Heat shock response to hypoxia and its attenuation during recovery in the flesh fly, Sarcophaga crassipalpis

In this study, pharate adults of the flesh fly Sarcophaga crassipalpis were exposed to two, four, seven, or ten days of severe hypoxia (3% oxygen) to evaluate its impact on emergence and the expression of genes encoding heat shock proteins (Hsps) and heat shock regulatory elements. A four-day exposure to hypoxia significantly reduced survival, but more than seven days was required to reach the LD50. Eight genes encoding Hsps, at least one from each major family of Hsps (Hsp90, Hsp70, Hsp60, Hsp40, and sHsps) and two genes encoding proteins involved in Hsp regulation (heat shock factor, hsf, and sirtuin) were cloned, and expression levels were assessed during and after hypoxia using qRT-PCR. Most, but not all hsps studied, were significantly up-regulated during hypoxia, and expression levels for most of the hsps reverted to control levels a few hours after return to normoxia. Hsp70 was the most responsive to hypoxia, increasing expression several hundred fold. By contrast, hsp90 and hsp27 showed little response to hypoxia but did respond to recovery. Neither hsf nor sirtuin were elevated by hypoxia, an observation consistent with their assumed post-transcriptional regulatory roles. These data demonstrate a strong Hsp response to hypoxia, suggesting an important role for Hsps in responding to low oxygen environments.

The flesh fly, S. crassipalpis, can survive up to 4 days of severe hypoxia (3% oxygen) with no mortality. We cloned and measured the expression of 8 heat shock protein genes and 2 heat shock regulatory elements. For the majority of hsps tested, expression patterns reveal a strong upregulation of the heat shock response during hypoxia that is rapidly attenuated during recovery. The attenuation during recovery correlates with a downregulation in two important regulatory elements, hsf and sirt.Figure optionsDownload as PowerPoint slideResearch highlights▶ The flesh fly is highly tolerant of hypoxia and requires 7 days to reach its LD50. ▶ Most of the 8 heat shock protein genes we examined are upregulated by hypoxia. ▶ Expression of most hsps reverts to control levels within 24 h of recovery. ▶ The most robust response is observed for hsp70. ▶ The regulatory elements (heat shock factor, sirtuin) are downregulated during hypoxia.