Expression of heat shock genes (hsp70) in the mammalian brain: distinguishing constitutively expressed and hyperthermia-inducible mRNA species.

The mammalian genome contains both constitutively expressed and heat-shock-inducible members of the hsp70 gene family. Riboprobes derived from members of these two classes of heat shock genes were utilized in Northern blot studies to analyze brain mRNA isolated from control rabbits and rats and from animals subjected to hyperthermic treatment. A riboprobe derived from a constitutively expressed hsp70 gene detected a 2.5 kilobase (kb) mRNA in brain tissue from control rabbits and a 2.3 kb mRNA species in control rat brain. These brain mRNAs showed little change in abundance in animals which were subjected to hyperthermic treatment. A riboprobe derived from a heat-shock-inducible hsp70 gene detected an abundant 2.7 kb brain transcript in hyperthermic rabbits which was not apparent in control animals. A time course study revealed that the induction of this mRNA species was transient and paralleled the rise and fall in body temperature. Peak induction was observed at 1 hr. The level of this message had greatly decreased by 5 hr and only trace levels were present at 10 and 24 hr. In the rat brain the induced hsp70 mRNA species was slightly larger than that observed in rabbit (2.9 kb vs. 2.7 kb). The riboprobe which detected the hyperthermia-inducible mRNA species was highly specific and did not cross react to the constitutively expressed mRNA species under the conditions employed in the Northern blot studies.