Heat-induced expression of a molecular chaperone decreases by selecting for long-lived individuals.

The 70 kDa heat-shock protein (Hsp70) exhibits a broad range of chaperone functions that respond both to internal and external stresses, and its heat-induced expression both declines with age and reduces age-specific mortality rates. Here we test for changes in both longevity and the level of Hsp70-induced expression as correlated responses to selection on both heat-stress resistance and longevity in D. melanogaster. Three replicated H lines were heat-stress selected and compared to their respective non-selected controls (C lines) in the 25th generation of heat-stress selection. The direct response in heat-stress resistance was 56% in males and 38% in females. Heat-stress selection improved longevity in males at normal temperatures. All lines were subsequently subjected to one generation of truncation selection on longevity (selection intensity, i=1.28 for H lines and 1.36 for C lines). The heat-induced Hsp70 expression seems to increase very weakly by heat-stress selection but shows a dramatic and persistent decline by selecting for long-lived flies. A mechanism of longevity selection, involving changes in Hsp70 regulation, is suggested.