Circadian control of structural plasticity in Drosophila

描述（由申请人提供）：生物钟作为时间过滤器，将基因表达、细胞代谢、生理和行为定时到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性的分子机制已经很好地理解，但尚不清楚这些信息如何进一步结构化以控制特定的行为输出。色素分散因子（PDF）的节律性释放已被提出将（一天中的时间）信息从核心起搏（PDF反应性）细胞传播到节律性运动活动背后的下游目标。事实上，PDF强度的这种昼夜变化代表了PDF电路与其输出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，涉及广泛的重塑轴突终端的PDF电路，显示更高的复杂性在白天和夜间显着降低复杂性。因此，时钟控制的结构可塑性可能是一个候选机制，有助于下游的起搏细胞的信息传输。本提案的目的是扩展这一初步观察，并通过培养大脑中的延时成像来表征PDF电路的结构。这种方法，再加上免疫组织化学，将揭示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采用新的遗传工具，允许基因表达的空间和时间控制进行探索。在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/活动周期的思考。 公共卫生相关性：昼夜节律系统进化为一种机制，使生物体能够适应由于地球自转而发生的光暗环境变化。由于其独特的遗传工具库，果蝇是一个完善的生物钟研究模型。尽管分子振荡背后的生化成分已经被详细描述，但时钟神经元将信息传递到下游通路的机制仍然难以捉摸。我们最近发现了一种新形式的网络可塑性，其中一个电路是中央的节奏休息活动周期经历了大量的昼夜节律重塑，可能是至关重要的时钟控制的行为。这项建议的目的是扩展最初的观察和表征这种形式的结构可塑性的分子机制。因此，该项目将揭示神经元生物钟调节生理和行为的一些新机制。

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.