Properties and Mechanisms of Melanopsin Photoreception

描述(申请人提供)：我们建议研究通过视网膜中一组非经典光感受器细胞有效调节哺乳动物生物钟的机制。这些天生对光敏的神经节细胞(IpRGC)表达一种名为黑素的G蛋白偶联受体。被黑素捕获的光子激活ipRGC，它将动作电位直接传递到视交叉上核和其他脑区的主生物钟。IpRGC是生物钟对光做出反应所必需的，而黑素蛋白的光转导在这一过程中起着重要的作用。我们的主要假设是，黑色素的光转导是针对昼夜节律的光接收而定制的。更具体地说，生物钟在广泛的时间和空间间隔内对光子进行求和，减少了局部光强波动的影响，以获得整体光强的准确表示。时钟使用该信息来使自己与当地时间同步。然而，昼夜节律光接收的时空总和的基础还不清楚。我们的目标是在这种背景下剖析ipRGC的光反应。我们将研究允许ipRGC在光照期间连续发出信号的机制，这是时间总和所必需的。此外，我们将探索黑素蛋白光转导的亚细胞组织如何使ipRGC对广泛的视觉空间做出反应以进行空间总和。我们的方法是使用BAC转基因小鼠来鉴定ipRGC，这种转基因小鼠在黑素启动子下驱动荧光蛋白的表达，并采用体外电生理学和光刺激的组合，从而能够在生物物理水平上进行分析。这项工作的意义在于，ipRGC是时钟的主要调节者，时钟控制着多达五分之一的表达基因。 在给定的组织中。生物钟失调与癌症、肥胖症、精神疾病和其他疾病有关。通过在昼夜生物学框架内对ipRGC光接收的系统研究，我们的研究有可能揭示维持健康和在疾病中受损的机制。

DESCRIPTION (provided by applicant): We propose to investigate the mechanisms that allow effective regulation of the mammalian circadian clock by a population of non-classical photoreceptor cells in the retina. These intrinsically photosensitive ganglion cells (ipRGCs) express a G-protein coupled receptor called melanopsin. Photon capture by melanopsin activates ipRGCs, which transmit action potentials directly to the master circadian clock in the suprachiasmatic nucleus, among other brain regions. IpRGCs are absolutely required for the clock to respond to light and melanopsin phototransduction plays an important role in this process. Our overarching hypothesis is that melanopsin phototransduction is tailored to circadian photoreception. More specifically, the circadian clock sums photons over broad intervals of time and space, diminishing the impact of local fluctuations in light intensity to obtin an accurate representation of the overall light level. The clock uses this information to synchronize itself to local time. However, the basis of spatiotemporal summation in circadian photoreception is not yet understood. Our goal is to dissect the ipRGC light response in this context. We will investigate the mechanisms that allow ipRGCs to signal continuously during illumination, which is necessary for temporal summation. In addition, we will explore how the subcellular organization of melanopsin phototransduction allows ipRGCs to respond to broad expanses of visual space for spatial summation. Our approach is to identify ipRGCs using a BAC-transgenic mouse that drives expression of a fluorescent protein under the melanopsin promoter, and employ a combination of in vitro electrophysiology and optical stimulation that allows analysis at the biophysical level. The significance of this work is that ipRGCs are the principal regulators of the clock, and the clock controls up to a fifth of all expressed genes in a given tissue. Dysregulation of the clock is implicated in cancer, obesity, mental illness, and othe ailments. Through a systematic investigation of ipRGC photoreception within the framework of circadian biology, our research has the potential to reveal mechanisms that maintain health and are compromised in disease.