Cellular expression and siRNA-mediated interference of rhodopsin cis-acting splicing mutants associated with autosomal dominant retinitis pigmentosa.

PURPOSE: To investigate the cellular expression of cis-acting splicing mutations in the rhodopsin gene (RHO) that lead to autosomal dominant or recessive retinitis pigmentosa (adRP/arRP) and the role of nonsense-mediated mRNA decay (NMD) in its pathogenic mechanism. To design a potential therapeutic RNAi-based suppression strategy for cis-acting adRP splicing mutants. METHODS: Cells were transfected with genomic constructs encoding the human wild-type (WT) and c.531-2A>G, c.936+1G>T, c.937-1G>T and c.745G>T RHO mutants. Total RNA was quantified by RT-PCR and protein was analyzed by immunocytochemistry. Three small interfering (si)RNAs directed against adRP mutant transcripts were designed and assayed in COS7 cells. RESULTS: The RHO cis-acting splicing mutations causing adRP, c.531-2A>G and c.937-1G>T, induce cryptic splicing. In contrast, the c.936+1G>T mutation, which causes arRP, results in exon skipping. Although the c.531-2A>G and c.745G>T RHO sequence predicted a premature termination codon (PTC) that should be a target for NMD, these mutant proteins were detected in transfected cells. The siRNAs designed to interfere with adRP mutants silenced the corresponding mRNA with varying efficiency. CONCLUSIONS: Although two RHO mutations that cause different RP phenotypes were the target for the NMD mechanism, a fraction of mutant RNA transcript may circumvent the NMD mechanism and be translated into protein. Thus, different levels of mutant protein may be necessary to trigger the RP phenotype. The findings demonstrate the potential use of siRNA to interfere with cis-acting splicing RHO transcripts. However, limitations in the mutation sequence and incomplete mutant transcript elimination should be considered in a therapeutic approach for adRP.

Transcriptional expression of cis-acting and trans-acting splicing mutations cause autosomal dominant retinitis pigmentosa.

Two types of mutations may lead to deficient pre-mRNA splicing: cis-acting mutations that inactivate a constitutive or alternative splice site within the pre-mRNA, and trans-acting mutations that affect the function of a basal factor of the splicing machinery. Autosomal dominant retinitis pigmentosa (adRP) is caused by mutations in at least 12 genes, with mutations in rhodopsin being the most prevalent. Two cis-acting mutations, g.3811A>G and g.5167G>T at the splice site in the rhodopsin gene (RHO; GenBank U49742.1) are linked to adRP in a Spanish population; while a cis-acting mutation, g.4335G>T, has been linked to recessive RP (arRP). Transcriptional expression analysis showed that the cis-acting splicing mutations linked to adRP promoted alternative splice sites, while the arRP linked mutation results in exclusion of exon 4. Trans-acting splicing mutations associated with adRP have also been found, and mutations in the pre-mRNA splicing factors PRPF3, PRPF8, PRPF31, and RP9 are associated with adRP in several populations. This report describes a new mutation in PRPF3 in a Spanish adRP family. We also investigated the transcriptional patterns in Epstein-Barr virus (EBV)-transformed lymphoblastoid cells from patients carrying a mutation in PRPF8. Despite the role of PRPF8 in the minor U12 splicing processes, microarray analysis revealed that mutations in PRPF8 not only did not result in significant differences in splicing efficiency of rhodopsin, but no apparent changes in expression of U12-type intron genes and splicing processes was observed. Microarray analysis revealed a panel of differentially expressed genes mapped to the RP loci, and future work will determine their role in RP.

Three novel and the common Arg677Ter RP1 protein truncating mutations causing autosomal dominant retinitis pigmentosa in a Spanish population.

BACKGROUND: Retinitis pigmentosa (RP), a clinically and genetically heterogeneous group of retinal degeneration disorders affecting the photoreceptor cells, is one of the leading causes of genetic blindness. Mutations in the photoreceptor-specific gene RP1 account for 3-10% of cases of autosomal dominant RP (adRP). Most of these mutations are clustered in a 500 bp region of exon 4 of RP1. METHODS: Denaturing gradient gel electrophoresis (DGGE) analysis and direct genomic sequencing were used to evaluate the 5' coding region of exon 4 of the RP1 gene for mutations in 150 unrelated index adRP patients. Ophthalmic and electrophysiological examination of RP patients and relatives according to pre-existing protocols were carried out. RESULTS: Three novel disease-causing mutations in RP1 were detected: Q686X, K705fsX712 and K722fsX737, predicting truncated proteins. One novel missense mutation, Thr752Met, was detected in one family but the mutation does not co-segregate in the family, thereby excluding this amino acid variation in the protein as a cause of the disease. We found the Arg677Ter mutation, previously reported in other populations, in two independent families, confirming that this mutation is also present in a Spanish population. CONCLUSION: Most of the mutations reported in the RP1 gene associated with adRP are expected to encode mutant truncated proteins that are approximately one third or half of the size of wild type protein. Patients with mutations in RP1 showed mild RP with variability in phenotype severity. We also observed several cases of non-penetrant mutations.

