Melanopsin Photoreception and Signaling

项目摘要 现在清楚的是，哺乳动物视网膜除了杆之外还具有至少一种其他感光器类别， 视锥细胞，由表达黑视素的视网膜神经节细胞（RGC）亚群组成 （OPN 4）并且是固有光敏的（ipRGC）。这些细胞主要投射非图像视觉 在大脑中的中心，服务功能，如昼夜光诱导和瞳孔光反射。在 与此同时，ipRGC适度地投射到大脑的图像视觉中心，可能是为了微妙的图像- 形成视觉功能，例如可能提供关于视觉中的绝对光强度的信息 现场迄今为止，已知IpRGC包括6种亚型M1-M6，其在黑视素水平上不同 内容，光敏性，体细胞和树突领域的大小，其树突分支的确切位置， 视网膜的内丛状层，以及它们在各自大脑中的轴突投射的详细位置 目标的 为了充分理解ipRGC系统，重要的是要知道它们的光响应特性和它们的光响应特性。 基本机制。近年来，我们在理解M1-ipRGC方面取得了很大进展， 包括光转导中几个关键组分的分子身份，如Gα q-亚家族 成员，PLCβ4酶和TRPC 6，7通道。这些成分非常类似于 蝇眼光转导最近，我们有了另一个令人兴奋的发现， 在M2-和M4-ipRGCs中发现的光转导途径。该途径涉及光诱导的 环核苷酸，其打开HCN通道（通过膜超极化和环核苷酸门控的通道）， 核苷酸）以产生膜去极化和动作电位。 这一申请是这些成功调查的继续。目标1：寻找 HCN-光转导途径的细节仍然悬而未决，包括确定（i）cGMP或 cAMP是第二信使，（ii）控制第二信使的效应酶的身份， 和（iii）HCN途径上游G蛋白的身份。目标2是表征 在M3-、M5-和M6-ipRGC中仍然未知光转导机制。我们的推测是 涉及两个途径，但这需要核实。目标3是量化两者的相对重要性 不同细胞亚型的信号通路。我们将研究灵敏度，强度-反应关系，单- 光子响应以及每个途径的响应动力学，希望最终能够得出与 各子类型的宏观功能。

PROJECT SUMMARY It is now clear that the mammalian retina has at least one other photoreceptor class besides rods and cones, consisting of a subpopulation of retinal ganglion cells (RGCs) that express the pigment melanopsin (OPN4) and are intrinsically photosensitive (ipRGCs). These cells project predominantly to non-image-vision centers in the brain, serving functions such as circadian photoentrainment and pupillary light reflex. At the same time, ipRGCs project moderately to the brain's image-vision centers, presumably serving subtle image- forming visual functions such as possibly providing information about absolute light intensity in the visual scene. IpRGCs are known so far to comprise 6 subtypes, M1-M6, which differ in the level of melanopsin content, photosensitivity, somatic and dendritic-field size, exact locations of their dendritic arborizations in the retina's inner plexiform layer, and the detailed locations of their axonal projections in the respective brain targets. To fully understand the ipRGC system, it is important to know their light-response properties and the underlying mechanisms. In recent years, we have made great progress in understanding M1-ipRGCs, including the molecular identities of several key components in phototransduction such as Gαq-subfamily members, the PLCβ4 enzyme and the TRPC6,7 channels. These components closely resemble those found in fly-eye phototransduction. Most recently, we have made the exciting discovery of yet another phototransduction pathway, found in M2- and M4-ipRGCs. This pathway involves a light-induced elevation of cyclic nucleotide, which opens HCN channels (channels gated by membrane hyperpolarization and cyclic nucleotide) to produce membrane depolarization and action potentials. This application constitutes a continuation of these successful investigations. Aim 1 is to seek some details of the HCN-phototransduction pathway still outstanding, including establishing (i) whether cGMP or cAMP is the second messenger, (ii) the identity of the effector enzyme that controls the second messenger, and (iii) the identity of the G protein upstream of the HCN-pathway. Aim 2 is to characterize the phototransduction mechanism(s) still unknown in M3-, M5- and M6-ipRGCs. Our speculation is that the same two pathways are involved, but this requires verification. Aim 3 is to quantify the relative importance of the two signaling pathways in different cell subtypes. We shall study sensitivity, intensity-response relation, single- photon response, and response kinetics of each pathway, hopefully eventually to derive correlations with the respective subtype's macroscopic functions.