Centre for Invasion Biology, Department of Conservation Ecology and Entomology, Stellenbosch University, South Africa.
Centre for Invasion Biology, Department of Conservation Ecology and Entomology, Stellenbosch University, South Africa.
J Insect Physiol. 2018 Apr;106(Pt 3):179-188. doi: 10.1016/j.jinsphys.2017.10.005. Epub 2017 Oct 13.
While single stress responses are fairly well researched, multiple, interactive stress responses are not-despite the obvious importance thereof. Here, using D. melanogaster, we investigated the effects of simultaneous exposures to low O (hypoxia) and varying thermal conditions on mortality rates, estimates of thermal tolerance and the transcriptome. We used combinations of 21 (normoxia), 10 or 5kPa O with control (23°C), cold (4°C) or hot (31°C) temperature exposures before assaying chill coma recovery time (CCRT) and heat knock down time (HKDT) as measures of cold and heat tolerance respectively. We found that mortality was significantly affected by temperature, oxygen partial pressure (PO) and the interaction between the two. Cold treatments resulted in low mortality (<5%), regardless of PO treatment; while hot treatments resulted in higher mortality (∼20%), especially at 5kPa O which was lethal for most flies (∼80%). Both CCRT and HKDT were significantly affected by temperature, but not PO, of the treatments, and the interaction of temperature and PO was non-significant. Hot treatments led to significantly longer CCRT, and shorter HKDT in comparison to cold treatments. Global gene expression profiling provided the first transcriptome level response to the combined stress of PO and temperature, showing that stressful treatments resulted in higher mortality and induced transcripts that were associated with protein kinases, catabolic processes (proteases, hydrolases, peptidases) and membrane function. Several genes and pathways that may be responsible for the protective effects of combined PO and cold treatments were identified. We found that urate oxidase was upregulated in all three cold treatments, regardless of the PO. Small heat shock proteins Hsp22 and Hsp23 were upregulated after both 10 and 21kPa O-hot treatments. Collectively, the data from PO-hot treatments suggests that hypoxia does exacerbate heat stress, through an as yet unidentified mechanism. Hsp70B and an unannotated transcript (CG6733) were significantly differentially expressed after 5kPa O-cold and 10kPa O-hot treatments relative to their controls. Downregulation of these transcripts was correlated with reduced thermal tolerance (longer CCRT and shorter HKDT), suggesting that these genes may be important candidates for future research.
虽然单一压力反应已经得到了相当深入的研究，但多重、相互作用的压力反应却没有得到很好的研究——尽管它们显然非常重要。在这里，我们使用黑腹果蝇研究了同时暴露于低氧（缺氧）和不同热条件对死亡率、热耐受估计值和转录组的影响。我们使用了 21 个组合（常氧）、10 或 5kPa O 与对照（23°C）、冷（4°C）或热（31°C）温度暴露，然后测定冷昏迷恢复时间（CCRT）和热击倒时间（HKDT），分别作为冷和热耐受的衡量标准。我们发现，死亡率显著受到温度、氧气分压（PO）以及两者之间相互作用的影响。无论 PO 处理如何，冷处理都会导致低死亡率（<5%）；而热处理会导致更高的死亡率（约 20%），尤其是在 5kPa O 时，大多数苍蝇都会死亡（约 80%）。CCRT 和 HKDT 都显著受到温度的影响，但不受处理 PO 的影响，温度和 PO 的相互作用不显著。与冷处理相比，热处理导致 CCRT 显著延长，HKDT 显著缩短。全基因表达谱提供了第一个针对 PO 和温度联合应激的转录组水平反应，表明应激处理导致更高的死亡率，并诱导与蛋白激酶、分解代谢过程（蛋白酶、水解酶、肽酶）和膜功能相关的转录本。鉴定了几个可能负责 PO 和冷联合处理保护作用的基因和途径。我们发现尿酸氧化酶在所有三种冷处理中都上调，无论 PO 如何。小热休克蛋白 Hsp22 和 Hsp23 在 10 和 21kPa O-热处理后均上调。总体而言，PO-热处理的数据表明，缺氧确实通过尚未确定的机制加剧了热应激。Hsp70B 和一个未注释的转录本（CG6733）在 5kPa O-冷和 10kPa O-热处理相对于对照时表达差异显著。这些转录本的下调与热耐受降低（较长的 CCRT 和较短的 HKDT）相关，表明这些基因可能是未来研究的重要候选基因。
