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C. B. Stevens, D. L. Stenkamp; Effects of Retinoic Acid on Gene Expression and Photoreceptor Development in Zebrafish Retina. Invest. Ophthalmol. Vis. Sci. 2007;48(13):4462.
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© ARVO (1962-2015); The Authors (2016-present)
Retinoic acid (RA) is an extracellular signaling factor essential for the development and function of the vertebrate retina. Research in our laboratory has shown that in the developing zebrafish retina endogenous RA signaling occurs in limited domains (Prabhudesai, et al., Dev. Biol. 287:157-167), suggesting that RA could be affecting photoreceptors through secondary signals from other cell types. Our goals are to determine which cells of the zebrafish retina are capable of responding directly to RA and to investigate further how RA is essential for photoreceptor development by using a loss of function approach.
Retina cells capable of transducing a signal in response to exogenous RA were identified by exposing embryos from the RARE-YFP zebrafish line (transgene: a series of retinoic acid response elements controlling expression of yellow fluorescent protein; Perz-Edwards, et al., 1999, Dev. Biol. 229:89-101) to 0.3uM RA at the beginning of photoreceptor development and labeling for cellular markers 24 hours later. RA loss-of-function was performed by incubating embryos in 10 uM diethylaminobenzaldehyde (DEAB) to inhibit RA synthesis at the beginning of photoreceptor development. The expression patterns of RA receptors were evaluated by in situ hybridization.
We found that exogenous RA upregulated YFP expression in multiple photoreceptor cell types, such as red/green double cones, suggesting these cells can transduce RA-mediated signals. In addition, Muller glia and cells of the retinal pigmented epithelium also responded. Rod bipolar cells did not express YFP in response to RA. Exposure to DEAB caused a decrease in expression of rod opsin, rod transducin and UV opsin, while showing no significant effect on expression of blue and red opsins. The RA receptor RXR-gamma is expressed prior to photoreceptor development in cells at the outer margin of the retina with higher expression near the optic fissue. In embryos exposed to RA, we found that RXR-gamma is expressed in the peripheral photoreceptor layer and in cells of the inner nuclear layer.
The data suggest that exogenous RA acts selectively on cell types in the developing retina. At the beginning of photoreceptor development, multiple cell types are still capable of generating a response to RA, and may represent sources for photoreceptor patterning signals. The receptor RXR-gamma is expressed in locations that could affect photoreceptor development. Finally our loss-of-function results show that endogenous RA is required for controlling development of specific photoreceptor cell types.
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