Circadian control of structural plasticity in Drosophila

描述（申请人提供）：生物钟作为一个时间过滤器，将基因表达、细胞代谢、生理和行为安排在一天中最关键的时刻，从而有助于生物体适应不断变化的环境。虽然在细胞水平上产生和维持节律的分子机制已经被很好地理解，但如何进一步构建这些信息来控制特定的行为输出却不太清楚。色素分散因子（PDF）的节律性释放被认为是将（一天中的时间）信息从核心起搏器（PDF反应性）细胞传播到节律性运动活动的下游目标。事实上，这种PDF强度的昼夜变化代表了PDF电路与其输出进行通信的唯一已知机制。最近，我们报道了一种新的昼夜节律现象，涉及PDF电路轴突末端的广泛重塑，该电路在白天显示出较高的复杂性，而在夜间显着降低复杂性。因此，生物钟控制的结构可塑性可能是促进起搏器细胞下游信息传递的候选机制。本建议的目的是扩展这一初步观察，并通过培养大脑的延时成像来表征PDF电路的结构。这种方法与免疫组织化学相结合，将阐明突触发生和突触消除是否同时发生。此外，负责这种实质性重塑的分子机制将利用允许基因表达的空间和时间控制的新型遗传工具进行探索。在像果蝇这样的模型系统中获得理解，很可能会影响目前对生物钟如何控制哺乳动物睡眠/活动周期的看法。

DESCRIPTION (provided by applicant): The circadian clock serves as a temporal filter to time gene expression, cell metabolism, physiology and behavior to the most critical moments in the day, thus contributing to the organism's adaptation to a changing environment. While the molecular mechanisms that generate and sustain rhythmicity at the cellular level are well understood, it is less clear how this information is further structured to control specific behavioral outputs. Rhythmic release of pigment dispersing factor (PDF) has been proposed to propagate the (time of day) information from core pacemaker (PDF reactive) cells to downstream targets underlying rhythmic locomotor activity. Indeed, such circadian changes in PDF intensity represent the only known mechanism through which the PDF circuit could communicate with its output. Recently, we reported a novel circadian phenomenon involving extensive remodeling in the axonal terminals of the PDF circuit which display higher complexity during the day and significantly lower complexity at nighttime. Thus, clock-controlled structural plasticity could be a candidate mechanism contributing to the transmission of the information downstream of pacemaker cells. The aim of the present proposal is to extend this initial observation and characterize the structure of the PDF circuit by time- lapse imaging in cultured brains. This approach, coupled with immunohistochemistry, will shed light on whether synaptogenesis and synapse elimination is concomitantly taking place. In addition, the molecular mechanisms responsible for such substantial remodeling will be explored employing novel genetic tools that allow spatial and temporal control of gene expression. Gaining understanding in a model system like Drosophila most likely will impact the current thinking of how the clock controls sleep/activity cycles in mammals. PUBLIC HEALTH RELEVANCE: Circadian systems evolved as a mechanism that allows organisms to adapt to the environmental changes in light and dark which occur as a consequence of the rotation of the Earth. Because of its unique repertoire of genetic tools, Drosophila is a well established model for the study of the circadian clock. Although the biochemical components underlying the molecular oscillations have been characterized in detail, the mechanisms used by clock neurons to convey information to the downstream pathways remain elusive. We have recently discovered a novel form of network plasticity whereby a circuit that is central to rhythmic rest-activity cycles undergoes substantial circadian remodeling and might be critical for clock control of behavior. The aim of this proposal is to extend the initial observations and characterize the molecular mechanisms underlying this form of structural plasticity. Thus, this project will shed light into some novel mechanisms by which neuronal circadian clocks regulate physiology and behavior.