Rd9 Is a Naturally Occurring Mouse Model of a Common Form of Retinitis Pigmentosa Caused by Mutations in RPGR-ORF15

Debra A Thompson,Peter Colosi,Lin Jia,Tiansen Li,Jacob Nellissery,Suja Hiriyanna,Mohammad I Othman,Garrett Grahek,John R Heckenlively,Hemant Khanna,Bo Chang,Anand Swaroop,Zhijian Wu,Naheed W Khan,Demetrios Vavvas

doi:10.1371/journal.pone.0035865

Abstract

Animal models of human disease are an invaluable component of studies aimed at understanding disease pathogenesis and therapeutic possibilities. Mutations in the gene encoding retinitis pigmentosa GTPase regulator (RPGR) are the most common cause of X-linked retinitis pigmentosa (XLRP) and are estimated to cause 20% of all retinal dystrophy cases. A majority of RPGR mutations are present in ORF15, the purine-rich terminal exon of the predominant splice-variant expressed in retina. Here we describe the genetic and phenotypic characterization of the retinal degeneration 9 (Rd9) strain of mice, a naturally occurring animal model of XLRP. Rd9 mice were found to carry a 32-base-pair duplication within ORF15 that causes a shift in the reading frame that introduces a premature-stop codon. Rpgr ORF15 transcripts, but not protein, were detected in retinas from Rd9/Y male mice that exhibited retinal pathology, including pigment loss and slowly progressing decrease in outer nuclear layer thickness. The levels of rhodopsin and transducin in rod outer segments were also decreased, and M-cone opsin appeared mislocalized within cone photoreceptors. In addition, electroretinogram (ERG) a- and b-wave amplitudes of both Rd9/Y male and Rd9/Rd9 female mice showed moderate gradual reduction that continued to 24 months of age. The presence of multiple retinal features that correlate with findings in individuals with XLRP identifies Rd9 as a valuable model for use in gaining insight into ORF15-associated disease progression and pathogenesis, as well as accelerating the development and testing of therapeutic strategies for this common form of retinal dystrophy.

Highlights

Retinitis pigmentosa (RP) is a group of clinically and genetically heterogeneous progressive retinal degenerative disorders that are characterized by rod and cone photoreceptor dysfunction and death, and which often culminate in blindness [1]
Our screening protocol identified retinal degeneration 9 (Rd9) mice as a naturallyoccurring model of human RP3, an X-linked retinal degeneration caused by mutations in Retinitis Pigmentosa GTPase Regulator (RPGR)
As in the majority of cases of RP3, and in a significant fraction of males with simplex RP [3], retinal degeneration in Rd9 mice is caused by a mutation in the alternatively-spliced exon ORF15

Summary

Introduction

Retinitis pigmentosa (RP) is a group of clinically and genetically heterogeneous progressive retinal degenerative disorders that are characterized by rod and cone photoreceptor dysfunction and death, and which often culminate in blindness [1]. X-linked forms of RP (XLRP) are among the most severe [2], comprising an estimated 15% of total non-syndromic, non-systemic cases [3,4]. Six genetic loci have been mapped for XLRP; of these, RP3 is the predominant subtype (www.sph.uth.tmc.edu/retnet/). RP3 is associated with mutations in the gene encoding Retinitis Pigmentosa GTPase Regulator (RPGR), which encodes multiple alternatively-spliced forms that all share a common aminoterminal domain with homology to Regulator of Chromosome Condensation 1 (RCC1) [4,5]. The major form of RPGR detected in most tissues (the constitutive form) is produced by exons 1 to 19, whereas the predominant form of RPGR in retina results from an alternatively-spliced transcript containing a unique terminal exon, ORF15. All of these mutations are deletions or duplications of purine-rich repeats in ORF15 that produce shifts in the reading frame which predict premature termination of translation

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Conclusion