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K. Boesze-Battaglia, A. Bragin, R. Dierova, M. Damek-Poprawa; The C-Terminal Tail of Rds is Necessary for Establishment and Maintenance of Photoreceptor Outer Segment Structure. Invest. Ophthalmol. Vis. Sci. 2010;51(13):1898. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
Any one of over 150 mutations within the PRPH2 gene result in a broad variety of late onset progressive retinal dystrophies characterized by abnormal photoreceptor structure. The pathogenic mechanism(s) underlying retinal degeneration slow (rds) mediated retinal dystrophies are unknown. RDS belongs to a family proteins characterized by regions known as intrinsically disordered domains (IDD). IDDs are random structures which are stabilized by interactions with one or several binding partners, in the case of RDS this domain is the multi-functional C-terminus. In these studies we analyze a recently developed in vivo mouse model designed to determine the role of the C-terminal tail of RDS in establishment and maintenance of outer segment (OS) structure.
A transgenic mouse colony was generated on an rds-/- background that express a FLAG-tagged version of the ROS polypeptide lacking the terminal ten residues (RdsΔ10FLAG). The transgene, RDSΔ10FLAG, containing mouse PRPH2 cDNA truncated by 30 nucleotides, was directed to rods by a 4.5-kb rhodopsin promoter. Removal of this region abolishes MREG binding to RDS and enhances C-terminal mediated membrane perturbations. Mice expressing either one or two copies of the transgene on a null rds-/- background were analyzed in these studies. We determined whether photoreceptor structure (assessed by light and electron microscopy) and function (assessed by Electroretinograms) were correlated with modifications of the RDS C-terminus.
The RDSΔ10FLAG gene product was expressed as a covalently linked dimer that resolved into a monomer in the presence of reducing agents based on western blot analysis. It complexed with ROM-1 as indicted by co-immunoprecipitation studies. The Rds-/- mice do not produce any OSs. Expression of a single copy of the RdsΔ10FLAG transgene could partially rescue this phenotype, as small nubby OSs where formed. Moreover, expression of RDSΔ10FLAG did not alter gross OS morphology as indicted in EGFP positive sections stained with anti-opsin. The degree of structural instability of the RDSΔ10FLAG mutant decreased relative to wild type as predicted by its PONDR score. These results suggest less structural flexibility in the absence of the terminal ten residues.
We propose that the IDD RDS C-terminal domain plays a direct role in the biogenesis of OSs. Moreover, the C-terminus is specifically required for the stabilization of OS structure.
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