Allelic Variation Suggest Rpgrip1 Is Important for Normal Outer Segments Development

Abstract

Purpose:: RPGRIP1 (retinitis pigmentosa GTPase regulator-interacting protein 1) is mutated in humans with Leber congenital amaurosis (LCA). Targeted mutagenesis in RPGRIP1 mice have been shown to lead to a disorganized outer segment and photoreceptor degeneration. Here we report another allele of RPGRIP1 found in the Neuromutagenesis Facility Program at The Jackson Laboratory that is phenotypically unique.

Methods:: The mutation of RPGRIP1^NMF247 was mapped using standard fine mapping procedures. The phenotype was characterized by fundus photography, light and electron microscopy, immunohistochemistry, and electroretinography compared in age-matched mutant and control mice.

Results:: The mutation in the NMF247 mutant was mapped to chromosome 14. By direct sequencing, we found a singe base pair substitution in the RPGRIP1 gene. The mutation was located in the splice acceptor site of intron 6 that results in the skipping exon 7 and a frame-shift that is predicted to lead to a premature termination in exon9. Fundus examination revealed that RPGRIP1^NMF247 mice have progressive retinal graininess and patchiness by 6 weeks of age. Severe outer nuclear layer degeneration (3~4 layer) was observed at P21 by light microscopy. By electron microscopy, at P12 outer segment were rarely observed and these OS disc that did form were disoriented and enlarged as previously reported. Rhodopsin was mislocalized to outer nuclear layer as early as P12. Rom 1 and opsin was also mislocalized at P28. Connecting cilia in RPGRIP1^NMF247 were present to be normal assessed either by electron microscopy or by anti-γ-tubulin staining.

Conclusions:: A number of splice variants of human and bovine RPGRIP1 have been reported. But there are only two splice variants reported for murine RPGRIP1. The new allele found in RPGRIP1^NMF247 is expected to affect both splice variants of murine RPGRIP1 whereas the previous targeted mutation would affect only the long variant.Since outer segment rarely were observed in RPGRIP1^NMF247 mice, this suggests that RPGRIP1 may play an essential role in proper development of outer segments

Keywords: gene mapping • photoreceptors • regeneration