Natural and Genetic Engineering of the Heat-Shock Protein Hsp70 in Drosophila melanogaster: Consequences for Thermotolerance

SYNOPSIS. Larvae of the fruit fly, Drosophila melanogaster,live within necrotic fruit, a challenging environment in whichlarvae can experience severe thermal stress. One response tothermal stress, the expression of heat-shock proteins (Hsps),has evolved distinctively in this species; the gene encodingHsp70 has undergone extensive duplication and accounts for thebulk of Hsps that are expressed upon heat shock. Genetic engineeringof hsp70 copy number is sufficient to affect thermotoleranceat some (but not all) life stages. Increases in Hsp70, moreover,can protect intact larvae against thermal inactivation of theenzyme alcohol dehydrogenase and thermal inhibition of feeding.Deleterious consequences of high levels of Hsp70, however, maylimit further evolutionary proliferation of hsp70 genes. Thesefindings illustrate how the perspectives of integrative andcomparative biology, if applied to even well-studied model organisms,can lead to novel findings.