PRPF4 mutations cause autosomal dominant retinitis pigmentosa

Abstract

Retinitis pigmentosa (RP), a disease characterized by progressive loss of photoreceptors, exhibits significant genetic heterogeneity. Several genes associated with U4/U6-U5 triple small nuclear ribonucleoprotein (tri-snRNP) complex of the spliceosome have been implicated in autosomal dominant RP (adRP). HPrp4, encoded by PRPF4, regulates the stability of U4/U6 di-snRNP, which is essential for continuous splicing. Here, we identified two heterozygous variants in PRPF4, including c.-114_-97del in a simplex RP patient and c.C944T (p.Pro315Leu), which co-segregates with disease phenotype in a family with adRP. Both variants were absent in 400 unrelated controls. The c.-114_-97del, predicted to affect two transcription factor binding sites, was shown to down-regulate the promoter activity of PRPF4 by a luciferase assay, and was associated with a significant reduction of PRPF4 expression in the blood cells of the patient. In fibroblasts from an affected individual with the p.Pro315Leu variant, the expression levels of several tri-snRNP components, including PRPF4 itself, were up-regulated, with altered expression pattern of SC35, a spliceosome marker. The same alterations were also observed in cells over expressing hPrp4(Pro315Leu), suggesting that they arose as a compensatory response to a compromised splicing mechanism caused by hPrp4 dysfunction. Further, over expression of hPrp4(Pro315Leu), but not hPrp4(WT), triggered systemic deformities in wild-type zebrafish embryos with the retina primarily affected, and dramatically augmented death rates in morphant embryos, in which orthologous zebrafish prpf4 gene was silenced. We conclude that mutations of PRPF4 cause RP via haploinsufficiency and dominant-negative effects, and establish PRPF4 as a new U4/U6-U5 snRNP component associated with adRP.

Functional and Genetic Analysis of Choroid Plexus Development in Zebrafish

“…Interestingly, by whole mount in situ hybridization and RNA-Seq analysis we determined that the point mutation in sart1 results in an obvious up-regulation of the transcript. Up-regulation of mutated splicing genes have been demonstrated in other studies such as prpf4, a gene encoding a protein that interacts with the U4/U6 di-snRNP and stabilizes the complex (Chen et al, 2014). A mutation from a proline to leucine in prpf4 led to its increased expression and also up-regulation of other splicing factors including sart1.…”

“…Because we did not detect expression of Zpr1 and SV2 in the eye and because mutations in splicing factors have previously been shown to contribute to retinal degeneration, (Chen et al, 2014;Yin et al, 2011) we hypothesized that cells in the eye may be undergoing apoptosis. To test this hypothesis, we used an activated Caspase-3 antibody.…”

“…Previous studies have identified increased expression of spliceosome transcripts when another component of the spliceosome itself, or a protein involved in spliceosome assembly is defective (Chen et al, 2014;Jia et al, 2012). Because Sart1 is involved in the recruitment of U4/U6.U5 tri-snRNP to the spliceosome, we wanted to observe whether additional factors involved in spliceosome assembly were also defective or up-regulated in order to compensate for possible defects in Sart1 function.…”

“…Because retinal degeneration has been shown as a result of splicing defects or mutations in spliceosome components (Chen et al, 2014;Tanackovic et al, 2011), we were interested to see if mutations in sart1 led to decreased expression of vision-related genes. Cone-rod homeobox (crx) is a transcription factor found in photoreceptor cells and mutations in this gene have been associated with cone-rod dystrophy (Freund et al, 1997).…”

Altérations de l’épissage et maladies rares

“…C'est le cas par exemple dans certaines rétinites pigmentaires qui constituent un groupe de troubles oculaires héréditaires entraînant une perte progressive de la vision. Il a été montré que les patients atteints de ces maladies portent des mutations au niveau des gènes codants du splicéosome comme PRPF4 (pre-MRNA processing factor 4) [30]. Des facteurs d'épissage peuvent également porter des mutations et entraîner des maladies.…”