The heat shock response in embryonic and young of the year juvenile round whitefish (prosopium cylindraceum)

Abstract

I investigated the effects of acute, increased temperatures on round whitefish embryos at the protruding mouth stage and young-of-the-year (YOY) juveniles at 3.5 months post hatch by characterizing the kinetics of the heat shock response (HSR). The HSR provides protection from a variety of stressors (i.e., thermal stress) at the cellular level and is characterized by the upregulation of a suite of proteins called heat shock proteins (Hsps). Round whitefish embryos were exposed to two heat shock (HS) temperatures (6 or 9 °C above control temperature) for 4 different lengths of time (1, 2, 3, or 4 h) followed by a 2 h recovery period at the control temperature of 4 °C, a typical incubation temperature for round whitefish embryos. Post-HS recovery was also examined by exposing embryos to a 2 h HS at 9 °C above control temperature followed by a recovery period of 0, 2, 4, 12, 24, or 48 h at the control temperature of 4 °C. YOY juveniles acclimated to an ecologically relevant 10 °C were exposed to three different HS temperatures (6, 9, or 12 °C above control temperature) for 4 different lengths of time (1, 2, 3, or 4 h) and not given a recovery period. Post HS recovery was examined by exposing YOY juveniles to a 2 h HS at 6, 9, or 12 °C above control temperature followed by a 0, 1, 4, or 8 h recovery period at the control temperature of 10 °C prior to sampling. In embryos, hsp70 mRNA levels were the only consistently upregulated heat shock protein (Hsp), whereas in YOY juveniles hsp70 and hsp47 mRNA levels were consistently upregulated. Furthermore, in comparison to juveniles, embryos took a longer time to initiate a HSR but once upregulated the HSR was long lasting in both life history stages. These data indicate that embryos and juveniles are able to trigger a protective HSR which presumably aids them in surviving a 3 h HS of +9 °C and a 4 h of HS +12 °C, respectively. This suggests HSR is one of the mechanisms available to round whitefish when experiencing thermal stress in fluctuating environments.