Can the stability of a mutant mRNA copy of PRPF31 with an 11bp deletion be compromised through alternative splicing?

Abstract

Abstract: : Purpose:To investigate the stability of the mRNA copy produced from a mutant PRPF31 disease allele. Mutations in PRPF31 causes autosomal dominant retinitis pigmentosa on chromosome 19q13.4. One of the disease causative mutations identified is an 11bp deletion (1115–1125 del) in exon 11 of PRPF31. Due to a frameshift this mutation is predicted to produce an aberrant truncated protein of 469 residues. Since the premature termination codon (PTC) is in the last exon of the gene the mutant RNA should escape nonsense–mediated decay (NMD). Methods: To investigate whether the mutant mRNA escapes NMD, RT–PCR was performed on total RNA from lymphocytes of three symptomatic affected individuals with the 1115–1125 del mutation in exon 11 of PRPF31. The PCR products were then cloned and analysed by sequencing. Results:The mutant mRNA was cloned indicating that the mutant allele escapes NMD however the mutant allele was greatly under represented. Moreover a rare mRNA species that lack the entire exon 11 of PRPF31 was also detected indicating alternative splicing. The PTC of this mRNA species occurs >50 nucleotides upstream of the final splice junction of PRPF31 making this mRNA a potential target for NMD. Conclusions:As the deleted 11bp sequence encompasses a predicted exonic splicing enhancer (ESE) hexamer GAAGCA, we suggest that this motif enhances the inclusion of exon 11 during the splicing of PRPF31 pre–mRNA. The absence of this motif therefore results in an alternatively spliced, potentially unstable mutant mRNA that may down regulate the mRNA copy number from the disease allele of PRPF31.

Keywords: gene/expression • retinal degenerations: hereditary • genetics