Regulation of the inducible heat shock 71 genes in early neural development of cultured rat embryos

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Abstract
Activation of the inducible heat shock 71 genes and their role in the heat shock response was studied in vitro in 9.5 day‐old rat embryos at neural tube closure. The transcriptional response of a 71 kilodalton (kD) heat shock gene induced after various regimes of heat shock and acquired thermotolerance was investigated. Expression and accumulation of the heat shock (hs) 71 mRNA in the neuroectoderm was studied by Northern and dot blot analysis. Specific expression in various cell types and regions of the neuroectoderm were examined by in situ hybridization. Exposure of embryos to a heat shock at 43°C for 7.5 min caused high levels of hs mRNA 71 accumulation in the neuroectoderm, pronounced protein synthesis inhibition, and regulated recovery. Specific neuroectoderm cell death followed, resulting in major developmental defects of the eye and forebrain region. A mild heat shock of 42°C for 10 min induced the heat shock response, hsp synthesis, and cell recovery, but produced no cell death or deformities. Preheating the embryo at 42°C resulted in acquired thermotolerance to an otherwise teratogenic 43°C heat shock. Thermotolerance was associated with a rapid recovery of protein synthesis associated with hs 71 mRNA expression. Dot blot analysis showed that after a 42°C heat shock, 71 mRNA was rapidly transcribed and transported into the cytoplasm where it was degraded within 2 hr of the initial response. The results suggest that the heat shock protein (hsp) 71 gene may have a protective rather than a rescuing function.