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J. M. Stujenske, F. Emran, J. E. Dowling; The Bug Eye Mutant Zebrafish Exhibits Visual Deficits That Arise With the Onset of an Enlarged Eye Phenotype. Invest. Ophthalmol. Vis. Sci. 2010;51(13):5578.
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The bug eye mutant has an enlarged eye phenotype presumably because of elevated intraocular pressure (John et al., 2003). Since elevated intraocular pressure is a significant risk factor for glaucoma, the bug eye zebrafish mutant may be a good model organism for the disease. To determine whether bug eye mutants exhibit visual defects, we performed an optomotor response (OMR) assay at several time points, from larval stages into adulthood. We also recorded electroretinograms (ERGs) of these mutants to determine whether the enlarged eye phenotype has functional consequences on the outer retina.
Materials and Methods: :
The OMR, in which zebrafish swim in the direction of moving alternating stripes, was used to assess visual responsiveness in both larval (Neuhauss et al., 1999) and adult zebrafish (Maaswinkel and Li, 2003). ERGs were recorded to measure outer retinal function (Wong et al., 2004). Resin embedded zebrafish were sectioned to analyze retinal anatomy (Schmitt and Dowling, 1994) at various ages.
At 5 days post-fertilization (dpf), bug eye mutants have ERGs, OMR, and retinal morphology indistinguishable from wildtype animals. By 2 months, bug eye mutants begin to develop an enlarged eye phenotype. At 3 months, the enlarged eye phenotype is more pronounced and some mutants show deficits in the OMR assay, including lower contrast sensitivity as compared to wildtype fish. Our data suggest that there is a correlation between the size of the enlarged eye and the degree of OMR deficit. Histological analysis of the bug eye retina reveals that there is a lower cell density in the ganglion cell layer by 5 months. By 7 months, the b-wave of ERG recordings from bug eye mutants have smaller amplitudes and longer latencies as compared with those of wildtype fish at brighter light intensities.
Following phenotypic onset at 2 to 3 months of age, the bug eye mutants begin to develop glaucoma-associated visual deficits, including lower contrast sensitivity. At 5 months, we have observed a lower density of retinal ganglion cells, the neurons affected in human glaucoma. By 7 months, bug eye mutants show diminished outer retinal function as judged by ERG recordings. In summary, the bug eye mutant provides a means to study glaucoma-associated phenotypes in the zebrafish.
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