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Greg P. Correia, Guo-Liang Xu, Jeong-Hoon Joo, Stephen P. Sugrue, Yujiang G. Shi; DNA Methylation, Hydroxymethylation and their Regulator Tet3 within the Cornea. Invest. Ophthalmol. Vis. Sci. 2012;53(14):4224.
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© ARVO (1962-2015); The Authors (2016-present)
Cytosine methylation (5mC) has long been known to be a key epigenetic regulatory mechanism for control of gene expression. Hydroxylation of 5mC to 5hmC by the Tet family of dioxygenases provides a potential mechanism for dynamic regulation of DNA methylation. Here, we aim to determine the regional location and distribution of 5mC, 5hmC, and Tet3 within the mouse eye and, for the first time, examine the consequences of Tet3 knockout on corneal epithelial differentiation.
Paraffin sections of postnatal and adult control mouse eyes, as well as E15.5 control and Tet3 knockout embryos were stained by routine immunohistochemistry with antibodies against 5mC, 5hmC, Tet3, cytokeratins 12 and 14 (K12 and K14).
In the postnatal control mice, 5mC was expressed across the corneal epithelium, limbus and conjunctival epithelium. 5hmC was observed in the nucleus of corneal epithelium and most other cells in the eye, but it was low in the basal cells of the corneal limbus. Tet3 was observed primarily in the nucleus of adult corneal epithelial cells. Notably, 5hmC and Tet3 were differentially expressed and distributed during corneal epitheliogenesis. While 5hmC is highly accumulated in nuclei of suprabasal cells in comparison to basal cells, Tet3 was expressed at a higher level in basal cells and concentrated in nuclei, with reduction of its appearance in the cytosol. Tet3 knockout mouse embryos showed some delay in corneal epithelial differentiation and stratification, demonstrated by K12 and K14 immunostaining, without other obvious ocular phenotype.
Our study shows that not only is there a difference in the distribution of 5mC, 5hmC, and Tet3 within the eye, but that there is also a difference in the distribution of these proteins within the corneal epithelial tissue itself. Given that Tet3 has been shown to function in epigenetic regulation, our data suggests that these key epigenetic factors are actively participating in the corneal epithelium maturation. The coordination of 5mC and 5hmC by Tet3 may dictate ocular epitheliogenesis, particularly, in control of cornea epithelium self-renewal and maturation. (NIH Grants EY07883, GM078458and DK077036)
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