Developmental Analysis of the rd10 Mouse

Abstract

Abstract: : Purpose: The C57BL/6J-rd10/rd10 mouse strain is a newly-described model of retinal degeneration. This strain bears a point mutation in exon 13 of the rod cGMP beta-phosphodiesterase (ßPDE) gene. The purpose of this study was to assess ßPDE protein expression, retinal degeneration, and visual transduction function during development. Methods: Protein from freshly isolated retinas of C57BL/6 (wildtype), C57BL/6J-rd10/rd10 (rd10), and C3H/HeNCrIBR-rd1/rd1 (rd1) mice at postnatal days (PN) 9 through PN20 and PN120 (adult) were subjected to western immunoblot analysis using a polyclonal peptide antibody raised against mouse ßPDE. Standard light- and dark-adapted ERGs were recorded at PN 17-37 and retinal morphology was evaluated by histological methods at PN 14-40. Results: Immunoreactivity corresponding to a protein size of about 86 kDa was visualized in extracts from wildtype and rd10 retinas. Immunoreactivity to wildtype extract increased steadily from PN9 through PN14, with no further increase through PN20. Immunoreactivity to rd10 extract appeared a day later (PN10), increasing through PN15, with no further increase through PN20. No immunoreactivity was found in extracts from rd1 retina at any stage, adult wildtype whole brain, or adult rd10 retina. Though equal amounts of protein were loaded in all lanes, the signal with rd10 extract was less than 50% of the wildtype at all stages. The rd10 ERG had a recordable dark-adapted a-wave up to PN30. The outer nuclear layer (ONL) and general morphology of rd10 retina appeared normal to PN16, when photoreceptor degeneration became apparent in central retina. Conclusions: The lack of immunoreactivity to proteins from rd1 retina or wildtype brain indicates the specificity of the antibody. That the rod-driven, dark-adapted a-wave exists indicates that the rd10 mutant ßPDE protein is at least partially enzymatically active. The persistence of rod visual cycle function and ßPDE protein expression well past degeneration onset suggests that the rd10 retinal degeneration is not caused by absence of ßPDE protein but may be caused by insufficient ßPDE expression and/or low unit enzymatic activity. This could lead to intracellular cGMP accumulation, slower than but similar to rd1 retina, and eventual cell death. We intend to measure rd10 retina ßPDE activity and cGMP levels in the future.

Keywords: animal model • retinal degenerations: cell biology • microscopy: light/fluorescence/immunohistochem