Retinal Characterization of a Mouse Homozygous for the Mutation That is the Most Common Cause of Bardet–Biedl Syndrome in Man: Met390Arg in BBS1

Abstract

Purpose: : To produce and characterize a mouse knock–in model of the most common genetic form of the autosomal recessive disorder Bardet–Biedl syndrome (Bbs1^M390R). In this study we assessed the disease progression in this animal for the first six months of age.

Methods: : Mice homozygous and heterozygous for the Bbs1^M390R mutation, were bred, genotyped and their eyes evaluated using: 1) histological and immunohistochemical assessment of retinal cells and structures; and 2) full field electroretinogram (ERG) of retinal function. Affected animals and normal littermates were assessed by ERG every two weeks from post–natal day 14 to six months of age, and every four weeks thereafter.

Results: : Histological analysis revealed a significant degree of retinal degeneration at the level of the outer nuclear layer by 16 weeks with increasingly severe attenuation with advancing age. Other layers of the retina appeared normal. TUNEL staining indicates that photoreceptor loss is mediated through apoptosis. Immunocytochemical analysis at the light microscopy level showed mislocalization of rhodopsin. Examination by transmission electron microscopy revealed disruption of the photoreceptor outer–segment ultrastructure with evidence of impaired disc morphogenesis. ERG analysis confirmed a progressive deterioration with initial observations at 2 weeks showing significantly reduced cone and rod responses culminating in an un–recordable response by six months of age.

Conclusions: : We have generated and characterized a knock–in mouse line containing the most common BBS mutation (Bbs1^M390R). Our analyses indicate that the progression of retinopathy is similar to that observed in humans and that this animal model is well suited for the development of cell/gene replacement therapies.

Keywords: retinal degenerations: cell biology • electrophysiology: non-clinical • immunohistochemistry