Plasticity of the heat shock response and development of thermotolerance during embryonic development of Lake Whitefish (Coregonus clupeaformis)

Abstract

Thermal discharge produced by industrial facilities has the potential to impact development of fish by increasing background temperature of the surrounding area. The overall objectives of this study were to: 1) Examine the interplay between how temperature and frequency of heat shock and post-heat shock recovery time can modulate the heat shock response to a subsequent more severe stressor; 2) determine if this interplay is the same at different embryonic stages; and 3) assess whether transient heat shocks confer protection to the embryo. These objectives were addressed by exposing embryos to repeated transient heat shocks and high-level heat shocks and then quantifying heat shock protein mRNA levels and whole animal responses such as, percent survival, time to hatch and morphometrics. Reverse transcription quantitative real-time PCR revealed that transient heat shocks increased or attenuated the heat shock response to severe heat shock depending on the post-transient recovery period. The most frequent transient heat shocks, every 3 days, had the lowest levels of hsp70 mRNA of all heat shock treatments. Embryonic stages had similar results, however, it seemed older embryos had a larger capacity to respond to heat shock as determined by greater increases in heat shock protein mRNA levels. Transient heat shock regimes were also able to confer protection to embryos exposed to a severe 4 h +18 °C high-level heat shock. In general, transient heat shock regimes seem to have some benefit to the embryo allowing for a quicker response to stress and therefore, greater tolerance.