Induction of heat-shock proteins in the embryonic chicken lens

The 11-day embryonic chicken lens displays a rapid and vigorous response to a heat shock. Exposure of the lens to elevated temperature (45 degrees C) dramatically increased the synthesis of three proteins with subunit molecular weights of 89,000, 70,000 and 24,000. These lens heat-shock proteins are identical to the heat-shock proteins of cultured chicken embryo fibroblasts in electrophoretic mobility and immunological cross-reactivity. Maximum induction of lens heat-shock protein synthesis occurred upon incubation at 45 degrees C for about 1-1.5 hr and was blocked in the presence of actinomycin D. The functional half-lives at 37 degrees C of the mRNAs encoding the lens heat-shock proteins were about 3-5 hr. Synthesis of normal lens proteins continued throughout the heat shock, but delta-crystallin was unusual in that its synthesis initially rose upon heat shock, a behavior similar to that of a heat-shock protein. Proteins which co-migrated with each of the major lens heat-shock proteins were detected immunologically in non-stressed lens extracts. The endogenous lens protein, p24, which cross-reacted with antibodies raised against the small heat-shock protein (hsp 24) from chicken-embryo fibroblasts and co-migrated in one dimensional SDS gels with a major beta-crystallin was shown to be structurally similar to the chicken small heat shock protein but was distinct from the beta-crystallins.