Sequence variations in the retinal fascin FSCN2 gene in a Spanish population with autosomal dominant retinitis pigmentosa or macular degeneration.

PURPOSE: Only one mutation in the retinal fascin gene (FSCN2) has so far been associated with autosomal dominant retinitis pigmentosa (adRP) and macular dystrophy (adMD), in a Japanese population. Our study was designed to identify mutations in the FSCN2 gene among Spanish persons with adRP or adMD. METHODS: Denaturing gradient gel electrophoresis and direct genomic sequencing were used to evaluate the complete coding region and flanking intronic sequences of the FSCN2 gene for mutations in 150 unrelated adRP and 15 adMD index patients, and in 50 sporadic cases of retinitis pigmentosa, together with 50 controls. Ophthalmic and electrophysiological examination of retinitis pigmentosa patients and their relatives was carried out according to pre-existing protocols. RESULTS: Sixteen nucleotide substitutions were detected in the coding sequence of the index patients. Nine of these, His7Tyr, Ala122Thr, Ser126Phe, His138Tyr, Arg149Gln, Ala240Thr, Ala323Thr, Asn331His, and Phe367Leu are missense mutations, one is a nonsense mutation (Lys302Stop), and six are silent mutations. Co-segregation of the mutations in the families showed no direct relation between mutation and disease. CONCLUSIONS: The photoreceptor-specific FSCN2 gene showed a relatively high number of sequence variations. The mutation 208delG in FSCN2, the only mutation so far associated with adRP or adMD, and which presumably causes a null allele, was not detected in these Spanish families. The nonsense mutation, Lys302Stop, detected in one adRP Spanish family is not the cause of the disease. These findings support the fact that the kind and frequency of the mutations depend on the ethnic population.

Mutations in the pre-mRNA splicing-factor genes PRPF3, PRPF8, and PRPF31 in Spanish families with autosomal dominant retinitis pigmentosa.

PURPOSE: Mutations in the systemically expressed pre-mRNA splicing-factor genes PRPF3, PRPF8, and PRPF31 have recently been associated with autosomal dominant retinitis pigmentosa (adRP). This study was intended to identify mutations in PRPF3, PRPF8, and PRPF31 in 150 Spanish families affected by adRP, to measure the contribution of mutations in these genes to adRP in that population, and to correlate RP phenotype expression with mutations in pre-mRNA splicing-factor genes. METHODS: Denaturing gradient gel electrophoresis (DGGE) and direct genomic sequencing were used to evaluate the complete coding region and flanking intronic sequences of the PRPF31 gene, exon 42 of PRPF8, and exon 11 of PRPF3 for mutations in 150 unrelated index patients with adRP. Ophthalmic and electrophysiological examination of patients with RP and their relatives was performed according to preexisting protocols. RESULTS: Three nonsense mutations caused by insertion and deletion sequences and two missense mutations (Arg2310Gly) and within the stop codon of the PRPF8 gene (TGA-->TTG), were detected in five unrelated heterozygous patients. Three patients were heterozygous carriers of different nonsense mutations in exon 8 of the PRPF31, gene and one Thr494Met mutation was found in exon 11 of the PRPF3 gene. Cosegregation of the mutation in PRPF8 and PRPF3 with adRP was observed. However, two nonsense mutations in PRPF31 causing adRP detected in two families showed asymptomatic carriers. CONCLUSIONS: Nine mutations, six of which are novel, in the pre-mRNA splicing-factor genes PRPF3, PRPF8, and PRPF31, causing adRP have been identified in the Spanish population. Their contribution to adRP is approximately 5% after correction in relation to mutations found in other genes causing adRP. The patients carrying a mutation in the pre-mRNA splicing-factor PRPF8 gene showed a type 1 diffuse RP. The existence of asymptomatic carriers of the nonsense mutation in the PRPF31 gene suggests incomplete penetrance for these mutations in the families.

Mutación Asp-190-Tyr en el gen de la rodopsina en una familia española afectada de retinosis pigmentaria autosómica dominante / Asp-190-Tyr mutation in the rodopsin gene in a Spanish family with autosomic dominant pigmentary retinosis

Ciertas mutaciones en el gen de la rodopsina causan retinosis pigmentaria autosómica dominante (ADRP). Se presenta una extensa familia afectada de ADRP. El análisis mediante electroforesis en gel de acrilamida con gradiente desnaturalizante y secuenciación directa de ADN detectó la presencia en heterozigosis del cambio G por T en la secuencia del ADN del tercer exón del gen de la rodopsina. Esta mutación destruye una diana de restricción para la endonucleasa Taq I y produce el cambio Asp-190-Tyr en la rodopsina. Todos los portadores de la mutación en la familia presentan un fenotipo de RP regional con una clínica variable. Esta mutación es la causante de la enfermedad en esta familia. (AU)