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Sumiko Watanabe, Toshiro Iwagawa, Akira Murakami; Roles of Histone H3K27 tri-methylation for maintenance of rod photoreceptors. Invest. Ophthalmol. Vis. Sci. 2015;56(7 ):5387.
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© ARVO (1962-2015); The Authors (2016-present)
Cell differentiation and maintenance are regulated by transcription factor- as well as epigenetic-network. We have been analyzing the roles of Histone H3K27 tri-methylation (H3K27me3) for retinal development using retina specific knockout mice of Ezh2, which is a H3K27 methyltransferase. We found that outer nuclear layer (ONL) became much thinner in Ezh2-CKO retina after birth, suggesting that H3K27me3 participates for maintenance of rod photoreceptors. In this report, we aimed to reveal more detailed molecular signature and mechanisms of roles of H3K27me3 for maintenance of rod photoreceptors.<br />
To compare molecular signature of rod photoreceptor and other cell types, we purified rod and other cells by using a cell sorter in terms of expression of Cd73, which is a specific cell surface marker of rod photoreceptors, from developing mouse retina. Using purified Cd73 positive (Cd73P) and negative (Cd73N) cell fractions, we performed RNAseq and ChIPseq for H3K4me3 and H3K27me3. Roles of Ezh1/2 and Jmjd3 for ONL maintenance were examined by loss- and gain-of-function analyses.
By bioinformatics approach using RNAseq data of Cd73P and Cd73N cells at P1, P5, P8, we selected genes specifically expressed either is rod photoreceptors (Cd73P-genes) or other cell types (Cd73N-genes). Analysis of ChIP-seq data suggested that H3K27me3 modification at loci of Cd73P-genes was observed neither in Cd73P and Cd73N cell fractions. In contrast, H3K27 at loci of Cd73N-genes was tri-methylated, and comparison between Cd73P and Cd73N fractions indicated that the Cd73N-gene-loci were H3K27 tri-methlated much stronger in Cd73P cells than in Cd73N cells. Immunostaining of rhodopsin and S-opsin of retinas derived from Ezh2-CKO or Ezh1-KO mice suggested that rod was degenerated but cone was relatively intact in the retinas of these mice.
Rod photoreceptor specific H3K27me3 modification in loci of genes, which are not expressed in rod, was observed. Since loss of function of Ezh2 or Ezh1 resulted in failure of proper maintenance of rod, we hypothesized that suppression of transcriptional activation of genes, which are unnecessary to maintain rod, by H3K27 tri-methylation in their loci is critical to prevent rod photoreceptors from degeneration.
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