Comparison of the effects of heat shock and metal-ion stress on gene expression in cells undergoing myogenesis.

Subjecting 9-day-old quail embryos to an elevated temperature in ovo causes limb, breast, and brain tissues to shift their patterns of protein synthesis from the production of a broad spectrum of different proteins to the new and (or) enhanced synthesis of a small number of heat-shock proteins (HSPs). The HSPs synthesized by undifferentiated breast tissue in ovo (relative masses (Mrs) 88 000, 82 000, 64 000, and 25 000) are similar to those synthesized by explanted breast tissue or by primary cultures of breast myoblasts heat-shocked in culture. Heat-shocked, 120-hour-old myotube cultures synthesize HSPs similar to those detected in heat-shocked myoblasts except that myotubes also exhibit enhanced synthesis of a 55 000 dalton polypeptide and little or no synthesis of a 25 000 dalton HSP; the failure to thermally induce a 25 000 dalton polypeptide in myotubes is related to the fused nature of these cells rather than to their state of differentiation. Myoblasts, as well as myotubes, cultured in the presence of elevated amounts of arsenite, copper, or zinc also synthesize new and (or) enhanced amounts of polypeptides with isoelectric points and immunochemical properties similar to the 25 000 and 64 000 dalton HSPs. However, elevated levels of these metal ions fail to stimulate new and (or) enhanced synthesis of other HSP-like proteins. These results demonstrate that, although the protein synthetic response of myogenic cells to chemical and thermal stress may be similar in some respects, a number of the synthetic responses are clearly different.