The role of nyctalopin in the mammalian retina

描述（由申请人提供）：完全性X连锁先天性静止性夜盲症（CSNB 1）是一种遗传性疾病，由视网膜中光感受器和ON-双极细胞（ON-BPC）之间的突触传递阻滞引起。光感受器在黑暗中释放神经递质谷氨酸盐，并降低对光的释放速率。ON-BPC通过mGluR 6代谢型谷氨酸受体响应谷氨酸。谷氨酸通过mGluR 6的结合导致阳离子通道的关闭和ON-BPC的超极化。mGluR 6在ON-BPC树突中转导谷氨酸作用的作用是脊椎动物视觉的核心，但对mGluR 6信号通路中的步骤了解甚少，ON-BPC阳离子通道的分子身份也未知。负责CSNB 1的人类基因NYX编码一种新的蛋白质，nyctalopin，属于富含亮氨酸重复序列（LRR）蛋白家族。一种小鼠突变体，nob（无b波）具有与CSNB 1相似的表型和nyx基因的缺失。mGluR 6的表达在nob小鼠中似乎是正常的，然而它们的ON-BPC未能对外源性施加的谷氨酸做出反应，这暗示了mGluR 6信号通路中的夜来香肽。虽然对ON-BPC光反应至关重要，但夜来香肽的细胞功能尚不清楚。神经系统中的相关LRR蛋白参与神经突生长和突触形成，其中它们通过其LRR结构域结合其他蛋白质，包括可溶性配体、受体和G蛋白。我们建议，夜来香蛋白被发现在感光体的ON-BPC突触，它与mGluR 6信号通路的组件相互作用。为了验证这一假设，我们将确定定位的夜魔蛋白在视网膜上的免疫荧光显微镜和免疫电子显微镜使用针对一个独特的夜魔蛋白肽的抗体。我们将通过免疫沉淀和酵母双杂交筛选鉴定与夜来香蛋白相互作用的蛋白质。这些结果将提供洞察的作用，nyctalopin在视网膜中的光感受器和ON-BPC之间的突触传递，并可能导致其他组件的ON-BPC途径的识别。

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.