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Yang Kong, Jeremy R Charette, Jürgen Naggert, Lihong Zhao, Patsy M Nishina; Frmd4b Suppresses Retinal Dysplasia in Nr2e3rd7 Mice by Restoring the Integrity of External Limiting Membrane. Invest. Ophthalmol. Vis. Sci. 2016;57(12):3148. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
To identify and characterize genetic modifiers, which are capable of suppressing the formation of rosette-like structures that cause retinal dysplasia in Nr2e3rd7 mice.
A sensitized chemical mutagenesis ophthalmic screen of Nr2e3rd7 mice was employed to search for heritable modifiers that reduce the pan retinal fundus spotting phenotype in homozygous Nr2e3rd7 mice. QTL analysis of the Tvrm222 mouse line combined with high-throughput sequencing of an exome capture library was used to identify the molecular basis of the modifier's mutation. Apart from fundus imaging, a longitudinal histological study was carried out to characterize the progression of altered retinal phenotypes. Finally, immunostaining with anti-zonula occludin 1 (ZO-1) and anti-β-catenin, as well as western blotting analyses were performed to reveal the defects that underlie the rd7-associated retinopathy and how the defects are corrected by the modifier.
The Tvrm222 mouse line, homozygous for Nr2e3rd7 from the sensitized ENU screen, was shown to have a reduced retinal spotting phenotype. Histologically, rosette-like structures associated with the rd7 retinopathy were repressed from two weeks of age onwards. We determined that Tvrm222 was caused by a missense mutation in the Frmd4b gene, leading to a significant alteration in its function.Immunostaining with anti-ZO-1 and anti-β-catenin revealed disruptive external limiting membrane (ELM) cell-cell junctions in Nr2e3rd7 mutants, which appears to be correlated with severity of dysplastic rosettes in the retina at early time points. The attenuation of retinal undulation as Nr2e3rd7 mice age, implies that the dysplasia is likely to be associated with dysfunctional cell types during early development. Remarkably, the fragmentation of the ELM in Tvrm222 mice is modified and comparable to WT controls. Our data suggests that this modification might be achieved by FRMD4B-mediated stabilization of cell junction molecules localized to the plasma membrane.
The retinal dysplasia in Nr2e3rd7 mouse is associated with the fragmentation of the ELM. The extent of fragmentation is closely related to the formation of rosettes in the retina. Mutated FRMD4B is capable of suppressing the retinal dysplasia in Nr2e3rd7 mice via its effects on the cell junction molecules, thus ameliorating fragmentation of the ELM.
This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.
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