Late-Onset Severe Retinal Degeneration in a Mouse Model Due to a Nonsense Mutation

Abstract

Purpose: : To determine the molecular mechanism underlying age-related retinal degeneration (arrd1) segregating in autosomal recessive mode in a naturally occurring mouse model.

Methods: : Retinal pathology was evaluated by fundus photography, ERG, morphology, immunohistochemistry and electron microscopy at various ages. Microsatellite marker and candidate gene analyses were carried out to map and clone the arrd1 gene. Molecular pathology of retina was determined by in situ hybridization, qRT-PCR and nonsense mediated decay (NMD) assay. Involvement of arrd1 gene in causing retinal degeneration in patients was evaluated by family-based association analysis. LD structure of ARRD1 gene was examined and custom Goldengate Illumina panel constructed to test for association in patients with the age-related macular degeneration (AMD).

Results: : The arrd1 mice had a normal ocular fundus appearance, ERG and retinal histology at age 6 months. Attenuation of vessels, RPE atrophy and presence of retinal dots were noted at 14 months which progressed to complete loss of photoreceptors and extinguished ERG by 22 months. Levels of photoreceptor specific gene transcripts were significantly low at 12 months and found minimal by 18 months. Genetic analysis revealed a nonsense mutation in the arrd1 gene which results in premature truncation of the putative protein. We identified a novel transcript, which is the predominant transcript of the arrd1 gene in retina. In situ hybridization localized this transcript to the nuclear layers of the retina. The arrd1 mutant transcript was significantly depleted in the retina of affected mice and it was observed to undergo NMD. Analysis of two independent cohorts of patients with AMD and several patients with late-onset dominant macular degeneration did not reveal an association between the human ARRD1 gene and AMD.

Conclusions: : We identified a naturally occurring mouse strain that develops late-onset progressive retinal degeneration with an onset around 9 months of age. A nonsense mutation was observed in the arrd-1 gene and degradation of the retinal transcript of this gene by NMD may underlie the molecular pathology observed in these mice. No association was observed between the ARRD1 gene and AMD.

Keywords: age-related macular degeneration • retinal degenerations: cell biology • photoreceptors