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Induction of photosensitivity by heterologous expression of melanopsin

机译：黑色素蛋白的异源表达诱导光敏性

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Melanopsin(1-8) has been proposed to be the photopigment of the intrinsically photosensitive retinal ganglion cells (ipRGCs)(7-15); these photoreceptors of the mammalian eye drive circadian and pupillary adjustments through direct projections to the brain(5,6,8 - 14,16 - 18). Their action spectrum (lambda(max) approximate to 480 nm) implicates an opsin(10) and melanopsin is the only opsin known to exist in these cells. Melanopsin is required for ipRGC photosensitivity(13) and for behavioural photoresponses that survive disrupted rod and cone function(14,17). Heterologously expressed melanopsin apparently binds retinaldehyde and mediates photic activation of G proteins(19). However, its amino- acid sequence differs from vertebrate photosensory opsins(1,20) and some have suggested that melanopsin may be a photoisomerase, providing retinoid chromophore to an unidentified opsin(3,20). To determine whether melanopsin is a functional sensory photopigment, here we transiently expressed it in HEK293 cells that stably expressed TRPC3 channels. Light triggered a membrane depolarization in these cells and increased intracellular calcium. The light response resembled that of ipRGCs, with almost identical spectral sensitivity (lambda(max) approximate to 479 nm). The phototransduction pathway included Gq or a related G protein, phospholipase C and TRPC3 channels. We conclude that mammalian melanopsin is a functional sensory photopigment, that it is the photopigment of ganglion-cell photoreceptors, and that these photoreceptors may use an invertebrate-like phototransduction cascade.
机译：Melanopsin（1-8）被认为是固有光敏性视网膜神经节细胞（ipRGCs）（7-15）的光色素。这些哺乳动物眼睛的感光器通过直接投射到大脑来驱动昼夜节律和瞳孔调节（5,6,8-14,16-18）。它们的作用谱（λ（最大）约480 nm）暗示一种视蛋白（10），而黑视蛋白是已知存在于这些细胞中的唯一视蛋白。黑色素对于ipRGC光敏性（13）和行为光反应是必需的，这些光反应能在破坏的杆和锥功能中存活（14,17）。异源表达的黑视蛋白显然与视黄醛结合并介导G蛋白的光激活（19）。然而，它的氨基酸序列不同于脊椎动物的光敏视蛋白（1,20），并且有人认为黑视蛋白可能是一种光异构酶，为未知的视蛋白提供类视色素发色团（3,20）。为了确定黑色素是否是功能性的感官色素，我们在稳定表达TRPC3通道的HEK293细胞中瞬时表达它。光触发了这些细胞的膜去极化并增加了细胞内钙。光响应类似于ipRGC，具有几乎相同的光谱灵敏度（λ（最大值）约为479 nm）。光电导途径包括Gq或相关的G蛋白，磷脂酶C和TRPC3通道。我们得出结论，哺乳动物的黑色素是一种功能性的感觉光色素，它是神经节细胞光感受器的光色素，并且这些光感受器可能使用无脊椎动物样的光转导级联。

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