Fralin Life Science Institute and Department of Entomology, Virginia Tech, Blacksburg, Virginia, USA.
PLoS Negl Trop Dis. 2013 May 30;7(5):e2239. doi: 10.1371/journal.pntd.0002239. Print 2013.
The impact of global climate change on the transmission dynamics of infectious diseases is the subject of extensive debate. The transmission of mosquito-borne viral diseases is particularly complex, with climatic variables directly affecting many parameters associated with the prevalence of disease vectors. While evidence shows that warmer temperatures often decrease the extrinsic incubation period of an arthropod-borne virus (arbovirus), exposure to cooler temperatures often predisposes disease vector mosquitoes to higher infection rates. RNA interference (RNAi) pathways are essential to antiviral immunity in the mosquito; however, few experiments have explored the effects of temperature on the RNAi machinery.
METHODOLOGY/PRINCIPAL FINDINGS: We utilized transgenic "sensor" strains of Aedes aegypti to examine the role of temperature on RNA silencing. These "sensor" strains express EGFP only when RNAi is inhibited; for example, after knockdown of the effector proteins Dicer-2 (DCR-2) or Argonaute-2 (AGO-2). We observed an increase in EGFP expression in transgenic sensor mosquitoes reared at 18°C as compared with 28°C. Changes in expression were dependent on the presence of an inverted repeat with homology to a portion of the EGFP sequence, as transgenic strains lacking this sequence, the double stranded RNA (dsRNA) trigger for RNAi, showed no change in EGFP expression when reared at 18°C. Sequencing small RNAs in sensor mosquitoes reared at low temperature revealed normal processing of dsRNA substrates, suggesting the observed deficiency in RNAi occurs downstream of DCR-2. Rearing at cooler temperatures also predisposed mosquitoes to higher levels of infection with both chikungunya and yellow fever viruses.
CONCLUSIONS/SIGNIFICANCE: This data suggest that microclimates, such as those present in mosquito breeding sites, as well as more general climactic variables may influence the dynamics of mosquito-borne viral diseases by affecting the antiviral immunity of disease vectors.
全球气候变化对传染病传播动态的影响是广泛争论的主题。蚊媒病毒病的传播特别复杂，气候变量直接影响与疾病媒介流行相关的许多参数。虽然有证据表明，较高的温度通常会降低节肢动物传播病毒（arbovirus）的外潜伏期，但较低的温度会使病媒蚊子更容易感染。RNA 干扰（RNAi）途径是蚊子抗病毒免疫的关键；然而，很少有实验探索温度对 RNAi 机制的影响。
方法/主要发现：我们利用埃及伊蚊的转基因“传感器”品系来研究温度对 RNA 沉默的作用。这些“传感器”品系仅在 RNAi 被抑制时表达 EGFP；例如，在效应蛋白 Dicer-2（DCR-2）或 Argonaute-2（AGO-2）被敲低后。我们观察到在 18°C 下饲养的转基因传感器蚊子中 EGFP 的表达增加，而在 28°C 下饲养的蚊子中则减少。表达的变化依赖于与 EGFP 序列的一部分具有同源性的反向重复序列的存在，因为缺乏这种序列的转基因品系，即 RNAi 的双链 RNA（dsRNA）触发物，在 18°C 下饲养时 EGFP 表达没有变化。在低温下饲养的传感器蚊子中的小 RNA 测序显示 dsRNA 底物的正常加工，这表明观察到的 RNAi 缺陷发生在 DCR-2 下游。在较凉爽的温度下饲养也使蚊子更容易感染基孔肯雅热病毒和黄热病病毒。
结论/意义：这些数据表明，微气候，如蚊子滋生地的微气候，以及更普遍的气候变量，可能通过影响疾病媒介的抗病毒免疫来影响蚊媒病毒病的动态。
