Regulation of rat heat shock factor 2 expression during the early organogenic phase of embryogenesis

A central step in the transcriptional regulation of heat shock protein (hsp ) genes is the binding of the heat shock factor (HSF) to the upstream heat shock elements (HSEs). In vertebrates, HSF2 has been suggested to mediate t he transcriptional regulation of hsp gene expression during development and differentiation. The expression levels of HSF2 were shown to vary widely a mong fully developed mouse organs. However, there exists limited informatio n on the regulation of HSF2 expression during the inductive stage of organ formation in mammalian development. In this study, we have cloned the rat H SF2 cDNA and examined embryos for HSF2 expression from days 9.5 (E9.5) to 1 5.5 (E15.5) of gestation that correspond to the period when the major organ primordia are being actively established. We show that rat HSF2 has 94.6 a nd 96.3% identity to mouse HSF2 in nucleotide and amino acid sequences, res pectively. By establishing a competitive RT-PCR, we show that about 503.6 p g of HSF2 mRNA were present per microgram of embryonic RNA in the primitive streak stage E9.5 embryos. The amounts of HSF2 mRNA then gradually decreas ed, resulting in an approximately 300-fold reduction in E15.5 embryos. The amounts of HSF2 mRNA in the embryos were found to be closely correlated wit h those of HSF2 protein and their HSE-binding activities. To our knowledge, this is the first detailed report on the structure and regulation of the r at HSF? during the early organogenic period of mammalian embryogenesis. (C) 2000 Elsevier Science B.V. All rights reserved.