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K. Alvarez-Delfin, A. C. Morris, J. M. Fadool; Characterization of a Zebrafish Locus That Regulates a Rod Versus an Ultraviolet Cone Photoreceptor Cell Fate During Retinal Development. Invest. Ophthalmol. Vis. Sci. 2007;48(13):1930.
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© ARVO (1962-2015); The Authors (2016-present)
The zebrafish (Dario rerio) has become a valuable organism for the genetic analysis of the development and function of the visual system. We have undertaken a large-scale genetic screen of chemically mutagenized free-swimming larvae to identify mutations affecting photoreceptor cell patterning. We identified the locus lot-of-rods (lor) that shows an increased number in rods photoreceptor compared with wildtype larvae and no other evident defects. This study describes the further characterization the lor phenotype and identification of the gene involved and its role in retinal development in zebrafish.
The initial screening was done in collaboration with Drs. M. Mullins and M. Granato at the University of Pennsylvania. lor mutants are identified by immunolabeling of whole mount larvae or frozen sections with specific-rod antibodies. The mutant phenotype was further characterized by labeling with cell specific markers for other photoreceptors and retinal neurons. BrdU incorporation and Tunnel labeling were performed in frozen retinal sections. Confocal images of immunolabeled whole eyes were used for spatial pattern analysis. The initial mutagenesis strategy included a mapping panel that facilitates linkage analysis. Linkage mapping was performed by standard procedures in the Zebrafish Mapping Facility, University of Louisville.
The lor phenotype of an increased number of rods was associated with a decreased number of UV cones and no discernible changes in other photoreceptors. Tunnel and BrdU labeling showed no increase in apoptosis or cell proliferation, respectively, in the lor mutants. Spatial pattern analysis of the photoreceptor mosaic suggests a change in fate from UV cone into rod photoreceptor. lor locus is linked to a region in chromosome 15 and candidate genes have been identifying.
This study demonstrated the utility of the genetic screen to uncover recessive mutations affecting photoreceptor patterning in zebrafish. More specifically the analysis of the lor mutation revealed that a gene exists in zebrafish for controlling UV cone versus rod photoreceptor cell fate decision. These data suggest a genetic pathway that directly contrasts those affected in the naturally occurring mutation in the rd7 mouse and the human Enhanced S-cone syndrome.
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