Graduate School of Science, Osaka City University, Sumiyoshi, Osaka, Japan.
BMC Biol. 2010 Sep 3;8:116. doi: 10.1186/1741-7007-8-116.
Most organisms have evolved a circadian clock in order to anticipate daily environmental changes and many of these organisms are also capable of sophisticated measurement of daylength (photoperiodism) that is used to regulate seasonal events such as diapause, migration and polymorphism. It has been generally accepted that the same elements are involved in both circadian (daily) and seasonal (annual) rhythms because both rely upon daily light-dark cycles. However, as reasonable as this sounds, there remains no conclusive evidence of such a molecular machinery in insects. We have approached this issue by using RNA interference (RNAi) in Riptortus pedestris.
The cuticle deposition rhythm exhibited the major properties of circadian rhythms, indicating that the rhythm is regulated by a circadian clock. RNAi directed against the circadian clock genes of period and cycle, which are negative and positive regulators in the circadian clock, respectively, disrupted the cuticle deposition rhythm and distinct cuticle layers were produced by these RNAi. Simultaneously, period RNAi caused the insect to avert diapause under a diapause-inducing photoperiod whereas cycle RNAi induced diapause under a diapause-averting photoperiod. The expression patterns of juvenile hormone-regulated genes and the application of juvenile hormone analogue suggested that neither ovarian development itself nor a downstream cascade of juvenile hormone secretion, were disturbed by period and cycle RNAi.
This study revealed that the circadian clock genes are crucial not only for daily rhythms but also for photoperiodic diapause. RNAi directed against period and cycle had opposite effects not only in the circadian cuticle deposition rhythm but also in the photoperiodic diapause. These RNAi also had opposite effects on juvenile hormone-regulated gene expression. It is still possible that the circadian clock genes pleiotropically affect ovarian development but, based on these results, we suggest that the circadian clock operated by the circadian clock genes, period and cycle, governs seasonal timing as well as the daily rhythms.
为了预测每日环境变化，大多数生物体都进化出了生物钟，而许多生物体还能够精确地测量光周期（光周期现象），以调节休眠、迁徙和多态性等季节性事件。人们普遍认为，生物钟（日常）和季节性（年度）节律所涉及的元素是相同的，因为两者都依赖于每日的光暗循环。然而，尽管这听起来合情合理，但昆虫中仍然没有这种分子机制的确凿证据。我们通过使用 Riptortus pedestris 的 RNA 干扰（RNAi）来解决这个问题。
表皮沉积节律表现出生物钟节律的主要特征，表明该节律受生物钟调节。针对周期和周期基因的 RNAi，分别是生物钟的负调节因子和正调节因子，扰乱了表皮沉积节律，这些 RNAi 产生了明显的表皮层。同时，period RNAi 使昆虫在诱导休眠的光周期下避免休眠，而 cycle RNAi 在避免休眠的光周期下诱导休眠。保幼激素调节基因的表达模式和保幼激素类似物的应用表明，卵巢发育本身或保幼激素分泌的下游级联反应都没有受到 period 和 cycle RNAi 的干扰。
本研究表明，生物钟基因不仅对日常节律至关重要，对光周期休眠也是如此。针对 period 和 cycle 的 RNAi 不仅对生物钟表皮沉积节律有相反的影响，对光周期休眠也有相反的影响。这些 RNAi 对保幼激素调节基因的表达也有相反的影响。生物钟基因可能会多效性地影响卵巢发育，但根据这些结果，我们认为由生物钟基因 period 和 cycle 控制的生物钟不仅控制着日常节律，还控制着季节性时间。
