Tissue-specific expression of zebrafish (Danio rerio) heat shock factor 1 mRNAS in response to heat stress

All organisms respond to environmental, chemical and physiological stresses by enhanced synthesis of an evolutionarily conserved family of proteins kn own as heat shock proteins (HSPs) or stress proteins. Certain HSPs are also expressed constitutively during cell growth and development, and they func tion as molecular chaperones. The transcriptional regulation of hsp genes i s mediated by the heat shock transcription factor (HSF). The stress respons e has been studied mostly in mammalian cell lines or organisms normally mai ntained under constant laboratory conditions. There is much less informatio n on the regulation of the stress response of animals, such as fish, that h ave to tolerate large fluctuations in environmental and internal conditions . To characterize the regulation of the heat shock response in fish, we hav e cloned the first heat shock transcription factor from fish, zebrafish Dan io rerio. Phylogenetic analysis confirms that the isolated zebrafish HSF be longs to the HSF1 family and is therefore designated zHSF1. Analysis by rev erse transcriptase polymerase chain reaction (RT-PCR) shows the presence of two zHSF1 mRNA forms that are expressed in a tissue-specific fashion upon exposure to heat stress. Both forms are expressed in gonads under all condi tions; in liver and to a lesser extent in the gills, the longer splice form of zHSF1 disappears upon heat shock. We present evidence for a unique tiss ue-specific regulation of HSF1 upon exposure to elevated temperature.