Heat-shock gene expression in animal embryonic systems.

We have examined the expression of heat shock or stress genes in fish, echinoderm, amphibian, and mammalian embryonic systems. In a Chinook salmon embryo cell line, elevation of the incubation temperature or exposure to metal ions (e.g., cadmium and zinc) induced a set of heat-shock proteins HSPs. Transcriptional inhibitor, in vitro translation, and Northern hybridization studies suggest that fish HSP synthesis is regulated at the transcriptional level. The synthesis of HSPs during early development of Arbacia punctulata, Xenopus laevis, mouse, and rabbit is a stage-dependent phenomenon. In each of the developmental systems, HSP synthesis could not be induced until after cleavage stages. The ability of the embryo to undergo a heat-shock response (i.e., HSP synthesis) was correlated with the ability to detect HSP mRNA accumulation by either in vitro translation or Northern hybridization assays. Thus, the stage-dependent synthesis of HSPs appears to be controlled at the transcriptional level. Finally, in all of the organisms studied, the capacity to synthesize HSPs and accumulate HSP mRNA also coincides with acquisition of thermotolerance.