Nyctalopin in the mammalian retina.

Abstract

Abstract: : Purpose: Complete X–linked congenital stationary night blindness (CSNB1) is a hereditary visual disease caused by mutations in the NYX gene. NYX encodes a novel protein, nyctalopin, belonging to the family of small leucine rich repeat proteoglycans (slrps). The dark adapted electroretinogram (ERG) of individuals with CSNB1 is characterized by a normal a–wave but the absence of a b–wave, as well as abnormalities in the light–adapted ERG. This phenotype is consistent with a defect in synaptic transmission between photoreceptors and ON–bipolar cells (ON–BPCs), and suggests a role for nyctalopin at the photoreceptor to ON–BPC synapse. We sought to test this hypothesis through a detailed characterization of the localization of nyctalopin in the mammalian retina. Methods: An antibody was raised against a unique peptide from the human nyctalopin sequence, and used for western blotting of retina proteins and for immunofluorescent labeling of lightly fixed retina sections from monkey, rabbit, mouse and rat. Double labeling immunofluorescence was performed for nyctalopin and markers of pre– and post–synaptic structures in the OPL. Confocal images of the staining were obtained on a Zeiss LSM510 microscope. Results: On western blots of retinal proteins, the nyctalopin antibody labels a single band at ∼52 kD, the predicted molecular weight of the protein. Immunofluorescent staining of retina sections revealed strong nyctalopin immunoreactivity in both the inner and outer plexiform layers (IPL and OPL) of all species examined. In the OPL, the nyctalopin staining was associated with both rod and cone terminals. In the IPL, nyctalopin staining was present throughout the IPL and was most prominent on putative rod bipolar cell terminals. Double labeling of nyctalopin with either mGluR6 or PKCa revealed that nyctalopin is intimately associated with ON–BPC dendrites in the OPL, but does not appear to reside within the dendrites. In the IPL, double labeling with PKCa confirmed the localization of nyctalopin immunoreactivity to rod–BPC terminals. Conclusions: The association between nyctalopin and both pre– and post–synaptic markers in the OPL indicates that nyctalopin plays a role in photoreceptor to ON–BPC synaptic transmission. The association of nyctalopin with both rod bipolar cell dendrites and terminals suggests that nyctalopin may be required for signaling in the rod pathway in both the OPL and IPL.

Keywords: synapse • photoreceptors • bipolar cells