Heat does not induce synthesis of heat shock proteins or thermotolerance in the earliest stage of mouse embryo development.

To study a possible role of HSP in the thermal response of mouse embryos, we examined heat survival and HSP synthesis of mouse embryos at the one-cell stage or the blastocyst stage. One-cell embryos were extremely heat sensitive and synthesized HSP at very low levels or not at all. At that developmental stage neither thermotolerance nor HSP synthesis could be induced by heat shock. In contrast, unheated blastocysts synthesized HSP constitutively, were comparatively heat resistant, and both thermotolerance and enhanced rate of HSP synthesis were induced by a non-lethal heat exposure. Our data demonstrate a correlation between HSP synthesis, thermal sensitivity and thermotolerance in this system, and strengthen the suggestion that gene activation of HSP synthesis is closely related to the differentiation process.