The role of nyctalopin in the mammalian retina

描述(申请人提供)：完全性X连锁先天性静止性夜盲(CSNB1)是一种遗传性疾病，由视网膜光感受器和双极细胞(ON-BPC)之间的突触传递障碍引起。光感受器在黑暗中释放神经递质谷氨酸，并减缓对光的释放速度。ON-BPC通过mGluR6代谢型谷氨酸受体对谷氨酸作出反应。MGluR6与谷氨酸的结合导致阳离子通道关闭和ON-BPC超极化。MGluR6在转导On-BPC树突中谷氨酸的作用是脊椎动物视觉的中心，但对mGluR6信号通路中的步骤知之甚少，On-BPC阳离子通道的分子特性也是未知的。人类编码CSNB1的基因NYX编码一种新的蛋白质Nyctalopin，属于亮氨酸丰富重复序列(LRR)蛋白家族。小鼠突变体nob(无b波)具有与CSNB1相似的表型和NYX基因的缺失。在NOB小鼠中，mGluR6的表达正常，但其On-BPC对外源性谷氨酸没有反应，提示nyctalopin参与了mGluR6信号通路。尽管Nyctalopin对On-BPC的光反应是必不可少的，但其细胞功能尚不清楚。神经系统中相关的LRR蛋白参与轴突生长和突触的形成，在突触形成过程中，它们通过LRR结构域与其他蛋白质结合，包括可溶性配体、受体和G蛋白。我们认为，Nyctalopin存在于On-BPC突触的光感受器上，在那里它与mGluR6信号通路的组件相互作用。为了验证这一假设，我们将使用针对一种独特的nyctalopin多肽的抗体，通过免疫荧光显微镜和免疫电子显微镜来确定nyctalopin在视网膜中的定位。我们将通过免疫沉淀和酵母双杂交筛选来鉴定与奈科洛平相互作用的蛋白质。这些结果将有助于深入了解Nyctalopin在视网膜光感受器和On-BPC之间的突触传递中的作用，并可能导致识别On-BPC途径的其他组成部分。

DESCRIPTION (provided by applicant): Complete X-linked congenital stationary night blindness (CSNB1) is a hereditary disease caused by a block in synaptic transmission in the retina between photoreceptors and ON-bipolar cells (ON-BPCs). Photoreceptors release the neurotransmitter, glutamate, in darkness, and reduce the rate of release in response to light. ON-BPCs respond to glutamate via the mGluR6 metabotropic glutamate receptor. Binding of glutamate by mGluR6 leads to the closure of a cation channel and hyperpolarization of the ON-BPC. The role of mGluR6 in transducing the action of glutamate in the ON-BPC dendrites is central to vertebrate vision, yet the steps in the mGluR6 signaling pathway are poorly understood, and the molecular identity of the ON-BPC cation channel is unknown. The human gene responsible for CSNB1, NYX, encodes a novel protein, nyctalopin, belonging to the family of leucine rich repeat (LRR) proteins. A mouse mutant, nob (no b-wave) has a similar phenotype to CSNB1 and a deletion in the nyx gene. Expression of mGluR6 appears normal in the nob mice, however their ON-BPCs fail to respond to exogenously applied glutamate, implicating nyctalopin in the mGluR6 signaling pathway. Although essential for the ON-BPC light response, the cellular function of nyctalopin is not known. Related LRR proteins in the nervous system have been implicated in neurite outgrowth and synapse formation, where they bind other proteins through their LRR domains including soluble ligands, receptors, and G proteins. We propose that nyctalopin is found at the photoreceptor to ON-BPC synapse where it interacts with components of the mGluR6 signaling pathway. To test this hypothesis, we will determine the localization of nyctalopin in the retina by immunofluorescence microscopy and immuno-electron microscopy using antibodies directed against a unique nyctalopin peptide. We will identify proteins interacting with nyctalopin by immunoprecipitation and yeast two-hybrid screening. These results will provide insight into the role of nyctalopin in synaptic transmission between photoreceptors and ON-BPCs in the retina, and may lead to the identification of other components of the ON-BPC pathway.