Properties and Mechanisms of Melanopsin Photoreception

描述（由申请人提供）：我们建议研究允许通过视网膜中的非经典光感受器细胞群有效调节哺乳动物昼夜节律钟的机制。这些内在光敏神经节细胞（ipRGCs）表达一种叫做黑视素的g蛋白偶联受体。黑视素捕获光子激活ipRGCs， ipRGCs将动作电位直接传递到视交叉上核的主生物钟，以及其他大脑区域。IpRGCs是生物钟对光的响应所必需的，而黑视素光导在这一过程中起着重要作用。我们的首要假设是黑视素的光传导是根据昼夜节律的光接受而定制的。更具体地说，昼夜节律钟在广泛的时间和空间间隔内汇总光子，减少局部光强波动的影响，以获得整体光照水平的准确表示。时钟使用此信息将自身与本地时间同步。然而，昼夜光接受的时空叠加基础尚不清楚。我们的目标是在这种情况下剖析ipRGC光响应。我们将研究允许iprgc在照明期间连续发出信号的机制，这对于时间求和是必要的。此外，我们将探讨黑视素光导的亚细胞组织如何使iprgc响应广泛的视觉空间以进行空间求和。我们的方法是使用bac转基因小鼠来鉴定iprgc，该小鼠在黑视素启动子下驱动荧光蛋白的表达，并采用体外电生理和光学刺激相结合的方法，允许在生物物理水平上进行分析。这项工作的意义在于ipRGCs是生物钟的主要调节者，而生物钟控制着细胞中多达五分之一的表达基因

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.