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O. Biehlmaier, C. Hodel, Y. Makhankov, S.C. F. Neuhauss; Myosin VIIa Mutant Zebrafish Show Light Adaptation Defects and Retinal Degeneration . Invest. Ophthalmol. Vis. Sci. 2006;47(13):2974.
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© ARVO (1962-2015); The Authors (2016-present)
Defects in the gene encoding for myosin VIIa (myo7a) cause Usher syndrome 1B and affected patients suffer of deafness, vestibular dysfunction, and blindness. Myo7a is expressed in inner hair cells, retinal photoreceptors, and in the retinal pigment epithelium. Here, we characterize the retinal phenotype of 3 different myo7a alleles in the mutant zebrafish mariner.
We examined light and dark adapted mutant larvae of the different affected alleles (mar ty220d, tc320b, tr202) at different developmental stages. The morphology of dark / light adapted, and light damaged retinas was assessed by standard histology and electron microscopy. Immunocytochemistry was used to identify subpopulations of retinal neurons and to localize myosin VIIa in the zebrafish retina. Furthermore, the optokinetic response (OKR) was used to analyze light adaptation defects, and electroretinogramms (ERGs) were measured to compare mutant and wt retinal functionality.
ERGs reveal reduced b–waves in the 3 mutant larvae, and OKR recovery is prolonged after dark adaptation in the mutants. Morphological and morphometrical analyses show that pigment migration during adaptation is impaired in all 3 mariner mutants. Immunocytochemical studies show only minor differences in the localization of synaptic proteins and receptors in wt and mutant larvae. The cellular localization of Myo7a will be determined by a newly raised peptide antibody and will be compared to mariner mutants. Electron microscopical analysis will elucidate morphological alterations in photoreceptors and RPE that contribute to the mariner phenotype. Additionally, light damage experiments will show whether the light adaptation defect found in our OKR–studies causes increased photoreceptor vulnerability to high light doses in the mariner mutant.
These data are consistent with the hypothesis that the primary defect in the visual system of MyoVIIa mutants is due to a defect in light adaptation. Thus, we suggest that the slow progressive blindness in human Usher disease might be caused by light damage due to impaired light adaptation.
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