Targeted Disruption of Mouse Ortholog (Spata7) of LCA3 Gene Causes Outer Segment Dysplasia, and Progressive Photoreceptor Degeneration Triggered by Rhodopsin Mislocalization

Abstract

Purpose: : LCA is a set of inherited, early onset retinopathies that affect about 1 in 50,000 in the general U.S. population and accounts for more than 5% of all retinal dystrophies. We recently identified the causative gene associated with the LCA3 locus, named SPATA7, which encodes a highly conserved but novel protein of unknown function and for which no animal models have been established. Interestingly, SPATA7 mutations are associated with both LCA and retinitis pigmentosa (RP), suggesting that a detailed understanding of SPATA7 function could have broad implications for our ability to diagnose, prevent, and treat human retinal diseases. To characterize the function of SPATA7, we have generated homozygous null alleles of mouse Spata7.

Methods: : We have generated homozygous knock-out mice using Cre-LoxP system

Results: : The phenotype of Spata7 mutant mice resembles the human LCA disease. In Spata7 knockout mice, progressive photoreceptor degeneration is observed over a period of 1 year due to cell apoptosis. Furthermore, light and electron microscopic analysis reveals that the outer segment of rods and cones were morphologically abnormal and disorganized in Spata7 mutant retina. Prior to apoptosis, Rhodopsin is mislocalized in the inner segment and cell bodies of Spata7 mutant photoreceptors as demonstrated by immune EM assay and immuno- histochemistry. Consistent with this observation, reduced rod Opsin expression partially rescued the Spata7 mutant phenotype, as measured by retinal morphometry, H&E staining and apoptosis assay.

Conclusions: : Our findings suggest that Spata7 is likely to play an important role in proper Rhodopsin transportation to the outer segment. Further studies of the molecular mechanism of this process using Spata7 mutant mice as a model will likely to provide important insights into LCA disease pathology, an essential step for designing effective therapeutic approaches for this disease.

Keywords: retina • development • mutations