Department of Physiology, Faculty of Biology, University of Murcia, 30100, Murcia, Spain.
Department of Physiology, Faculty of Biology, University of Murcia, 30100, Murcia, Spain.
J Therm Biol. 2021 Apr;97:102880. doi: 10.1016/j.jtherbio.2021.102880. Epub 2021 Feb 18.
In the wild, the environment does not remain constant, but periodically oscillates so that temperature rises in the daytime and drops at night, which generates a daily thermocycle. The effects of thermocycles on thermal tolerance have been previously described in fish. However, the impact of thermocycles on daytime-dependent thermal responses and daily rhythms of temperature tolerance and sensing expression mechanisms remain poorly understood. This study investigates the effects of two rearing conditions: constant (26 °C, C) versus a daily thermocycle (28 °C in the daytime; 24 °C at night, T) on the thermal tolerance response in zebrafish. Thermal tolerance (mortality) was assessed in 4dpf (days post fertilization) zebrafish larvae after acute heat shock (39 °C for 1 h) at two time points: middle of the light phase (ML) or middle of the dark phase (MD). Thermal stress responses were evaluated in adult zebrafish after a 37 °C challenge for 1 h at ML or MD to examine the expression of the heat-shock protein (HSP) (hsp70, hsp90ab1, grp94, hsp90aa1, hspb1, hsp47, cirbp) and transient receptor potential (TRP) channels (trpv4, trpm4a, trpm2, trpa1b) in the brain. Finally, the daily rhythms of gene expression of HSPs and TRPs were measured every 4 h for 24 h. The results revealed the larval mortality rates and the expression induction of most HSPs in adult zebrafish brain reached the highest values in fish reared under constant temperature and subjected to thermal shock at MD. The expression of most HSPs and TRPs was mainly synchronized to the light/dark (LD) cycle, regardless of the temperature regime. Most HSPs involved in hyperthermic challenges displayed diurnal rhythms with their acrophases in phase with warm-sensing thermoTRPs acrophases. The cold-sensing trpa1b peaked in the second half of the light period and slightly shifted toward the dark phase anticipating the acrophase of cirpb, which is involved in hypothermic challenges. These findings indicated that: a) thermal shocks are best tolerated in the daytime; b) the implementation of daily thermocycles during larval development reduces mortality and stress-cellular expression of HSPs to an acute thermal stress at MD; c) daily rhythms need to be considered when discussing physiological responses of thermal sensing and thermotolerance in zebrafish.
在野外，环境并非保持恒定，而是周期性波动，导致白天温度升高，晚上温度下降，从而产生每日温度循环。先前已经描述了温度循环对鱼类热耐受性的影响。然而，温度循环对日间依赖性热反应和温度耐受性以及温度感知表达机制的日常节律的影响仍知之甚少。本研究调查了两种饲养条件的影响：恒温和每日温度循环（白天 28°C，晚上 24°C）对斑马鱼热耐受反应的影响。在两个时间点评估了 4dpf（受精后天数）斑马鱼幼虫的热耐受（死亡率）：光照中期（ML）或黑暗中期（MD）后，进行急性热休克（39°C 持续 1 小时）。在 ML 或 MD 进行 37°C 挑战 1 小时后，评估成年斑马鱼的热应激反应，以检查热休克蛋白（HSP）（hsp70、hsp90ab1、grp94、hsp90aa1、hspb1、hsp47、cirbp）和瞬时受体电位（TRP）通道（trpv4、trpm4a、trpm2、trpa1b）的表达。最后，每 4 小时测量 HSP 和 TRP 的基因表达的日常节律，持续 24 小时。结果表明，在恒温饲养的幼虫中，幼虫死亡率和大多数 HSP 在成年斑马鱼大脑中的诱导表达在 MD 时进行热冲击时达到最高值。大多数 HSP 和 TRP 的表达主要与光/暗（LD）周期同步，无论温度制度如何。涉及高温挑战的大多数 HSPs 表现出昼夜节律，其峰值与温暖感应 thermoTRPs 的峰值相位一致。冷感应 trpa1b 在光照期的后半段达到峰值，并略微向暗期移动，预测涉及低温挑战的 cirpb 的峰值相位。这些发现表明：a）热冲击在白天最耐受；b）在幼虫发育期间实施每日温度循环可降低死亡率，并减少 HSP 在 MD 时对急性热应激的细胞表达；c）在讨论斑马鱼热感觉和热耐受性的生理反应时，需要考虑日常节律。
