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Lisa Maria Riedmayr, Sybille Boehm, Martin Biel, Elvir Becirovic; Differential Disease Profiles of Two Retinitis Pigmentosa Point Mutations in Rhodopsin Correlate with the Mutant Effects on mRNA Splicing. Invest. Ophthalmol. Vis. Sci. 2018;59(9):4496.
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© ARVO (1962-2015); The Authors (2016-present)
Mutations in rhodopsin (RHO) are the most frequent cause of retinitis pigmentosa (RP). These RP-linked rhodopsin mutations show variable disease onsets and progression. This phenomenon is remarkably illustrated for two RHO point mutations in exon 3 (c.620T>G and c.620T>A), which affect the same nucleotide, but show completely different disease profiles in the affected individuals. Assuming that both point mutations represent classical missense mutations, several studies failed to explain their differential disease penetrance. The initial hypothesis of this study was that the c.620T>G mutation, which is characterized by an early disease onset and a rapid disease progression, might affect mRNA splicing and thus compromise the corresponding protein more profoundly.
Minigenes comprising all five coding exons and the intervening intronic regions of RHO were expressed in HEK293 cells and in murine rod photoreceptors. For rod photoreceptor specific expression, the transgene driven by the murine RHO promoter was subretinally injected in wild type mice and expressed by means of recombinant adeno-associated virus (rAAV)-mediated gene transfer. mRNA splicing was analyzed using RT-PCR with minigene-specific primers. Protein localization was addressed by confocal microscopy on transfected HEK293 cells and on immunostained slices of injected retinas.
The c.620T>G mutation generates a novel acceptor splice site in exon 3. This splice defect leads to an in-frame deletion of 30 aa in rhodopsin. The c.620T>A mutation, however, does not affect mRNA splicing. The truncated protein caused by the c.620T>G mutation was completely mislocalized in HEK293 cells and in murine rod photoreceptors. By contrast, the c.620T>A mutation did not affect protein localization in these cells.
Our results suggest that the severe disease symptoms of the c.620T>G mutation most likely result from aberrant mRNA splicing. This highlights the importance of analyzing the effects of exonic point mutations on mRNA splicing prior to declaring them as missense mutations. Finally, we postulate that the differential penetrance of many other exonic point mutations in RHO and in other RP-linked genes might also be explained by their differential effects on mRNA splicing.
This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.
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