A comparison of Hsp70 expression and thermotolerance in adults and larvae of three Drosophila species

Heat shock proteins (Hsps) and other molecular chaperones perform diverse p hysiological roles. One is to facilitate, in part, organismal thermotoleran ce, of which the functional consequences depend on Hsp70 concentration and developmental stage in Drosophila melanogaster. To test whether an Hsp70-th ermotolerance relationship is a general phenomenon within Drosophila, I ass ayed Hsp70 concentration at a range of temperatures in intact larvae and ad ults of three species, D. melanogaster, D. simulans, and D. mojavensis, and compared those results to the increase in survival to heat shock that occu rs after an Hsp70 inducing pretreatment. Larvae of D. melanogaster and D. s imulans responded similarly to heat; they expressed Hsp70 maximally at 36-3 7 degrees C, and their tolerance of 1 h heat shocks increased by 1.5-2 degr ees C. By contrast, D. mojavensis, which tolerates higher temperatures than do D. melanogaster and D. simulans, expressed Hsp70 only at higher tempera tures, although the 36 degrees C pretreatment still increased thermotoleran ce. Critically, the temperature that maximally induced Hsp70 was a poor ind ucer of thermotolerance in D. mojavensis and may have harmed larvae. Result s for Drosophila adults, which tolerated heat poorly compared to larvae, li kewise suggest that a close link between peak Hsp70 expression and maximal induction of thermotolerance is a feature of D. melanogaster, and not of th e other species. Neither D. simulans nor D. mojavensis adults increased tol erance after exposure to the temperatures that maximally induced Hsp70. (C) Harcourt Publishers Ltd 1999.