PLACE, S.P.*; HOFMANN, G.E.; Univ. of California, Santa Barbara; Univ. of California, Santa Barbara: Transcriptional response of hsp70 genes to heat stress in several species of fish in the suborder Notothenioidei

Antarctic notothenioid fishes have evolved at -1.86 ° for 15-25 million years. These fish provide a unique system in which to study the effects of the removal of thermal selection pressures and temperature variation on cellular processes and biomolecules, such as molecular chaperones, whose regulation and function are directly tied to environmental temperature. The ubiquitous roles of molecular chaperones in all taxa have been well described, especially in the cellular response to thermal stress. This response, the heat shock response (HSR), has been shown to be altered and possibly absent at the protein synthesis level in some species of Antarctic notothenioids (Hofmann et al., 2000). To determine if the transcriptional up-regulation of the inducible Hsp genes has also been evolutionary altered, we measured levels of hsp70 mRNA in several species of notothenioid fishes that live at different temperatures. In an effort to establish where along the phylogenetic tree of notothenioids the loss of the HSR has occurred, we included two cold, temperate New Zealand relatives in this analysis: Notothenia angustata, a closely related nototheniid, and the non-Antarctic notothenioid, Bovichtus variegatus, a functional outlier within the notothenioids. For the latter species, previous data indicated a typical HSR at the protein level. Northern blots indicated that hsp70 mRNA was present in cells of Antarctic species at all temperatures, suggesting constitutive expression of an inducible gene; mRNA in B. variegatus and N. angustata showed significant increase with heat shock. These data suggest that regulation of the hsp70 genes in notothenioid fish has undergone an unusual alteration during evolution in the subzero waters of Antarctica. Supported by NSF grant OPP 0087971 to GEH