as well as the range of functional temperature seems to have been modified during the adaptation to the habitat temperature of the species. Studies in the intertidal sculpins imply that a relatively small difference in the habitat temperature can cause these modifications.

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