Abstract
Abstract: :
Purpose: To characterize a dominant mutation, night blindness c (nbc), that causes patchy retinal degeneration in aged zebrafish. Methods: The nbc mutant was isolated from a F1 generation of chemically-mutagenized zebrafish because it showed an elevated behavioral visual threshold as compared to wild-type fish. The nbc fish has been out-crossed with wild-type animals. Visual thresholds of nbc fish were determined using a behavioral assay based on visually mediated escape responses as well as by ERG. Retinal structures were examined by conventional histology and electron microscopy. Results: The behavioral visual thresholds were similar between wild-type and nbc fish when measured before 6 months of age. In aged animals (1.5 years), about 33% (4 out of 12) of the tested mutants showed elevated behavioral visual threshold levels. ERG thresholds were also elevated in some of the tested mutants (2 out of 4). Many aged nbc fish showed patchy retinal degeneration involving primarily the rod photoreceptor cells. Truncation of rod outer segment was often observed, particularly in the central retina. Homozygous nbc embryos showed normal retinal morphology. However, the embryos died 8-10 days post-fertilization, probably due to a lack of swim bladder. Conclusion: The nbc mutation may represent a mild type of dominant retinal degeneration. The variability in visual threshold displayed by nbc mutants may be due partially to the continuous generation of retinal photoreceptor cells throughout the life of the fish.
Keywords: 561 retinal degenerations: cell biology • 341 cell death/apoptosis