15 Developmental Expression of the Heat Shock Genes in Drosophila melanogaster

Abstract

I. INTRODUCTION
Soon after the cloning of the genes encoding the major heat shock proteins (hsps) of Drosophila melanogaster in the late 1970s and early 1980s, it was realized that their expression is not restricted only to conditions of stress. This notion arose from at least three different approaches. First, the availability of DNA probes (O’Connor and Lis 1981) and the production of a specific antibody (Chomyn and Mitchell 1982) confirmed what was already suspected from previous studies (e.g., Mirault et al. 1978; Lindquist 1980; Storti et al. 1980): The hsp83 gene is transcribed and translated in appreciable amounts at normal temperature both in tissue culture cells and in several tissues during the fly development. Second, even if the major hsp, hsp70, is not detectable in uninduced cells, at least three highly homologous genes are expressed in flies at normal temperatures (Ingolia and Craig 1982a; Craig et al. 1983). Finally, a study designed to isolate genomic sequences preferentially transscribed in the beginning of the pupal period led to the recloning of the cluster of genes encoding the low-molecular-weight hsps (Sirotkin and Davidson 1982). It is obvious from these instances that most of the heat shock (hs) genes of D. melanogaster studied so far are not only stress-inducible, but are also expressed at normal temperatures at least in some tissues and during specific periods of development. This expression of the hs genes in the absence of stress is the subject of this chapter. We first review the structure and the developmental...