Thermal stress and the heat shock response in embryonic and young of the year juvenile lake whitefish
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We investigated the effects of thermal stress on embryonic (fin flutter, vitelline circulation stage) and young of the year (YOY) juvenile lake whitefish by characterizing the kinetics of the heat shock response (HSR). Lake whitefish were subjected to one of three different heat shock (HS) temperatures (3, 6, or 9 °C above control) for six different lengths of time (0.25, 0.50, 1, 2, 3, or 4h) followed by a 2h recovery period at the control temperature of 2 °C or 14 °C for embryos and YOY juveniles, respectively. The duration of the HSR was examined by allowing the fish to recover for 1, 2, 4, 8, 12, 16, 24, 36, or 48 h following a 2h HS. In embryos, at the fin flutter stage, only hsp70 mRNA levels were upregulated in response to the various HS treatments. By comparison, all three typically inducible hsps, hsp90α, hsp70 and hsp47, were upregulated in the YOY juveniles. In both instances the HSR was long lasting, but much more so in embryos where hsp70 mRNA levels continued to increase for 48 h after a 2h HS and remained significantly higher than untreated controls. Collectively our data indicate that both embryo and YOY juvenile lake whitefish have a robust HSR which permits them to survive a 4h, 9 °C HS. Moreover, both life history stages are capable of triggering a HSR following a moderate 3 °C HS which is likely an important protective mechanism against environmental stressors during embryogenesis and early life history stages of lake whitefish.
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