Evaluation of splicing efficiency in lymphoblastoid cell lines from patients with splicing-factor retinitis pigmentosa
Section of Ophthalmology and Neuroscience, Leeds Institute of Molecular Medicine, University of Leeds, Leeds LS9 7TF, United Kingdom; Department of Statistics, University of Leeds, Leeds LS9 7TF, United Kingdom; Section of Musculoskeletal Disease, Leeds Institute of Molecular Medicine, University of Leeds, Leeds LS9 7TF, United Kingdom; Wellcome Trust Centre for Cell Biology, University of Edinburgh, Edinburgh, United Kingdom; Department of Human Genetics, University of Cape Town Medical School, Cape Town, South Africa; CERA, University of Melbourne, Royal Victorian Eye and Ear Hospital, Melbourne, VIC, Australia
Purpose: Retinitis pigmentosa (RP) is caused by mutations in a variety of genes, most of which have known functions in the retina. However, one of the most perplexing findings of recent retinal genetics research was the discovery of mutations causing dominant PP in four ubiquitously expressed splicing factors. The aim of this study was to use lymphoblast cell lines derived from RP patients to determine whether mutations in two of these splicing factors, PRPF8 and PRPF31, cause measurable deficiencies in pre-mRNA splicing. Methods: cDNA was prepared from lymphoblastoid cell lines derived from RP patients bearing mutations in the splicing factor genes and controls, grown under a variety of conditions. Introns representing the U2 and U12 intron classes, with both canonical and noncanonical donor and acceptor sequences, were analyzed by real-time PCR to measure the ratio of spliced versus unspliced transcripts for these introns. In addition, plasmids encoding the retinal outer segment membrane protein-1 (ROM-1; exon 1 to exon 2) gene, both in the wild-type form and with mutations introduced into the splice donor sites, were transfected into cell lines. The spliced versus unspliced cDNA ratios were measured by real-time RT-PCR. Results: Splicing of four canonical U2 introns in the actin beta (ACTB), glyceraldehyde-3-phosphate dehydrogenase (GAPDH), PRPF8, and retinitis pigmentosa GTPase regulator (RPGR) genes was unaffected in PRPF8 mutant cells. However, the splicing efficiency of RPGR intron 9 was significantly decreased in PRPF31 mutant cell lines. In contrast, a consistent decrease in the splicing efficiency of all U12 and noncanonical U2 introns was seen in PRPF8, but not in PRPF31, mutant cells, with statistical significance for STK11 intron 3. Conclusions: In spite of the ubiquitous expression patterns of the genes implicated in splicing factor RP, no pathology has yet been documented outside the retina. The observed differences in splicing efficiency described herein favor the hypothesis that these mutations may have a subpathological effect outside the retina. These observations argue against a defect in some yet to be discovered additional function of these proteins and support the alternative hypothesis that this form of RP does indeed result from aberrant splicing of retinal transcripts. © 2008 Molecular Vision.
beta actin; complementary DNA; glyceraldehyde 3 phosphate dehydrogenase; guanosine triphosphatase regulator protein; messenger RNA precursor; outer membrane protein; premessenger ribonucleic acid processing factor 31; premessenger ribonucleic acid processing factor 8; regulator protein; retina outer segment membrane protein 1; unclassified drug; adult; article; canonical analysis; controlled study; enzyme regulation; female; gene function; gene mutation; gene sequence; genetic transfection; human; human cell; intron; lymphoblastoid cell line; male; mutant; pathogenesis; priority journal; retinitis pigmentosa; reverse transcription polymerase chain reaction; RNA splicing; RNA transcription; ubiquitination; Adult; Aged; Carrier Proteins; Cell Line; Eye Proteins; Female; Genes, Dominant; Humans; Introns; Lymphocytes; Male; Membrane Proteins; Middle Aged; Multivariate Analysis; Organ Specificity; Retinitis Pigmentosa; RNA Precursors; RNA Splicing; Transfection