Functional Phenotyping of Mouse Mutants Reveals Novel Genes that Impact the Mammalian Outer Retina

Abstract

Purpose : The mammalian outer retina is comprised of photoreceptors, glia, bipolar cells, and the retinal pigment epithelium (RPE). Many of these cell types have a critical functional role in the initial stages of vision, which can be assessed by electroretinography (ERG). In this project, we used flash ERG to identify single-gene knockout (KO) mouse strains with abnormal outer retinal function.

Methods : A total of 523 KO strains, generated on a C57BL/6NJ (B6N) background as part of the International Knockout Mouse Consortium, were screened by ERG at 15 weeks of age. ERG stimulation and recording conditions were configured to examine the function of rod photoreceptors, bipolar cells, the cone pathway and the RPE. Cohorts of >4 mice were tested for each KO strain. Results from KO strains were compared to those from interwoven cohorts of wildtype control B6N mice. The major ERG components were examined separately. A given KO was considered a ‘hit’ when (a) those results differed significantly from control, (b) this difference was consistent across the individual animals within the KO cohort, and (c) this difference was consistent between the two eyes of each mouse. Mouse strains were also examined for general ocular dysmorphology and histopathology, and for nuclei counts within the outer nuclear layer.

Results : Of the 523 strains examined, a significant difference from control was observed in 21 strains for the rod ERG, including 17 for the a-wave, 11 for the b-wave, 8 for the c-wave, and 8 for a slow negative component following the c-wave. Fifteen strains presented with significant differences in the cone ERG, three of which also presented with rod ERG abnormalities. While the majority involved a reduction in ERG component amplitude, a number of strains exhibited a consistent increase in ERG amplitude. Only two genes (Cfap418, Syne2) have previously been associated with abnormal outer retinal function.

Conclusions : This work has identified 30 genes that were previously not associated with outer retinal dysfunction. Current studies are focused on the consequence at the cellular level of inactivation of these genes and how this relates to the observed functional abnormalities. In addition, KO strains that were characterized by a reduced ERG amplitude are being evaluated as candidate genes for human retinal disease in patients in whom a causative gene has not been identified.

This abstract was presented at the 2024 ARVO Annual Meeting, held in Seattle, WA, May 5-9, 2024.