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Cheng Li, Yuhua Xue, Wei Li, Zuguo Liu; Transcription Factor Brd4, a Potential Marker of Corneal Epithelial Stem Cells. Invest. Ophthalmol. Vis. Sci. 2014;55(13):503.
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To explore the expression and functional role of Bromodomain-containing protein 4 (Brd4) in maintaining the properties of corneal epithelial stem cells.
Brd4 expression in human corneal tissue, limbal epithelial primary explant and clonal cultures was evaluated by immunostaining and reverse-transcription polymerase chain reaction. The functions of Brd4 were evaluated in human and mouse (TKE2) corneal epithelial cultures treated with a Brd4 inhibitor, shRNA-Brd4 or FBS-containing DMEM by colony-forming efficiency, clone growth capacity, MTT, immunostaining, and Western blot analysis. The wound healing experiments on mouse cornea were performed with or without Brd4 inhibitor.
Brd4 protein was expressed exclusively in the basal cells of human limbal epithelium, but not in the suprabasal layers of limbus and full thickness of corneal epithelia. The Brd4 immunolocation was correlated with ABCG2 and p63 but not K12. Brd4 was expressed in the majority of epithelial cells in early-stage clones and in the margin of late-stage human clones. Brd4 was positively expressed in mouse TKE2 progenitor cells cultured in keratinocyte serum-free defined medium, while it became negative in DMEM that promoted TKE2 cell differentiation. In the presence of Brd4 inhibitor or shRNA, Brd4 expression and the proliferative capacity decreased in human limbal epithelial clones and mouse TKE2 cells, which were accompanied by cell differentiation. The wound healing was dramatically delayed in the mouse corneas treated with the Brd4 inhibitor.
Our findings demonstrated for the first time that the transcription factor Brd4 serves as a potential marker of corneal epithelial stem/progenitor cells and plays an important role in determining or maintaining the phenotype and functional properties of human corneal epithelial stem cells.
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