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Shannon M. Conley, Michael W. Stuck, Justin L. Burnett, Muna I. Naash; Reconstitution Of Some Rds Functions In A Rom-1/rds Chimeric Knock-in Model. Invest. Ophthalmol. Vis. Sci. 2011;52(14):40.
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Mutations in retinal degeneration slow (RDS) are associated with rod- and cone-dominant diseases. RDS forms homo- and hetero-oligomers (with its homologue ROM-1) which play a significant role in the morphogenesis of outer segment (OS) disc rims. Mice lacking RDS (rds-/-) cannot form OSs while mice lacking ROM-1 (rom-1-/-) are relatively normal. Here we further our understanding of the divergent roles of RDS and ROM-1 by studying knock-in mice expressing a chimeric protein composed of the ROM-1 body and the RDS C-terminus (RRCT).
Knock-in mice were generated expressing the body of ROM-1 linked to the C-terminal of RDS in the RDS gene locus. Photoreceptor structure was analyzed by light and electron microscopy, while rod and cone function were assayed by ERG.
At postnatal day 30, OS ultrastructure is similar in rds+/- and rds+/R and is characterized by disorganized, round membranous whorls in the OS in contrast to the orderly stacks of OS discs that are seen in the WT. OS ultrastructure is improved in the rdsR/R compared to rds-/-; rdsR/R animals exhibit whorl like OSs similar to, but much smaller than, rds+/- while rds-/- exhibit no OSs at all. Consistent with this structural improvement, rod and cone function are improved at P30 in rdsR/R compared to rds-/-. Rds-/- have no detectable ERG signal; waveforms are completely flat. In contrast, rdsR/R exhibit nicely shaped scotopic and photopic waveforms although amplitudes are significantly reduced compared to WT levels (scotopic- 6.4%±2.7%, photopic-38.27%±10.8% of WT). Interestingly, maximum scotopic and photopic amplitudes are reduced in rds+/R compared to rds+/- (scotopic-30.4±8.4% vs. 54.0%±9.4% of WT, respectively, photopic-65.5%±18.1% vs. 99.0%±23.0% of WT, respectively) suggesting a dominant-negative effect of the knock-in allele. Studies on RDS/ROM-1 complex formation in knock-in animals are ongoing.
In contrast to mice lacking RDS (rds-/-), mice expressing the RRCT allele (ROM-1 body/RDS C-terminal) exhibit both rod and cone function and form OSs (albeit abnormal). These data indicate that the chimeric protein can perform some of the normal functions of RDS and support existing work demonstrating that some RDS functions are mediated by the C-terminal. The beneficial effect of the RRCT allele is more pronounced in cones, underscoring the idea that rods and cones have differential requirements for RDS and ROM-1.
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