Engineering candidate genes in studies of adaptation: The heat-shock protein Hsp70 in Drosophila melanogaster

One approach to elucidating the relationships among genes, trails, performa nce, and fitness is to choose genes of candidate evolutionary interest whos e 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 exemplifi es this candidate gene approach. The heat-shock protein Hsp70 was chosen fo r analysis because its biochemical phenotype (i.e., molecular chaperone act ivity), regulation, and encoding genes are well understood. Investigation o f the thermal. environment of Drosophila larvae in the wild and natural Hsp 70 expression establishes an ecological context for the candidate gene. Eng ineering of the hsp70 genes via site-specific homologous recombination, exp ression off of a heterologous promoter, and expression of an innocuous prot ein off of the hsp70 promoter show that Hsp70 can be sufficient for a signi ficant component of inducible thermotolerance but can have deleterious cons equences. Study of nonengineered variation in Hsp70 expression reveals that the genetically engineered effects have counterparts in nature. Thus, in c omplementary fashion, both generic engineering and the more classical appro aches of evolutionary biology each contribute essential insights to adaptat ion.