Pires Susana S, Hughes Steven, Turton Michael, Melyan Zare, Peirson Stuart N, Zheng Lei, Kosmaoglou Maria, Bellingham James, Cheetham Michael E, Lucas Robert J, Foster Russell G, Hankins Mark W, Halford Stephanie
Nuffield Laboratory of Ophthalmology, University of Oxford, Oxford OX3 9DU, United Kingdom.
J Neurosci. 2009 Sep 30;29(39):12332-42. doi: 10.1523/JNEUROSCI.2036-09.2009.
Melanopsin is the photopigment that confers photosensitivity to a subset of retinal ganglion cells (pRGCs) that regulate many non-image-forming tasks such as the detection of light for circadian entrainment. Recent studies have begun to subdivide the pRGCs on the basis of morphology and function, but the origin of these differences is not yet fully understood. Here we report the identification of two isoforms of melanopsin from the mouse Opn4 locus, a previously described long isoform (Opn4L) and a novel short isoform (Opn4S) that more closely resembles the sequence and structure of rat and human melanopsins. Both isoforms, Opn4L and Opn4S, are expressed in the ganglion cell layer of the retina, traffic to the plasma membrane and form a functional photopigment in vitro. Quantitative PCR revealed that Opn4S is 40 times more abundant than Opn4L. The two variants encode predicted proteins of 521 and 466 aa and only differ in the length of their C-terminal tails. Antibodies raised to isoform-specific epitopes identified two discrete populations of melanopsin-expressing RGCs, those that coexpress Opn4L and Opn4S and those that express Opn4L only. Recent evidence suggests that pRGCs show a range of anatomical subtypes, which may reflect the functional diversity reported for mouse Opn4-mediated light responses. The distinct isoforms of Opn4 described in this study provide a potential molecular basis for generating this diversity, and it seems likely that their differential expression plays a role in generating the variety of pRGC light responses found in the mammalian retina.
黑视蛋白是一种光色素，赋予视网膜神经节细胞（pRGCs）的一个亚群光敏感性，这些细胞调节许多非成像任务，如检测光线以进行昼夜节律调节。最近的研究已开始根据形态和功能对pRGCs进行细分，但这些差异的起源尚未完全了解。在此，我们报告从小鼠Opn4基因座鉴定出两种黑视蛋白异构体，一种先前描述的长异构体（Opn4L）和一种新的短异构体（Opn4S），后者更类似于大鼠和人类黑视蛋白的序列和结构。Opn4L和Opn4S这两种异构体均在视网膜神经节细胞层中表达，转运至质膜并在体外形成功能性光色素。定量PCR显示Opn4S的丰度比Opn4L高40倍。这两种变体编码预测的521和466个氨基酸的蛋白质，仅在其C末端尾巴的长度上有所不同。针对异构体特异性表位产生的抗体鉴定出表达黑视蛋白的RGCs的两个离散群体，即共表达Opn4L和Opn4S的群体以及仅表达Opn4L的群体。最近的证据表明，pRGCs表现出一系列解剖学亚型，这可能反映了小鼠Opn4介导的光反应所报道的功能多样性。本研究中描述的Opn4的不同异构体为产生这种多样性提供了潜在的分子基础，并且它们的差异表达似乎在产生哺乳动物视网膜中发现的各种pRGC光反应中起作用。
