Cloning of zebrafish (Danio rerio) heat shock factor 2 (HSF2) and similar patterns of HSF2 and HSF1 mRNA expression in brain tissues.

The transcriptional activation of heat shock protein (HSP) genes is initiated by the binding of heat shock factors (HSFs) to heat shock elements (HSEs) located at the promotor regions. Multiple HSFs exist in larger eukaryotic organisms in order to sense various types of stress signals. Here we report the cloning of zebrafish (Danio rerio) HSF2 (zHSF2) cDNA (GenBank accession number AF412833 ) that has an open reading frame of 1470 nucleotides, encoding a polypeptide of 489 amino acids. Domain architecture analysis of the deduced zHSF2 sequence revealed the presence of a DNA-binding domain at the N-terminal end, an adjacent oligomerization domain and a vertebrate heat shock transcription factor domain. Amino acid alignment showed a 70% sequence identity between zHSF2 and human or mouse HSF2, while only a 45% identity was found between zHSF1a and zHSF2. Recombinant zHSF2 bound with a very high specificity to HSEs arranged as inverted arrays of 5'-nGAAn-3', as replacing one GAA with GTA almost abolished the formation of HSE-binding complex. Similar patterns of zHSF1a and zHSF2 mRNA expression in the brain regions of developing zebrafish were detected by whole mount in situ hybridization and paraffin sectioning, suggesting that most of the two HSF gene activities were controlled by a common mechanism during the embryonic development of zebrafish. The levels of both zHSF1a and zHSF2 mRNA in zebrafish tissues were moderately increased after heat stress.