Tissue-specific variations in the induction of Hsp70 and Hsp64 by heat shock in insects

Abstract

The patterns of heat-induced synthesis (37°C to 45°C) of heat shock proteins (Hsps) in different tissues of grasshoppers and cockroaches from natural populations and in laboratory-reared gram-pest (Heliothis armigera) were examined by ³⁵S-methionine labeling and sodium dodecyl sulfate-polyacrylamide gel electrophoresis fluorography. Whereas 45°C was lethal in most cases, optimal induction of Hsp synthesis was seen between 37°C and 42°C. The ongoing protein synthesis was not much affected at these temperatures, except in the tissues of adult H armigera exposed to 42°C. The profiles of the Hsps induced in the tissues of the insects, however, were different. From the relative abundance of the synthesis of 70-kDa (Hsp70) and 64-kDa (Hsp64) polypeptides, three categories of heat shock response were identified: (1) induction of abundant Hsp70 but little Hsp64 (malpighian tubules, male accessory glands, and ovaries of adult grasshoppers), (2) abundant Hsp64 but little Hsp70 (testes of adult grasshoppers, testes and malpighian tubules of adult cockroaches, and testes, malpighian tubules, and fat bodies of H armigera larvae), and (3) induction of both Hsp70 and Hsp64 in more or less equal abundance (ovaries of adult cockroaches, salivary glands of H armigera larvae, and malpighian tubules, male accessory glands, testes, and ovaries of adult H armigera). Cockroaches collected from storerooms showed detectable synthesis of Hsp64 and/or Hsp70 only after heat shock, but those collected from drains showed detectable synthesis of both Hsp70 and Hsp64 in different tissues without heat stress. Western blotting showed that the 64-kDa polypeptide in these insects is a member of the Hsp60 family. Grasshopper testes, which synthesized negligible Hsp70 but abundant Hsp64 after heat shock, developed thermotolerance. Thus, heat shock response is modulated by developmental and environmental factors in different tissues of insects.