Identification of a new mouse model of Complete Congenital Stationary Night Blindness

Abstract

Purpose: : The electroretinogram (ERG) has been used to identify mice and humans with mutations in genes that encode proteins critical to the G-protein coupled cascade required for depolarizing bipolar cell function. This cascade is critical to night vision. Mice and patients with mutations in several members of this pathway have a no b-wave (nob) ERG phenotype and complete Congenital Stationary Night Blindness (cCSNB). An ERG screen identified a new mouse (nob5), which arose as a spontaneous mutation. Our goal was to determine if the mutation was in a new gene or in one of the genes already known to cause cCSNB.

Methods: : Complementation studies were performed by crossing nob5 with Nyx^nob, TRPM1^-/- and GRM6^-/- mice. Retinal function of the F1 progeny was assessed with the ERG. A mapping panel was generated by crossing nob5 mice with C57Bl/6J mice, and subsequently intercrossing the F1 mice. The F2 progeny were phenotyped using the ERG, followed by genetic mapping to localize nob5 in the mouse genome. Retinal morphology was evaluated by immunohistochemistry and confocal microscopy.

Results: : The progeny of nob5 crosses to TRPM1^-/-, Nyx^nob and GRM6^-/- mice had normal ERG b-waves, which ruled out nob5 being an allele of any of these genes. Genetic mapping localized the nob5 locus to chromosome 11, which eliminates other genes associated with a no b-wave phenotype (Gα0 and Gβ5). We are currently using both candidate gene approaches and next generation sequencing to further refine the critical region and to identify both the gene and the mutation that underlies the nob5 phenotype.

Conclusions: : The nob5 phenotype results from a mutation in a novel gene essential to the GRM6 mediated signal transduction cascade that is critical to depolarizing bipolar cell function.

Keywords: bipolar cells • gene mapping • positional cloning