The heat shock response shows plasticity in embryonic lake whitefish (Coregonus clupeaformis) exposed to repeated thermal stress

We examined the impact of repeated thermal stress on the heat shock response (HSR) of thermally sensitive lake whitefish (Coregonus clupeaformis) embryos. Our treatments were designed to mimic temperature fluctuations in the vicinity of industrial thermal effluents. Embryos were either maintained at control temperatures (3 degrees C) or exposed to a repeated thermal stress (TS) of 3 or 6 degrees C above control temperature every 3 or 6 days throughout embryonic development. At 82 days post-fertilisation, repeated TS treatments were stopped and embryos received either a high level TS of 12, 15, or 18 degrees C above ambient temperature for 1 or 4 h, or no additional TS. These treatments were carried out after a 6 h recovery from the last repeated TS. Embryos in the no repeated TS group responded, as expected, with increases in hsp70 mRNA in response to 12, 15 and 18 degrees C high-level TS. However, exposure to repeated TS of 3 or 6 C every 6 days also resulted in a significant upregulation of hsp70 mRNA relative to the controls. Importantly, these repeated TS events and the associated elevations in hsp70 attenuated the upregulation of hsp70 in response to a 1 h, high-level TS of 12 degrees C above ambient, but not to either longer (4 h) or higher (15 or 18 degrees C) TS events. Conversely, hsp90 alpha mRNA levels were not consistently elevated in the no repeated TS groups exposed to high-level TS. In some instances, hsp90 alpha levels appeared to decrease in embryos exposed to repeated TS followed by a high-level TS. The observed attenuation of the HSR in lake whitefish embryos demonstrates that embryos of this species have plasticity in their HSR and repeated TS may protect against high-level TS, but the response differs based on repeated TS treatment, high-level TS temperature and duration, and the gene of interest.

Automated summary

The study found that lake whitefish embryos have plasticity in their heat shock response (HSR), with repeated thermal stress potentially attenuating the upregulation response to high-level thermal stress. However, the response differs based on the type of thermal stress treatment, the temperature and duration of high-level stress, and the specific gene of interest.