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D.M. Defoe, L.B. S. Adams, T.J. Flanigan, E.M. Levine; Expression Of A Positive Cell Cycle Regulator In Developing Neonatal RPE Cells . Invest. Ophthalmol. Vis. Sci. 2004;45(13):1312.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: To better understand the factors that control proliferation of the mammalian retinal pigment epithelium (RPE), we have begun to examine the expression of critical cell cycle regulators during RPE 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 or epithelial flat–mounts were labeled with antibodies to either cyclin D1 (a positive cell cycle regulator), p27(Kip1) (a negative cell cycle regulator) or BrdU (4 hours following intraperitoneal injection), and examined by immunofluorescence confocal microscopy. Results: Expression of cyclin D1 protein by RPE cells was absent at all embryonic stages examined. However, by P0, scattered cells with cyclin D1–immunoreactive nuclei appeared, being more numerous in the central, compared with the peripheral, retina. Peak labeling occurred at P3, but began to decline somewhat by P5. Throughout these postnatal times, BrdU incorporation could be detected in cells of the epithelium, in a pattern similar to that observed for cyclin D1. Double–labeling studies indicated that cells expressing high levels of cyclin D1 were devoid of p27(Kip1) immunoreactivity and vice versa. Conclusions: Cyclin D1 expression in the rat RPE correlates with cell cycle progression during the postnatal period, but not the embryonic period. This expression pattern corresponds spatially and temporally with the unique property of endoreplication, previously demonstrated in neonatal rodent RPE.
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