Melanopsin Photoreception and Signaling

描述（由申请人提供）：近年来，在哺乳动物视网膜中发现了除视杆和视锥之外的光感受器系统，其由表达视色素、黑视蛋白并且是本质光敏的（ipRGC）视网膜神经节细胞的亚群组成。这些ipRGC包含不同的亚型。M1细胞具有最强的黑视素免疫反应性、最高的固有光敏性和最大的饱和光反应。M2和M3细胞具有较弱的黑视素免疫反应性、较低的光敏性和小得多的饱和光反应。M1、M2和M3细胞在视网膜的内丛状层中的树突状分支的位置也不同。IpRGCs 主要投射到大脑中的非图像视觉中心（例如，大多数M1细胞），但它们也适度地投射到图像视觉中心（例如，M2细胞）。最后，据说存在M4和M5 ipRGC，但这些不能用黑视素免疫反应性检测到，并且具有极低的光敏性和小的光响应。该提议仅涉及M1-M3 ipRGC，其可以具有关于非图像视觉和图像视觉两者的差分功能。 为了充分理解黑视素系统，重要的是要详细了解ipRGC的光响应及其潜在机制。我们最近对M1细胞进行了广泛的生理/生物物理研究，并成功地解决了它们的单光子响应，估计了它们的黑视素密度，并从分子上鉴定了它们的一些关键光转导成分。这笔赠款将是这些成功调查的延续。目的1是研究M2和M3 ipRGCs的强度-响应关系、响应动力学、单光子响应、膜黑视蛋白密度和它们的光信号阈值，总体目标是比较/对比M1、M2和M3细胞。目的2是确定跨M1，M2和M3细胞的光转导的其他分子组分，包括信号G蛋白。我们还将研究TRPC通道光响应的门控机制。目的3是开始理解ipRGC的光响应的终止机制，包括潜在的黑视蛋白磷酸化、抑制蛋白与黑视蛋白结合和G蛋白失活的意义。目的4是研究M1，M2和M3 ipRGCs如何适应稳定的光，以及受体电流的这种适应如何转化为动作电位放电，从而向大脑发出信号。我们还将研究Ca 2+在光适应中的参与。总之，ipRGC是哺乳动物视网膜中唯一已知的非视杆/非视锥光感受器。它们对非图像视觉很重要，显然对图像视觉的微妙方面也很重要。因此，详细了解它们的功能对健康和疾病中的视力至关重要。

DESCRIPTION (provided by applicant): In recent years, a photoreceptor system besides rods and cones has been discovered in the mammalian retina, consisting of a sub-population of retinal ganglion cells that express the visual pigment, melanopsin, and are intrinsically-photosensitive (ipRGCs). These ipRGCs comprise distinct subtypes. M1 cells have the strongest melanopsin-immunoreactivity, the highest intrinsic photosensitivity, and the largest saturated light response. M2 and M3 cells have weaker melanopsin-immunoreactivities, lower photosensitivities, and much smaller saturated light responses. M1, M2 and M3 cells also differ in the location of their dendritic arborizations in the inner plexiform layer of the retina. IpRGCs project predominantly to non- image-vision centers in the brain (e.g., most M1 cells), but they also project moderately to image-vision centers (e.g., many M2 cells). Finally, there are supposedly M4 and M5 ipRGCs, but these are not detectable with melanopsin-immunoreactivity, and have extremely low photosensitivities and small light responses. This proposal deals only with M1-M3 ipRGCs, which may have differential functions with respect to both non-image and image vision. In order to fully understand the melanopsin system, it is important to know in detail the ipRGCs' light responses and their underlying mechanisms. We have recently carried out extensive physiological/biophysical studies of M1 cells, and succeeded in resolving their single-photon response, estimating their melanopsin density, and molecularly identifying some of their key phototransduction components. This grant will be a continuation of these successful investigations. Aim 1 is to study M2 and M3 ipRGCs with respect to their intensity-response relations, response kinetics, single-photon-responses, membrane melanopsin densities, and their light-signaling thresholds, with the overall goal of comparing/contrasting M1, M2 and M3 cells. Aim 2 is to identify additional molecular components of phototransduction across M1, M2 and M3 cells, including the signaling G protein. We shall also examine the gating mechanism for the TRPC channels underlying the light response. Aim 3 is to begin to understand the termination mechanisms for the ipRGC's light response, including the significance of potential melanopsin phosphorylation, arrestin binding to melanopsin, and G- protein deactivation. Aim 4 is to study how M1, M2 and M3 ipRGCs adapt to steady light, and how this adaptation in the receptor current translates into action-potential firing and therefore signaling to the brain. We shall also investigate the involvement of Ca2+ in light adaptation. In summary, ipRGCs are the only known non-rod/non-cone photoreceptors in the mammalian retina. They are important for non-image vision and apparently also for subtle aspects of image vision. Therefore, learning in detail how they function is of fundamental importance to vision in both health and disease.