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Sarah Cheng, Hyun-Jin Yang, Anand Swaroop; Epigenetic Regulation of Rod Photoreceptor Development. Invest. Ophthalmol. Vis. Sci. 2013;54(15):6111.
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© ARVO (1962-2015); The Authors (2016-present)
Stringent control of gene expression is critical for photoreceptor development and function. A handful of transcription factors regulate photoreceptor-specific gene expression. Interestingly, a group of their downstream target genes, including phototransduction genes, exhibit delayed onset of expression in developing rod photoreceptors, suggesting additional regulatory mechanisms. In this study, we have explored epigenetic regulation of photoreceptor gene expression, with focus on gene-silencing histone modification H3K27Me3 and gene-activating histone modification H3K4Me3.
Rod photoreceptors were purified from Nrl-GFP mice by fluorescence activated cell sorting. We performed chromatin immunoprecipitation using the flow-sorted mouse rod photoreceptors to characterize changes in H3K4Me3 and H3K27Me3 profiles during rod development. We then knock-down specific components of histone modifying complexes using in vivo electroporation of P0 mouse retina with shRNA. Expression of rod genes is analyzed at P6-10 by immunohistochemistry.
We found that rod genes were marked with H3K27Me3 in newborn rod photoreceptors. There was then subsequent change in histone modification profile towards H3K4Me3, which accompanied gene activation as rods further differentiate. The knock-down experiments are in progress. We expect that changes in methylation components would bias retinal gene expression profile toward a more immature state.
This is the first study to directly examine epigenetic regulation of gene expression during development of a single retinal cell type in vivo. Our results affirm that histone modifications are important contributors to gene regulation in developing rod photoreceptors.
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