Heat Shock Responses of Closely Related Species of Tropical and Desert Fish

Over the past twelve years, we have studied heat shock proteinsin two tropical species, a half dozen desert species and a numberof hemiclones of viviparous fishes in the genus Poeciliopsis.Heat shock protein (Hsp) isoform patterns were determined usinghigh resolution two-dimensional polyacrylamide gels. Two familiesof Hsps were studied in detail, the nucleocytoplasmic 70 kilodaltonHsp70 family and the 30 kilodalton Hsp30 family related to -crystallin.The temperature dependence of Hsp accumulation was investigatedusing both intact fish and cultured cells. When the thresholdtemperatures were mapped onto thermal preference profiles, itwas apparent that the Hsp70 threshold (33°C) was closelylinked to the most frequently selected temperatures and theHsp30 threshold (37°C) was closely linked to high temperaturesthat fish rarely selected, indicating that fish deploy thesetwo molecular chaperones differently. One tropical species P.gracilis is a genetic reservoir for most of the Hsp70 isoformsof the desert species. Acquired resistance to 41°C was stronglycorrelated with Hsp70 abundance for gracilis that containedHsp70 isoform 3 whereas fish lacking this isoform showed similarlevels of acquired thermotolerance which did not correlate withHsp70 abundance, suggesting multiple, compensating mechanismsof acquired resistance. Isoform 3 was degraded in cultured cellsfrom a desert species during several hours of recovery at normaltemperature following heat shock whereas two other Hsp70 isoformswere stable. The implications of this property of isoform 3are discussed.