Rod and Cone Opsin Mislocalization in an Autopsy Eye From a Female Carrier of X–linked RP With a Gly436Asp Mutation in the RPGR Gene

Abstract

Abstract: : Purpose:Knockout mice lacking the retinitis pigmentosa GTPase regulator gene (RPGR) show extensive opsin mislocalization in cones and probably in rods as well with subsequent retinal degeneration (Hong et.al., PNAS 2000). We evaluated the retina from a carrier of X–linked retinitis pigmentosa (RP) with the RPGR Gly436Asp mutation (Sharon et.al., Am J Hum Genet, 2003) to determine if mislocalization of cone and rod opsin can be seen in this human carrier. We compared our findings with those from a normal subject. Methods: Retinal punches from mid–peripheries of formaldehyde fixed autopsy eyes were taken from two comparably aged females: a carrier of X–linked RP with RPGR Gly436Asp mutation and a normal autopsy eye. Frozen sections were stained with antibodies against red/green and blue cone opsins, rhodopsin, and glial fibrillary acidic protein (GFAP), followed by labeling with fluorochrome conjugated secondary antibodies; these were viewed by fluorescence microscopy and digitally photographed. The same areas of the fellow eyes were examined by electron microscopy. Results: The RPGR Gly436Asp carrier showed a mosaic pattern of mislocalized and non–mislocalized cone and rod opsin in remaining photoreceptors. No cone or rod opsin mislocalization was seen in the normal subject. A GFAP signal, as an indicator of retinal degeneration, was evident in the Muller cells of the RPGR Gly436Asp carrier but not in the normal subject. Conclusions: These findings suggest that the RPGR protein is essential for normal vectorial transport of opsins to the photoreceptor outer segments in both humans and mice. A defect in this protein or its absence can lead to photoreceptor degeneration.

Keywords: retinal degenerations: hereditary • photoreceptors • pathology: human