REGULATION OF HEAT-SHOCK PROTEIN-70 SYNTHESIS BY HEAT-SHOCK IN THE PREIMPLANTATION MURINE EMBRYO

Induced thermotolerance in murine embryos occurs at the 8-cell stage w hen embryos are maintained in vitro but not until the blastocyst stage if development proceeds in vivo. Present results indicate that abilit y of embryos to undergo induced thermotolerance is not limited by heat shock protein 70 (HSP70) synthesis. Exposure of 8-cell embryos to 40 degrees C enhanced synthesis of 2 constitutive HSP70 proteins (HSC70 a nd HSC72) and induced another protein, HSP68; exposure of 43 degrees C was required to induce similar responses in expanded blastocysts. Unl ike induced thermotolerance, increased synthesis of HSP70 molecules di d not depend on whether embryos were cultured or developed in vivo. Th us, other biochemical mechanisms in addition to HSP70 confer thermotol erance in the preimplantation-stage murine embryo. The observation tha t the temperature threshold for induction of HSP70 synthesis increased from the 8-cell to the blastocyst stage is indicative of these other biochemical processes.