INDUCTION OF HSP72 IN HEAT-TREATED RAT EMBRYOS - A TISSUE-SPECIFIC RESPONSE

Previous studies have demonstrated that heat exposure on gestation day 10 (GD10) resulted in disrupted somite development in rat embryos 24 hr after exposure and in thoracic skeletal malformations in neonatal r ats examined 3 days postpartum. The production of abnormal somites was correlated with the location of skeletal elements that developed from the affected somites. Heat has also been shown to induce changes in g enetic expression whereby new proteins are synthesized and the express ion of constituent proteins may be repressed. In the present study, he at-induced alterations in protein synthesis during rat organogenesis t hat may be associated with previously observed malformation was invest igated. GD10 rat embryos were exposed in utero to a heat treatment pre viously demonstrated to produce skeletal malformations; maternal core temperature was raised and maintained at 42-42.4 degrees C for 5 min. In addition, explanted GD10 embryos were cultured in vitro and exposed to temperatures of 42-42.5 degrees C for 15 min. At various times pos texposure, embryos were labeled with S-35-methionine and processed for SDS-PAGE. In both in vivo and in vitro heat treated embryos, a transi ent enhanced de novo synthesis of 70- and 90-kD proteins was observed 1-8 hr after exposure. Actinomycin D studies were conducted to determi ne whether transcription of new mRNA was required for the enhanced syn thesis of the 70- and 90-kD proteins in heat-treated embryos. Results from these studies demonstrated that the expression of these proteins was transcriptionally regulated. The 70-kD protein was identified, usi ng Western blot analysis, as a eukaryotic inducible stress protein (hs p72), and the presence of this protein was detected between 2 and 27 h r post-treatment. Immunohistochemical results indicated that following heat shock, hsp72 accumulates in the neuroectodermal tissues of the e mbryos. The data demonstrate that although heat-induced expression and accumulation of the hsp72 precedes aberrant somite morphology, the la ck of hsp72 accumulation in the somite mesoderm may explain the sensit ivity of this tissue to heat. (C) 1995 Wiley-Liss, Inc.