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R.L. Bradford, R. Adler; Gene Expression Patterns During Photoreceptor Development in the Chick Embryo Retina . Invest. Ophthalmol. Vis. Sci. 2003;44(13):2816.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: The development of the highly specialized photoreceptor phenotype requires the expression of many cell-specific genes, such as those involved in outer segment formation and in phototransduction. The mechanisms that coordinate their expression in developing photoreceptor precursors are not understood. As a first approximation to their investigation, we report here the temporal and spatial patterns of expression of genes encoding rod and cone visual pigments, phototransduction molecules, ion channels, retinoid binding proteins, and outer segment structural molecules. Methods: Retinas were isolated from chick embryos at stages when photoreceptors are being generated (ED 5, 6), are post-mitotic but not yet morphologically or molecularly differentiated (ED 8, 12), or are undergoing outer segment formation and molecular differentiation (ED 15-18). Retinas were either lysed for RNA isolation, cDNA synthesis and PCR analysis, or fixed and processed for in situ hybridization as flat mounts or in histological sections. Results: Three different patterns of gene expression were observed by PCR. Cone arrestin, rod ß-phosphodiesterase (PDE), rod light-dependent ion channel, peripherin and TULP-1 were only detectable at and/or after ED 15. Other mRNAs became detectable between ED 8 and ED 12, including cone visual pigments and α-transducin, and the guanylate cyclase activating protein. Finally, IRBP, visinin, rhodopsin and rod ß-transducin, and cone γ-transducin, Δ PDE and light-activated channel, were already detectable at ED 5-6. In situ hybridization signals for all these molecules were observed on, or after ED 15; flat mount analysis, however, showed differences in their spatial distribution at different developmental stages. On the other hand, only visinin and IRBP were detectable by in situ hybridization on, or before, ED 8. Conclusions: Different photoreceptor-specific genes show different temporal and/or spatial patterns of expression, suggesting that they are likely to be regulated through different mechanisms. We are currently testing this hypothesis using in vitro systems in which we have already shown differential regulation of visual pigments by growth factors and second messenger molecules.
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