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DM Defoe, EM Levine; Upregulation of the Cyclin-Dependent Kinase Inhibitor p27(KIP1) in Differentiating and Postnatal RPE Cells . Invest. Ophthalmol. Vis. Sci. 2002;43(13):2445.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: To better understand the factors that maintain the quiescent state of RPE cells in the adult retina, we have begun to examine the expression of critical cell cycle regulators during epithelial development. Methods: Ocular tissues were obtained from albino rats at both embryonic (E13, E14, E15, E16, E17 and E18) and postnatal (P0, P3 and P5) stages and fixed in 4% paraformaldehyde. Radial cryosections were labeled with monoclonal antibodies to either PCNA (an indicator of cycling cells) or p27(Kip1) and examined by immunofluorescence confocal microscopy. Results: Proliferating (PCNA+) RPE cells were uniformly distributed throughout the epithelium at E13 and E14. By E15, however, anti-PCNA-labeling was restricted to more peripheral areas. At later times, labeling was essentially absent from the RPE layer, except at its extreme periphery. The pattern of p27(Kip1) immunoreactivity was the reverse of that seen with PCNA. Nuclear accumulation of p27(Kip1) was first apparent in the central-most cells of the RPE layer at E15 (two days after it appeared in retinal neurons). Immunostaining of this layer expanded to include more peripheral regions at E16 and E17. By P0 the entire epithelium was labeled, and this labeling persisted through P5. Conclusion: p27(Kip1) is expressed in a pattern coincident with the spatial and temporal onset of RPE cell differentiation. Our data suggests that this regulator may be an important factor controlling cell cycle withdrawal and maintenance of the differentiated state.
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