Response to heat shock of gene 1, a Drosophila melanogaster small heat shock gene, is developmentally regulated

Heat shock proteins and aging in Drosophila melanogaster

Heat shock proteins (Hsps) are conserved molecular chaperones that are upregulated following exposure to environmental stress and during aging. The mechanisms underlying the aging process are only beginning to be understood. The beneficial effects of Hsps on aging revealed in mild stress and overexpression experiments suggest that these proteins are part of an important cell protection system rather than being unspecific molecular chaperones. Among the Hsps families, small Hsps have the greatest influence on aging and the modulation of their expression during aging in Drosophila suggest that they are involved in pathways of longevity determination.

Drosophila melanogaster is polymorphic for a specific repeated (CATA) sequence in the regulatory region of hsp23

To identify sequence variation associated with a selection response for heat tolerance in Drosophila melanogaster, we sequenced 1400bp of the heat shock protein 23 gene (hsp23) promoter region in four heat-selected and two control lines. The region was found to be variable for a specific (CATA) repeated sequence, and the sequence CTT seems to be a hot spot for mutation. The repeated tetranucleotide sequence was located in several short repeats scattered throughout the entire region. Similar variable repeats are also located downstream the of hsp23 gene in the intergenic region between hsp23 and hsp27. We detected nine different hsp23 alleles. Their frequencies in the selection and control lines seemed to be mainly determined by genetic drift. The function of the CATA repeats is not yet known, though these regions have homology to SAR elements located in the intergenic region between two hsp70 genes, suggesting a similar function.

Transcriptional regulation in Drosophila during heat shock: a nuclear run-on analysis

We used a nuclear run-on assay as a novel approach to study the changes in transcriptional activity that take place in Drosophila melanogaster during heat shock. In response to a rapid temperature upshift, total transcriptional activity in cultured KC161 cells decreased proportionally to the severity of the shock. After extended stress at 37 degrees C (15 min or more), transcription was severely reduced, and at 39 degrees C most transcription was instantaneously arrested. However, strikingly different responses were observed for individual genes. Transcription of histone H1 genes was severely inhibited even under mild heat shock conditions. Transcription of the actin 5C gene decreased progressively with increasing temperature, while transcription of the core histone genes or of the heat shock cognate genes was repressed only under severe heat shock conditions. Transcriptional activation of the D. melanogaster heat shock genes was also investigated. In unshocked cells, hsp84 was moderately transcribed, while transcriptional activity at the other protein-coding heat shock genes was undetectable (less than 0.2 polymerases per gene). Engaged but paused RNA polymerase molecules were found at the hsp70 and hsp26 genes, but not at the other heat shock genes. The rates of transcription increased with increasing temperature with a peak of expression at around 35 degrees C. At 37 degrees C, induction was less efficient, and no induction was achieved after a rapid shift to 39 degrees C. Increased transcription of the heat shock genes was observed within 1-2 min of heat shock, and maximal rates were reached within 2-5 min. Despite very similar profiles of response, different heat shock genes were transcribed at strikingly different rates, which varied over a 20-fold range. The noncoding heat shock locus 93D was transcribed at a very high rate under non-heat shock conditions, and showed a transcriptional response to elevated temperatures different from that of protein-coding heat shock genes. An estimation of the absolute rates of transcription at different temperatures was obtained.