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1.  TOPORS, implicated in retinal degeneration, is a cilia-centrosomal protein 
Human Molecular Genetics  2010;20(5):975-987.
We recently reported that mutations in the widely expressed nuclear protein TOPORS (topoisomerase I-binding arginine/serine rich) are associated with autosomal dominant retinal degeneration. However, the precise localization and a functional role of TOPORS in the retina remain unknown. Here, we demonstrate that TOPORS is a novel component of the photoreceptor sensory cilium, which is a modified primary cilium involved with polarized trafficking of proteins. In photoreceptors, TOPORS localizes primarily to the basal bodies of connecting cilium and in the centrosomes of cultured cells. Morpholino-mediated silencing of topors in zebrafish embryos demonstrates in another species a comparable retinal problem as seen in humans, resulting in defective retinal development and failure to form outer segments. These defects can be rescued by mRNA encoding human TOPORS. Taken together, our data suggest that TOPORS may play a key role in regulating primary cilia-dependent photoreceptor development and function. Additionally, it is well known that mutations in other ciliary proteins cause retinal degeneration, which may explain why mutations in TOPORS result in the same phenotype.
PMCID: PMC3033188  PMID: 21159800
2.  Functional characterization of a novel c.614-622del rhodopsin mutation in a French pedigree with retinitis pigmentosa 
Molecular Vision  2012;18:581-587.
To identify and functionally characterize the mutation responsible for autosomal dominant retinitis pigmentosa (adRP) in a large, six-generation French family.
Twenty individuals from this family participated in the genetic investigation. Six affected and 14 unaffected individuals from three-generations were available for linkage analysis using microsatellite markers flanking the rhodopsin (RHO) gene. A two-point logarithm of odds (LOD) score calculation was undertaken using GENEMARKER and MLINK software. Sanger sequencing of RHO was performed. Cellular localization of the mutant protein was performed by transforming SK-N-SH cells with pEGFP-N1-Rho, pEGFP-N1-Rho(P23H), and pEGFP-N1-Rho(c.614–622del).
The proband had nyctalopia, visual field constriction, peripheral bone spicule pigmentation of the fundus, central acuity (6/24 RE; 6/12 LE) at 55 years of age. Linkage analysis of this family suggested RHO as a possible candidate since the flanking marker D3S1292 yielded a LOD score of 2.43 at θ=0. Cloning of an exon 3 PCR product and direct sequencing of single clones identified a novel deletion in the third exon of RHO, c.614–622del (p.Y206-F208del). The deleted mutant protein localized to the endoplasmic reticulum and formed inclusion bodies.
This novel deletion in exon 3 of the RHO gene, c.614–622del results in a classical form of adRP in a multi-generation French family. Protein expression analyses confirmed that the deletion led to protein misfolding and suggest this is a class II mutation, similar to P23H, the most common class II mutation seen in North America.
PMCID: PMC3298422  PMID: 22419850
3.  A common allele in RPGRIP1L is a modifier of retinal degeneration in ciliopathies 
Nature genetics  2009;41(6):739-745.
Despite rapid advances in disease gene identification, the predictive power of the genotype remains limited, in part due to poorly understood effects of second-site modifiers. Here we demonstrate that a polymorphic coding variant of RPGRIP1L (retinitis pigmentosa GTPase regulator-interacting protein-1 like), a ciliary gene mutated in Meckel-Gruber (MKS) and Joubert (JBTS) syndromes, is associated with the development of retinal degeneration in patients with ciliopathies caused by mutations in other genes. As part of our resequencing efforts of the ciliary proteome, we identified several putative loss of function RPGRIP1L mutations, including one common variant, A229T. Multiple genetic lines of evidence showed this allele to be associated with photoreceptor loss in ciliopathies. Moreover, we show that RPGRIP1L interacts biochemically with RPGR, loss of which causes retinal degeneration, and that the 229T-encoded protein significantly compromises this interaction. Our data represent an example of modification of a discrete phenotype of syndromic disease and highlight the importance of a multifaceted approach for the discovery of modifier alleles of intermediate frequency and effect.
PMCID: PMC2783476  PMID: 19430481
4.  Disease mechanism for retinitis pigmentosa (RP11) caused by missense mutations in the splicing factor gene PRPF31 
Molecular Vision  2008;14:683-690.
Missense mutations in the splicing factor gene PRPF31 cause a dominant form of retinitis pigmentosa (RP11) with reduced penetrance. Missense mutations in PRPF31 have previously been shown to cause reduced protein solubility, suggesting insufficiency of functional protein as the disease mechanism. Here we examine in further detail the effect of the A216P mutation on splicing function.
Splicing activity was assayed using an in vivo assay in transfected mammalian cells with rhodopsin (RHO) and transducin (GNAT1) splicing templates. Pull-down assays were used to study the interaction between PRPF31 and one of its cognate partners in the spliceosome, PRPF6.
Splicing of RHO intron 3 and GNAT1 introns 3–5 mini-gene templates was inefficient with both spliced and unspliced products clearly detected. Assays using the RHO minigene template revealed a direct negative effect on splicing efficiency of the mutant. However, no effect of the mutation on splicing efficiency could be detected using the longer GNAT1 minigene template or using a full-length RHO transcript, splicing of which had an efficiency of 100%. No unspliced RHO transcripts could be detected in RNA from human retina. Pull-down assays between PRPF31 and PRPF6 proteins showed a stronger interaction for the mutant than wild type, suggesting a mechanism for the negative effect.
Splicing of full-length RHO is more efficient than splicing of the minigene, and assays using a full-length template more accurately mimic splicing in photoreceptors. The RP11 missense mutations exert their pathology mainly via a mechanism based on protein insufficiency due to protein insolubility, but there is also a minor direct negative effect on function.
PMCID: PMC2324120  PMID: 18431455

Results 1-4 (4)