Seasonal Adaptation of a Circadian Clock

项目摘要 在这个提议中，我们将使用果蝇作为模型系统，以了解昼夜节律（E24小时）系统如何适应环境条件的季节性变化，重点是温度的相对不典型的作用。这个建议的一个主要基础是基于我们长期的工作，表明在D。黑腹果蝇3 ′-末端内含子（称为DMPI 8）从关键时钟成分周期（PER）的温度依赖性剪接是一种显著的“温度传感器”，其调节每日清醒-睡眠周期的分布，引起季节性的适当反应。与许多昼行性动物一样，果蝇表现出早上和晚上的活动，中间有一个午睡，晚上大部分时间都在睡觉。在温暖的日子里，dmpi 8内含子的剪接是低效的，导致每RNA水平的缓慢积累，这是增强中午午睡的事件，并且可能最小化与炎热的中午时间期间的干燥相关的风险。最近的进展表明，多个次优剪接信号[即，5'和3'剪接位点（ss）]是dmpi 8剪接效率热敏性的基础，并赋予D.黑腹果蝇具有将中午午睡延长到下午中后期的能力，这可能有助于其适应温带气候，在温带气候中，温暖的日子通常与长时间的炎热有关。事实上，温度依赖性的变化，每3 '-末端剪接效率和调整日常唤醒活动周期是不存在的几个物种的果蝇，自然局限于非洲赤道地区，其中温度和日照长度经历全年波动很小。有趣的是，这些非热响应物种在其每3 '末端内含子上具有强的5'和3 'ss，这可能限制了它们在温带气候中定居的能力。 据推测，低温有利于剪接因子与次优剪接信号的相互作用。我们将采取多方面的实验策略，包括生物化学，分子，细胞培养和整个动物的方法来了解顺式和反式作用因子调节每3 '-末端内含子的剪接效率，以及它们如何调节果蝇的觉醒-睡眠周期。这将包括表征新发现的天然多态性per差异调节dmpi 8剪接，并可能在地理上有所不同。我们还将确定dmpi 8剪接的影响是否优先从早晨或晚上的节律性大脑中心和/或最近描述的觉醒/睡眠起搏器介导。 通过使用各种自然种群和果蝇物种进行比较研究，这项拟议的工作提供了一个独特的机会，整合基因表达和神经回路控制复杂的行为与生态和进化的影响的研究。从更广泛的角度来看，我们的工作表明，自然选择在剪接信号水平上起着重要的作用，在生命形式的热适应。

Project Summary In this proposal we will use Drosophila as a model system to understand how circadian (E24 hr) systems adapt to seasonal changes in environmental conditions, with an emphasis on the relatively uncharacterized role of temperature. A major foundation of this proposal is based on our long-standing work showing that in D. melanogaster the temperature-dependent splicing of the 3'-terminal intron (called dmpi8) from the critical clock component period (per) is a prominent 'thermosensor' that adjusts the distribution of daily wake-sleep cycles, eliciting seasonably appropriate responses. As in many diurnal animals, Drosophila manifests morning and evening activity bouts separated by a midday siesta and largely sleep during the night. On warm days splicing of the dmpi8 intron is inefficient leading to slow accumulation of per RNA levels, events that enhance midday siesta and likely minimize the risks associated with desiccation during the hot midday hours. Recent progress indicates that multiple suboptimal splicing signals [i.e., 5' and 3' splice sites (ss)] are the basis for the thermosensitivity in the splicing efficiency of dmpi8, and endow D. melanogaster with the ability to prolong its midday siesta into the mid-to-late afternoon, presumably facilitating its adaptation to temperate climates where warm days are typically associated with extended periods of heat. Indeed, temperature-dependent changes in per 3'-terminal splicing efficiency and adjustments in daily wake-activity cycles are absent in several species of Drosophila that are naturally restricted to Afro-equatorial localities, wherein temperature and daylength undergo little fluctuation throughout the year. Intriguingly, these non-thermal responsive species have strong 5' and 3'ss on their per 3'-terminal introns, perhaps limiting their ability to colonize temperate climates. Presumably, low temperatures favor the interaction of splicing factors with suboptimal splicing signals. We will undertake a multi-faceted experimental strategy that includes biochemical, molecular, cell-culture and whole animal approaches to understand the cis- and trans-acting factors regulating the splicing efficiency of per 3'-terminal introns and how they modulate wake-sleep cycles in Drosophila. This will include characterization of newly identified natural polymorphisms in per that differentially regulate dmpi8 splicing and might vary geographically. We will also determine whether the effects of dmpi8 splicing are preferentially mediated from the morning or evening rhythmic brain centers and/or the more recently described arousal/sleep pacemakers. By undertaking comparative studies using a wide variety of natural populations and Drosophila species, this proposed work offers a unique opportunity to integrate studies on gene expression and neural circuits controlling complex behaviors with ecological and evolutionary implications. On a broader perspective, our work suggests that natural selection operating at the level of splicing signals plays an important role in the thermal adaptation of life forms.