Heat-shock protein expression is absent in the Antarctic fish Trematomus bernacchii (family Nototheniidae)

The heat-shock response, the enhanced expression of one or more classes of molecular chaperones termed heat-shock proteins (hsps) in response to stres s induced by high temperatures, is commonly viewed as a 'universal' charact eristic of organisms. We examined the occurrence of the heat-shock response in a highly cold-adapted, stenothermal Antarctic teleost fish, Trematomus bernacchii, to determine whether this response has persisted in a lineage t hat has encountered very low and stable temperatures for at least the past 14-25 million years, The patterns of protein synthesis observed in in vivo metabolic labelling experiments that involved injection of S-35-labelled me thionine and cysteine into whole fish previously subjected to a heat stress of 10 degrees C yielded no evidence for synthesis of any size class of hea t-shock protein. Parallel in vivo labelling experiments with isolated hepat ocytes similarly showed significant amounts of protein synthesis, but no in dication of enhanced expression of any class of hsp, The heavy metal cadmiu m, which is known to induce synthesis of hsps, also failed to alter the pat tern of proteins synthesized in hepatocytes, Although stress-induced chaper ones could not be detected under any of the experimental condition used, so lid-phase antibody (western) analysis revealed that a constitutively expres sed 70 kDa chaperone was present in this species, as predicted on the basis of requirements for chaperoning during protein synthesis. Amounts of the c onstitutively expressed 70 kDa chaperone increased in brain, but not in gil l, during 22 days of acclimation to 5 degrees C, The apparent absence of a heat-shock response in this highly stenothermal species is interpreted as a n indication that a physiological capacity observed in almost all other org anisms has been lost as a result of the absence of positive selection durin g evolution at stable sub-zero temperatures. Whether the loss of the heat-s hock response is due to dysfunctional genes for inducible hsps (loss of ope n reading frames or functional regulatory regions), unstable messenger RNAs , the absence of a functional heat-shock factor or some other lesion remain s to be determined.