Engineering Candidate Genes in Studies of Adaptation: The Heat-Shock Protein Hsp70 in Drosophila melanogaster

One approach to elucidating the relationships among genes, traits, performance, and fitness is to choose genes of candidate evolutionary interest whose significance is well understood from in vitro and cellular studies and to explore the consequences of manipulating these genes in whole organisms in an evolutionary context. Ongoing research on Hsp70 in Drosophila exemplifies this candidate gene approach. The heat-shock protein Hsp70 was chosen for analysis because its biochemical phenotype (i.e., molecular chaperone activity), regulation, and encoding genes are well understood. Investigation of the thermal environment of Drosophila larvae in the wild and natural Hsp70 expression establishes an ecological context for the candidate gene. Engineering of the hsp70 genes via site-specific homologous recombination, expression off of a heterologous promoter, and expression of an innocuous protein off of the hsp70 promoter show that Hsp70 can be sufficient for a significant component of inducible thermotolerance but can have deleterious consequences. Study of nonengineered variation in Hsp70 expression reveals that the genetically engineered effects have counterparts in nature. Thus, in complementary fashion, both genetic engineering and the more classical approaches of evolutionary biology each contribute essential insights to adaptation.