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Nyctalopin Expression in Retinal Bipolar Cells Restores Visual Function in a Mouse Model of Complete X-Linked Congenital Stationary Night Blindness

¹Departments of Biochemistry and Molecular Biology, ²Ophthalmology and Visual Sciences, ³Psychological and Brain Sciences, University of Louisville, Louisville, Kentucky; ⁴Research Unit Retinal Signal Processing, The Netherlands Institute for Neuroscience, Royal Netherlands Academy of Arts and Sciences, Amsterdam, The Netherlands; ⁵Department of Ophthalmology and Visual Science, Washington University School of Medicine, St. Louis, Missouri; ⁶Research Service, Cleveland Veterans Affairs Medical Center, Cleveland; ⁷Cole Eye Institute, Cleveland Clinic Foundation, Cleveland; and ⁸Department of Ophthalmology, Cleveland Clinic Lerner College of Medicine of Case Western Reserve University, Cleveland, Ohio

Submitted 29 May 2007; accepted in final form 19 September 2007

Mutations in the NYX gene that encodes the protein nyctalopin cause congenital stationary night blindness type 1. In no b-wave (nob) mice, a mutation in Nyx results in a functional phenotype that includes the absence of the electroretinogram b-wave and abnormal spontaneous and light-evoked activity in retinal ganglion cells (RGCs). In contrast, there is no morphological abnormality in the retina at either the light or electron microscopic levels. These functional deficits suggest that nyctalopin is required for normal synaptic transmission between retinal photoreceptors and depolarizing bipolar cells (DBCs). However, the synaptic etiology and, specifically, the exact location and function of nyctalopin, remain uncertain. We show that nob DBCs fail to respond to exogenous application of the photoreceptor neurotransmitter, glutamate, thus demonstrating a postsynaptic deficit in photoreceptor to bipolar cell communication. To determine if postsynaptic expression of nyctalopin is necessary and sufficient to rescue the nob phenotype, we constructed transgenic mice that expressed an EYFP-nyctalopin fusion protein on the dendritic tips of the DBCs. Immunohistochemical and ultrastructural studies verified that fusion protein expression was limited to the DBC dendritic tips. Fusion gene expression in nob mice restored normal outer and inner visual function as determined by the electroretinogram and RGC spontaneous and evoked responses. Together, our data show that nyctalopin expression on DBC dendrites is required for normal function of the murine retina.

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