Isolation of the mouse nyctalopin gene nyx and expression studies in mouse and rat retina.

Purpose: It has been shown recently that mutations in NYX (nyctalopin on chromosome X), encoding a novel protein associated with the leucine-rich repeat (LRR) protein superfamily, are responsible for the complete form of X-linked congenital stationary night blindness (CSNB1). This study describes the isolation and molecular characterization of the mouse orthologue Nyx and its expression pattern in the retina.

Methods: Nyx was isolated by conventional DNA library screening and polymerase chain reaction (PCR)-based approaches. Gene expression in different mouse tissues was studied by RT-PCR. Subsequently, the expression pattern of Nyx and its gene product in mouse and rat retinas was investigated by RNA in situ hybridization and immunohistochemistry with Nyx-specific antibodies.

Results: The Nyx gene encodes a protein of 476 amino acids that contain 11 consecutive LRR motifs flanked by amino- and carboxyl-terminal cysteine-rich LRRs. At the amino acid level, Nyx is highly homologous to its human orthologue (86% identity). The gene is expressed in the eye but also, at lower levels, in brain, lung, spleen, and testis. Nyx expression was found during all stages of postnatal retinal development and was confined to cells of the inner nuclear layer and the ganglion cell layer in adult mouse and rat retinas.

Conclusions: These data suggest an important function of the Nyx protein in the inner retina and provide evidence that CSNB1 is based on a defect in the inner retinal circuitry.