Thermoprotection in the Drosophila hsf4 mutant

In Drosophila larvae, acquired synaptic thermotolerance following heat shock has previously been shown to correlate with the induction of heat shock proteins (Hsps) including HSP70. We tested the hypothesis that synaptic thermotolerance would be significantly diminished in a temperature-sensitive strain (hsf4) which has been reported not to be able to produce inducible Hsps in response to heat shock. Contrary to our hypothesis, considerable thermoprotection was still observed at hsf4 larval synapses following heat shock. To investigate the cause of this thermoprotection, we conducted DNA microarray experiments to identify heat-induced transcript changes in these organisms. Transcripts of the hsp83, dnaJ-1(hsp40) and gstE1 genes were significantly up-regulated in hsf4 larvae after heat shock. In addition, increases in the levels of Hsp83 and DnaJ-1 proteins but not in the inducible form of Hsp70 were detected by Western blotting. The mode of heat shock administration differentially affected the relative transcript and translational changes for these chaperones. These results indicate that the compensatory up-regulation of constitutively expressed Hsps, in the absence of the synthesis of inducible Hsps including HSP70, could still provide substantial thermoprotection to both synapses and the whole organism. Keywords: heat shock response Two strains were used in this study; the mutant cn bw hsf4 strain, and the dp cn bw cl control strain from which the mutant was derived. For each strain, co-reared larvae were separated into a control group and a treatment group at random. RNA from the heat-shocked larvae and from the respective controls were directly compared on cDNA microarrays (GPL311). Two independent biological samples from each genotype were collected. In addition, an inter-strain comparison was made using the RNA from the untreated controls from each genotype. This was also performed in duplicate.